I have been making my first Hydrocal castings and have a simple question--what is the optimal amount of time to leave it in the mold before removing? As a follow-up, what is the harm in leaving it in the mold for an extended amount of time? (I have already learned the problems of removing it too soon.) As always, thanks in advance for anticipated sagely advice.
Richard
Plaster gets wram as it sets up and I was taught that you should wait until it is no longer warm to de-mold it. This has worked well for me. I have had no trouble with castings that sat in the mold for an extended period as long as a suitable mold release was used prior to pouring the plaster. You can also wait until the plaster begins to set up somewhat and place it against a surface where you want your rock casting to adhere. There is a nice discussion this in the thread about "which is the best plaster"
Joe
Edit: This is the thread I was referring to: http://cs.trains.com/mrr/f/11/t/210248.aspx
I like to put the mold in place on the hardshell and wait until it gets warm. I then remove the mold at that point. I like to dunk the molds in water and clean them before the plaster sets up completely. In my experience, If the mold has lots of detail chunks of plaster will get caught in it no matter what you do. It is eaiser to remove these while the plaster is not fully cured.
Have fun,
Guy
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I remove the casting from the mold after and hour or so.
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NP2626 I remove the casting from the mold after and hour or so.
I haven't done a plaster of hydrocal mold in quite some time, let's say eight years, but I recall that the instructions say to leave the item for at least an hour. I waited for about two or three, but never found that I needed any longer.
On an only-somewhat-related subject, if you are affixiing your plaster molds to already extant ground goop or plaster cloth terrain, you are miles ahead by placing them before the terrain has dried. This applies to plaster rock molds or to another batch of mixed ground goop...add it to the previous surface BEFORE that earlier surface dries!!! Otherwise, you'll lose a lot of water wicked into the dried previous surfaces, and your newest pour/plaster won't cure so well as a result of the water loss.
selector NP2626 I remove the casting from the mold after and hour or so. I haven't done a plaster of hydrocal mold in quite some time, let's say eight years, but I recall that the instructions say to leave the item for at least an hour. I waited for about two or three, but never found that I needed any longer. On an only-somewhat-related subject, if you are affixiing your plaster molds to already extant ground goop or plaster cloth terrain, you are miles ahead by placing them before the terrain has dried. This applies to plaster rock molds or to another batch of mixed ground goop...add it to the previous surface BEFORE that earlier surface dries!!! Otherwise, you'll lose a lot of water wicked into the dried previous surfaces, and your newest pour/plaster won't cure so well as a result of the water loss.
There is an easy solution to this, which is to spray the area with wet water prior to application of the new plaster.
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"If you think you can do a thing or think you can't do a thing, you're right." -- Henry Ford
If you're unsure of your bond for a hardened casting, mix a small batch and butter the backside . any oozing is not a problem as it can be removed, carved or used to place "bits" aroung the casting for blending. I will place a partially hardened mold and allow to conform to any irregular shape of the base. Some additional holding in place is usually needed to firm up.
A hint, dry fit or get a very good idea as the the placement of castings before "plopping" them in place. A feel of the type of casting, type rock, strata etc. This is to eliminate that popped on patchwork look, individual or broken bits can be fitted to your satisfaction.
Modeling B&O- Chessie Bob K. www.ssmrc.org
CTValleyRR selector NP2626 I remove the casting from the mold after and hour or so. I haven't done a plaster of hydrocal mold in quite some time, let's say eight years, but I recall that the instructions say to leave the item for at least an hour. I waited for about two or three, but never found that I needed any longer. On an only-somewhat-related subject, if you are affixiing your plaster molds to already extant ground goop or plaster cloth terrain, you are miles ahead by placing them before the terrain has dried. This applies to plaster rock molds or to another batch of mixed ground goop...add it to the previous surface BEFORE that earlier surface dries!!! Otherwise, you'll lose a lot of water wicked into the dried previous surfaces, and your newest pour/plaster won't cure so well as a result of the water loss. There is an easy solution to this, which is to spray the area with wet water prior to application of the new plaster.
Yes, although I never did like going to all that effort and time. I have done the pre-wtting, but only when I couldn't manage to get to the previous pour in time. My method has been to do large batches added to other large batches so that I had several hours, even over-night, to come back and apply molds or to add yet another adjacent batch.
OK, ITH AS BEEN TN THE MOLD LONG ENOUGH ALREADY! TAKE IT OUT!
ROAR
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What is the best mold release agent?
RicZ
Don't know what's "best" but I've had good luck using wet water for my rubber molds and PAM kitchen spray for my solid molds.
Since Woodland Scenics molds are rubber, albeit heavy rubber, I assume "wet water" would be better than PAM. It is too bad Woodland Scenics does not provide more information with their products.
Wouldn't PAM leave a residue that would interfere with painting?
I only use a very light spray of PAM and I only use it on solid forms (ie those made out of styrene or wood). I have not had any problem with the PAM treated molds transferring enough mold release to the plaster castings to interfere with either staining or painting. As I mentioned in my earlier post I use wet water for rubber molds (both Woodland Scenics and home made ones from latex rubber.)
If it turns green and fuzzy, then it *is* Moldy.