Hull UV Protection

Fiberglass over plywood is ridiculously tough.  There are wood and fiberglass boats still around after 50 years.  However, fiberglass has an Achillis Heel -- sunshine.  Fiberglass rapidly degrades with exposure to UV rays.

Thus, it is recommended to paint or varnish fiberglass with something offering UV protection.

We wanted the boat to show off it's lovely woodiness, so we chose varnish.  There are fancy marine varnishes that are made for marine applications.  Spar Varnish is one example.  They are relatively expensive (though not compared to epoxy which is ridiculously expensive).  However, there are exterior varnishes that are equally good that you can pick up at the hardware store/lumberyard which are just as good.

  

In a moment of insecurity, I called and checked in with Gayle at Glen-L just to make sure. She gave me a thumbs up on my selection of exterior UV varnish.

After varnishing, it looked pretty much the same as after the last finish coat of epoxy.  But in my mind, I knew I'd protected the fiberglass from it's Nemesis the big ball of fire in the sky.

Fiberglass Finish Coats

After the fill coat, the texture of the fiberglass cloth was still visible, so we embarked on a series of finish coats. 

I think we finally put three more coats on after the fill coat.  The Finish Coat, the Aren't We Done Yet Coat, and the Good Lord Please Let This Be The Last Coat. 

I took a moment to pose proudly with my dense foam roller in my work clothes now almost completely rigid from layers of spilled epoxy.

Between layers, we attacked the bumps, bubbles, drips, and encapsulated bugs with an orbital sander and sandpaper.

And each layer was smoother and more handsome than the last.

Until finally...

 We had something that looked purdy fancy and shiny.

 Whew.  Finally.

And so we could set aside the epoxy for a while.  We thought we wouldn't need it again until we do the upper decks after the boat is flipped.  (However, we needed epoxy to do a "scarf joint" on the skegs, so stay tuned for that.)

Fiberglass Fill Coat

At this point, we have the fiberglass bonded to the boat with a layer of epoxy.  The texture of the cloth is still quite visible, so we have to add enough epoxy that it is invisibly hidden.

Since by now we are grizzled veterans of fiberglassing, the work was not so stressful and only required a team of two -- one person to mix and deliver the epoxy to the other person who is applying it with a dense foam roller.

 We had to work quickly on a hot day to apply the epoxy before it kicked off. 

Then we went around and brushed over any drips or places where it was funky.  We had varying success preventing drips.  Later we noticed plenty of places where it required work with a sander to make sure the next coat was smooth.

Each day after we finished a fill or finish coat we were pretty sure our work was done and that the texture of the underlying cloth was invisible.

And each work day when we returned, we could still see the texture of the cloth through the previous coat.  So we were obligated to add another finish coat.  Rinse.  Repeat.

Fiberglass Bond Coat

Okay, so let's review.

Fiberglass (of more accurately glass-fiber reinforced plastic) is a composite laminate of hardening plastic goo reinforced with Ziggy Stardust-esque silvery spun glass fabric.  We have already applied the "seal coat" and need another several layers before we're done.  I found the Glen-L instructions for applying fiberglass for you.  This is pretty much what we used.

Here's the application sequence for the "dry method:"

1. Seal Coat - seals the wood surface prior to applying the cloth
2. Bond Coat - used to wet out and bond the cloth to the surface
3. Fill Coat - fills the weave of the cloth
4. "Finish" Coat - provides enough resin build-up for final sanding and finishing
5. Aren't We Done Yet? Coat - enough epoxy hopefully to hide the texture of the cloth
6. Seriously, This Is The Last Coat - finally enough to more or less completely hide the texture underneath

And then after that we have to protect it like a new born baby from dangerous UV rays with paint or varnish.  We'll do varnish.

We agonized over this day for weeks.  We thought it would be stressful and it did not disappoint.  We enlisted the help of Jen to complete our three person team.  This was one of those days we talked a lot about The Plan and worked out roles beforehand.  Kai was the epoxy mixer (and later the touch-up person).  Jen was the epoxy applier/roller/splooger.  And I was the smoother downer/problem fixer/epoxy redistributor. 

All summer, it had been ridiculously hot and sunny.  But the day we chose to do the stressy bond coat, the sky threatened to rain and spit occasional little dribblets on us.  Grrr. 

We stapled the cloth in place to the hull smoothing out the wrinkles best we could.  Though the instructions suggested removing staples before the cure, we found it was better to wait until the epoxy was completely cured before removing the staples lest you pull up the cloth.  Note that putting the staples in, we were careful to make sure they stuck out enough to allow them to be easily pried up with a screwdriver.

