GT23

[BarraMan]

A graphite-epoxy bottom will last forever. Mine was 12 years old when i sold it to another member. It was straight graphite over the primer. If you put it on over neat epoxy rough up the epoxy with 80 or 120 grit sandpaper.
Tom

Not my experience Tom!

And yes, I sanded between coats of epoxy!

[TomW1]

Sorry to hear that Barraman but I bought CL OD18 and he ran it up oyster shells before I bought it from him, and I ran it up on sand and small gravel beaches without any problems. He had it 8-10 years before I got it and I sold it to Craig without doing anything to the bottom. So that is over 15 years of use on the graphite bottom.

Tom

[drbobopp@gmail.com]

Searching for that glassy slick ready-for-the-water planing bottom, free of the prickly eruptions I'd been suffering from, I carried out an experiment based on your recommendations:
1) I used warmed epoxy.
2) I used a stick to stir it by hand, and gently at that
..........I did not have time to rig up the vacuum de-bubbling method.
3) I put it on with a 1/8 inch foam roller, as wet-edged as I could, covering but one square yard of her 40-acre bottom ....as a test.
5) I waited til bubbles...or just tiny rough eruptions(?) appeared
6) I tried a blow dryer.
7) I then applied a brush to one portion of the curing epoxy

Results:
It is clear that avoiding mechanical power mixing, and/maybe the warmed epoxy, helped. There was still a slightly rough-to-the -touch character to the surface, but it was far better than the 10-grit feel (!) I got from cold, power-mixed epoxy.

I could not seem to get any effect from the blow dryer. Maybe my technique (or lack thereof)?

Not sure about my roller/technique

The zone that I gently brushed, after roller-applied epoxy, did the best. But even it was not perfectly glassy, and required sanding.

Conclusions:
1) The goal of a perfectly smooth, glassy, unsanded, uncoated, unpainted epoxy-only bottom surface is elusive. And maybe unwise. Given ultraviolet light and barnacles.
2) So why not just sand and paint? I've already purchased ablative paint.

Questions:
I still have many small divots, dimples, and other such small, vague depressions in the surface. How important is it, from a performance standpoint, never mind appearance (on my FS-14 build, we produced a truly beautiful slick teal hull. But for this build, not required), that the surface be slick? Do tiny indentations really matter?

If yes, as I suspect, then I'll add some more epoxy layers before the bottom paint. Which brings me to last question:
I've been using SLOW curing hardener. Partly on the advice of boatbuilder.com, because I'm in Alabama and its often hot as hell. But when trying to lay up several neat coats in the window, the window can be long. Especially in winter. We had 18degrees here last month. Tonight 45. So I want to try some FAST hardener for these layers, so it doesnt take all day and night.... Maybe I can get in more than 2 layers in a day that way,.... What y'all think?

[fallguy1000]

I would make a medium hardener. Mix 50-50 fast and slow. Kick time in cold weather will be closer to 1-2 hours.

The only issue with bottom imperfection is it is a grade A attachment point for sea critters. The fastest way to build the bottom is epoxy neat coats at 2 oz per yard plus some loss to roller. The slow cure is fine; once you get past sticky; you can roll on the next coat; it does not need air to cure. Epoxy is an exothermic reaction; needs heat or makes heat. Cold retards the reaction, but the first bit of warm weather it'll cure harder and harder.

If you don't want to go graphite; I really like Interprotect 2000e. In cold weather a bit of thinner might be needed; I forgot which is recommended. A couple layers is plenty over all that epoxy; don't get wound up about their 5 coat rule.

Then ablative paint is put on almost immediately after the interprotect, but before it is fully cured. Read the instructions; I think it is primer morning ablative evening and a 2nd coat of ablative morning or so.

[fallguy1000]

The bottom imperfections are cheapest and easiest to fix with neat coats. The build is about 3-4 mils per layer. After 3-4 coats; the finish will be orange peeled, but the dimpling should be less.

This layer should help with your error and give the weak over graphited layer a hard shell.

Then you sand it with 80 grit to get rid of the orange peel. It will be hard on the sandpaper. If the stuff corns on you; the epoxy layers need more heat. You may need to bag the job with plastic and run the shopvac into it and or an oil radiant heater.

Our weather is supposed to get warmer next week here in Mn.

The shopvac creates heat and so running the vac inside a tented hull can raise the temp if you have no other means and the air circulation also helps.

[fallguy1000]

The bubbles may also be outgassing. When you put too much graphite in; the new epoxy layer is going into voids or the dimples in the finish and an air bubble comes up. This should diminish on follow on layers. A less viscous or runnier epoxy flows into those pockets faster and the air has more time to exit. Warming epoxy is of little value on a cold substrate. It is chilled instantly rolled on thin. Warming epoxy on a warm substrate would make sense. Here, a waste of time, imo. But maybe it'll flow into pinholes better?

If you don't neatcoat; the primer or ablative coats will probably pinhole or worse; fisheye, and drive you mad.

[drbobopp@gmail.com]

All very interesting.
I wondered whether FAST and SLOW hardener could be mixed to adjust the time frame. Will try that technique.

It is hard to know how much time to spend on the bottom, as this will be my only pass at it. She's huge, with a superstructure, and will never again be upside-down (we hope).

Cold weather not likely again this year in south Alabama. It's 62 outside now....maybe some high forties at night left. I also have propane heat in the boatshed, so guess I could easily enough "warm up the boat" before coating with warmed epoxy. If it's even worth it. The bulk of the bubble/pricklies was likely caused by the vigorous mechanical mixing. Also was using 3/8inch nap roller, too many passes, not being wet-edged enough....etc...

I'll check out the Interprotect.

Prolly will add some more neat coats to fill in these tiny divots. Then maybe the interprotect......finally an ablative. ....

[jbo_c]

I mixed a little over a quart of graphite-epoxy at a time and applied with a plastic squeegee. No loss to a roller or brush. It “flowed out” pretty well. A little orange peel is all I had. Plenty good for me.

Jbo

[fallguy1000]

QA is always a challenge.

Risk/reward analysis.

Risk of leaving dimples is fisheyes or pinholes in paint finish all the way to ingress to substrate.

Reward is mitigating risk.

When the reward is making it incrementally nicer; it is always harder.

[drbobopp@gmail.com]

Gonna put 2-3 neat epoxy layers on her bottom tomorrow.....

I plan to cover that with Petit Vivid ablative bottom paint. Not gonna use a primer under the bottom paint. That is OK, right?

Other question: Would it be unwise to lay the bottom paint on 'in the window' of the last neat coat? Or should I let the epoxy cure? ...then sand, and paint.....?