Preparing Models and Molds

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One of the most common frustrations in making molds and casting parts comes from parts sticking to molds. This is the number one source of problems cited by toolmakers and why we constantly investigate newer and better ways to seal and release models and molds to ensure easy part release.

And nothing has yet matched the following combination of
Freeman Wood and Plaster Sealer, Freeman Wax Release, and, with a notable exception of casting a urethane against a urethane, which we’ll address at the end of this video segment.

Sealing your pattern/model

Sealing is required anytime you work with wood, plaster or sheet wax, since these materials are known to interact with tooling plastics. Applying a sealer, such as what we are doing here with this
pure bristle brush, will not only prevent the moisture in the wood or plaster from reacting with the tooling plastics, it also smoothes the surface.

Here we are applying our
Freeman Wood and Plaster Sealer, a fairly thin viscosity, lacquer-based paint, on a piece of wood.

And here is what the first application of the sealer looks like.

After the first coat has dried (which will take about half an hour), you’ll notice that the sealer has swelled the grain and made it rough. So you’ll want to take
sand paper or scotch-brite and lightly sand it down to make it smooth again. Sanding is not necessary when working with plaster or sheet wax.

When you’re done, wipe it off with a cloth and then apply a second coat of sealer.

After allowing the second coat to dry, you will again want to sand the wood very lightly and then wipe it off with a cloth.

We are now ready to apply the release agents.

Applying Release Agents

After the sealer has been applied, it is time to cover the entire surface with Freeman Wax Release - a semi-paste, typically applied with a brush.

You may allow this coat to dry or immediately wipe the off excess with a cloth.

We suggest at least two coats of Wax Release to make sure your entire part is covered evenly.

Next, you’ll apply two layers of
Partall PVA Mold Release, which is a polyvinyl alcohol that you can apply with brush or a spray.

PVA forms a thin film – almost like a plastic wrap – which serves as a barrier coat for any of the active ingredients in the epoxies, urethanes, or polyesters.

The green color ensures complete coverage.

Each coat will require a half hour of drying time unless you use a fan or air hose.

Here you see the second coat being applied. Note how the material self-levels, which makes using a spray unnecessary, although some people prefer to use a spray in order to prevent brush marks.

After the second coat of PVA has dried thoroughly, you will apply a final coat of Freeman Wax Release.

Be very careful when buffing this last coat – do so very gently so as not to break through the layers of the PVA.

Your part or model is now ready for casting

Casting Urethane Against A Urethane

The only exception to this releasing procedure is when casting a urethane against another urethane, such as we’re doing here, pouring our Repro fast-cast urethane into a mold made out of Repro. In these cases, you should only apply the PVA once – to either the model or the mold, but not both.

Here, since we used the wax, PVA, wax procedure on the original model, we do not want to use PVA on the mold itself. Instead, we only apply three coats of wax release to the mold before casting our part. Otherwise, we risk having the solvents in the urethane react with the PVA in a way that forms a bond, rather than enabling easy part release.