I've used both CS-1900 and Fire Barrier 2000+ (but haven't burn-tested either product).
The OP asked about a material suitable for small dabs. That wouldn't be CS-1900. Once you mix it in the SEM cartridge you can slow the reaction by freezing it, but you won't stop it. I used the CS-1900 to seal the firewall recess and some spots around the lower edges of the firewall where it intersects the skin. I put the leftover back in the freezer. When I checked it a week later it was useless. Besides that, it's curious material. It's a polysulfide, but unlike regular "proseal", it's barely sticky at all. To the point that I wondered if it would stay put when cured. It does though; once it kicks it adheres well.
Fire Barrier 2000+ on the other hand is a type of silicone sealer. Like any silicone it'll last for quite a while as long as it's not exposed to the atmosphere. Since the cartridge I got had a nozzle with no cap, I just put a piece of clear packing tape over the tip when I'm done. This stuff is sticky, like any silicone. And like any silicone, at least when I handle it, the stuff defies gravity and gets all over me. Occupational hazard.
Also: Fire Barrier 2000+ is intuminescent; it swells mightily when it gets hot. The stuff is really meant to go inside crevices or (for example) a tubular firewall penetration. There, it'll swell up and seal in the face of heat or fire. Dan's previous testing showed that it doesn't adhere well at all to an exposed surface. Using it as a fillet sealant will keep out fumes under normal circumstances, not sure how effective it would be in a fire.
I know nothing about CS-1900's behavior under the same circumstances. My application of CS-1900 was both as a fay sealant and as a fat fillet at firewall gaps in the corners. Dan, it would be interesting to learn the result of any test you do. I've been suspicious of those fillets ever since I applied them, though under normal conditions the stuff is staying put.
RV-7 Flying as of June 24, 2012
960+ hours as of June 30, 2020. Where did the time go?