Varying epoxy texture

I am finishing up the epoxy on the exterior of a skerry. The boat is currently upside down for this work. The flat bottom is quite glossy. The panels get less glossy, and have more of a matte finish as they get successively more vertical, first through third panels.

I'm guessing this has to do with gravity. The epoxy pools on the bottom (which is flat), less on the first panel, and much less on the third panel which is almost vertical.

But I don't think this is the entire explanation. I'm not sure why, but when applying the epoxy with a roller, the texture seems sometimes thicker, sometimes more grainy, as I roll it.

Any advice on how to control the texture better? I'd like to get the epoxy on the outside as smooth as possible before moving on. Or does that not matter, due to the varnish and paint I'll be applying eventually?

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RE: Varying epoxy texture

   I don't roll on epoxy. I squeegee it. Once to get the glass to lay down and saturate the cloth. And usually once again to fill the weave.  Then the smooth comes in after sanding.

You will likely see during sanding that the "gloss" you now see is just thick epoxy and is real wavy, drippy,  and likely too thick. The "matt" finish might be fabric that has not been filled. If so it will not be shinny and you can feel the texture of the cloth. 

RE: Varying epoxy texture

Sorry, I was unclear. I did squeegee on the first coat of epoxy. The roller was for subsequent coats. For a skerry, the glass covers the bottom and first panel only. The texture that I'm talking about is mostly occurring on the second and third panels.

I applied another coat yesterday, and it's getting better. I think the problem, at this point,is someow related to something about the batch of epoxy I've mixed, how I'm applying it, or perhaps something about the roller.

I am wondering whether brusing on epoxy will be better at smoothing out the remaining matte-like patches.

RE: Varying epoxy texture

It definitely matters. Paint and varnish coats are too thin to smooth out a rough surface. That's what fairing compound, primer and sanding are for. On varnished boats unthickened epoxy is the fairing compound.

Your instincts are good. Keeping control of the surface texture at each stage will reduce the amount of sanding at subsequent stages.

When rolling epoxy, the ultimate texture is controlled by the amount of epoxy in the roller, the amount of pressure that you apply and the speed of application. You want to apply as thin a coat as possible to prevent sags and drips (also known as sanding). Lots of thin coats are much better than a few thick ones.

Rolling a thin epoxy coat always produces a textured surface since the roller itself is textured and because its porosity works air bubbles into the surface. That's why it's best to tip the coat with a disposable foam brush after application, to get rid of the bubbles. A thin coat usually won't self level. My thought is that you are correct in that your glossy bottom is the result of a thick coat and that the less glossy ones are where the coat got too thin to self level. I'm also thinking that the graininess is tiny tiny air bubbles. A magnifying glass will answer that.

The way I do my boats is to separate the operations. Wetting out the glass is done with a squeegee, gloved hand or even pre-impregnating the glass before applying it. Filling the weave is done with a roller. I usually apply at least 5 thin coats of epoxy with a roller to fill the weave (tipping with a foam brush). When I'm done filling, there are no drips or sags to be sanded.

For finishing I sand with #220 since there's no big globs to knock down. Lately I've taken to using a longboard instead of my hand sanding blocks and the results are really much better, especially over glass. Once I get close enough to the glass that I do not want to sand anymore, I apply more epoxy with the roller to the glossy areas and repeat. When the entire boat is smooth and not glossy and only has a few shiny pinholes, it's ready for varnish.



RE: Varying epoxy texture

Thanks, Laszlo, this is useful. But I have a dumb question: What does "tipping with a foam brush" mean? I see this term used often, but I'm finding it difficult to figure this out using google.

RE: Varying epoxy texture

"Tipping" a surface coating after application is when you use a clean foam or bristle brush to go over the fresh surface, well before any curing or drying has taken place, using a Very Light touch.

The object of the step isn't to move any finish around, it's to help the coating in its self-leveling capability (oil paints and varnishes do this better than most epoxy!) as well as breaking any air bubbles that have formed before they create a crater or other imperfection as the material hardens.

RE: Varying epoxy texture

What spclark said. It's called tipping because you very, very lightly rub the very tip of a dry brush over the freshly-rolled surface. If you get much more than the tip, especially with a bristle brush, you'll get brush marks.


RE: Varying epoxy texture

Well, I tried that: rolling, and then tipping out using a foam brush, with a light touch.

That helped somewhat. I have two remaining problems on the 2nd and 3rd panels (which are at angles of maybe 45 degrees and 75 degrees below horizontal, since the boat is upside down).

1) Drips. I guess there was too much epoxy in places, so now I have drips.

2) There are still matte patches. Either I missed those spots, or the epoxy is dripping down from there.

How do I fix these drips -- scraping? sanding? What about the matte texture, maybe brushing would be better than rolling?

And I guess I need to be more vigilant about drips in the future.

RE: Varying epoxy texture

   Regarding drips, I had quite a few on the hull of the Shearwater hybrid I have been building.  This is my first build and I think I put too much epoxy on at one time and didn't pay enough attention to drips.  I would think that all the epoxy had firmed up and then later I would find some drips.  I found that a cabinet scraper would take most of the drips off.  I can see still see where a drip was but most of the volume of the drip is gone.  I still need to do the final sanding before varnishing, so I'm hoping that orbital sanding will get rid of the remaining traces of the drips.

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