I regulalry use the technique....i wouldn't call it a 'saturation' coat....just a 'skim' or 'seal' coat.

the technique is useful if you are trying to get a lightweight build and it helps make the glass application process go a bit easier in my view...and reduce 'expoxy starvation' in the glass coat.  but it does add an extra step/time.

let me give you a bit more background on why it works and why 'saturation' is probably a misnomer.  

you apply as light and thin a coat as you can on this skim/seal coat. the goal is basically just to get epoxy to clog up/seal the pores of the wood with as little epoxy as possible (so you actually do not want to 'saturate' it).    once it cures (dry to the touch), you have now sealed the wood....so when you go to apply your glass coat and all the epoxy associated with that, you now don't have to worry about the epoxy in that coat getting drawn into the wood and 'starving' the glass coat.  what would happen in the 'starving' is that you will think you have wetted out the glass, walk away, and before the epoxy hardens, the pores of the wood, acting like a straw, would continue to wick away the epoxy until the wood was saturated or the epoxy kicked off and plugged the pore...and you would now come back to a 'white spot' or starved glass section.  the boat, of course, would also be heavier having used more epoxy.

the technique also helps avoid bubbles/outgassing in the glass coat becuase the wood is now sealed and can't blow bubbles back into the glass coat.

hope that helps

h

H, Thanks for the great response!  My buddy echoes your statement that the coast should be called seal or skim rather than saturation!  I cannot wait till I get to that point.   

Also gives you a chance to sand the wood if the grain raises up. JRC   

Yep, the grain is another issue that the skim coat helps address. Without that coat in place, dragging the fiberglass cloth across the panels would be difficult. Small imperfection can snag the cloth as you move it into place, or move it while in the process of applying epoxy, and this potentially could show up in the finish.

With that being said, I'm seriously considering using penetrating epoxy on my Passagemaker, which is designed specifically to wick down into the fibers.  The PM manual actually has you coat all parts first prior to stitching it together.  Also make sure you know whether you need to mechanically etch the surface of the epoxy before bonding the parts together based on time since the coat of epoxy, blushing vs. non-blushing, etc.

And the skim coat is applied with what?  Roller, brush?

I like a roller and squeegee. The squeegee lets you get the coat really thin, which is all you need.

Laszlo

Thanks guys for the information!  Can all parts be skimmed coated prior to stiching/glueing? 

Lou 

Yes, but...

Depending on how thick you make the coat, it can stiffen the wood as it cures. If you then have to bend the wood to a strong curve, you may not be able to do it. Also, once you put the epoxy on, wetting the wood to make it easier to bend doesn't work. Finally, if the epoxy cures completely, you may need to sand it before applying more epoxy or glass.

So, if you have a boat with gentle curves, manage a thin skim coat and can get to the stitching and gluing as soon as the epoxy cures beyond tacky, you should be fine. If your answer to any of these is no, you may want to wait with the skim coat.

Good luck,

Laszlo

For applying epoxy to raw fiberglass, I use the little yellow hand squeegee to get the perfect amount of saturation, not too much, not too little.  For everything else, I use the 4" foam rollers.  I probably went through two dozen of them building the EP.  Roll slowly as they create bubbles.  You can blow on them with a hair dryer to pop them and accelerate slow curing times.

   Is there any harm in sealing the wood with a sanding sealer or polyurethane before glassing as long as you sand in between?

i would not do what you are suggesting - even if you sanded it.

you don't want sanding sealers or paint underneath epoxy.  if you epoxy over paint, it subverts the bonding of the epoxy to to the wood.   you might get it to work or stick but it will be nowhere near as strong or water-proof as the epoxy directly on the wood.

painting over epoxy is fine.  not the other way around.

Yes, there is huge harm in using sanding sealer before epoxy.  That would inhibit the essential bond you're looking for.  Sanding sealer is for making furniture out of pine.  Not sure what you mean by polyurethane, but that normally means a coat of paint in the boat world.  Put nothing between the raw wood and the epoxy and or fiberglass, not blood, sweat, tears, sawdust, etc.  The longevity of your build requires the epoxy to bond deeply with the fibers of the okoume.