Mold making

[Klat-2]

Hello,

Can someone direct me to anything about using Holdens Latex HX-80?
Never sets up and can't get answers on using this stuff.
I work in clay and have web site at Gallery29Bronze.com
but really want to do the molds myself.
All help and input appreciated.

Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind. Dr. Seuss

[Andrew Werby]

Can someone direct me to anything about using Holdens Latex HX-80?
Never sets up and can't get answers on using this stuff.

[I've never used that brand, but they are all basically the same. If you brush a very thin layer onto a dry surface, what does it do? The trick with the stuff is to keep adding thin layers before the one below it has dried entirely. Eventually, you build up a thick enough coating that can be peeled off and used as a mold (once you've created a plaster shell for it).]

I work in clay and have web site at Gallery29Bronze.com
but really want to do the molds myself.

[I'd suggest chalking the latex up to experience and getting some 2-part silicone rubber, which works much better. Start with the tin-cure version, as it's less particular about what it's applied to. Mix it in one vessel, then scrape it into another and mix some more, then paint it on like latex. Most will drip off, but it makes a skin. Use a thickener in the rubber and apply successive layers; it goes a lot quicker and thicker than the latex, and you don't have to wake up in the middle of the night to put the next layer on.]

Andrew Werby
www.computersculpture.com

[raspero]

Or you can use two part polyurethane. It is half the cost of silicone. I use Smooth-On Reo Flex 30.

It has some disadvantages (and one advantage besides the cost). Most silicone is runny. It runs off of surfaces that even approach the vertical. There are some that are brushable but I haven't tried them. I tried a brushable polyurethane once and it was way too stiff for my liking. Polyurethane stays in place better. I brush on a couple of coats as it comes from the can and then thicken it with Cab-o-sil to a mayonnaise consistency for the build up of layers.

I don't think it picks up the finest of details as well as silicone, but for most of my work it does great. Also the fumes are terrible; they irritate your throat (and who knows what else); I wear a respirator.

Richard

[Mack]

PotlyTek's Poly 74-30 liquid rubber and to thicken; Poly fiber II.... brush it on straight for a couple of coats for the detail then and mix in the Poly Fiber II and smear it on for the thickness. I have breathing problems and have had no trouble with either of these. It's good rubber. Cab-o-sil is dangerous for me and probably for everyone. Wear a mask
and stay ventilated. This is all one to one ratio mix and a simple kitchen scale makes it a snap to mix. I cover the rubber with one of their liquid plastic products to make a "mother mold" and spray mold release on everything..

[raspero]

Yeah, the other disadvantage of polyurethane is that it sticks to damn near everything—it's a powerful adhesive—whereas silicone (real mold making silicone, not the silicon caulk) basically will only stick to itself, eliminating the need for a mold release.

Richard

[Klat-2]

Thank you. I have a start at least. I have one nearly horizontal piece of an alligator I was thinking about trying first. The problem is detail. Much detail. I'll upload later to shw what I mean. Thanks one and all for the input.

[JAZ]

I've been in Newfoundland for the past ten days, so just saw your post. It sounds like you are getting good advice. You can also find info using the Search button at the top of the page. There are some other successful sculptors on this site who do their own molds. Hopefully it works out for you.
JAZ

[raspero]

Another factor you must consider is air bubbles. They are not a problem with polyurethane, and so far I have had no trouble with them when brushing on silicone—I am careful to work them out of the first coat; the rest of the coats, I don't care—but when pouring silicone you may need a vacuum chamber.

Richard

[Klat-2]

Looks like I'll be giving Poly-Tek a try. Down loaded there PDF and checked on some other sites about this product. Do a trial on some small pieces first and let you know.
Thanks all

[Mack]

Good luck...and I like this:
"Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind." Dr. Seuss

[Klat-2]

The Dr. is one of my favorites for quotes. That just says who I am.

[Peggy Campbell]

Mack, do you weigh your silicon by the grams to make sure you are getting the split 1/2 and 1/2, I am so afraid to just be brave and pour into the same size container since they say on the product there is hardly any room for % of error?

