Urethane Rubber Mold for Plaster or Concrete Casting

April 17, 2017

Our 75 Shore A Urethane Rubber is a pourable material great for making molds that stand up well to repeated castings of cement, concrete, Hydrocal, plaster and other gritty and/or abrasive materials. It is a 1:1 by volume mix ratio, so no scale is needed.  For this project, I will be making a one piece block urethane rubber mold and casting in plaster.

Materials needed:

  • Original part
  • AeroMarine Products 75A Concrete Molding and Stamping Urethane Rubber with mold release (the kit comes with a silicone paste to use as a mold release)
  • Mold box (or cardboard, glue gun, and paint to make one)
  • Plastic mixing containers and plastic utensils
  • Plaster of Paris (or concrete, Hydrocal, or whatever you prefer)
  • Gloves
  • Non-sulfur modeling clay (for anchoring your original to the bottom of the mold box)

Your work area:

  • Clean, level work surface, covered in paper or plastic for easier clean-up.
  • All materials comfortably within reach.

Project steps:

  • If you don’t have a plastic mold box, go ahead and make one from cardboard and hot glue. This post has specific details on this process, https://www.aeromarineproducts.com/two-part-pourable-silicone-pumpkin-mold/   After you have made the mold box, paint it with any paint you have laying around. I used some brown spray paint I had left over from another project and let the paint dry for several hours. The purpose of the paint is to seal the cardboard, which may have retained some atmospheric moisture. Urethane reacts poorly to even small amounts of moisture, causing bubbles and a weak finished product. Because of this, you don’t want to work with urethane on a rainy day or when the humidity is over 50% or use wood paper or waxed mixing cups and utensils.
  • Once you have the mold box made, affix some of the clay to the back of your original and press it into the bottom of the mold box. This will keep the piece from moving around during the molding process.


  • Next, use a rag or paper towel or paint brush to apply the mold release to the original and the inside of the mold box. Urethane likes to bond to most things, so we need a mold release to make sure we can remove the urethane rubber mold once it is cured.

  • Since the 75A Urethane Rubber is a 1:1 by volume mix ratio, I use plastic solo cups to measure out equal parts of the A side and the B side. Then, pour both sides into a clean plastic container and stir vigorously, taking care to scrape the sides and bottom of the mixing container. Because this product only has a 5 minute pot life, you want to mix quickly. Fortunately, it is a very low viscosity product which mixes easily.
  • Pick a corner of the mold box and pour in the urethane. Don’t pour directly on the piece.
  • Let the urethane rubber mold cure for 12 hours.
  • After 12 hours, remove the urethane rubber mold from the mold box and wash with dish soap and warm water to remove any mold release residue.

  • I’m casting with plaster of Paris, which needs to mixed 2 parts powder to 1 part water. I measure out the water and powder and then slowly add the powder to the water, stirring the whole time to avoid lumps.
  • Pour the plaster into the urethane rubber mold and let set up for 20 to 30 minutes.
  • To remove the casting, I lay a folded towel down on my work space and hold the mold over it, bending and flexing the sides until the casting pops out and lands on the towel.

That’s a urethane rubber mold and a plaster of Paris casting! You can paint the plaster casting however you choose. I’m still deciding on how I am going to paint this piece. If you have any questions about this project or others, please email us at info@AeroMarineProducts.com

Make your own Silicone Soap Mold

April 3, 2017

A silicone soap mold is a fun project to do with any one or two part silicone rubber mold. Soap making supplies can be found at most craft stores (We go to Michael’s). Here, I used a rubber duck mold I had already made for another project.  If you want to make a 2 part mold, you can read the detailed post about the two part mold making process at, https://www.aeromarineproducts.com/two-part-pourable-silicone-pumpkin-mold/  If you choose to make a 1 part mold, you can read about one part block mold process, with detailed directions and a video at, https://www.aeromarineproducts.com/making-one-piece-silicone-mold/

Materials needed:

  • Either an already made silicone mold or an original part (like the rubber duck I chose), sulfur free modeling clay (for a two part mold only) and a mold box.
  • Glycerin soap from a craft store
  • Glycerin soap colorant and/or scent (essential oils work well)
  • Plastic bowl and microwave to melt soap

Your work area:

  • Clean, level work surface, covered in paper or plastic for easier clean-up.
  • All materials comfortably within reach.

Project steps:

  • Step one if you don’t have a mold is to make a mold. Please see the links above to make a one part block or two part mold. Any silicone mold can be a silicone soap mold!
  • If you have a two part mold, it must be taped together to prevent any leaking. I like to use blue painter’s tape for this. Most molds I tape in 4 strips. Make sure that the tape is holding the mold firmly together, but not so tight that it distorts the mold. You shouldn’t see any gaps and the parting line should almost be almost invisible.


  • Next, follow the directions on the glycerin soap packaging. For the soap I bought, that means chopping the block of soap into small pieces and microwaving it in 30 second increments and stirring the soap until liquid.

  • Then I added some silver metallic soap colorant and some lavender oil.

  • Pour into your silicone soap mold.

  • The glycerin soap I have says to let it set up for at least 40 minutes before demolding. Always follow the directions on the packaging for the soap you have.
  • I removed the tape and took the mold apart to reveal my silvery lavender smelling duck soap.


  • There wasn’t much flash. I easily smoothed away the little bit of flash with my finger.

