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Mccv1
08-05-2014, 09:19 PM
hello everyone. Building our first wooden boat and I have the hull stitched and glued together (12.5 coble from Paul Fisher) and getting ready to lay the glass tape on the joints. I tried it on some scrap plywood and I have some questions. First, my first coat of epoxy on the bare plywood dries up really rough and it looks like there are tiny little bubbles in it. I expected that it would be nice and smooth. Any suggestions? Second, after epoxying the glass tape, I expected that the tape would be transparent and nearly unnoticeable. I made sure the tape was wet so I don't think it's because there are dry spots but there is a clear difference between the epoxied wood and tape. I can clearly see the tape. Was I incorrect in assuming that the tape would "disappear" once wet and then dried? Thanks in advance for any input.

cracked lid
08-05-2014, 09:41 PM
You need more coats. Additional coats should be added before full cure of the previous to eliminate the need for surface prep in the way of blush removal and sanding to provide tooth for the next coat. The bubbles could be from several issues. A common one is out gassing from the plywood as the ply is getting warmer due to warming during the cure due to the environment.

There is a lot of information here and all over the internet about how to use epoxy and fiberglass with plywood in boat building applications. Use the search function, do some reading, and learn how to do it properly before you start using up materials and supplies.

Larks
08-05-2014, 10:25 PM
Some photos might help. I'm not sure that I understand how you are laying the tape: do you mean that you are painting on a coat of epoxy and letting it dry before applying the glass and that you are seeing bubbles in the bare epoxy? Or bubbles under the glass after the epoxy has cured?

Also, when you say that you can see the tape, do you mean that you can see the texture/weave of the tape or that the tape is white? Until the weave is filled you will be able to see it but it should be reasonably transparent. If you're wanting a clear finished hull, i.e. varnished and not painted, you will need to fill the weave with more epoxy, but over time, not all at once as it will just run off. If you are going to paint it then you can fill the weave with fairing fillers and sand it smooth later on.

When I've taped my S&G builds, I'd paint on a layer of epoxy where the glass will go, then a second one as the first will have soaked in a little, then lay down a strip of glass tape and either roll or pat it down (with a gloved hand or the epoxy brush) and then go onto the next seam and start taping that one the same way. By the time I've done that seam a bit of epoxy will have soaked into the glass on the first one and I'd come back to that and paint on more epoxy (in relatively small doses) where the glass hasn't soaked up and use the end of the brush to gently dab it into corners and some flat areas where it might need it.

After that I'd move back to the second seam and do the same there. I'd generally keep coming back to them as the epoxy kicks to check that there aren't any bubbles/lifts in the glass.

I'd certainly not overdo the epoxy when laying the tape as it'll just run when you leave it, but it's a balance as to how much to use to properly wet it out while not overdoing it. Once it's kicked but not completely dried, is still tacky but otherwise firm, you can come back and fill the weave of the cloth with epoxy and fillers. If you can't get to it until after it has fully dried (I rarely do), give it a sand (without tearing into the glass) and wipe down with thinners before filling the weave.

If it helps, have a look through what I've done so far with my skiff build and you'll see how I've been doing it:
http://forum.woodenboat.com/showthread.php?177243-Building-a-Selway-Fisher-14-Thames-Skiff-or-the-sanity-boat-MkII

I've not had the problem with out-gasing in the ply, if that's what is happening, but perhaps experiment with a heat gun after your first coat of epoxy and keep an eye on it to go go over it while it is still wet or tacky if bubbles come up. There's no reason why you need to apply the glass straight away onto the ply with the first coat of epoxy, it's really just more convenient, you can apply a coat of epoxy and let it harden than sand it to key it, wipe with thinners and then do the same as above.

slug
08-06-2014, 02:23 AM
The little bubbles are caused by the wood breathing . Outgassing.

This outgassing occurs when the temp of the wood is rising. Air in the wood pores bubbles out. To avoid always apply epoxy to bare wood when the temp of the wood is falling ..

standard procedure for epoxy coating wood is falling temp, apply first primer coat with a squeegee, not a roller...a light wet out, then apply the second coat fifteen minutes later with a roller. If third or forth coat are needed apply with roller inside the epoxy green time to avoid sanding.

Lewisboater
08-06-2014, 07:54 AM
The glass will not "disappear" until there are sufficient coats of epoxy to fully fill the weave. Even then... It doesn't disappear completely, only mostly. Usually you can't tell it's there from 10 ft or farther unless the light is just right with a bright finish. If you poke your eye to within a foot of the surface... yep, you'll still see it right off. The glass fibers bend light differently than the solid epoxy, and seeing as the fibers are round, they will reflect and refract in many directions, making it visible to an extent.

Tom Lathrop
08-06-2014, 11:51 AM
Sounds like you may have allowed the pre-coated epoxy to harden before placing tape over it. Not a good procedure since the roughness you mention will make it very difficult to get the bubbles out. Tape should go on over wet epoxy or dry wood, not hardened epoxy. Sanding the set up epoxy will make it smoother with less bubbles and visible glass threads but that is a weaker bond and not recommended procedure either.

v10builder1
08-06-2014, 12:04 PM
Much good info here.

