Plaster for vacuum form moulds?

Bobster

Active Member
I found a good book on making industrial models using plaster from the 1960Â’s at a used book store. I would like to use plaster on wood to make vacuum form moulds. Will the plaster surface hold up to vacuum forming?

Regards,

Bobby
 

WookieeGunner

Well-Known Member
In short, no. Look for a substance called Ultra-Cal or Hydro-Cal. It is similiar to Plaster, but will hold up to vacuum forming better.
 

Bobster

Active Member
<div class='quotetop'>(WookieGunner @ Jul 7 2006, 04:48 PM) [snapback]1276254[/snapback]</div>
In short, no. Look for a substance called Ultra-Cal or Hydro-Cal. It is similiar to Plaster, but will hold up to vacuum forming better.
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Thank you. I found several versions of the Hydrocal product at the USG site.

http://www.gypsumsolutions.com/brand.asp?brand=hydrocal

Is there one that would work better for forming? How many pulls can I expect before re surfacing is needed?

Bobby
 

AlpineDarthMaul

Active Member
Out of the two choices you have, I'd go with the Ultra-Cal. It dires much harder than Hydro-Cal. And it should hold up pretty well to vaccuforming as long as you powder the mold (with baby powder) and dont have any extreme undercuts. It should last a long time... (Can't say how many pulls tho)
 

Fizbin

Well-Known Member
Actually, just about all gypsum products don't hold up well to vacuforming in the long run. The chipping will start shortly after a few pulls, depending on the shape of your mold. But if you're only wanting to make 3 or so pulls from it, then by all means, use it. If you're looking to make more pulls from a single mold, then I suggest using a heat resistant resin (like Smooth-Cast 385 from Smooth-On) or constructing the mold completely out of wood.

Just my 2 cents. ;)
 

rigormortis

Well-Known Member
You might wish to look up a product called "HydroStone" vs Hydrocal. An armorer I know uses it because it cures much harder and may be cheaper.
 

Jimbo890

Well-Known Member
UltraCal-30 is a good product, but I prefer wooden molds. Easy to make, easy to patch, and don't weigh a ton. Cheap too.

UltraCal-30 is just plain old plaster of paris, with some portland cement, usually in a 8:1 ratio, so you can make your own from a trip to the local hardware store.

For a lot of info dealing with home vacuum forming, check out

http://www.tk560.com/phpBB2/index.php

Cheers,

Jim
 

Bobster

Active Member
Wow, great site Jim. Thank you for the link. I like wood for the moulds but for some items speed of construction is more important than longevity.

Thank you rigormotis for the "HydroStone" recomendation. It looks like a good option.

Regards,

Bobby
 

Reactor drone

Well-Known Member
I'm using hydrostone at the moment...largely because I have 3 an a half bags sitting in the laundry :p and I've found it to be good for vacforming.

For simple shapes I'll use wood but for something complex you can sculpt it in plasticine and take an alginate mould off it.Pour in the hydrostone and voila..instant vacform mould.
 

drcrash

New Member
Actually, just about all gypsum products don't hold up well to vacuforming in the long run. The chipping will start shortly after a few pulls, depending on the shape of your mold. But if you're only wanting to make 3 or so pulls from it, then by all means, use it. If you're looking to make more pulls from a single mold, then I suggest using a heat resistant resin (like Smooth-Cast 385 from Smooth-On) or constructing the mold completely out of wood.
Hmmm... I've had pretty good luck with water putty and Ultracal casts... but then I hardly ever make more than a few of anything.

I'm wondering if it would help to pull .015 plastic over the plaster and leave it on, like people do to stabilize brittle water-based clay sculpts. Maybe that would help protect the pointy bits from chipping off?

I'm also wondering if water putty might be a better choice than Ultracal. It's not as hard as Ultracal, but not as brittle, either. (You can sand and saw and drill it.) I've used water putty because it's easy to work and re-sculpt, but I've never stress-tested it, pulling a bunch of plastic over the same molds.

Doug Walsh (who usually dispenses good advice) says that the heat ratings of resins aren't very useful---resins that aren't rated for the heat often work better than ones that are. He recommends BC8002 Kwik Kast Gray for vacuum forming bucks; it's an easy 1:1 mix urethane that cost about half as much as most urethanes.

Gobler over on tk560.com likes BJB's TC1630. It's a fast-setting urethane that will set up in a (damp) alginate mold, which is cool. (Apparently a lot of fast setting urethanes will, but that's the one I know about.)

I haven't tried either of those, but when I get around to making more than a few of anything, I intend to.
 

Weps

New Member
I know there are cases of making silicone molds and then filling them with resin to make the additional parts. Will alginate handle this sort of thing? I'm assuming you just need the right release agent, but I'm completely new to this kind of thing...
 

drcrash

New Member
I know there are cases of making silicone molds and then filling them with resin to make the additional parts. Will alginate handle this sort of thing? I'm assuming you just need the right release agent, but I'm completely new to this kind of thing...
Alginate is water-based, and it shrinks and distorts as it dries, so it's only good for one-offs (or maybe two- or three-offs). You don't usually use it for making a bunch of parts, but for making a copy or two.

