Brush-On 40 -Still reeks of fumes?

Hey all!

Mixed Smooth On's "Brush-on 40" into an ultracal mold. (Eyeballed the ratio, which might be my first error.)

Let it set up 16 hours, full cure time, then demolded. Even after sitting 24 hours outside of mold- it smells just terrible? Wondering if my mix ratio was bad? The surface has a mild stick- not quite 'tacky' but not dry, either.

Considering mixing and stipppling on a new layer of Brush-on over this cast, to see if that helps.

Thanks!

Hi
If you have doubts about eyeballing the ratios follow the mixing instructions to make sure. Run a small test out of the mold and see what happens.
Alsd make sure there is no moisture getting in your mix (use new dry mixing cups, throw away kind).
https://www.smooth-on.com/products/brush-on-40/
¿What release are you using?

I have used brush on 40 quite a bit over the years. I have never had “fumes” that you are talking about. Can you be more specific? Have you used it before? Out of all the urethanes for mold making i find that my least favorite. Yes, its cheaper than silicone but unless you make a large mold of something made of cement or marble, i never liked it. There are a few very important things you need to know when using it. You must always always always (cant stress enough) mix each part thoroughly. Part A will have a very thick paste like on the bottom that needs to be broken up and mixed good. The next big one is “eyeballing “ each amount. I can tell you from a ton of experience that one of those two was your problem. I still have pieces that are tacky from two years ago because i did the same thing as you. You can be off a tiny bit, maybe a gram or two, but tacky means way to much. Because part b is like a peanut butter, i use to use a gram scale. You would be surprised how you may think you have the same amount by sight, only to have giant air pockets in your part B. Another big problem i always found with using it to make molds is no matter how thin a print coat i made, it always seemed to develop bubbles. Can i ask how old the material is? That can also play a huge part with the fume aspect. A gallon kit usually lasts about 2.5 months before the humidity in the air starts to basically ruin it. At 3 months, its no longer good and turns into a solid (part a). Of course that is unless you use smooth ons gas to help prolong its life. What are you molding?

Customrelic said:

I have used brush on 40 quite a bit over the years. I have never had “fumes” that you are talking about. Can you be more specific? Have you used it before? Out of all the urethanes for mold making i find that my least favorite.

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Well, this kit is 2+ years old. Hah. A bit of a gamble, out the gate. And, the mix ratio says "By volume" so originally I was going to use a scale, however, chose to eyeball, since I assume, volume is not referencing actual weight. Just stippled another layer of the Brush on 40 over the first pull -same thing, 24 hours later, tackiness.

These are the soles for the feet of a werewolf. Reoflex 60 was my original plan, but I was in a pinch and hoping to use this brush=on 40 I had. Might just have to buckle down more $$ for materials.

Blargh said:

Well, this kit is 2+ years old. Hah. A bit of a gamble, out the gate. And, the mix ratio says "By volume" so originally I was going to use a scale, however, chose to eyeball, since I assume, volume is not referencing actual weight. Just stippled another layer of the Brush on 40 over the first pull -same thing, 24 hours later, tackiness.

These are the soles for the feet of a werewolf. Reoflex 60 was my original plan, but I was in a pinch and hoping to use this brush=on 40 I had. Might just have to buckle down more $$ for materials.

Click to expand...

oh boy. I would say thats your problem right there lol. Hopefully your able to clean it up easily and use some new stuff