I too have cursed the out-gassing bubbles, and I stumbled on a "solution". The out-gassing may well be addressed by coating on the falling temperature, but in coastal Virginia in summer, it is hard to see when surface temperatures are falling (night-time). The bubble problem was minimized on my project by using a resin with a thinner viscosity. I am coating existing (not new construction) bare wood w/ epoxy, under Interlux Brightsides topcoat.

At the outset, I was using the standard resin from Boatbuilder.com with medium speed hardener, and I have had great results, except for the bubbles. On this project, I ran out, and finished up using Smooth-on resin with medium speed hardener. The Smooth-on turned out to just be significantly thinner "out of the pump". In addition to WAY fewer bubbles, the resin "layed out" a good bit flatter in horizontal surfaces, and "ran" much less on vertical surfaces. This is not a structural resin application.

This is in response to the OP's question about what to do about the bubbles.

To comment on another of the OP's questions, on my stitch and glue projects, I have been squeegeeing epoxy resin on both sides of all the panels and hitting the edge grain before assembly. My finished products do run to the heavy side of the design weight.

Thanks.

Joe

mcdenny
08-06-2014, 12:23 PM
hello everyone. Building our first wooden boat and I have the hull stitched and glued together (12.5 coble from Paul Fisher) and getting ready to lay the glass tape on the joints. I tried it on some scrap plywood and I have some questions. First, my first coat of epoxy on the bare plywood dries up really rough and it looks like there are tiny little bubbles in it.

You didn't put it out in the sun to cure faster did you? Surefire way to get bubbles. Shouldn't get outgassing if applying indoors where wood and room air are the same temp. A few degrees don't matter.

I expected that it would be nice and smooth. Any suggestions? Second, after epoxying the glass tape, I expected that the tape would be transparent and nearly unnoticeable. I made sure the tape was wet so I don't think it's because there are dry spots but there is a clear difference between the epoxied wood and tape. I can clearly see the tape. Was I incorrect in assuming that the tape would "disappear" once wet and then dried?

Yes, as said above the tape should be clear(ish) definitely no longer white. If it's white it did not get wet out sufficiently. It't much thicker than a coat of resin so sticks up above the surface - you can see that clearly.

Thanks in advance for any input.

Good luck on your new boat. Posting pictures, kind of confusing at first, will help. 1 pic = 1k words.

Gib Etheridge
08-06-2014, 02:00 PM
As the primer coat soaks into the wood it displaces air in the pores. The displaced air forms bubbles. Go over it with very gentle brush strokes, called "tipping", to burst the bubbles. You may want to tip it several times before it gets tacky. Once it is tacky you may want to go over it again with a thin coat and a plastic squeegee to fill the burst bubble holes. Then you'll want to tip that coat as it cures.

If it hardens before you apply the glass you will want to wash off the amine, which can be done satisfactorily with warm water and a scotchbrite (soap leaves a residue too) but there is pretty good evidence that a bit of white vinegar (acetic acid) in the water is better than just water. You will definitely need to rinse well to remove all traces of the vinegar before going any further. White vinegar, by the way, is an excellent solvent for cleaning uncured epoxy off of your hands. Follow that with dish soap and hot water.

Once the glass is on and saturated tipping is a good idea since there will still be air in the small pores from the previous bubbles. Be sure to apply enough coats, preferably wet on wet to avoid the whole amine cleaning operation each time, to cover the cloth well enough that you never sand through into the cloth when sanding prior to varnishing or painting. Always clean the amine off before sanding, it plugs up the paper really quickly. Plugged but still sharp paper can be unplugged by scrubbing with crepe rubber, available at building supplies. Sometimes it helps to wire brush the paper before using the crepe. Once sanded smooth prior to the final finish, whatever it may be, clean off any traces of amine again, it retards curing of the finish.

Dusty Yevsky
08-06-2014, 02:49 PM
Another possible source of bubbles is excessive use of the squeegee. Avoid "working" the epoxy after you have applied it to the tape. What works for me is pouring enough epoxy on the tape when it is properly position to saturate it and then slowly squeegeeing out the excess. Don't move epoxy around on the tape to cover up dry spots and don't use the excess either. This will introduce micro bubbles that are visible in a bright finish. These are next to impossible to get out. Instead pour fresh epoxy on the dry spots and discard the excess or use it where it wont be seen, like under a deck. If pouring epoxy on the tape isn't feasible then soak the length of tape in a tightly fitting container. This is very messy though.

Jammersix
08-06-2014, 05:07 PM
I just went and looked at "boatbuilder.com", and it doesn't appear to sell anything.

Mccv1
08-08-2014, 08:44 PM
Thank you all for the input. I'm going to try some of these suggestions things this weekend.