There you have home made soap from a silicone soap mold. Pretty easy  to do and because the soap sets up fairly quickly, you can make many soaps from one mold in a day. If you have any questions about this project or any others, send us an email at AeroMarineProducts.com or visit or our web site, https://www.aeromarineproducts.com/


Trouble Shooting-Common Problems with Silicone, Latex, Urethane, Epoxy

March 23, 2017

Sometimes, when working with new materials or working familiar materials in a new way, you run into issues. We previously wrote a post about common problems with curing, https://www.aeromarineproducts.com/curing-issues-trouble-shooting/   This post will focus on issues that might have a curing component (soft spots, sticky areas, etc.), but mostly on problems with the materials acting in unexpected and unwanted ways. These aren’t all the problems that could come up, only the more common problems and issues. You can always email us at info@AeroMarineProducts.com if you have questions.


  • The silicone has partially cured, but is still tacky  First, make sure the silicone has had adequate time to cure by checking the cure time on the Technical Data Sheet. The Technical Data Sheet can also tell what causes cure inhibition for that silicone. Second, double check that you shook the catalyst for 60-90 seconds before measuring and mixing.  Insufficiently shaken catalyst is a very common way to get tacky silicone. Also, if it is too dry or too cold, that can cause the curing process to take longer.
  • Soft/partially cured spots  This is almost always from material that hasn’t been mixed well enough. However, if you give the silicone a few extra days, the soft spots will usually cure in the end.
  • Silicone is very brittle  Too much catalyst will make your silicone brittle. Check the Technical Data Sheet and make sure you are adding the correct amount of catalyst.
  • Air bubbles on the working surface of the mold  A few things can cause this. 1. You poured the silicone directly onto the piece. To avoid air bubbles, pick a corner of the mold box to pour and don’t pour the silicone directly on the original. 2. You poured the silicone too quickly. Pour “high and thin” as this gives the silicone time to flow around the original so pockets of air don’t get trapped. 3. There is a lot of fine detail on the original. Lots of detail gives air bubbles lots of places to cling to. Try brushing some of the silicone on the original before you pour the silicone. This method gets the silicone into crevices and helps break the surface tension that lets bubbles stick. If you are using brushable silicone and get air bubbles on the working surface of the mold, you applied the first coat too thickly. The first coat should always be the thinnest coat to ensure no air bubbles.

 Air bubbles on the working surface

  • Brushable silicone is sagging off the original The silicone has been applied too thickly. Apply the silicone more thinly, in several coats, in order to build up an appropriate mold thickness.

 Saggy silicone.

  • Silicone is sticking to the original  Silicone will chemically bond to materials that contain silica. The most common silica containing things are silicone, glass, quartz, and some pottery glazes. If you have any doubts about what your original is made of, do a small test patch on an unobtrusive area of the original piece before doing the full mold. Silicone can also mechanically bond to very porous materials. If you have a very porous original (old plaster, wood, or concrete are common porous materials), paint it first. If you don’t paint it first and the silicone sticks, patience and elbow grease can usually get the silicone off. Just peel it off very slowly to avoid damaging the original.


  • Air bubbles  It could be a few things; 1. The latex was brushed on too quickly. Slow down and brush it on your piece a little more slowly. 2. The latex was applied too thickly. Nice thin, even coats will yield the best results. 3. Using a heat gun on either too high of a setting, too closely to the mold, or holding it too long in one spot. If you are using a heat gun to speed up the dry time, use the low setting, hold the gun at least 8 inches away from the latex and keep it moving at all times.

Urethane Rubber:

  • Lots of bubbles, a foamy gray appearance  Moisture contamination. Urethane does not like contact with moisture before it’s cured. Don’t use paper, waxed or wood mixing containers or utensils and don’t mix the material on a rainy day or when the humidity is over 50%.
  • Urethane is sticking to the original or the mold box  Urethane likes to bond to most things. Check the Technical Data Sheet for a full list of what it won’t bond to. Use silicone paste (which comes with the 1/2 gallon and 2 gallon kits that we sell) or petroleum jelly on the original piece and the mold box.
  • Ripples or waves in the material or air pockets forming around the original The material is not being poured before it begins to gel. Mix and pour the urethane within 3 minutes so it has time to flow before starting to gel.
  • Soft spots  Material wasn’t mixed well enough. Don’t forget to scrape the sides and bottom of the mixing container and mix very well.

Urethane Casting Resin:

  • Bubbles, foamy appearance  Moisture contamination. Urethane does not like moisture before it’s cured. Don’t use paper, waxed or wood mixing containers or utensils and don’t mix the material on a rainy day or when the humidity is over 50%.
  • Extra Oily  Too much Part B in the mix. Make sure that you are measuring 1:1 by volume. To take care of the extra oil, dust with or submerge the part in talc, wait 12-24 hours and then wash the part with dish soap and water.
  • Soft spots  The urethane casting resin wasn’t mixed thoroughly. Don’t forget to scrape the sides and bottom of the mixing container and mix well.


  • “Oil and water” or blotchy appearance  This is usually caused by an oil based stain on the wood or actual oil stains on concrete. Try to remove all large oil stains from the concrete before applying the epoxy. If your wood is colored with an oil based stain, do thin brush coats of the epoxy, followed by a light sanding and then wipe with acetone before the next coat. Repeat these steps until the epoxy looks even.  Then, do your pour coat to the desired finish (but no more than 1/4 to a 1/2 inch at a time, depending on the surface area).
  • Lots of small bubbles  The substrate is either very porous or you are mixing with an electric or drill mixer. For porous wood or concrete, do a brush coat or two before doing the pour coat. Always mix the epoxy by hand to avoid whipping air into the mix and to avoid the friction from setting off the cure reaction early.
  • Many small or large bubbles that form about 10-20 minutes after pouring  This occurs when you pour the epoxy too thickly.  Too thick a pour will have the epoxy boiling. You can sand out all the bubbles and then do thinner pours to avoid repeating the problem.
  • Waves or ripples in the epoxy  Either the epoxy is being poured after it has started to gel or you are holding a propane torch or heat gun too close to the surface of the epoxy. Also, please remember that a hair dryer is not the same thing as a heat gun and should not be used on the epoxy because it will make waves in the epoxy. Mix the epoxy well and pour it within 5-10 minutes (quicker mixing and pouring for larger batches) to avoid the epoxy curing while you are still removing waves or ripples.
  • Epoxy cured cloudy white  The epoxy got wet while it was curing. You can sand off the white and pour or brush coat again. Always check the weather forecast before doing any outside work with the epoxy because it needs to be kept dry while curing.
  • Epoxy got super hot and cured in the mixing container  Possible causes: 1. You mixed too large a batch. 2. The ambient temperature was too high. If the temperature is over 75F, mix smaller batches than you normally would because the epoxy will cure faster as the ambient temperature increases over 75F. 3. You used a drill or electric mixer and the friction kicked off the cure process. Always mix the epoxy by hand.

