Has anyone ever tried to mix cement with resin for the mold making? if so what’s the pro and con for doing it? I have tried for sealing holes in the concrete floor but never try for mold yet.
Cement is to concrete what resin is to a fiber reinforced lamination. What you are trying to make is known as polymer concrete, a mix of resin and aggregate.
You can do this but there are drawbacks. It is heavy. And by heavy, I mean heavy. Even small molds have handling issues. We have a mold that is about 30" x 54" x about 1" thick and it probably weighs around 150 lbs. The material is not particularly strong in tensile so you can get cracks with a relatively small amount of force.
The pro’s that I can see after building about a dozen molds like this are they are cheaper and quicker to build. If you are only using them for a short run and are careful with them, they are okay.
The first couple we built, we just skinned the face surface with a 3/4 oz mat and vinyl ester resin and then filled with the polymer mix. After cracking one, we beefed up the glass a bit with a couple of 1.5 oz mats on the face and a 24 oz woven roving on the back.
The reason why I want to use this mix is for backing purpose, I need the mold to stay in its shape over period of time and also quick build up.
Yes, that is what we used it for as well. If you are certain that this is the way you want to go, the mix we used consists of the following:
67% dry play sand
28% resin
5% micro balloons
These percentages are by weight, not volume. The mix will flow a bit so it needs to be poured into a form. You could add more filler and make a thicker mix to trowel on If you wanted to. Also, I used AOC’s LPT-68000 Low Profile Tooling resin.
Peak exotherm for the mold I mentioned in my other post was 161 degrees F. Fairly low for a mass of material so it shouldn’t be a problem if the pattern is well made.