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bubbles in epoxy


Tgabe

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I need some help here.

 

I glassed the two inside faces of the centerboard case and one side (so far) of the centerboard.

 

Here were my steps:

1. thin coat of epoxy on directly on the wood

2. lay the fiberglass cloth over the wet epoxy

3. apply more epoxy with roller on top of the cloth, smooth with brush

4. about 6 hours later, I put on another coat of epoxy to fill the weave.  I used a roller and brush and tried to brush out the bubbles.

 

The next morning it was covered with little pimples, like a bad case of acne.

So I have sanded them all out and now want advice before I put on another coat.

How do I get a smooth finish without the bubbles.

 

Other questions:

Should the solid wood pieces also be epoxy coated, or just varnished/painted?

Things like the centerboard handle and the centerboard case supports, the center thwart, transom reinforcement, etc.

How about all the decking supports - coat in epoxy?

 

CS17   #375  slow going

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How warm was it when you applied the epoxy? Sometimes you get bubbles from the substrate off gassing or reacting to the "pores" being covered. When time allows I like to apply the epoxy to the substrate, let that dry, and then do the followup sheathing/coating. A squeegee will also help get those bubbles out better than a roller,or brush will.

Everyone has their own techniques but I like to coat everything I can with epoxy, and then do my top coats over that. I'm leery of having ANY bare wood on a small boat as moisture can "travel" via capillary action,etc.

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It's the change in temperature that is the problem. Air expands when heated, so if you coat with epoxy when it's cold and then the temp rises the gas that is in the wood will expand, forming bubbles. Tips include epoxy coating in the evening when the temp is dropping or warming the wood first (heater/lie it in the sun). 

Cheers

Peter HK

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In my experience heat will usually help promote them. One old technique people have used is to wait until after the hottest time of the day, and then apply the epoxy. The reasoning being that as things cool down there will be less opportunity for buildup of heat beneath the coating.


Peter types faster than I do...

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Yep, you've experienced outgassing and it happens when the substrate has two things - first pools of epoxy on the surface or raw wood and second, the temperature of the substrate rises while the epoxy is still wet.

 

The solution is also two fold. First is to never leave pools of epoxy on the surfaces of raw wood. Without these pools (thin coatings count as a pool), there's nothing for the bubbles to rise up through and get stuck. The way you do this is pour epoxy onto the substrate, then mash it in with a putty knife or plastic applicator, sweeping it around as you do, literally forcing it into the surface. Once this is done, you scrape excess epoxy to areas that haven't gotten enough yet, continuing to move it around, mashing it in and scraping excess as you go. The end result is wet looking wood, but no shiny spots, which would indicate a pool of goo. At this point you let this get to the green stage, then you can apply more epoxy for 'glass work or building film thickness. These subsequent coatings don't need the mash and go technique, it's just on raw wood that this is necessary.

 

The other thing that cause outgassing is rising temperatures during the early stages of the cure. The way to avoid this is to warm the piece up first, then wait a few minutes, before applying goo. This insures the temperature is falling when the goo goes on. A lot of builders will move the piece outside and let the sun heat it up, then move it back inside for the epoxy run. You can also use the time of day to advantage, starting an epoxy run, when you know temperatures will be falling, not going up.

 

With experience you can wet the raw wood and immediately move onto laying 'glass, assuming the temperatures are constant or falling.

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