These are some of the more common problems that can arise when using our products. For more information on our products, check out our website, https://www.aeromarineproducts.com/ or send us an email at info@AeroMarineProducts.com


Silicone Candle Mold- One Piece Clam Shell Mold

March 8, 2017

A silicone candle mold is a popular project that many customers ask about frequently. For this post, I’ll be doing a one piece clam shell mold from an electric candle. Candle molds can involve more than one part, depending on the complexity of the original. Often, people want to make candle molds from a glass bottle. This can be problematic because silicone will chemically bond with glass. You can apply a thick coat of silicone to silicone mold release to the bottle before pouring the silicone, but if any little spot is missed, the silicone will fuse to the bottle. A safer (but more time and resource consuming) way is to make a latex mold of the glass bottle and then cast plaster into the latex mold. Paint the plaster copy and make a silicone mold from the plaster copy. The electric candle I used as my original for this project is made of wax, which is fine for silicone.

Materials needed:

  • Candle wax (I used paraffin wax I purchased at a grocery store)
  • Candle wicks (Purchased at a craft store)
  • AeroMarine Products 128 Pourable Silicone
  • Original part (I used an old, broken electric candle)
  • Mold box (or cardboard and hot glue to make one)
  • Scale
  • Mixing container and mixing utensils
  • Non-sulfur modeling clay
  • Candle wax colorant and/or scent (optional)
  • X-Acto knife
  • gloves

Your work area:

  • Clean, level work surface, covered in paper or plastic for easier clean-up.
  • All materials comfortably within reach.

Project steps:

  • For this silicone candle mold, I want to position my original upside in the mold. That is, I want the top of the candle anchored to the bottom of the mold box. This will make it possible to anchor the wick to the bottom of the candle when pouring the wax.
  • Since I was using an electric candle as an original, I sealed the battery casing with some clay to prevent any silicone from seeping in.


  • Then I anchored the candle using the same clay to the bottom of my mold box, which is just a plastic gallon mixing container in this case.

  • I mixed up my AeroMarine Products 128 Pourable Silicone according to the directions (10:1 silicone to catalyst by weight) and poured it into my mold box. For more specific directions on using this silicone, refer back to this blog post, https://www.aeromarineproducts.com/two-part-pourable-silicone-pumpkin-mold/
  • After my silicone had set for 24 hours, I cut the mold box apart to easily release the silicone candle mold.

  • I then used an X-acto knife to make two cuts through the silicone on opposite sides of the mold. This is the clam shell part. I cut slightly less than halfway down the mold. This makes it much easier to pop the wax candle out without damaging it.


  • Once the original was out, I started heating up my paraffin wax on a stove top. I used blue painter’s tape to tape the clam shell part closed. I used a glue gun to anchor the wick to the bottom of the silicone candle mold. Nothing actually bonds to silicone (except more silicone) but this provides a good mechanical bond that will hold the wick to the bottom while the wax solidifies. I also used a fork glued to the side of the mold to hold the wick in place at the top of the mold.

  • The wax took maybe 15 minutes on low heat to melt completely, then i mixed in the red colorant and a caramel scent oil.

  • Next, I carefully poured it in to the silicone candle mold. As you can see, I still made a bit of a mess and I was a little short on wax. Next time I will know that this mold needs one and a half packs of paraffin wax. This is why I keep a notebook of mold making projects where I write down how much of what material was used in the molding and casting of each project and the results. This way, I don’t repeat the same mistakes.

  • After two hours, I removed the tape and trimmed the wick. I pulled the mold slightly apart to check how firm the wax was. It seemed a little soft, so I didn’t de-mold it yet.

  • I ended up letting the wax set up over night, just to be sure the wax had hardened enough to be removed from the mold without damaging it. I removed the tape and pulled the mold apart while pushing on the bottom of the mold to pop the candle out.

Even though it got a little messy and I ran a little short on wax, the candle turned out nicely. The important thing is that now I know exactly how much wax I need to melt for the next pour to turn out perfect.  I wrote it down in my molding and casting log book so I don’t forget. If you have any questions about this or any other projects, send us an email at AeroMarine Products.com


Silicone Putty Seashell Mold for Kids

February 8, 2017

This is a fun and easy project to do with kids. You can simplify it by making it a simple one piece mold and/or leaving out the colorant. I find that seashells are an easy shape to mold from the silicone putty. Other small, simple shapes can work as well.

Materials needed:

  • AeroMarine Products Silicone Mold Making Putty
  • AeroMarine Products White Urethane Casting Resin
  • Urethane Colorant
  • Silicone to Silicone mold release (or petroleum jelly)
  • Plastic mixing containers and utensils
  • Gloves
  • Two small pieces of cardboard

Your work area:

  • Clean, level work surface, covered in paper or plastic for easier clean-up.
  • All materials comfortably within reach.

