GT23

[drbobopp@gmail.com]

I do see bubbles. ... I believe that to be the problem . I have the graphite surface pretty well sanded smooth, and now 4 neatcoats in. I see the bubbles forming as the epoxy sets.
Then as it cures the bubbles seem to collapse and harden into little hard prickles. This is not surface roughness coming up thru the neat coat. Overall, the bottom is becoming more even and shiny with these neat coats. I might stop here but for those prickles. I will neatcoat a small section of the bottom and try the blowdryer trick.

As for bottom paint: mostly she'll be on a trailer.....but with a coat of anti-fouling paint on her bottom, I have the option of leaving her in a slip for a few weeks if need be. I remain undecided. If I could get a really slick glassy epoxy surface, that I did not have to sand to get rid of the prickles, I would dispense with the bottom paint....But if I must sand it anyway to rid the prickles, then it's no longer beautiful slick black, but sanded/ugly...... in which case might as well paint it.

[Jaysen]

There is the possibility that you are mixing bubbles into the epoxy or apply a bit “late” in the cup time. Former can be from high speed mixing the later just too big a batch. I’ve had some success with a heat gun on LOW to get bubbles to move out of the epoxy.

That said, sometimes it’s best to break out the 30grit and start over. Sorry.

[fallguy1000]

Another way to deal with bubbles caused by outgassing is to warm the resins over a water bath. This does reduce the cure time, but makes the epoxy thinner and less capable to hold air.

The air bubbles may be air entrained from the graphite being less than fully mixed or some chemistry fun.

I had one epoxy that loved to bubble over fresh plywood. Raka

[pee wee]

I don't know what kind of equipment you have available, but placing the mixed resin in a vacuum chamber will swell the bubbles and get them to float to the surface.

[drbobopp@gmail.com]

All very interesting. I am indeed using a high-speed mixer, a paint mixer drill bit on a power drill. And it puts a hell of a lot of bubbles in the epoxy, I have noticed....Just didn't until now make the connection. Duh. I'll mix it manually. ...

I have vacuum equipment... A good new pump (the one fallguy recommended)..... will think about that...Any easy way to construct a small vacuum chamber for this purpose?

I'll also warm the epoxy. And police it for bubbles with a blow-dryer as it sets up.

I also use a roller to apply the epoxy. Any objection to that?

[fallguy1000]

I have mixed over 300 gallons of epoxy.

Never used automatic mixing equipment; just a wood paint stirrer or tongue depresser and 1.5 - 2 minutes.

[Jaysen]

I also use a roller to apply the epoxy. Any objection to that?

Rollers suck up epoxy and could add bubbles if you roll fast. I think fallguy used notched trowels with small notches to spread the epoxy. Just make sure you keep well away from gel times.

[fallguy1000]

Rolling epoxy is fine. You need to make sure not to roll after gelation. And it is best to work epoxy with a wet edge method. Means don't go back over it much.

Also, don't use 3/8" roller.. 1/8 - 1/4" max nap

[pee wee]

It sounds like manual mixing is the answer.

For discussion re: vacuum chamber, I would go with something like a paint bucket for quick and easy. No need for massive vacuum power. When I was doing some resin inlays I made a frame out of mdf with a gasket on the bottom and acrylic sheet (let me monitor the progress) on the top, the acrylic would bow in but it was strong enough for what I was doing.

[drbobopp@gmail.com]

Ok, all that is gonna be helpful. I appreciate y'all.

I will mix manually. I do think that this particular mixer-drill-bit that I have been using of late is much worse for producing bubbles than earlier, differently shaped ones I had used.
Or it could be that I just never noticed the prickly finish too much on earlier projects. You gotta sand the epoxy surface anyway, in most all situations, to prepare for whatever is coming next--primer, fairing, paint, more epoxy, whatever.

But in this case, I would like to leave a slick, glassy, unsanded epoxy surface on the bottom for efficiency (will be black due to the underlying graphite layers shining thru). She will be a trailer boat, so I'm gonna forego anti-fouling paint.

I'm gonna do a test section first, before the whole thing. The GT-23's bottom is the size of some folks' backyard!

So:
Manual mixing
Warm epoxy
vacuum chamber, if I can figure it out. Will try paint can idea.
thin-napped roller
wet edge method
avoid gelling
gentle blow-drying bubbles

I will get back with you on results....thanks again