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Super Easy Latex Molding for Concrete

August 28, 2019

Latex is a great, inexpensive material for making glove molds. Because it goes on one coat at time and needs time to dry between coats, it can take quite a while to make the mold. You can use AeroMarine Products Black Rubber Powder as both a latex extender to reduce the amount of latex used, as well as a latex thickener so fewer coats need to be applied. Latex starts to break down when exposed to higher temperatures so it’s not good for casting exothermic urethane or epoxy. It is great for concrete, plaster, hydrocal and other stone mimicking materials.

Materials needed:

  • An original to cast from (I used a terra cotta planter)
  • AeroMarine Products Latex Mold Making Rubber
  • AeroMarine Products Black Rubber Powder, a latex additive
  • Quick-set concrete
  • Mold release that is safe for latex and concrete. I used a silicone based paste.  However, a 1% dish soap and water solution or a 1:5 mix of castor oil and denatured alcohol work well too.
  • Gloves, eye protection (googles), barrier mask
  • Plastic measuring/mixing containers and utensils
  • Inexpensive brushes (I used 1 inch chip brushes)
  • A piece of cardboard for your original part to sit on while the mold is being made.
  • Mothermold materials, I used a plastic bucket and cardboard with duct tape. For a more lasting or production quality mothermold, plaster with fibers or epoxy with fiberglass works well.

Your work area:

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

Project steps:

  • First I wiped down the planter with a damp cloth. It doesn’t need to be scrubbed clean.  It needs to be free of dust and loose dirt.
  • Once the planter air dried, I set it on a piece of cardboard on my work bench.
  • I got my container of AeroMarine Products Latex Mold Making Rubber and gave it a good shake for about 20 seconds and then opened it.
  • Using a chip brush, I brushed a nice thin coat of latex all over the planter. I took care to work the latex into the details, making sure that the latex wasn’t applied thickly enough to have any air bubbles. Once I got to the bottom outside of the planter, I extended the latex an inch or two out from the planter on to the cardboard. This gives the mold a small lip that helps with casting and de-molding. This first coat is so thin it almost looks translucent, especially once it dries.

  • I brushed a small square of latex onto a corner of my cardboard. With each coat of latex I apply, I brush on a coat onto this little square. This gives me an idea of how the latex is building on the planter and I can poke and prod it without disturbing my actual mold.
  • I let this coat air dry for an hour or two until I could see it was cured all over. The AeroMarine Products Latex changes from a cream color to a sort of band-aid tan as it dries which helps you know when each coat is fully cured.
  • I rinse out my brush with room temperature water and let it air dry. The latex can dry faster the brush, so I usually have two brushes in rotation. After 3-6 coats, the brushes get too gummy and clumpy to use and I toss them. You can also just toss each brush after you use it since a box of chip brushes is pretty inexpensive. I’m just kind of a cheapskate and like to re-use things if possible.
  • I repeated the process of brushing on a thin coat of latex and letting it air dry 3 more times. The first 4 layers are considered the print coats as they pick up all the detail from the surface of the planter (or whatever you’re molding).  That is why you apply the latex very thinly to be bubble free.
  • After the print coats are done, I started adding AeroMarine Products Black Rubber Powder to my latex. The black rubber powder thickens and extends the latex, meaning you can use less latex and apply fewer coats. I poured the amount of latex I thought I could use in a coat (approx. 5 ounces) into a plastic cup and then added the same amount (by volume) of black rubber powder. I mixed well with a plastic utensil until the black rubber powder was evenly distributed through the latex. It should look like a cookies and cream shake when well mixed.

  • I applied the thickened latex to the planter (and my little square in the corner) evenly.
  • To speed up the drying process for these coats of latex, I used a heat gun (not a hair dryer) on the lowest setting. I kept the heat gun about 6-8 inches from the surface of the mold and kept it moving so as not to overheat any one area. This helps reduce the cure time from 2-4 hours to about 45 minutes to an hour.

Freshly applied Latex with Black Rubber Powder

Cured Latex with Black Rubber Powder

  • I repeated the process with the latex mixed with black rubber powder and the heat gun 10 times.
  • I applied 2 finishing coats of plain AeroMarine Products Latex to the planter. I like to do this because it smooths out the bumpiness the black rubber powder gives the latex.
  • So, all together I applied 16 coats of latex to this planter.  4 coats of plain latex, followed by 10 coats of latex mixed 1:1 with black rubber powder, followed by 2 coats of plain latex again.
  • I peeled the latex mold off my original, slowly and carefully so as not to damage it.

  • So here I deviated from the mold making norm. Normally for a latex mold you would make a mother mold to support the thin latex mold. The mother mold can be made out plaster with fibers or fiberglass and epoxy or a urethane paste or various other materials. However for this project I didn’t want to put in the time or expense of doing a “proper” mother mold because I knew I was only going to use this mold a few times. So I used a gallon plastic measuring container, cut down to size and cardboard with duct tape.

  • For proper mother mold technique, look here: https://www.aeromarineproducts.com/silicone-glove-mold-and-fiberglass-mothermold/    https://www.aeromarineproducts.com/making-brushable-silicone-mold-mother-mold-part-2-2/
  • Once my mother mold was ready and my silicone paste mold release applied to the inside of the mold cavity, I mixed my quick set concrete according to the manufacturer’s directions. The concrete I used gave some latitude with how much water to add to make to concrete more or less viscous. Because I don’t have any of the usual concrete tools, like a vibrating rod, to get bubbles out, I made the mixture as thin as the directions allowed.
  • I drummed my fingers all around the mold as I was pour the concrete to help the bubbles rise and pop.
  • Once the concrete was set (check manufacturer directions) I cut my mother mold off and carefully peeled my latex mold off the casting.
  • And I think it turned out pretty nice!

So that’s how to use AeroMarine Products Latex Mold Making Rubber and AeroMarine Products Black Rubber Powder to make a mold for concrete casting! If you have questions about this project or any other project, give us a call at 877-342-8860 or drop us an email at [email protected]  You can also contact us through our website at http://www.aeromarineproducts.com 

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