Project steps:

  • Make sure everybody is wearing gloves.
  • Place your seashell on one of the small pieces of cardboard. The cardboard should be a few inches bigger all the way around than the seashell.

  • Separate out equal parts Silicone Putty Part A and Part B. This product isn’t especially fussy. You can measure out the parts visually and see that the two parts are approximately equal.

  • Use your hands to squish the two parts of Silicone Putty together, folding and mushing it until it is all mixed together and one uniform color.
  • Press the Silicone Putty over the seashell, starting at the top and smushing downward. Make sure to press around the edges of the shell. Don’t press down so much that that silicone becomes very thin. You want the silicone putty to be about a quarter inch thick.

  • Lightly press the second cardboard piece on to the top of the Silicone Putty. Thiscreates a flat spot for the mold to set on when its time to pour resin into the mold. It should look like a cardboard-silicone sandwich. Try to get the cardboard as even as possible.

  • Let the Silicone Putty cure for at least 20 to 30 minutes. This type of silicone (platinum catalyzed) can be affected by the cold, so if it’s chilly (under 68F), let it sit for a little longer.
  • After the Silicone Putty has cured, remove the top piece of cardboard and peel the mold off the bottom piece of cardboard.


  • If you are doing a one part mold, You can pull the shell out of the mold and skip ahead to the resin mixing and pouring part of this post.
  • For the two part mold, leave the shell in place. I usually cut some notches with an X-acto knife to help me line up the bottom and top parts of the mold. This isn’t 100% necessary. However, it does make it make it easier to line the mold halves up.

  • Next we need a silicone-to-silicone mold release to keep the two halves from sticking together. I used an aerosol called Petrolease, but plain petroleum jelly brushed on to the silicone works just as well. Make sure you get the mold release into the notches as well. You want a good barrier so that no part of the silicone will stick together.

  • Mix together another batch of the Silicone Putty and press it into the shell and onto the silicone, taking care that it fills any notches that you may have cut.
  • Let the silicone cure for 20 to 30 minutes. Once it is cured, separate the two halves and remove the seashell.

  • Measure out equal parts of Casting Resin Part A and Part B. If you are using colorant, add it to the Part B before you mix the two parts together. Mix well with plastic utensil/stir stick, scraping the sides and bottom of the mixing container.

  • If you are doing a one piece mold, pour the mixed Casting Resin into the mold, filling it up.

  • If you are doing the two piece mold, fill the mold cavity up about half way and then place the convex part of the mold gently on top, lining up the notches. A little Casting Resin will squish out of the Silicone Putty mold. That’s okay because this shows you that mold is completely filled. It is also why this type of mold is frequently called a squish mold.


  • Let the Casting Resin cure for at least 30 minutes, a little longer in colder weather. Then pop your new seashell out of your mold and trim away any flash.

  Here you can see the difference between the one piece mold and the two piece mold.

  • You can also multi colored shells by measuring out two sets of Casting Resin and adding to only one, or different colors to both.

  • If you can, have one person mix each color at the same time, or mix them very quickly, one after the other. Pour the colored casting resin into the mold at the same time. The slower you pour, the more swirled the colors will be. Just be mindful of the pot life.

You can use the Silicone Putty mold many times over to create an entire beach of seashells! You can find the products for this project and more information on our website,https://www.aeromarineproducts.com/  You can always send us an email if you have any questions at info@AeroMarineProducts.com.




Food Grade Silicone Mold for Chocolate

January 25, 2017

In this post, we’ will make a multi part food grade silicone mold for chocolate. Our Food Grade silicone is FDA approved and is great for casting candies, chocolate, fondant, sugar and the like. It is not approved for use in ovens, however. For this project, we will use ice cube trays in fun shapes instead of already made original pieces. Sometimes, I find interesting molds that aren’t designed for what I want to cast into them, so I’ll go over how to cast a suitable material into the original mold to make a piece to cast from for the new mold.

Materials needed:

  • AeroMarine Food Grade Silicone Mold Making Rubber
  • AeroMarine Urethane Casting Resin
  • Urethane mold release
  • Ice cube tray of interesting shapes
  • Tupperware container, or other suitable plastic container
  • Scale
  • Mixing containers and utensils
  • Non-sulfur modeling clay
  • X-acto knife
  • Chocolate suitable for melting
  • Pam spray or butter
  • Food flavoring suitable for chocolate (optional)
  • Double boiler
  • Rubber spatula
  • Candy/food thermometer

Your work area:

  • Clean, level work surface, covered in paper or plastic for easier clean-up.
  • All materials comfortably within reach.

Project steps:

  • Spray the ice cube tray(s) with the urethane mold release and let it sit for a few minutes. This allows the propellants in the mold release to evaporate, leaving behind just the mold release itself.

 Urethane mold release

  • Measure out the urethane casting resin. This material is mixed 1:1 by volume, so I just use solo party cups and pour the same amount of the A side and B side into two separate cups. Then I pour each cup into my clean, empty mixing cup and mix with a plastic utensil. Mix vigorously for about 90 seconds, taking care to scrape the sides and bottom of the mixing container. Then pour into the ice cube trays.

 Don’t worry about pouring perfectly, any flash can easily be trimmed away

  • After 30 minutes, the casting resin should be set enough to remove the pieces from the molds. Trim away any flash with an X-acto knife. I always make more pieces than I need for my mold so I can pick out the nicest looking ones.

  • After selecting your pieces, smush a little clay on to the bottom of each piece and press into the bottom of the Tupperware container. The clay will hold the piece in place so it doesn’t float when you pour the silicone. Remember to keep the pieces at least a half inch apart from each other and a half inch away from the sides of the container.