(That can be plenty useful for taking a sculpt and making a vacuum forming mold out of it, though, or for copying a shape you want to modify without messing up the original, or just making a backup copy. But if you need to make a bunch of something, you probably want to pay the money for silicone.)

Most things will not stick to damp alginate---you don't need a mold release to cast plasters in it, for example, and I don't think you need one to cast wax or hot melted modeling clay---but I'm not sure about the urethane resins. (I haven't tried them yet, and urethanes are notoriously good at sticking to anything and everything.) My impression is that people just pour quick-setting urethane into alginate molds and it works, but I could be completely wrong.

Most slow-setting urethanes will not set up properly in wet molds... the water diffuses through them and screws them up.

(I've heard of people doing strange things with alginate, hitting it with a hair dryer to dry just the surface without shrinking and distorting it noticeably, spraying it with a fast-drying sealer, and then a release... and then casting things in it that you otherwise "can't cast in alginate." That all sounds a little too iffy for me to try.)
 

Weps

New Member
Ah. You think the best route might be using the alginate/plaster cloth for a quick pull and then just fill it with Kwik Kast for a nice master? How large/complex of a surface can you lay up that way, since you said alginate sets in around 20 minutes?
 

drcrash

New Member
Ah. You think the best route might be using the alginate/plaster cloth for a quick pull and then just fill it with Kwik Kast for a nice master?
Right, just make a negative mold in alginate, lay on a few layers of plaster bandage, then after the plaster sets, demold it, support in a sand box or something, and pour quick setting urethane into it. That's the theory, anyway.

BTW, I don't know if Kwik Kast will work that way. I have heard that TC1630 will, from a vacuum forming guy who's used it that way an also used it as a coating for vacuum forming molds.

How large/complex of a surface can you lay up that way, since you said alginate sets in around 20 minutes?
The alginate actually sets in about 8 minutes (a bit slower if you use very cold water---which you can if it's not a lifecast where you have to worry about goosebumps.) That's plenty of time to cover a human face, and enough for a whole head or a torso. (I think most people actually use the regular set for faces.) You spend more time making the mother mold than actually putting on the alginate.

People doing large lifecasts usually have an assistant to help smear the alginate on and/or to dip plaster bandages and hand them to them, to get the mother mold made quickly. That's mostly so that the model doesn't have to hold a pose for too long, but you do want to get the alginate covered with a layer of bandages pretty quickly so that it doesn't dry fast and distort.

Here's a video of a torso casting:

http://youtube.com/watch?v=2bD9hE6Ctqo

Life casting something that's not alive is generally easier. (In a pinch, you can do it in two batches, and get the 2nd batch alginate to stick to the first batch by treating the surface with bicarbonate of soda solution at the joint.)

I've been pleasantly surprised how easy alginate is to work with. We just mix it without worrying about bubbles---pour the alginate into/onto the water, and immediately mix with a paddle thingie chucked into an electric drill. Mix for a minute or so, and start smearing it on.

It amazes me that that doesn't seem to whip a ton of air into it and make a bunch of bubbles. It just creams up and goes on really nicely. You do get some big bubbles, but you can see them and smear them with your finger; they pop and aren't a problem.

We use the slow setting stuff from www.pinkhouse.com. The other brands are probably pretty similarly easy to work with, but it's reasonably priced and we like it a lot, so we've stuck with it.

We had some bad early experiences with Instamold, which is just regular-set alginate. It didn't mix smoothly and just got like lumpy oatmeal. I think that was probably just a bad batch---old stuff that had absorbed too much humidity.
 

yanvaq

New Member
I Have a small business where we vac form plastic shipping trays and such . We use BJB1630 for most of our production molds and it works great. we have some molds with literaly 1.000 + pulls and isill going strong just a little expensive . Also my sis is a dental teck and she made mt Klingon teeth and ther is a new alginate out that came in 2 combined syringes like epoxy and it does not breakdown like the other ,have no idea what it cost. if you want to make a lot of pulls of somthing make a wood and bondo mold then vacform plastic over it then pour BJB 1630 into that pull and you can make ass many pulls as you want . You can sand it and carve it put bondo on it but you can not put more on to its self wont work . also you cain't put plaster or hydrocall or simaler product on to wood the wood absorbs the moisture and swells up.
 

Jumpin Jax

Sr Member
Wouldn't be a definite no on plaster. I formed Forttusken's 2-1b neck and shoulders with his plaster mold. But as with the rest of the posts, it depends how many times you use it.
JJ
 

minieffects

Well-Known Member
For the most of the vacuum forming that I have done its been a mix. Years ago at Boss Film we used wood like jelutong. Hydrocal plaster is still commonly used when alot of pulls need to be done. Mdf (multi density fiber board) is used for patterns that are flat or have more planer surfaces. I would say the most used material is 6# or 8# foam. You can carve it pretty quick and get a lot of detail. Then you pull .030" or .040" styrene over it to seal it, trim that out , baby powder it for release and pull what ever thickness you want after that. The thinner pull of styrene seals the foam and helps protect the foam from damage. Its not a pattern that lasts forever but then again most stuff we do for the film industry doesnt need to last long.

hope this helps

minieffects
 
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