The Glen-L instructions suggested that for places where the cloth met it be double-lapped with tapered edges tapered.  That is, lay one layer of cloth, sanding the edge to a taper after it cures.  Then lay the other layer of cloth overlapping, and then sand that other edge after it cures.  That meant that since we couldn't do the overlap in one day, we needed at least two days to finish the bond coat.  

So we got all clever and did half of the bottom and one side on Day One.  Then the other half and other side on Day Two.

Each of us had a set of tools.  Kai used the usual measured containers and an endless supply of stir sticks.  Jen used a dense foam roller with a long handle.  And I used a wide trowel and a fiberglass roller that I handmade with alternating-sized washers and a paint roller.  My job was to go behind Jen and trowel any pools of excess resin into areas that needed more of it, and then roll down the stubborn cloth that had bubbles or warbles in it with the roller.

The magic of this process is that as soon as the glass cloth is covered with wet resin it turns transparent.  So it is easy to see if you've applied enough resin to wet it out.  Here I'll interject a warning:

Do not skimp on resin during the bond coat.  Make sure every bit of the fiberglass cloth is wetted out and transparent.  The next coat WILL NOT cover any areas that got too little resin.

We had some spots like this.  We learned the hard way.  Take a look at the very edge of the corner on the photo above.  Tiny but still irritating.  These places where there are air bubbles behind the fiberglass are potential places for air and moisture to gather and rot to form.

However, other blemishes, like little bits of resin-saturated glass fiber that stuck out (got snagged by my trowel in many cases) or awkward corners, were easy enough to sand down and resin over in the next layer.

In general, places we had worried about, particularly the seams looked great.  After they cured I would have to sand them down in preparation for the next layer.

After this first bond coat layer cured overnight, we sanded down any wacky blemishes and tapered all the places where the glass cloth would overlap.

Then we laid the cloth over the other half of the bottom and the remaining side and applied epoxy over that.

When this second half of the bond coat had cured, we tapered those edges and the result was quite beautiful.  The texture of the cloth was clearly visible, so the next step is the fill coat.

You'll notice there are few photos of us actually working this work day.  Uh, no surprise.  We were definitely eyes on the prize in order to get this done in a way that didn't suck.

Fiberglass Seal Coat

We fretted over fiberglassing the hull so much, we put off beginning with this step for weeks.  We read and reread our instructions from Glen-L, Ken Hankinson Fiberglass Boatbuilding book, and anything else we could find.  We went over scenarios and thought of terrible things that could go wrong.  We thought it would be so harrowing and difficult, that in the end, it was a bit of letdown.

Here's where we left the boat last time.  Filled, shimmed, routed, sanded lovingly.  Lawrence came by a couple times and asked, "What are you building, a boat or a piece of fine furniture?"

Before we started the day, we had to wipe the whole boat down and make sure there was no sawdust, grease, debris, or anything anywhere.

But really, this was just the seal coat, the first of four or five coats we'd put on the hull.  We wouldn't even get out the glass cloth until the next coat.

And now a quick primer on fiberglass:  Fiberglass is a composite laminate material.  The layer(s) of spun glass cloth or mat embedded in a matrix of polyester or epoxy resin are what gives it strength.

In some boats where the hull derives its strength from the fiberglass, it is typical to use alternating layers of mat (a loosely woven nest of randomly aligned spun glass) and glass cloth.  In our boat, the fiberglass covering on the plywood hull served only the purpose of keeping it watertight and creating a durable wear-resistant maintenance-free surface.  So we had only to put one layer of glass cloth between several layers of epoxy.

There are many methods of applying fiberglass to a boat hull, but they break down to the so-called wet and dry methods.  "Wet" means the fiberglass cloth (or mat) is laid over a just applied layer of resin and then "wet out" with more resin on top.  This sounded hectic. We imagined laying cloth over a wet sticky layer of resin and fighting wrinkles and having the cloth misaligned and pulling our hair out and getting sticky head to foot.

We were relieved to discover in our Glen-L instructions that they recommended the dry method.  "Dry" means simply that the first coat is rolled out without the cloth and allowed to set.  Then the cloth layer is laid out over this dry layer and more resin on top of that to wet it out.  This allows us to carefully align the cloth without the stress of either sticky goo or the ticking clock.

In this first seal coat, all we were doing was covering the hull with epoxy.  Kai mixed up big batches of epoxy and put them in paint trays for me to roll out with a dense foam roller.

Then Kai came around with extra resin and touched up spots I'd hit too lightly and brushed down any air bubbles.  Because we weren't mixing the resin with filler, it had a longer pot-life and so didn't tend to kick off early, even though we were mixing it in larger quantities.

The result was beautiful, though vaguely reminiscent of a horribly outdated style of 70's handmade varnished pine bedroom furniture.

Though it was a hot day in the barnyard, we were feeling pretty good about our work and the results.