casting with polyester resin..bad?

[Kommissar]

so i'm delving into casting and molding right now, and i used the only resin i had on hand for a few test pieces of a mold i'm happy with.. fiberglass standard polyester resin, the stuff you get a home depot.

is that considered bad form? i'm aware more expensive resins create a better cast, with fewer airbubbles, but is it wrong for me to use polyester resin?
would you buy a polyester resin cast of something?

thanks for the advice.

 

[exoray]

Don't waste your time...

It's not a casting resin, PERIOD... Any cast will be brittle (the bigger the part the more brittle) and in time (no much) it will dry out to the point that if you look at if funny it will crack and if you drop it, you will be playing a game of 1001 pickup parts...

I personally would never buy any cast part done in polyester, without a fiber matrix, and you will likely find few that will around here... There are plenty of horror stories many can tell about people who have attempted to do just what you plan to do and they are not happy endings...

Get the right stuff, use polyester for laminating as it works very well for that purpose, and casting resin works very well for casting...

And honestly it's not that much cheaper, you can get urethane casting resin for about $50/gallon in small 2 gallon kits (about $35 a gallon in 10 gallon kits) that isn't that much more then Home Depot sells the polyester resin for...

 

[kwalsh0000]

Plus urethane resin is also better for your health (well... its just not as bad or as smelly as polyester ) Still wear proper safety equip either way to keep safe from the fumes and besides you will get a much sturdier casting without having to lay fibreglass.

 

[Nwerke]

Also, polyester resin can heat up ('exotherm') pretty sharply, which may ruin moulds or cause cracking in the piece, in extreme cases it may catch fire or char in the mould.

Oh, and it may shrink while it is at the gel stage of setting. You can then get a thin layer on the surface of the part which is still liquid. When this finally sets, it sets as a network of ridges all over the part.