AlumiliteHigh Strength 2 Mold Making Rubber

I've just now broken into the hobby of resin casting and mold making and I chose this rubber due to its high tear strength, high elasticity, and high heat resistance properties. I've read some bad reviews on this rubber but there's nothing that I've seen that would cause me not to purchase it again. Any failures were due to my lack of experience and followed from the way I made my molds and not from the material they were made from.Alumilite High Strength 2 strong silicone based mold making rubber. It's a two component system which means that another chemical must be mixed into it to make it vulcanize (or 'cure-that is, turn solid). This chemical is called the Catalyst and is included in a kit along with a small spoon and two small measuring cups. Mix ratio is ten parts rubber to one part catalyst. I find that it's helpful to use the milliliter scale graduations on the cup and measure the rubber 25 milliliters at a time since the cups are graduated in 2.5 ml increments hence if 25 ml of rubber is needed then the 5 ml of catalyst needed is already marked on the cup. two are provided. I use one for the rubber and the other for the catalyst.The liquid rubber is a thick, very sticky liquid and is white in color. The catalyst is a bright pink with a faint alcohol smell not unlike cheap wine. when mixed in the right proportions the catalyzed rubber is a pale pink color and is almost entirely opaque.Here are a list of pros and cons to this rubber:Pros:+* Easy to use; the mixing is not as difficult as I expected. I have not yet had rubber fail to cure due to a bad mix* Very strong-rubber has good elongation (stretch), high heat tolerance. I held a cigarette lighter to a piece of scrap rubber for 8 or 10 seconds and it merely scorched and some turned to powder but the scrap was still quite strong. I understand (Though I haven't tried it) that the rubber can withstand the heat of casting low temp melting alloys like pewter. It certainly easily tolerates the heat produced by curing resin*Tin cure silicone- it can be used in conjunction with all manner of mold making materials including sulfur containing clays (According to the Alumilite website-I've yet to try this but I trust this is true according to other reading)-platinum silicones are sensitive to sulfur and will not cure in its presence.*easy to clean up-peels off most surfaces cleanly once hardened. It would not even adhere to MDF foam, which is the most porous substance I tested it on. Peeled neatly off the surface of the aging plywood work bench I use.* faithfully replicates details in high definition. Makes good crisp reproductions of objects*Thin rubber and requires no vacuum degassing (though I understand this is always recommended if possible. I HAVE had some small bubbles trapped in my molds and a few more course ones. I chalk this up to not being very experienced. Experienced mold makers have means of getting air bubbles out of their silicone after pouring and limiting the bubbles that get trapped during pouring.*Plenty of rubber to make several small molds of a few inches in sizeCons:*Expensive: The rubber is rather expensive for just a pound. Silicones tend to be expensive I've noted, so to be fair this isn't a deal breaker.*Messy: The liquid rubber is hard to pour from the jar without getting some running down the side of the jar. I wear vinyl gloves when mixing to keep it off my skin*Long cure time: This is the biggest problem I have with this silicone. It takes 12 to 18 hours according to the package to set enough it can be used and 48 hours for full cure (This is the point at which all chemical reaction between the rubber and catalyst stops. You don't have to wait till this finishes to begin making casts). It would be more convenient if the rubber set in 2 or 4 hours; but it takes one full day. Unfortunately chemistry is what it is and that's the rules for this rubber. This is not a hobby for hasty people or people who desire instant gratification.*Hard to remove from mold making container. I've had to cut open two containers (plastic vitamin bottles with the tops cut off) to get my molds out. Even with a thin layer of petroleum jelly applied to the next container I had trouble getting it out. It does seem to stick slightly to the material you mold it in; at least when it's plastic.I love this rubber and would be willing to buy it again. The main flies in the ointment for me are its cost and the long cure time. Neither would keep me from buying it again. I've produced a lot of failed molds due to my lack of skill at making them-this was my fault and not the fault of the rubber. So the majority of this batch hasn't worked for me because of placing my mold positive too close to a container wall causing a thin spot (you can't see inside to reposition it once it's in the rubber), or from cutting various molds open badly. Due to it's slightly expensive nature I won't be able to buy more right away-though again this a fact of silicone rubber of this type. It's not OVER priced..I just have a slim budged. Another potential problem not mentioned above was that when making a mold of a light pastic object the object tended to want to float when I wanted it to stay well down in the rubber. I solved this by using a hot glue stick which I pushed against the top of the mold object and taped the other end against a piece of wood over the mold so it was held down. The stick will created a hole in the mold when it's removed so this would be for molds that pour from the top.As I mentioned above the silicone also tends to stick inside the container you form the mold in. Professionals use a clay to form their containers or else use thin pieces of corrugated plastic. I didn't have any on hand so I used cut off vitamin bottles and then some small tupperware containers of the cheap semi disposable type that I bought. I had to cut the vitamin bottles away to get the molds out so if you need a round mold you can do this if you're willing to sacrifice a bottle. The tupperware didn't need to be cut as I got it to flex enough to release the mold.I'd recommend this rubber for first time or intermediate mold makers. If you don't have to worry about needing very high strength (if your molds will be simple like plastic car bodies for example and won't have lots of undercuts so there's no worry about tearing the rubber) or if you don't need to worry about sulfur causing your molds not to cure you could also try another rubber like Oomoo which is highly praised among hobbyists. It costs about the same so there's no real benefit in price. It depends on what your specific needs are. Most of the cons I mentioned with this rubber would, I expect, apply to most or all silicones. I hope this helps someone.

The hardness on this is a 20-25 A Shore which is perfectly fine for creating molds for duplication (and the detail that can be discerned is amazing). However, I will say this; in the case that you are wanting to make 'rubber' parts from a 3D printed mold, you may want to look for a higher durometer rating. Also, after mixing the silicone, it is really thick, just an FYI. Finally, although it is not really needed with this stuff, a degassing chamber makes things so much easier and better.

I needed to make a stamp type mold. I could have spread it much thinner and used a larger frame because the end result is very strong. All of these mold materials are pricey so if you are making a stamp for a textured surface go thinner and your roller will make better detail and the mold will still be multi application. I got very good detail.

The final product is extremely flexible and accurately reproduces details without issue. It does take about 24 hours to fully cure, so be aware, and I have not been able to get a bubble free finish without using a vacuum pump.

Used to make a mold for a vintage handle and worked great! Only enough for a pretty small mold - I came out with two 6 liquid ounce pieces. Mold has been used and heated multiple times and never causes issues. Will definitely use this product again.

Name brands always rise the prices, but the product is good. I'm sure there are other products that rival the outcome, but for now alumilite is where it's at!

Product almost impossible to use correctly. Had to scrape out of the container with a popsicle stick, took several days to set up. Been using this for years, first time I had a problem.

I've used their products before and very happy with the results. I haven't used this yet but I expect the same excellent resluts.