Concrete Mold Making

I've been thinking about making a concrete mold from a master AAC block carving, and I ran across an excellent resource today. It's a web site for a company named Smooth-On.

They have some really excellent step-by-steps on how to make molds for 3-D models.

Here's my shopping list to make it happen:

2-Gallon Kit “Brush on 50” Polyurethane Rubber for the mold. $98.00
Sealer - will be plain old shellac, which I already have.
Release agent “In & Out” (brush or spray on) $31.50
Plasti-paste 1-1/2 gallon (to create the "mother mold" around the inner polyurethane mold) $44.00

All this adds up to around $175 plus shipping. It seems a bit excessive for (1) mold.

I know a few of you have done this type of work before. Any advice would be much appreciated.

Mahalo!

Aaron

This method sounds very similar to early (current?) fiberglass boat making. It all starts with a wooden plug from which the mold is made. The plug is waxed and resin soaked fiberglass is laid over it. The molds were good for about 50-100 boats before a new mold had to be made. Would fiberglass be sturdy enough to serve as a concrete form? Maybe the old boat-making procedure would be cheaper?

In the '80s I did some simple stuff with clay (for the original) and plaster for the mold), as well as fiberglass mold products from TAP Plastics. (Taylor Art Products I think they used to be called) For a long time I had a life sized swordfish mold, and made latex swordfish stoles for christmas gifts. (as well as cement and ceramic swordfish)

For the cement, I've used vasoline or diesel for the mold realease, but I was just goofing around and not working on particularly fine priducts.

It's heavy (cement) and thus the outword force can be great on larger projects, but I've only had a few things ever burst...I just taped the hell out of things and clamped and rubberbanded the hell out of things (old innertubs)

Hi give me a call I can see if I can cut your cost on some of that stuff I make molds all the time .Regards Jymmy 626 893-4338 cell .

Silverline & Gigantalope,

After reading that website step-by-step, I realized that there's lots of methods for this type of thing. Here's a quick recap of the method that seems best for say 2 foot or larger tikis:

1. Seal the piece. There are many sealers, but shellac seems to be the easiest and cheapest to me (besides I've got plenty on hand).
2. Apply the mold release.
3. Apply around 4 coats of brush-on polyurethane rubber over the piece, building it up to about 3/8" thick.
4. Use a marker to pre plan where the splits in the mold will need to be be when the mold is removed and apply "border" lines accordingly.
5. Use modelling clay to set up little "walls" (for lack of a better word) along the "borders" where the splits in the mold will occur.
6. Apply the "mother cast" over the polyurethane mold for strength. You can either use a special casting product or plaster and burlap. Do one of the sections up to the modelling clay walls, let it dry.
7. Remove the modeling clay, apply vaseline to the dried edges of the piece you just cast, then cast the next section right up to it.
   8 ) When all the sections are cast over, use a mallet and screwdriver to split them along the border lines and remove the mother cast.
8. Use a razor/knife to cut open the polyurethane mold (careful where the seam goes), and take off the mold.
9. When ready to pour concrete, put all of the pieces back together (polyurethane mold back inside of the mother cast), spray/brush mold release on the inside of the mold. Use straps, bungees, etc. to hold it all tight together. Then pour the concrete, let it cure, and remove the mold.

This is all from researching the web, and I might have missed a thing or two, but that's the general gist of it as far as I can tell. If anyone has some more tips I'd love to hear them.

The "smooth-on" website also has a step-by-step video for $20 that is probably well worth the money.

Tyger Jimmy,

Thanks for the offer! I will call you tomorrow at lunch if you don't mind.

I will do a step-by-step on this once I get it started. It may be a while, though.

Cheers,

Aaron

AA I love you step by steps. They are helpful and fun to watch the progress that we don't have to invest the work into.

Of everyone here, I give you the award for trying new things in new materials. You are a true tiki inventor. "The Ben Franklin of our TC".

Tiki has really got me doing art and doing it in many ways like yourself.

TeaKEY, I could never live up to that! :) I just post the steps because they are always interesting to me when others do them. The best things about the Creating forum are seeing the process, then the results. Everybody does things a bit differently, that's the fun part. Thanks, though!

Palama sent me some tips and some great links on mold making:

On 2005-12-02 09:38, Palama Tiki wrote:
Here's the polytek site and another site for moldmaking (more along the miniature line, but some good info)...

http://www.miniaturemolds.com/makeyour.htm

http://www.polytek.com/tips/tips.html

More helpful step by steps at the Polytek site. They also have a video available, but it's $38.00. I spoke with one of the techs over there and he gave me a bit more insight. He said 3 coats of the polyurethane is best (around 1/4" thickness) because the thicker you go the stiffer the mold gets and thus more wear and tear. So more is not necessarily better. Also, it is good to shellac the inside of the mother mold so that it does not soak up the oils from the inner mold and cut down on the life of the mold. The product pricing was marginally better at the Polytech site and they have "trial pricing" on the first order. He suggested that I use plaster and burlap for the mother mold to cut down on cost. I'm still kicking that around because it's less durable than the specialized mold plaster.

Thank you Palama!

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CONCRETE??

I have no idea of what mix or type of concrete to use for molding. Any suggestions out there?

A-A