  • Weigh out the Food Grade silicone and catalyst. I weighed out 250 grams of Part A and 25 grams of catalyst. Pour the catalyst into the silicone Part A and mix thoroughly, until one nice uniform color (kind of a lilac/light pink).
  • Pick a spot in the mold box, not on the pieces, and pour high and thin to reduce air bubbles.


  • Let the silicone cure for 24 hours.
  • Once the silicone is fully cured, pull it out of the Tupperware. Sometimes this takes a bit of effort or an extra pair hands. Then pop the pieces out of the silicone. Trim any flash with an X-acto knife.

   Now we’re ready to make some chocolate!

  • I used a double boiler to melt and temper the chocolate. Tempering the chocolate is what makes it shiny and smooth, here’s a link for an easy how-to: http://www.instructables.com/id/How-to-Temper-Chocolate/?ALLSTEPS
  • I added a few drops of orange extract to give the dark chocolate a little extra flavor, but that is optional.  You can add any flavoring you like.

 I used dark chocolate, but milk chocolate and semi-sweet will also work well.

  • I gave my mold a light spray with PAM to help the chocolate release from the Food Grade silicone mold. Then I pour the tempered chocolate into the mold and put it in the refrigerator to cool down.

 The candy thermometer is used to make sure the chocolate is the correct temperature to be tempered.

  • These took about an hour and a half to two hours to harden in the refrigerator. Once I          de-molded the chocolate, I cleaned my mold and melted and poured more chocolate. I kept the already made chocolate pieces in a bowl in the refrigerator.


That’s how we make lovely orange flavored chocolates for our loved ones for Valentine’s Day! The Food Grade Silicone can be wash with dish soap, dried, and stored in a zip-lock bag for future use. As always, if you have any questions, you can email us at info@AeroMaineProducts.com

Curing Issues- Trouble Shooting

January 13, 2017

At some point, everybody mixes up some silicone or epoxy or urethane and it just doesn’t cure right. There are many things that can affect the curing process. This blog post isn’t meant to cover every thing that could possibly go wrong. These are some of the most common reasons for our products to have issues curing. As always, if you have any questions, send us an email at info@AeroMarine Products.com and we would be happy to help you.

 Curing problems common to all materials:

  • Ratios- Was the correct amount of Part A and Part B (or catalyst) used? Some materials need to be mixed by weight, some need to be mixed by volume. The Technical Data Sheet and the label on the front of the bottle will tell you the correct mixing ratio.
  • Mixing- Was the material well mixed? Our materials should be mixed by hand, using a wooden paint stir stick (silicones and epoxies) or a plastic mixing utensil (urethanes), taking care to really scrap the sides and bottom of the mixing container.  If your material cures hard in some spots and is tacky or soft in other spots, it is almost always because the material wasn’t mixed well enough.
  • Use by date- What is the use by date on the container? As we’ve covered in other posts, some materials go bad more quickly than others, while some remain viable, under certain conditions, past the use by date. Always check the use by date if the product has been sitting on your shelf for a while and mix a small test batch if it is past the use by date.

The use by date is shown here on the fourth line of the label, under the cure time.

Curing problems common to silicone:

Tin catalyst silicone (128,125, and 115 translucent silicone):

  • Dry weather- Tin catalyzed silicones are condensation cure, meaning they pull moisture from the air as part of the curing process. If the weather or environment is very dry, it can affect the cure time. If you can increase the humidity in the area where it is curing, that will help.

 The humidity is at 68%, which makes it a good day to work with tin catalyst silicone.

  • Cure inhibitors- Sulfur containing clay and latex gloves are the most common cure inhibitors for these types of tin catalyzed silicones. Check that any clay you are using does not contain sulfur and make sure the gloves you are wearing are not latex gloves.
  • Catalyst issues- For the 128 pourable and brushable silicones as well as the 115 translucent silicone, the catalyst will separate if it sits for more than a few hours. Therefore, it needs to be shaken vigorously before use.
  • Additives- Different additives (silicone diluent, silicone thickener, silicone accelerator) need to be added to either the silicone Part A or the catalyst to work. The Technical Data Sheet will tell you which part and how much to add.

Platinum catalyst silicone (Food Grade silicone, silicone putty, and 150 potting and high temp):

  • Cure inhibitors- Platinum catalyzed silicone has many cure inhibitors. The most common cure inhibitors for platinum catalyzed silicones are: tin (tin catalyzed silicone), sulfur, latex, alcohol, ethanol, methanol, ethyl acetate, vinyl acetate, melamine, amines and nitriles. Most of these are listed in the Technical Data Sheet. If you have questions, please give us a call.
  • Catalyst- Always shake the catalyst thoroughly before use.
  • Cold weather- platinum catalyzed silicones are addition cure and can be affected by lower temperatures. Warm up your work area if possible to help it cure in a timely manner.


  • Cure inhibitors- Once again, sulfur containing clay can cause curing issues.
  • Application- Latex needs exposure to air to cure. Too thick of a coat will cause the latex to take a very long time to cure, and if it’s much too thick, it might not completely cure at all. Apply the latex in very thin coats for best results.

 A nice thin, quick curing coat of latex.

 Too thick a coat of latex, lots of bubbles, it will take forever to cure, and it might not cure all the way through.

  • Cold weather- Cold temperatures can also slow the cure time. A heat gun can be used to speed up the dry time, just make sure to use it on the lowest setting, keep it at least 8 inches away from the latex, and keep it moving. You can also set the piece out in the sun or raise the temperature of the room where you are working  to 72F.

