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3rd coat complete...on track?


mjshp

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I finished the third coat of epoxy on the interior of my s10N, and having no previous experience with epoxy, wondered if this texture is ok. If not what, am I doing wrong and how can I avoid the same issue on the outer hull?

 

As always, thanks for your input and guidance.

 

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post-2157-0-25114500-1368681263_thumb.jpg

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You have a great barrier coat there. The texture is just amplification of the underlying texture. Sanding will be the only way to smooth it. and sand it you should and then paint it. Sanding between coats will keep it flat on the outside so your last coat of epoxy is nice and smooth. Personally i think 1 coat epoxy sanded and then another coat is enough to seal the wood if you plan to use a good primer and topcoat.

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Sealing wood requires a film thickness of at least 10 mils. Typically, this requires 3 normal, neat coats, though 2 coats often can get it close. The only time I recommend 2 coats, is if you plan on a cloth sheathing over it.

 

The texture you're seeing, looks to be roller stipple and not a raised expression of the surface below. The plywood below this coating appears to be meranti, which is much smoother then what the coating suggest it is.

 

When applying the epoxy with a roller, tip it off, just as if you where painting a top coat. Also apply the epoxy in a sufficiently warm environment, or it's viscosity will cause similar issues.

 

The fix for this, unfortunately, is to sand down the stipple effect and apply more epoxy. If you want a mirror finish, you'll need to long board it, but if applying paint over it, you can use a DA and sort out major highs and lows with subsequent coatings of epoxy and building primer.

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There is something about Okoume that often leads to a bumpy, pebble finish when the first coat of epoxy is applied. I assume it must be some type of raised grain response. That has to be sanded off after the first coat. Subsequent coats don't seem to have that problem. The only way I know to avoid that is to lightly sand the Okoume plywood before even the first coat of epoxy. Once sanded smooth, subsequent coats don't seem to demonstrate this.

 

Also helps if the epoxy you use does not suffer from blush. If you get that, best to scrub, rinse and lightly sand between coats.

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The first coat of epoxy on any wood, should be just enough to wet the wood, not pool on the surface. I smash it in, with a plastic applicator or putty knife, then scrape excess off the surface, moving it around to drier areas. This serves a few purposes - first it prevents out gassing, as there's nothing on the surface for bubbles to rise up through - second it pushes goo into the wood - it's much more difficult for a blush to form and lastly it seals just the pores, leaving a nice base for subsequent coats. Okoume does lift a little when first coated, this technique helps a little in this regard.

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Follow up-- I talked with the epoxy guru at the local chandelry today, he also thought that the roller type was contributing to the issue. So, I picked up some mohair rollers--the pink and the candy stripe kind.  I will sand the exterior to 220, then squeegee in the first coat, the roll the next coats with the new rollers.

 

I'll circle back with the results in a few days. 

 

Now off to sand, sand, sand and sand some more.

 

Did I mention sanding?

 

Thanks to everyone who chimed in.

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mjshp, 

 

I think you'll find the mohair rollers soak up a lot of epoxy. You could probably load up a 1/4 mohair roller with epoxy and coat the entire bottom without reloading the roller if you tried. We use very thin about 1/8" disposable foam rollers for our coating followed up with a foam brush to tip off the little air bubbles. 

 

We use these...

http://www.amazon.com/Wooster-Brush-R730-9-8-Inch-Roller/dp/B00125NQT4/ref=sr_1_4?ie=UTF8&qid=1368754783&sr=8-4&keywords=foam+paint+roller

at the shop but we buy them in bulk so they are pretty cheap and we cut them in half to make 4.5" rollers out of them unless the job has a lot of big flat surface area. 

 

Also, since you got that much texture, i think everyone here is assuming that you were "hot recoating" i.e. putting on coat 2 and 3 within a 24hr window of the previous coat to avoid sanding. Just wanted to make sure that was the case, otherwise you could have issues with the later coats bonding to the previous if they were not sanded.  

 

-Alan

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@Alan, yes, hot coating.  The shop ranges from high 70s (with the heat on) to mid-60s. 6-12 hours between the three coats.

 

Follow up: knocked it all down with 8 hours of sanding.  It was amazing how uneven it was.  Today, I'll go back to sanding--you know the Zen approach to sanding, sand till you think it is done, the walk away to come back later and sand some more.

 

I feel like I could keep the sand paper company in business!

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UPDATE:

 

The mohair roller was a disaster. For the interior I ended up sanding everything flat, then reapplying with the smoothest foam roller I could find.  This resulted in a much smother finish.

 

For the exterior, sanded to 220 then followed PAR's advice to squeegee in the first coat, because of timing constraints I rolled and tipped the second coat, then sanded the second coat to 220 and rolled and tipped a 3rd coat, which is pretty smooth.

 

Next the primer and then paint!

 

Here are the rollers I used: 

http://www.amazon.com/Shur-Line-03715C-4-Inch-Refills-Contractor/dp/B002K8PT74/ref=sr_1_2?ie=UTF8&qid=1369626886&sr=8-2&keywords=foam+paint+roller

 

 

And a photo of the smooth exterior.

post-2157-0-25052500-1369627625_thumb.jpg

 

Thanks to everyone for their help and ideas.

 

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