[Mack]

Peggy:
I went online and found a site "Eat Smart" and they sell a little inexpensive scale that you can set to grams, ounces etc. It has a "tare" function...you put your empty cup or whatever you are using for the mix on the scale, press the button and zero shows on the screen. Pour in part A say 100 grs. and then part B until it reads "200 grs." and you're good to start mixing. Not a bad idea to jot down how much part A you poured,say, 127grs. and times it by 2 (354grs.). I screwed up in my math in the middle of a resin pour recently and didn't find out about it till I opened the mold. Big mess but it was fixable. But the scale is great.
Keep it clean by putting a paper plate cut to size on it. It's taken away, for me, a lot of the potential anxiety in this process.

[Art-Deco]

Ive been using Smooth-On rebound 25 for the last few years with 100% success in every way. I switched over to it after a disasterous time with Quantum.

Rebound 25 is REAL easy to use, it's mixed 1:1 part A to part B no scales needed, no toxic Cab-o-Sil or fiber stuff needed either, and it has virtually NO odor whatsoever.

You can add the thixotropic stuff to it to make it stay on vertical surfaces, usually one teaspoon of it added to a quart batch will do the trick.
All I use on a clay model is some clear krylon, followed by a light brushed on release.
Rebound cures in a few hours and with the above I can remove the rubber from a green unfired water clay model and the model stays perfectly intact, you can also make the mold on firm MOIST clay models as the wetness in the clay does not affect the rebound 25 at all.
The krylon and release stuff works fine on MDF boards too.

it runs about $185 for what they call a gallon kit, but it's actually TWO gallons since it's a gallon of part A and a gallon of part B.

I'm real happy to be rid of Quantum and it's 1:10 mix too, and having to have a stupid gram scale- especially when you are in the middle of mold making and the damn electronic scale starts acting funny and no longer reads the RIGHT weight- happened to me!

I also tried their casting resin for a client's order, they have a resin that is white, cures in minutes and is a real simple 1:1 mix too, pours water thin and clear and then in minutes hardens up white.

[Klat-2]

Thanks for the heads up. Just ordered the trial and will give this a try too.

[Art-Deco]

Originally Posted by Klat-2

Thanks for the heads up. Just ordered the trial and will give this a try too.

Cool, can't go wrong with the trial kit, don't forget that if you want the stuff to stay put you need to get a little bottle of that thixotropic additive called Thi-Vex, they have a little 3 oz bottle as I remember- you'd only need to add a few drops to a cup or two of compound and in seconds after stirring it in the rubber becomes something like mayonaise- you can brush, spatula it on vertical, surfaces easy.
Without the Thi-Vex the rubber is great for pouring a little plaque mold, really need it for anything else.

All you have to do is measure out equal parts of A and B, mix them WELL and completely so no residue of one part or the other remains unmixed in the bottom of the container, and then drop a few drops of Thi-Vex in and mix for 15 secs and see how it "feels" if it's still "runny" add a few more drops in.

I use disposable plastic cups for measuring out a batch, a few plastic bowls are great for mixing in, and I use a couple of large wooden spoons for the mixing. Helps to have some disposable plastic spoons, paper towels and a sheet of cardboard to work on for mixing. I also make heavy use of those disposable acid brushes, and the "chip" brushes which are natural bristle, and cheap, they work well and plan to toss them as I don't know of any solvent that will clean the rubber from them, and they are usually about a buck or so a piece for a 2" brush and you'd use alot more solvent that that trying to clean them.

I typically apply a thinly brished on print coat into all the details on the whole surface WITHOUT Thi-Vex, wait about an hour or so, if the rubber is slightly tacky but doesnt stick to your fingertip, you can apply another coat with the Thi-Vex.
I usually put that on pretty heavy but carefully to avoid trapping air bubbles.
I wait 90 minutes, and apply another good heavy coat- paying particular attention to corners and all 90 degree edges as well a raised spots, if I want a fairly think rubber, I'll apply 1-2 more heavy coats and then let sit overnight, and then build the mother mold.

As for how much I use, my Art Deco panel shown in another thread here is about 17x22" 2" deep I used about 1-1/4 gallons out of the 2 gallon total
"1 gallon kit", maybe a little less, and the rubber is nice and thick.