Urethane (rubber and casting resin):

  • Cure inhibitors- Again, sulfur containing clay can affect the curing process.
  • Shake Well- Both the A and B sides of these materials should be shaken well prior to mixing, especially the urethane rubber.
  • Cold weather- Urethanes do cure more slowly in colder weather. If possible, warm up your working area to 72F or set the bottles in the sun for 10-30 minutes before use. If pouring the urethane into a mold or form, make sure the mold/form is warmed up as well.
  • Batch size- Smaller batches (especially smaller than 6 oz) cure more slowly than larger batches, as do thinner pours that have a lot of surface area to let off heat. Warm the material, warm the work area and just be patient. It will cure eventually.


  • Double mix and pour- Because both epoxy resin and hardeners are both clear, it can be difficult to tell if the material is well mixed, which is why we recommend using the double mix and pour method. To do this, measure out your epoxy and hardener and pour them into a clean mixing container. Mix well for for a few minutes, taking care to scrape the sides and bottom of the container. Don’t whip or beat the epoxy because that will create air bubbles. Then pour the epoxy/hardener into a new, clean mixing container and mix for a few more minutes. From there, you can pour or brush or roll the material on as desired.
  • Cold weather- The epoxy curing process slows down at 65F and decreases very dramatically under 50F. Warm up the materials and your work area to 72F and be patient. It will cure eventually.
  • Batch size – Smaller batches (under 8oz) cure more slowly. Same as with cold weather, warm things up or be patient.

These are the more common issues that can affect the curing process for the various materials we carry. For more information, along with Technical Data Sheet for all the materials we have, please go to our website,  https://www.aeromarineproducts.com/



5 Frequently Asked Molding and Casting Questions

December 27, 2016

Here are 5 questions that we get asked on a weekly basis. As always, if you have any questions, you can contact us at info@AeroMarineProducts.com

  • How do pick what type of material will be best to make my mold?

The type of material you will make your mold from depends on what you will be casting into the mold. Are you replicating a garden gnome and casting in concrete? Are you making chess pieces and casting in a urethane resin? Are you making candles and working with wax? The end product is what determines the molding material to use.

For concrete, Plaster of Paris, and Hydrocal, liquid latex is what you would use for a brushable mold. Our 75A urethane rubber would be used if you wanted to make a pourable block mold. The reason for this is the abrasion resistance of the latex and and urethane rubber. These materials are able to withstand repeated castings of coarse materials.

If you are going to be casting with an epoxy resin, urethane resin or wax, you will want a material like silicone mold making rubber that has a good heat resistance as all of those casting materials are warm to hot while curing.

The other general rule of selecting a molding material is the hard/soft dynamic between the casting material and mold. If you are going to be casting a hard part (most common), you want the mold itself to be soft and flexible. That way, the mold will give and flex for the part to come out. If you want your piece to be cast from a soft material, like a silicone, you would want the mold to be more rigid and the part will flex to come out of the mold. It is extremely difficult to remove a hard cast from a hard mold or a soft part from a soft mold. There are some exceptions to this rule, mostly when working with fiberglass and resin, but it is a good rule of thumb.

  • What is the shelf life of my product?

All of products have a use by date printed on their label. This is usually six months from the packaging date. That is how long we expect the product to reliably last. However, some products may last longer on the shelf than others.

128 Silicone with pourable or brushable catalyst- The white silicone base will last at least six months if stored in a closed container in a room temperature (68-72 F) environment. Sometimes it can last up to year, if it isn’t opened and closed too often. By 18 months it is usually too viscous to work well. The catalyst has a similar shelf life, always good up to six months, sometimes lasting up to a year.

125 Silicone, simple 1:1 mix ratio- This silicone will last on the shelf, UNOPENED, for six months. However, once you open this product and expose the “A” side to air, it needs to be used within sixty days. This is because the catalyst is in the “A” side and it will start to cure slowly once opened.

Latex-  If stored in a closed container in a room temperature environment, the mold making liquid latex will last at least six months, sometimes 12 to 18 months. However, if latex gets too cold, it will be ruined. Do not store the latex in environment where it will get below 50 F. So unheated garages and sheds during the winter and fall months are not a good idea. If your latex looks chunky, like cottage cheese, it has gotten too cold and needs to be thrown out.

Urethane Casting Resins- If stored in an air tight container, it will last six months. Urethane is very moisture sensitive before it is are mixed and cured, so using it on a rainy or humid day, using paper or wood mixing utensils and/or containers can cause moisture contamination that leads to bubbles in the urethane. You can make sure your casting resin lasts by using a dry gas nitrogen blanket (like X-Tend it) to displace the air in the bottle after every use.

Epoxy Resins- Epoxy resins and hardeners can last for years on the shelf. We label it with a six month use by date, but it doesn’t really go bad. Sometimes the resin side will freeze (at about 50 F) and become crystallized and cloudy looking, but it just needs to be warmed up to return to its former clarity with no impact on the resin’s strength and durability. The 21 hardener will darken over time, turning more yellow. This is purely a cosmetic issue which doesn’t affect the strength or durability of the final product.

With all of these products, if it is past the use by date on the label, a small test batch will tell you if the product is viable.

  • How should I store my molds when not in use?

Molds should be stored in a room temperature (68-72 F) environment, out of direct sunlight, in an air tight bag or container. If possible, it always best to store the mold with a cast piece in it. Glove molds should be stored with their mother molds in place. Latex molds are especially sensitive to heat and should never be stored anywhere where the temperature could reach over 72 F.

  • How long will a mold last?

Production life ( the amount of casts you will get from a mold) is hard to predict. Things that affect production life include:

Mold release will prolong the life of your mold, especially if used every time you do a cast.

Detailed and/or complex molds don’t last as long as simple molds.

Molds stored properly will last longer than molds just tossed on a shelf.

The materials used in the molds will also contribute to production life. Generally the hotter the casting material becomes while curing, the harder it is on the mold. Also more abrasive materials will wear the mold out faster.

