i am ready to fiberglass inside of hull on my sheerwater double and i am not sure how many coats of epoxy. the manual does not say




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RE: fiberglass

On the inside of the hull and deck you do not need or want to fill the weave like you do on the outside of the boat because you want some traction (in the cockpit floor), and the inside does not get the abuse the outside does.  You do need to make sure that there is a completee layer of epoxy, however, so that water cannot get to the wood. 

I put on a total of 2 coats of epoxy when I did my build - one coat to wet out the fiberglass cloth, which I squeegeed on, and then one thin fill coat just to make sure there was complete coverage.  

I will admit that fiberglassing the inside of the hull was my first experience with the process and it was a tough place to start - whenever I squeegeed up from the center, the cloth would pull away from the seams and leave an air bubble underneath, so I would squeegee back down toward the seam to get the cloth in contact with the seam and end up with a pile of epoxy.  I had no idea how long of a working window I had since it was my first experience, and I was quite harried by the end of it.  However, it turned out well.  Fiberglassing the outside is so much easier!

Good luck,




RE: fiberglass

Thamks for the info, frank and i are going to epoxy the glass today, it should go well.

Thanks again for the info

RE: fiberglass

Not to hijack this thread... but on a similar line.  I saw a video on youtube from Pygmy Boats that show them putting epoxy on the hull first.  Letting that cure then putting the glass down.  Is there an advantage to doing it that way?  

RE: fiberglass

Hey Ken.  If the plywood is older or checking, you will definatelt want to epozy cioat first, filling all checks(cracks).  I have done it both ways and neither method has ever failed.    ~BRUCE~

RE: fiberglass

It'll work if you precoat, but personally I no longer do it that way. It's more epoxy (money and weight) and labor than just putting the cloth down directly onto the wood. If you let the epoxy cure completely, you have to sand it before putting on the glass. The idea of putting on liquid gold just to sand it off so I can then apply more seems wasteful to me.

Skipping the precoat also increases the glass to resin ratio, which is the holy grail of strong laminations. Remember how in the manual it warns not to let the glass float? When you precoat you are deliberately floating the entire sheet of glass. Not much and usually not enough to really make a difference that you can measure outside a laboratory, but it's still happening.

The rationale for precoating is to seal the wood pores to keep the wood from rotting. A properly wetted layup will do that without the need for a precoat, especially if the weave is filled afterwards.

Finally, Bruce makes a good point about filling checks before applying glass. Not doing so could result in voids which could lead to delamination. The only thing I'd add is that it's a lot cheaper, somewhat lighter and a lot less work (sanding) to fill checks with thickened epoxy, rather than the straight stuff. Personally, though, I'd get a different piece of wood if I could.

Have fun,


RE: fiberglass

Me again...   I guess I'm "gun shy", after having the MAS turn cloudy on me.  My thoughts are to pre-coat, allowing it to gas off.  Then, after curring & sanding, applying the glass cloth and more resin.  If there is a problem, like the devistating one I had, it won't effect the THIN wood itself.  Burning off all the F/G, then sanding the 3mm deck was a lot of work and I was always worried about sanding thru the top layer of ply, (Which I did in a few small areas!!!!).  As for weight, I pre-coated with a very thin layer and, opting NOT to enter my Wood Duck-12 in the World National Around-The-World kayak races, I'm good with it....   ~BRUCE~ 

RE: fiberglass

I also did a very thin seal coat of epoxy before I put the glass on - not necessary, but it being my first time I was worried about bubbles from outgassing.  I rolled on a thin coat and the squeegeed it hard to minimize thickness.  If you glass soon afterwards (within 24 hours with MAS epoxy) you dont' need to sand or prep. 

RE: fiberglass

>>>>>The rationale for precoating is to seal the wood pores to keep the wood from rotting. A properly wetted layup will do that without the need for a precoat, especially if the weave is filled afterwards.



That's not it.  It was chapter-and-verse for years to roll a coat of epoxy over the wood prior to fiberglassing for one reason:  older-generation epoxies were too viscous to soak through the fiberglass and into the wood. It was quite hard to wet out the fabric, and coating the hull first gave you a head-start on, and a fighting chance of, getting the fabric wet out properly.

Among several dreadful side-effects, the policy of rolling on a coat first (followed quickly by the 'glass, before the old-school epoxy "blushed,") meant that it was very hard to smooth the fabric effectively.  Wrinkled 'glass stuck to the hull, and you'd roar and cuss and, eventually, weep as the wrinkles got set in place. Atop that, the viscous epoxy tended to "foam up" as you worked feverishly to get the honey-consistency goo into the fabric, leaving an ugly cloudy finish.

MAS epoxy came along in the mid-90's with a low-viscosity brew that flows right through the 'glass and into the wood.  Very few of us looked back.  WEST System has their 207 hardener and System 3 has their Silvertip brew to match MAS.  

On rare occasions I'll pre-wet the wood before 'glassing.  This includes scenarios where I have to get fiberglass to stay put on a vertical surface (the stickiness is an asset in that case).  Or if I have a lot of end-grain or extremely absorbent wood and a smallish area to 'glass (no wrinkling issues), I'll pre-wet.

Cedar strips are an interesting case because they tend to soak up the low-viscosity epoxy like a sponge.  I don't pre-coat before 'glass, but I DO stand by to apply more epoxy about an hour after the 'glass is wetted out, as the cedar can drain too much epoxy from the 'glass.

Here's more useful info on wetting out 'glass.


RE: fiberglass

Thanks!  Great explinations.  I won't "pre wet" when I do my build.  

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