2 part foam [again]

[outwoods taxidermy]

what is it with this stuff'' sometimes it works and sometimes it dont,
i was moulding some roe heads both out the same mix 1 shrunk after a few days and the other was perfect
 i dont get it as they were both done at the same time....

[bill@hogheaven]

Never saw one shrink. Keep all the variables the same. Temp of molds & foam, amount poured, should always be the same & measured by weight. Moisture is a problem, dont store small amounts so condensation can occour in the container. Keep time curing in the mold & mixing time the same. Dont mix manually, use a drill. Get the picture?

[outwoods taxidermy]

these were mixed by weight to the gram and a cordless drill used to mix it both out the same pot but 1 had some shrinking around the nose area
and the other dident, also pva was used as a releaser in the fibreglass mould...........

[bill@hogheaven]

Did you have equal amounts of foam in each mold? that would change the density if not. Incomplete mixing? Sometimes you just have to scratch your head & do it over.

[Ravenson]

ok what type of mold release are you using and what foam are you using? oops sorry i see you are using PVA.  The reason I ask do not use a silicone  based mold release with foam especially soft foam.  the silicone fluid in the release can cause the foam to shrink. I have seen foam shrink up to a week after it was cast, and a basket ball size piece of 5 pound flex foam can shrink down to around the size of a tennis ball  all because of the mold release.  One more thing in my experience foam likes a warm mold to get the best castings warm you mold up.   Remember foam is a lot of small bubbles  anything that can cause the bubbles to break can deflate the foam, also some foams do not reach full cure till several days latter.

Jeff 

[outwoods taxidermy]

ok thanks'' but i'l trial and error again..........

[Ravenson]

lol I hate to say it but in my experience trial and error is the way it goes with foam.

Jeff

[Rick Carter]

two things can make the foam mannikin collapse. Improper mixing. Needs to be mixed at least 25 seconds high speed. Or improper percentage of A vs. B re-read the percentage in the directions. all urethanes are not a 50 to 50 mix.

[outwoods taxidermy]

it does say on the labels to mix 50-50, i use a cordless drill to mix until start to rise then i pour but still get different reactions..... thanks anyway

[jermh1]

what brand of foam is it?
I got a batch of 2.5lb foam 10gal, kit about 4yrs ago and its still going strong, just about out 1/2 gal left, and it just goes  no problems, after a long sit, I have to break the crust on part A but no problems foaming up and hardening. from 40deg to 90 hand mix or drill. warmer and drill mixing gives better expansion, but it still works the other way.   it was from IPS not sure if they changed their name or formula, but it works for me, and after seeing some bad foam posts on here I am a bit leary about getting more foam.
Jeremy

[Jim B]

Most foam these days,is formulated to mix 50/50 by VOLUME,not weight.Find out for sure,which yours is.Generally,the problem would be an improper mix or it was water contaminated.If your mixing container wasn't perfectly dry,that could do it.I'm not sure if PVA has a little water in it or not.If it does,maybe the foam hit some PVA that wasn't dry yet.I'm not sure why you are using PVA.I would use several coats of paste wax and let them dry.