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towazy
New Hire
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 Posted - 07/29/2012 : 2:13:06 PM
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I am casting my own bridge abutments for the BMLA bridges for my layout. I have built the mold from styrene and lined it with basswood strips to simulate a poured concrete abutment. I am going to use hyrocal for the casting. I am hoping to reuse the mold for at least four castings. Im looking for ideas or recommendations on how to get the casting out of the mold with minimal damage to the mold. Should I use anything to act as a mold release?
If I end up damaging the master mold,I guess I could always make a rubber mold of the initial casting.
This is my first posting to the list,although I've been lurking and following for many years and have gotten tons of ideas and methods from the many talented posters.thanks for sharing.I admire the artistic talent represented here greatly! I have built a number of craftsman kits,and have a number more in "storage" just waiting for the layout to get further along.
Tom
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desertdrover
Engineer
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Posted - 07/29/2012 : 2:34:36 PM
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I have done other types of pours the same way using a siliconized snow plow coating. Spray your wood strips inside the mold first with any siliconized spray then pour your hyrocal.
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Louis
Pacific Northwest Logging in the East Coast
Post count: 5000 posts added to below count.
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mabloodhound
Fireman
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Posted - 07/29/2012 : 2:37:59 PM
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Tom,
Without seeing a photo of the mold, it is hard to determine if it will be reusable.
Will the basswood strips slid out of the mold with the finished casting?
If yes, then it may be possible to reuse it, and just put the basswood lining back in.
Remember, any negative angle in the sides will trap your casting so it must be at least perfectly square or even with a slight camber towards the opening.
Otherwise, a rubber mold would be the way to go.
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towazy
New Hire
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Posted - 07/29/2012 : 2:57:24 PM
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Thanks for the replies. Dave,the mold is styrene glued together. The basswood is glued to the inside of the mold with contact cement,Walthers Goo. It is all 90 degree angles. My plan was to remove one or two sides of the mold to remove the casting,then reglue the styrene sides back on for the next pour,but I'm not sure if the basswood boards will stay or come out with the casting. I was wondering if there is some way to make the casting less sticky to the wood lining.
DD,your idea of silicone sounds interesting. Will it effect the wood? The wood is unsealed because I want the grain texture to show. Can you elaborate further on what you did and your methods?
Tom
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dave1905
Fireman
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Posted - 07/29/2012 : 3:29:15 PM
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Pam, paste wax, furniture polish.
What I dis when I made tunnel portals, etc. was to make the sides of the model separate from the face.
I glued the face to a piece of plywood and then glued the sides (left, right, top, bottom) to the narrow sides of some 1x2's. The 1x2's were screwed to the plywood. I poured plaster in the mold, let it set, then unscrewed the 1x2's and removed them, then pulled the casting off the face. I waited just long enough that the plaster was solid, but still warm. If you let the plaster fully cure until its cold and hard, it will be a woolly bugger getting it away from the mold.
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Dave Husman
Iron Men and wooden cars
Visit my website : www.wnbranch.com |
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eTraxx
Fireman
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NE Brownstone
Crew Chief
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Posted - 07/29/2012 : 4:49:50 PM
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I'm an advocate of making a silicon mold then casting duplicates. The reason being that once you break down the original mold you may damage it and you may have to start from scratch, which may or may not be a big deal. But, if you make a mold you can pour abutments to your heart's content. Got a few modeling buddies, sell a few extras to pay for the mold materials.
OOMOO from Smooth-on (you can get it from Micro Mark) is cheap enough and easy enough to use without any need for degassing. Build up your original mold exactly how you already planned, but seal the wood all around because the wood will absorb water from the plaster and may get all bent out of shape. Ask me how I know. A clear sanding sealer works well, just don't sand it. You are using as a sealer only and it won't destroy the wood grain detail unless you over seal it. If it is sealed well it will release from the mold fine.
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mabloodhound
Fireman
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Posted - 07/29/2012 : 5:08:40 PM
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The PAM or similar cooking spray sounds like a good idea.
Be sure to let us know how things go.
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RonH56
Fireman
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Posted - 07/29/2012 : 6:22:48 PM
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Tom,
Call me a Chester if you like... But for concrete abutments I use either wood or my favorite- 1/2" thick foam ( not beaded type) paint em up with latex paints and done in an hour or so.
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"What the heck wuz that?"
Ron Haviland
Owner/Operator
Red Water Railway Co.
L.B. & S Shortline RR.
Podunk, New England
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desertdrover
Engineer
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Posted - 07/29/2012 : 9:12:27 PM
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quote:
Originally posted by towazy
DD,your idea of silicone sounds interesting. Will it effect the wood? The wood is unsealed because I want the grain texture to show. Can you elaborate further on what you did and your methods?
Tom
Once you glued down your wood strips to your styrene they should hold if you glued them down well.
Once you spray the wood with silicone (it won't affect the wood or grain), it just makes it slippery so the hyrocal won't stick to it. The water from the hyrocal should not be a problem, because the silicone will bead up any dampness and keep it from soaking into the wood.
Keep spraying each pour, you should be able to make many casts before it's no good.
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Louis
Pacific Northwest Logging in the East Coast
Post count: 5000 posts added to below count.
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towazy
New Hire
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Posted - 07/30/2012 : 10:57:45 AM
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Thanks for the ideas guys. I went ahead and poured the hydrocal last night. I waited for it to set,about half an hour,and took it out of the mold.There was just a very little "sticking",but I liked the effect it left. In a couple of places it has the look of deteriorating concrete where the outer,smooth layer falls off leaving the underlying aggregate showing. There also were a few bubble holes,which I filled promptly and easily as the casting was not cured yet.
As for the mold,I could reuse it,but there would be a loss in quality as the hydrocal tended to fill in and obscure the wood grain and even in between the individual boards.Maybe if I had let the casting completely cure in the mold first this wouldn't have occured,I'm not sure. I guess I could reline the mold with new stripwood,which I might do as I only need one more casting.This time I'll let the casting cure in the mold and see what the effect is.If I was in need of many more,I'd probably make an RTV mold of the first casting and go in that direction.
Tom
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desertdrover
Engineer
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Posted - 07/30/2012 : 11:30:35 AM
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quote:
Originally posted by towazy
Thanks for the ideas guys. I went ahead and poured the hydrocal last night. I waited for it to set,about half an hour,and took it out of the mold.There was just a very little "sticking",but I liked the effect it left. In a couple of places it has the look of deteriorating concrete where the outer,smooth layer falls off leaving the underlying aggregate showing. There also were a few bubble holes,which I filled promptly and easily as the casting was not cured yet.
As for the mold,I could reuse it,but there would be a loss in quality as the hydrocal tended to fill in and obscure the wood grain and even in between the individual boards.Maybe if I had let the casting completely cure in the mold first this wouldn't have occured,I'm not sure. I guess I could reline the mold with new stripwood,which I might do as I only need one more casting.This time I'll let the casting cure in the mold and see what the effect is.If I was in need of many more,I'd probably make an RTV mold of the first casting and go in that direction.
Tom
So I take it, from what you sad, you didn't silicone the wood/mold first?
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Louis
Pacific Northwest Logging in the East Coast
Post count: 5000 posts added to below count.
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