NOBLNG Posted January 7, 2021 Share Posted January 7, 2021 (edited) Is primer a smooth enough finish over milliput and Tamiya putty on a resin casting master? Or is some sort of paint or sealer required? Thanks, Greg. Edited January 7, 2021 by NOBLNG Quote Link to comment Share on other sites More sharing options...
peteski Posted January 7, 2021 Share Posted January 7, 2021 Greg, the mold material will pick up the surface finish of your master, and the resin cast parts will look exactly like the master. It will even pick up fingerprints. If you want your cast parts to have primer-like finish, then yes, it is good enough. If you want your cast part to have gloss finish, then make the master glossy. What is the master made of? If it is porous, make sure the use enough coats of primer or other sealer to prevent the mold material from soaking into the master. Quote Link to comment Share on other sites More sharing options...
NOBLNG Posted January 7, 2021 Author Share Posted January 7, 2021 37 minutes ago, peteski said: What is the master made of? If it is porous, make sure the use enough coats of primer or other sealer to prevent the mold material from soaking into the master. It is a die cast that I have modified with Milliput, Tamiya basic putty and styrene pieces glued on. The Milliput I have sanded with #3000 and it is very smooth. I am wondering if a barrier of some sort is necessary to protect it from the silicone or the mould release? Quote Link to comment Share on other sites More sharing options...
peteski Posted January 7, 2021 Share Posted January 7, 2021 Assuming that you use RTV silicone for the mould material, read its specs sheets and instructions on its use. The cure of some RTV silicones (there are platinum-cure or tin-cure materials) can be inhibited by some materials. Make sure that all the materials in the master are compatible with the RTV rubber. Hopefully the entire master is covered with primer. Otherwise, the areas of milliput might have slightly different texture from the primed metal. If the master has a coat of primer and you are also using mould release agent (which often is not needed with silicone RTV), then I believe you should be all set. Again, read all the documentation provided with the RTV silicone. Quote Link to comment Share on other sites More sharing options...
robdebie Posted January 7, 2021 Share Posted January 7, 2021 9 hours ago, peteski said: Hopefully the entire master is covered with primer. Otherwise, the areas of milliput might have slightly different texture from the primed metal. If the master has a coat of primer and you are also using mould release agent (which often is not needed with silicone RTV), then I believe you should be all set. Again, read all the documentation provided with the RTV silicone. Agreed, cover your master with one final layer to achieve a uniform texture, otherwise there's the risk of imperfections showing up after mold-making. Here's a bomb that I did, as an example. I used Mr Surfacer from a spray can, but basically any paint / primer will do. Peteski is right that platinum-cure silicone rubber is sensitive to some materials and then will not cure. But I never had that happen with cured (!!) paint. Rob Quote Link to comment Share on other sites More sharing options...
NOBLNG Posted January 7, 2021 Author Share Posted January 7, 2021 Thanks Pete and Rob. I will put a coat of primer on it all and sand it as smooth as I can get it. Quote Link to comment Share on other sites More sharing options...
Chariots of Fire Posted January 8, 2021 Share Posted January 8, 2021 Agree with what has been said. Don't forget to put a release agent on if you are doing a two part mold. Wouldn't hurt to do the master either to be sure that nothing sticks in the process. Quote Link to comment Share on other sites More sharing options...
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