West system 105/206 with cs for filets

[RocketSquirrel]

Does anyone use 105/206 west system thickened with colloidal silica for filets? I ran into an issue possibly. I mixed the epoxy to the correct ratio (made a little too much..), then added the cs gradually to get the thickness I wanted. I mixed for maybe 5 minutes total trying to get the lumps out, I dont know how people get it all out. After laying it out and getting the filets where I wanted them, I noticed the cup was getting very warm and the bottom was solid. Im thinking it was in too small of a cup. It's supposed to get warm but I've read tall narrow cups can decrease the working time. Has anyone had this happen? Anyone have a secret to mixing in fillers to get lumps/bubbles out?

 

[Andrew Brown]

The cup heating is just the runaway reaction. It heats when it cures, heat makes it cure, and the cycle repeats. As you mentioned, it's far worse when the volume is minimized with a narrow cup. Shallower, wider mixing cups really helps. I also will mix epoxy, then split it in 2-3 cups when doing larger batches. The smaller volume stops the runaway reaction.

Lumps... ugh. I have the same issue. I started using a 50/50 mix of high density filler and coloidal silica. Seems to thicken it up enough with using less CS, so few clumps and still thixotropic enough for me. The high density filler seems to mix much more uniform. I also mix very, very well to get rid of clumps, then let it sit to outgas for about 20 min. It's far from perfect, but I'm not going to vacuum degas. This is predicated by not having a run-away thermal reaction.

 

[lr64]

I've read that some people pour the epoxy out onto metal trays. On the boats I built, I would work in small batches. But I still had a smoking cup of epoxy one hot day. As far as lumps with the filler, I don't remember having that problem. . Maybe my mind is going. Or maybe it's peculiar to West epoxy that is starting to set?* One of my boat projects had 4 fillets that were 12 to 14 feet long! I've used a number of fillers, too.

* I have used Raka epoxy. At some point, I've probably used a little West, but not much.

 

[secretagent]

I used West 105+207+407 for fillets all the time. No bubbles, no warmth, and at least 20 minutes of working time; I agree with the the above statement that it was probably the container.

I mix mine to “peanut butter” in a disposable bowl; here’s what it looks like for internal fillets on the fin can.

 

[cls]

Yep, definitely use a wide shallow place to mix. Also, I like to mix the CS (and whatever else like dye) with the resin, then add hardener.

You should have had 6 or 8 hours working time with that 206! Must have been a hot day?

 

[Handeman]

I buy cheap paper bowls, 8" plates and 12" plates at he dollar store to mix on. I measure the parts into plastic cups, but always mix on the paper plates. Never had heating issues with that. YMMV.

 

[3stoogesrocketry]

Did you weigh the epoxy to get the correct ratio or use the pumps?

 

[dr wogz]

I used West 105+207+407 for fillets all the time. No bubbles, no warmth, and at least 20 minutes of working time; I agree with the the above statement that it was probably the container.

I mix mine to “peanut butter” in a disposable bowl; here’s what it looks like for internal fillets on the fin can.View attachment 638309
View attachment 638310

My 'go to' for thickening / for fillets.. the Cs is strong, but can be a bear to sand smooth!

 

[Handeman]

Did you weigh the epoxy to get the correct ratio or use the pumps?

I was using US Composites which was a 3-1 mix by volume or weight, so I just measured the by volume.

 

[3stoogesrocketry]

I was using US Composites which was a 3-1 mix by volume or weight, so I just measured the by volume.

Question was for the op as he stated west's and it's a 5 parts resin to 1 part curative by weight

 

[prfesser]

Yes, in a compact mass there's less surface area for heat to escape. So it's absorbed....by the epoxy mixture. Higher temperature. Faster cure reaction. More heat generated, epoxy gets hotter. I had about a 1-cup batch that started smoking (used a very fast curative, tho)

You might try mixing a little liquid at a time into the additive, especially when working with fumed silica. (If you've tried to mix water into condensed soup you'll understand.) I use slow curative, mix epoxy in the proper proportion, then add it a little at a time to the silica. Of course that means knowing about how much silica to use.

Or measure resin and curative, then add each to measured quantities of additive.

It's a PITA but if you weigh the silica and the epoxy/curative, you'll have an accurate ratio of the ingredients for future use.