Difference in silicon mold material

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Haynie

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I am going to make some silicon molds for blanks. This is more of a curiosity than anything else.

What is the difference in the color. Does it just have to do with knowing which cures faster. So, if a mold is blue it cured at a certain rate and has a certain tear strength, and a pink mold has certain specifications?

Are the colors consistent between manufactures?

For casting blanks do I need a mold with high tear strength?
 
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Sorry to bump, but I just made a caulk mold and found it easy, but it cured far, far more slowly than advertised. I had it in the frame for I think 3 days in the garage where it was mid-60s during the day and 40s at night. It firmed up a bit, but was still very mushy. I then brought it into the house and it took an additional 3 days before I was able to remove the mold from the frame. Another day before it felt firm and ready to use.

This was the vinegar smelling caulk. Does that smell ever go away?

Tonight I'll try the mold out for the first time. It's a 5 blank slab. Should be fun:smile:
 
I made a door and window silicone mold as well. It is dependent on air for curing (had to remove the wax paper from the base earlier than planned). Mine was kept in the house to cure. My wife didn't like the smell so I had it in a cardboard box in direct sunlight.

After a day I removed the wax paper and the plug from the top. It spent the next two days on the dash of my Civic where it baked at about 100 degrees (estimated). It still stinks a little like vinegar but it's been in the Kitchen and no one has complained. It is a week and a half old now and I am so proud.
 
There is a difference in the silicones, the blue is usually Oomoo and you can expect to get about a year out of it, the pink is usually Smooth-On Mold-max and you can get about 3 or more years out of it with care. The Oomoo is cheaper to buy and you basically get what you pay for.
 
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I've made several silicone caulk molds - they have all taken about a week to cure. After 2 or 3 days I remove the saran wrap that was on the mold bottom to let it breath better
 
I just bought my 100% silicone (Clear) from Lowes today. It's waterproof,and Mold resistant for 5 yrs. It cures in 24hrs. I should be making one tonight, or maybe two. The good stuff is $6.00 a tube. The cutting board ones are just not working out. When I add my resin and add pressure it wants to push it out the sides and is messy. Resin costs toooo much to watch it seep out the sides.
 
The addition of a little corn starch will make the silicone set up much faster and seems to increase the strength. Little is the main word here. I have made some and if you put in more than about 25% corn starch by volume, the material becomes very hard to get a smooth cavity mold. YMMV.
Charles
PS, I now buy my molds form the pros here. We have many great vendors that make molds that work very well. WELL worth the money after blowing a gallon of PR on some home made failures.
 
In addition to what has been said the color will tell you what the tear resistance is if you go to the manufactures web sites it list that fact also. That is important is important so you will know that some can tear easily when remove items form the molds. And yes that is when there are curves and undercuts, but square corners will also tear easier.

One of the problems with the silicone that is used for caulk is that it cures from the outside in, so it skims over and then it can a year or better to completely cure.

This is more noticeable, when it starts out as a milky white and clears as it dries. I had somebody that used caulk as a fill for some cement patch by the basement window. It was white for two years till it cured three inches to the bottom of the hole.
:clown:
 
OK, first cast is in my mold, but I forgot to spray pam on it first. Could be a one shot deal:redface:. I have no idea.

Wish I thought the cast would be worth it. A smarter person would have gone with a single color for a first cast. Not me. What a mess! I had three cups with three colors going, all sitting in some sort of disposable foam bowls of hot water. Well, one paper cup gave way and the resin leaked into the hot water. Luckily, I'm smart enough to understand the styrofoamy bowl would hold. Wait. No, of course it didn't:biggrin:. Water logged resin spread like plague across my table.

So I figured I'd better dump one of the other colors in the mold so I only had one cup to babysit. As they looked like they were starting to gel, I started slowly stirring the second color in to make nice swirls. Then it suddenly stopped pouring and came out in a chewed gum consistency. I just dumped it in and started pulling it around like taffy. Then I hurried and mixed my third color up and dumped it in, tearing the taffy apart so color would get into the entire mold.

In the end, it looks like the fumes got to me and I puked in the mold.:redface: Chunks and everything. We'll see.

It was fun though. Mostly:biggrin:
 
OH MY WORD! NOW THAT will be a story for the ages. Let me share an experience I had on my first casting session. I wanted a blue blank, so I opened the bottle of blue dye. After reading the directions, we were to put several drops of dye into one of the cups. My brother, who was assisting me, said that the hole in the top of the bottle must be too small, as it was almost impossible to get any drops out. Getting tired of the slow progress, he squeezed the bottle with incredible force. KABOOM! The entire cap flew off the bottle, and about 80% of the dye was released onto the table, all over our hands, and everything else near by. My brother's old jeans were re-dyed to as-new and you just wouldn't believe how dark a blue we got on the blank! It took me five days before the dye would START to wash off my hands.

I think I can say one thing for certain--your next attempt at casting will go easier than your first.
 
I've made several Silicone molds. They worked fine. But, after using the commercial molds from Fred Wissen, (PTownSubbie), unless I need some wierd thing, that he does not make, it's commercial from our IAP vendors for me. His molds are very easy to use and the design of these molds is great. I have no connection to his business, I am just a VERY SATISFIED repeat customer
 
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One other technical bit is there are two types of cures for silicone mold material. One is called Condensation cure or tin catalyzed . Some of the problems with the molds not curing are not common with the tin cure are. Some sulfur containing modeling clays can slow the cure of condensation RTVs. However , the condensation cure RTV will eventually cure when the clays are removed.

The other is Addition cure or platinum catalyzed, materials known to inhibit cure are Sulfur-Containing clays, modeling clays, natural rubber such as latex and rubber gloves, masking tape, amine or sulfur containing materials, natural body oils, greasy fingers and condensation cure (catalyzed) silicones.

Never mix brands unless you know that they are the same type. Also most have temperature and relative humidity numbers that can affect the cure rate.
:clown:

 
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