RTV silicone (mold)
18 replies to this topic
Posted 15 August 2008 - 11:10 AM
Guys, I am price shopping for a RTV silicone with about a 40 shore hardness and decent strenght (ie not tear easily). Does anyone make an economical RTV silicone? I am currently using Moldmax 40 and it's good stuff but is there anything cheaper and just as good?
Posted 18 August 2008 - 11:39 AM
Check out Alumilite's line of silicone. Been using it for a while now, and really like it. Hobby Lobby sells it and if you use their 40% off coupon it makes it affordable. Just bought another tub this morning for less than $20.
Posted 19 August 2008 - 04:13 AM
Thanks David where do I get the hobby lobby coupon? Also what shore hardness is it? Thanks
Posted 19 August 2008 - 09:00 AM
BB, there is a way to stretch out the Silicine by 2 to 3 times for little money.
Just pick up Clear All Purpose Silicone Sealant($2.87 @ Walmart for 10 oz's) from the Paint section of Walmart. Lay out beads of it on a clean dry surface. When the beads cure, use them this way;
Skim coat the model with regular RTV. After it begins to set but is still tacky, place the cured Sealant into the Mold Box, nearly to the top, and then fill it with more RTV to join and encapsulate everything. As long as your model is covered with RTV Everything else is filler.
You will hardly notice the stuff and your mold will be as good as if you used alll RTV. I've used it with Smooth-on Mold Max 30 and Hobby Silicone and there was no problem with either of those two.
Posted 19 August 2008 - 10:55 AM
Thanks Smokey, I was a little late in responding.
As usual, Husky is very helpful. He also has a tutorial on building molds in which he expresses the same tip he just offered here.
Good luck, and keep us posted on your progress.
Oh, yes. The hardness. Alumilite produces two hardnesses that Hobby Lobby carries. One is high strength 3 (10A hardness) which is the most flexible and should be used when you have any deep undercuts. The other is high strength 2 (20A hardness) which they say should be used when you need flexibility and good dimensional stability. I have used them both and find them both acceptable. Hope this helps.
Posted 19 August 2008 - 03:10 PM
Husky, I'm trying really really really hard to get a visual of what you are saying. You got pics by chance or a copy of that tutorial? Are you using a whole tube of that Wally world silicone on one mold? Thanks guys for the help! I was actually thinking of using thin wall panel shaped as the shape of the mold box and drill holes in it and pour RTV again over the top and use that as a filler idea but I am too scared to try it as much time as it takes me to prep a prototype in clay.
Posted 19 August 2008 - 03:42 PM
With Husky's permission, I would like to try to answer your last question. Hopefully he will correct me if I am wrong.
The silicone you want to buy from Wal-Mart comes in squeezable tubes. Has several names (tub and tile caulk, silicone sealer, etc.) and any of these will do. Squeeze the silicone out in strips onto wax paper (for ease in handling later). Let it cure overnight or until it is hardened. Cut the strips into pieces 1/4" or larger, depending on the size of your mold. Don't worry about waste in this silicone. Any chunks you have left over, put 'em in a zip lock bag for use in future molds.
After you have your form made, mix enough silicone to just cover the master. Let this pour set a little (check the curing time of the silicone you are using) but at about half of the time it should cure, drop the silicone pieces you cut into the mold and pour the rest of your silicone into the mold. This will bond to the first pour, cover all the chunks, use less of the molding silicone, and you will have a solid mold.
Hope this not far off what Husky had in his info. I think I told you that it was a tutorial and I was wrong. I got info from a post of his some time ago.Will try to find it again and let you know where to find it.
Posted 19 August 2008 - 04:45 PM
Yep!! Also, any rtv that gets stuck in the mixing pot can also get recycled. How's the method work foy you, Dave?
Actually, the Walmart stuff seems harder than my Mold Max 30.
Posted 19 August 2008 - 05:07 PM
Very cool info and it was exactly as I thought you said. One other question and I do do my clay beds exactly like you do yours. How do you figure out the volume of RTV to use so you don't pour so much or too little? I use 4 "L" shape pieces to surround my mold box instead of legos. It's just a little faster.
Posted 19 August 2008 - 05:25 PM
BrianB, two methods.
#1, the box is rectangular, so the volume can be easily calculated by multiplying the length x width x height. You might want to subtract the lure volume, but I wouldn't bother, too deep is better than too shallow.
#2, More accurately, fill with water to the level you require. Pour the water into a container and weigh the water in grams. This will give you the volume in cm3, 1 gram of water = 1 centimeter cube. But now you have to dry the setup, as drops of water will probably leave pockets.
I use method #1 for RTV, method #2 for Plaster of Paris.
Posted 19 August 2008 - 09:12 PM
Vodkaman, Parden me It's been a while since I was in school. If I do L x W x H would that give me volume as in ounces of RTV to use??
Also, I understand the purpose of silicone. But why not substitute a thin vaneer wood say an 1/8 of an inch thick and drill holes in it so that you can bind it to the mold when you pour some RTV over the top of it and sandwich it? Seems easier/cheaper/time and more solid?
Posted 19 August 2008 - 11:36 PM
You can figure out your cubic inchs and weigh your RTV. Figures I found were(specific volume) 24.7 cubic inchs/lb which would be 1.55 cubic inchs/ ounce(weight)
Correct me if I'm wrong, been long time since I was in school also LOL
Posted 20 August 2008 - 02:18 AM
sorry guys...havent been around a while.
1. rtv-silikone will cure faster when water ist added (durability and strenght of the mold decreasing). i use some drops of water for long curing rtv as an shortcut. if you use the "bombs away method" YouTube - How to make a simple Silicone Mold Part 2 shown at 4:08
so, no airpockets in the mold, even when water is added. the rtv will lose its viscosity "linear" to the amount of water added.
2. measure the amount of rtv needed with rice instead of water (lure allready in place). the volume of rice is pretty much the same as rtv. (volume vs weight).
thx Husky for all the hints
Posted 20 August 2008 - 08:44 AM
Husky, method has been working great for me. By using this I can probably 2-2 1/2 molds out of same amt. of RTV that I at first only got 1 mold. I must thank you for this info.
Posted 20 August 2008 - 07:51 PM
Dramone. re - post 15.
#1. Well I never knew that!
#2. excellent idea!
Thanks Dramone & Husky.
Posted 20 August 2008 - 08:08 PM
Good to know Dramone, did'nt know y'all had rice in Switzerland LOL
Posted 21 August 2008 - 02:06 AM
how to "stretch" rtv with caulk for molds. (reuse of old molds also)
i made a short tutorial a while ago for a german site, based on Husky's hints (yes, i put his name on top of the tut, because it was not my idea and to give him the credit). ok, it's written in german, but the pic's will speak for their own . send me a pm if interestet.
oops...i'm not a club member, so no pm...sorry
Edited by dramone, 21 August 2008 - 02:15 AM.