Library life (how long a properly stored mold will last when not in use) is easier to predict and are as follows:

Tin catalyst silicone molds (like our 125 or 128 silicones) last about 5-7 years when stored properly

Platinum catalyst silicone molds (like our Food Grade silicone or silicone putty) last 20+ years when stored properly.

Latex molds last 10-20 years when stored properly.

Urethane rubber molds (like our 75A urethane rubber) last 20+ years when stored properly.

  • Can I color or paint the urethane casting resin?

Yes, our urethane casting resin can be colored. We carry white, black, red, yellow, and blue colorant for the casting resin. Any colorant for use with urethane will work with our casting resins. People frequently use powdered pigments and dyes in the casting resin. Always mix up a small test batch to make sure you are getting the color and result you want.

The casting resin can also be painted. For best results, dust or submerge your part in talc for 12 to 24 hours, and then wash with a liquid dish soap (like Dawn) with cold water and pat dry. Do not sand after the talc and washing. Some people also like to use a primer such as Plasti-Kote, a sandable primer that works well and can be found at most auto supply stores. Acrylic paints work very well. Other types of paints should be tested first. For a spray paint, Krylon Fusion works great.

Hopefully this information has been helpful to you.

From all of us at AeroMarine Products, have a lovely holiday!



Mold and Cast An Epoxy Glitter Ornament

December 21, 2016

For this project, I made an epoxy and glitter ornament. The original piece was sculpted from modeling clay. The silicone mold is a simple one piece block mold. The epoxy and glitter was poured in layers to give the finished product dimensionality.

Materials needed:

  • AeroMarine 300/21 Epoxy Resin
  • AeroMarine Products 128 Pourable Silicone
  • Modeling clay
  • Cardboard
  • Hot glue gun
  • X-acto knife
  • Small, inexpensive paintbrush
  • Epoxy mold release
  • Glitter
  • Scale
  • Level
  • Gloves
  • Thin ribbon

Your work area:

  • Clean, level work surface, covered in paper or plastic for easier clean-up.
  • All materials comfortably within reach.

Project steps:

  • To start, I cut out a piece of cardboard a  bit larger than I wanted the ornament to be. I sketched out an outline of the shape I wanted sculpt. I used medium non-sulfur plasteline clay to sculpt the ornament shape. I should mention I did not go to art school and I have no formal training in sculpture so I tend to stick to basic, simple shapes if I need to sculpt an original. I say this because many people are intimidated by trying to sculpt a shape for an original and they needn’t be. However if you don’t want to sculpt the shape yourself, you can frequently find pre-cut wooden shapes at a craft store or even a cookie cutter that you could use to cut out the shape from rolled out clay.


  • Next, I cut cardboard for sides of the mold box and hot glue them into place around my clay original. Remember to keep the sides a half inch to an inch away from the piece.

  • I used AeroMarine 128 Pourable Silicone to make the mold. I have covered the mixing and pouring of this product in more detail in the previous post about the two part pumpkin mold. For a brief recap, make sure your work surface is level before you pour, mix the silicone 10:1 by weight (I use a scale that weighs grams) with the catalyst and mix until it is an uniform color. Don’t forget to scrape the sides and bottom of your container while mixing.
  • Since the ornament has some detail where the top meets the round part, before I poured the silicone, I used a brush to work a bit of the silicone into the detail part. This helps ensure that the silicone gets into the detail area with no air bubbles. You should use an inexpensive brush for this because silicone can be difficult to remove fully from the bristles.

  • Once the silicone is poured, let it cure for 24 hours. Then take it from the mold box and remove the clay original from the mold. Find the most level area of your work space and place the mold there. An inexpensive level from Target or Home Depot will help you find the best spot to place your mold.
  • I sprayed a light coating of Epoxy Mold Release into the silicone mold before I started measuring and mixing my epoxy. This  helps the finished casting pop easily from the mold. Using a mold release saves wear and tear on the mold and prolongs the life of the mold.
  • I used AeroMarine Products 300/21 Clear Epoxy Resin to pour into the mold. This product has a 2:1 by volume mix ratio. I used very small Solo cups to measure out 2 parts 300 resin and 1 part 21 hardener. You cannot vary the mix ratio with this product to speed up or slow down the cure process. It has to be mixed 2 parts of 300 resin to 1 part of 21 hardener for it to cure properly. I used a disposable plastic knife to mix the the combined 300 resin and 21 hardener.


  • For the first pour of resin, I just want to coat the bottom of the mold with a thin layer of epoxy. I want to layer the epoxy and glitter because the glitter tends to settle at the bottom of the epoxy and it doesn’t look as nice.

  • After the first pour of epoxy is tack free, that is, it doesn’t come away on your finger if you touch it (about 12-24 hours), then do the next pour. First, I sprinkled some red and green craft glitter into the mold.

  • Next, I mixed and poured the next layer of epoxy, filling the mold up about halfway.

  • After that layer of epoxy cured, I sprinkled some silver glitter into mold. Then I mixed and poured the next layer of epoxy, almost filling it to the top, but leaving room for one more thin pour.

  • Once that layer has cured, I mixed up and poured the final, thin, plain layer of epoxy. This just ensures that there are no glitter bits poking out, everything is totally encased in the epoxy.
  • After waiting 24 hours for the epoxy to cure, popped the ornament out of the mold. Because the clay wasn’t as smooth as it could be, the epoxy appeared a little frosty. Fortunately this is very easy to fix. I mixed a small amount of epoxy and brushed a thin coat on.

  • Once the epoxy cured the ornament had a high gloss finish and you could see all the glitter suspended within it.

  • Tie a short length of ribbon through the hole on top and it’s done.

