www.TK560.com

[DarthVader1]

Not sure if this topic has been discussed already, but I have a question in regards of plaster castings for vacuuforming.

For those who already done it...is there anything special I have to do with the castings before putting them in the vacuum platten? Say...spray them with some kind of lacker or something to prevent the dust that comes from plaster items or something.

The main point here is, I am about to do some plaster castings really soon, and they will be undergoing a process of sanding and filling little areas with bondo or bondo putty (more likely). Do I have to do anything in special, or what could be the reaction if I use some kind of lacker against the hot plastic while in the vacuum platen?
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Robert
BH/TK/TB/TS 060

[crashmann]

Plaster is one of the most popular and economical materials for making vacuum form molds. However, Plaster of Paris is some of the messiest stuff to work with - I've got molds that are a few years old and they still shed plaster powder! They are also very brittle, and the corners will chip if you just look at them wrong.

You need to find UltraCal or HydroStone. Definitely find a local dealer using this web page:

http://www.gypsumsolutions.com/distributor/BrandDistributors.asp?brand=31

Having it shipped to you will cost as much as the material itself! Both Ultracal and HydroStone are very "hard" when mixed properly (3 parts plaster to 1 part water by weight), and use a paint mixer to ensure there are no lumps. The molds will still chip if you have 90° corners.



You do not want to paint the plaster - it will crack, chip, and flake off from the hot plastic landing on it.

If you are repairing or building up plaster molds, you may want to consider Durham's Water Putty. It sticks wherever you put it, and it gets very hard. After curing, it can be worked with tools. Just don't lay it on too thin, as it will just flake off. Bondo also works well.

Before forming, you'll want to lightly dust the molds with talcum powder. Not so much that you fill in the details, but just enough to provide a fine coating. This will facilitate the release of the plastic after it cools and begins to contract on your mold.

Good luck!

Charlie

[fz1]

Ultracal 30.
Best stuff to use. Hard as a rock and does not turn powdery like plaster.
Most mold supply shops sell it also.

[DarthVader1]

Man, I wish I would've read crashman's posting before. BTW, I have the same paint mixer already (Squirrel Mixer). Today I bought two 25-pound bags of Plaster of Paris at Lowe's....I didn't know PoP was that messy.

Well, let's hope it doesn't chip in the corners.
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Robert
BH/TK/TB/TS 060

[crashmann]

Hah-hah! At least Lowes has a good return policy

If you're just doing a limited run, the Plaster of Paris will probably work fine. Double check the mix ratio, as not all plaster is 3 to 1.

It's not too late to find some other plaster, so be sure to find a local distributor.

Charlie

[DarthVader1]

That's what I am trying to do. Hey, at least I still have the receipt to return just ONE of the two bags of PoP I bought.

BTW, I bought a 4 lb can of Durham's Water Putty. I will experiment with it a bit during the weekend. I am thinking about creating a layer (about an inch) of the DWP, to then fill it up with regular plaster once the layer is dried up. What do you think?
_________________
Robert
BH/TK/TB/TS 060

[PARATECH1]

Use a portion of a liquid concrete hardener instead of that portion of water. You can find this in a plastic bottle at Lowes in the concrete section. You will be presently surprised at how much harder your molds will be.

It always sucks big time when you spend a lot of time making a mold only to have it crack. If it is a mold with a lot of detail and it will take a lot of time to make it's crazy to not use the concrete hardener instead of all or a large percentage of the water.

You can seal the molds with a liquid concrete sealer. Just use a garden pump type sprayer to mist it in stages. Clean the sprayer out as soon as possible if you wish to use it again. Once this stuff dries inside the nozzle tips it is very difficult to clean and make it usable again. Wal Mart sometimes carries a small hand trigger pump that has a 'MIST" setting ( NOT "SPRAY" or 'STREAM"). They can usually be found in the hairbrush and toothpaste type area. They are usually only a dollar or two.

You can use the stream or spray settings on a hand trigger sprayer if you have used the hardener additive. This sprayer is like the two patterns offered on a Windex bottle. Once sprayed with a stream or spray use one of those cheap disposable foam brushes to even it out. This way you will have even coverage and won't have puddles and pooled areas.

[DarthVader1]

[PARATECH1]

Definately. Use the liquid hardener instead of a portion of the water used in the plaster.

I have my own business building synthetic rock creations for theme parks, homes, businesses, homes, etc. and it's one of the cheaper methods people use to make molds and backing for small molds.

[DarthVader1]

Thanks. Right now I am experimenting with the Durhams Water Putty. Believe me when I say this, I just used a small-portion-measure (say, like 3 parts a size of a small cup of coffee, and one and a half parts of water-compared to the recommended 3 and 1).

For my mistake, I've decided to clean my mixing tools, instead of rotating the mold to have a thick crust, and the DWP casting became hard after those 5 mins. I will post pics soon.
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Robert
BH/TK/TB/TS 060

[PARATECH1]

The photo the drill/mixer combo Crashman shows above is an excellent point.

If you ever use a drill with a mixing bit always make sure you use a portable battery operated drill instead of an electric one. You can easily burn up a motor over time with an electric one. The biggest thing that usually happens in using a portable battery operated drill is only draining the battery. I've seen a lot of people burn up electric drills because of this very thing.

For mixing amounts a paint stick is fine. Just make sure you mix the bottom middle and the bottem sides.

[DarthVader1]

That's interesting. Thanks for the tip on the portable and electric drills. I have a portable drill as well. What I like about portable drills, is that you could control the mixing speed.
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Robert
BH/TK/TB/TS 060

[crashmann]

The Durhams Water Putty is some fun stuff to play with! Just like HydroStone, it sets up and turns rock hard in a matter of minutes! I found it stuck to my Nitrile gloves too much, but dipping the gloves in a bowl of water allowed me to smooth the putty nicely.

Building up a layer of Durham's followed by Plaster of Paris sounds like a viable plan. The Durham's should not chip or turn to dust, and the plaster filler should keep the mold from being crushed.

I haven't found the cement hardener in my local hardware stores yet, but I did find some cement adhesive. I'm going to try that on my next broken mold

Charlie

[DarthVader1]

[DarthVader1]

Well, the experiment result ended partially a disaster. As expected, the face details came out really good, except the corners where the details are located, started to chip or flake off.

The good thing is, DWP is awesome, and I didn't have to use a release agent, but I have to use a large quantity of it on one shot so it comes out in one piece, and not building it in crusts.

In another note, I found a local supplier for the plaster called HydraStone, which is used for ceramic molds. Not sure how it works, but the person said that it's stronger than UltraCal 30, even though they could order it for me. What do you guys think? Crashmann???
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Robert
BH/TK/TB/TS 060