Questions about building a mold master


railBuilderDhd

railBuilderDhd

Active Member
I'm building a master for hydrocal castings and I have a few questions. For the master I'm using foam-core center and styrene to build up the building facade. First what is a good glue to use to glue styrene to foam-core? I'm trying Elmers glue but it's not drying and I can't use the regular glues for styrene as they will melt the foam and will not stick to the paper areas.

The second question I have is the ends of the foam-code, do they need to be covered with styrene so the rubber used to create the mold will not sick the the foam? I've posted a photo of what I'm thinking needs to be done to cover the foam so the rubber will not stick to the master.

samples:
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Adhesive for Foamboard

I have had great success with glueing foamboard to styrene using Liquid Nails Projects (in the blue tube).

Advantages: It's cheap (Wal-Mart, about $1.49); you get a huge tube; it dries fairly slowly giving you time to position; it dries strong - I mean STRONG! It is sanded easily and is paintable, and cleans with soap & water while still soft.

Disadvantages: You get a huge tube; it's thick and viscous, so you need to apply sparingly and use a spatula to spread it thin; the adhesive is dispensed with a caulking gun and is hard to reseal such that it won't dry up; requires mineral spirits to clean up after it dries.

Just make sure that you get the right one; there are at least five different formulations, and three of them attack foam. But the Projects one is foam friendly.

David Martin, Ph.D.
 
First, you will need to cover any part of foamcore that's being used as a master with styrene or the hydrocal will stick to the foamcore and tear it up.

I agree with David about the Liquid Nails Projects. I put just a small amount on scrap styrene and us a small trowel to transfer it to the building and spead it as needed. It took me a while to finally realize that you need a really thin coat to for it work right. When I'm done, I use a big nail to seal the hole in the Liquid Nails tube and then put the tube in one of the big ziplock freezer bags and seal it. Keeps down the smell and the remaining Liquidnails seems to last longer.
 
Thanks all for the postings and great helpful info. I'll keep posting as I go to show my progress, victories and failures (such as the foam-core). I would like to hear any comments on the new master being built such as any issues that I may be facing down the line. This is my first time to try this I'm not sure what I really need to be looking for when I build the styrene master. I do have one concern about the areas I have styrene glued together and I sand the edges to be flush do I need to worry about the sanded area being a problem with the rubber sticking to the master?

New Samples:
styreneMaster02.png

Here you see the front of the North end of the building.

styreneMaster01.png

This shows the backside of the wall with the styrene supports.
 
Types of foamboard

So far, it looks real good. Nice precise angles and corners. Don't forget that the foamboard comes in other thicknesses besides the 3/16" sold at Wal-Mart.

Elmer's, who makes the Bienfang foamboard, also makes thicknesses of 1/8", 1/4", and 1/2"; most available in white on white as well as black on black.

Try Cheap Joes (http://www.cheapjoes.com/art-supplies/8742_bienfang-foamboard.asp) for great prices and low shipping costs. I have no vested interest here, but I just bought $130 worth and it would have cost me considerably more at Wal-Mart.

There are also some very nice tools for cutting perfect circles (http://www.cheapjoes.com/art-supplies/18295_foamboard-circle-cutter.asp) and edges for mating up wall sections (http://www.cheapjoes.com/art-supplies/18300_foamboard-rabbit-cutter.asp).

David Martin, Ph.D.
 
As David said, your masters look fine to me. As long as your sanded area is smooth to the touch, you shouldn't have a problem with rubber sticking, although all molds will have some rubber stick somewhere. Just plan on the idea of using some body putty to touch up any small imperfections.
 
Here is an update on what I've been able to accomplish today. I'm happy so far with what I'm getting done and how it looks. Now that I see it in the photo I can see I have more clean-up than I thought but that's how it always goes.

Question: Do I need to worry about the areas I sanded on the styrene and the rubber sticking to those areas?

UPDATE:
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Thanks for looking and all your helpful comments.
Dave
 
Dave, if you read my response directly above your post, I think I answered your question about the sanded styrene. Just spray a little more mold release in those areas. No mold is ever perfect so you'll have touchup to do on each mold no matter of careful you are.
 
Well, I'm at a point I need some help with to figure out how I should move forward with the mold master. I know one of the first rules is creating a mold is never have the mold lap back on itself. Well when I run the quoin to the side wall I have a ledge from where the quoin ends and the edge of the front wall master ends. I was thinking that since most of the quoin is not very deep so the area that lapse back on itself is little so would this be something that I would be able to pull the hydrocal out of the mold when it's cast with a chance of not getting stuck or destroying the master. I know there are the top and other ledges that stick out a bit far but I think it may still work. I still have more work to clean up the corner where the front and side styrene joins but I needed to know if I will need to change the side before I do any more work.
I would love to hear how others have work out this problem before and please give me some suggestions on how to move forward.

Samples of the quoin side:

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Thanks
Dave
 
Boy, Dave, you've picked a tough detail to reproduce in mold. As you say, the mold should be as flat as possible and the sides whould not lap back to the mold surface. In this case, the corner stones and ledges are way too far out to work in a mold and wrap too far around the wall. I'd do two things. The first is cut back the ledges to about half of how far they project now. The second would be break the mold into two pieces, one the main structure and the second the quoin. I know this is more work but you're right about both the mold and master getting torn up if you try to proceed now.
 
Jim,
Thanks for the reply. I've talked with a friend (Tony Burgess) who thinks if I cut the ledges down to about half and use strong RTV rubber I should be able to get casting out without tearing the mold. I've worked down the ledges and will need to replace some of the one on the left side because I cut a little too close to the stones and the top 3 stones on the from right side are to short from the left edge to the right. Not by much but it's better to fix it now then find out after I've carved the second master. You can see what I'm talking about in the 5 photo from the top of this tread.

Dave
 
Dave, with a lot of mold release and RTV rubber, it might work but I'm still dubious. Cutting back the ledges will help but getting the outer edge of that quion to peel cleanly with the rest of the mold is going to be tricky. I hate to see you waste the work on the master but the only way you'll know for sure is give it a try, I guess. Good luck and let us know how it turns out.
 
Jim,
I'll keep you posted and I was thinking if it doesn't work out than I can do like you mentioned and cut the styrene master into parts and cast those into molds. I will try it as one first then if needed I can cut into multiple parts.
Dave
 
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