I did an ornament shape with glitter for this project.  However, you can do any any shape and embed a variety of things in the epoxy like pictures, bottle caps, coins, etc, by following the same basic steps. If you are embedding paper products, they must be sealed with a clear urethane or acrylic sealant first. Otherwise, the epoxy will give the paper a “wet” look. If you have any questions, you can always contact us at info@AeroMarineProducts.com!





Two Part Pourable Silicone Pumpkin Mold

December 1, 2016

For this project, we will use pourable silicone to create a two part mold of a pumpkin. Two part silicone mold requires two separate pours of silicone, so these types of molds usually take two or three days to make.

Materials needed:

  • Small pumpkin
  • AeroMarine 128 Pourable Silicone with Catalyst
  • Non-sulfur, non-drying modeling clay (Plasticine, Plastalina)
  • Cardboard (or foam board)
  • Hot glue gun
  • X-Acto knife
  • mixing cups and mixing utensils
  • Scale that weighs grams
  • Small plastic straw, swizzle stick or plastic toothpick (to vent the stem of the pumpkin)
  • Silicone-to-Silicone mold release
  • Gloves
  • Sharpie pen

Your work area:

  • Clean, level work surface, covered in paper or plastic for easier clean-up.
  • All materials comfortably within reach.

Project steps:

  • First, we need to construct a mold box to fit the pumpkin from cardboard and hot glue. I measure and cut the cardboard for the sides and bottom of the box first, but don’t glue them together yet.


  • Next, we need to embed half the pumpkin in modeling clay. The clay acts as a place holder for the second half of the mold. I like to clay the piece in before I glue the sides on the mold box, I find it easier than trying to work the clay into the already constructed box.


  • Then, use the hot glue gun to glue the sides of the box into place. Next, I apply a seam of hot glue to the outside of the box where the cardboard pieces meet. This ensures that the box is tightly sealed, with no place for silicone to leak out. I then use a small amount of clay to seal any gaps between the mold box and the clay.
  • Because of the curve of the pumpkin’s stem, I’m worried that an air bubble will form at the tip of the stem when it is time to cast the piece. So I’m going to press a plastic toothpick into the clay from the tip of the stem to the edge of the mold box.
  • We also need to create registration marks, or keys, in the clay.  These indentations and matching protrusions will help the two sides of the mold lock together correctly, so when I cast the piece there isn’t a lot of flash, which is casting material leaking between the two sides of the mold. I use the end of a sharpie pen to make indentations in the clay, as you can see in the picture. You can also see the toothpick embedded in the clay as well.


  • Now that the mold box is ready, we need to weigh out and mix the silicone. The 128 Silicone is a tin catalyzed, condensation cure silicone that is mixed 10:1 with the pourable purple catalyst. For the first pour of this mold, I put the empty mixing container on the scale and zeroed the scale out. This is so I’m only weighing the silicone, not the plastic mixing container. I weighed out approximately 2600 grams of silicone and 260 grams of catalyst. As you can see in the following picture, the catalyst is quiet a bit thinner than the silicone. Just mix carefully and slowly, taking care to scrape the sides and bottom of the mixing container, until it is one uniform color.


  • When I pour the silicone into the mold box, I pick a corner away from the piece and pour the silicone “high and thin”, that is, I hold the container a foot and half above the mold box (high) and pour slowly so the silicone comes out in a thin ribbon (thin). This helps reduce air bubbles in the silicone and lets it flow slowly around the piece, which further prevents any air bubbles.

img_20161117_102317 img_20161117_102331

  • Once the silicone is all poured, I lift the mold box about an inch or two of my work table and drop it several times. I do this for a few minutes. This helps encourage any bubbles to rise to the surface of the silicone and pop.
  • This silicone takes 16-24 hours for a full cure, so I’ll come back the following day to finish the second half.


  • After the first pour is cured, I rip apart my carefully constructed mold box, taking care to keep the pumpkin embedded in the silicone.


  • Next, I pull all the clay off the pumpkin. Make sure you don’t pull the plastic toothpick out because it needs to stay in the silicone like the pumpkin.
  • I use another toothpick to clean off any little bits left behind after I remove the bulk of the clay.

img_20161117_091151 img_20161117_092036

  • Then I cut more cardboard to make another mold box to fit around our first half of the mold. Before I glue to mold box in place, I generously spray the mold release on all sides of the first half of the mold. That way if any silicone leaks down between the box and the first pour, it won’t bond and make my parting seam hard to find.
  • Once the box is constructed, I spray more mold release on the first half of the mold. I focus on making sure the silicone, not the pumpkin, is well coated with the release. Some will get on the pumpkin and that’s fine, but the important thing is to make sure the silicone has a good, thick coat of mold release. I’m using Petrolease, which we carry, but you can also use plain, old Vaseline.


  • Now I weigh and mix more silicone, this time approximately 1800 grams of silicone and 180 grams of catalyst because this side is slightly smaller than the other. I pour high and thin into a corner, pick up and drop the mold box for a few minutes and leave it to cure until the following day.
  • The second pour is cured.  Again, I tear apart the carefully constructed mold box. You can see in the next photo where some of the second pour leaked down between the first half and the box, but because of the mold release, it pulls way easily and can be trimmed away.


  • After trimming the excess silicone, I can see the parting line and easily pull the two halves apart. Next, I can remove the pumpkin and the tooth pick to see the finished mold. Sometimes little flecks of clay can be left behind on the mold. The best way to clean a silicone mold is with warm water and dish soap. Do not use and abrasive soap or an abrasive sponge because you don’t want to scratch the mold.


That’s it!  Here is a lovely two part mold of a pumpkin. From here, you could use a urethane casting resin to cast a pumpkin and paint or decorate it anyway that you wish.



Next Page »