Double Layer

Submitted by bug_hunter on Tue, 11/12/2019 - 16:20

Hey Guys,

New question, new topic.

I am considering a double layer of 4oz fabric on the hull bottom for some added protection.  I think some call it a football. What is the process.  As an knowledge-less rookie, I would wetout and install the football, let it partially cure, do a little sanding, wetout and install a full sheet covering the entire hull, let it partially cure, place a fill coat, then a final coat.

Any thoughts/insight would be appreciated.

Thanks,

Greg

JohnAbercrombie

Tue, 11/12/2019 - 19:55

Usually I just put both layers of glass on dry and wet them out together.

You should test with your glass and epoxy (glass a piece of plywood ?) to make sure that both layers will wet out well.

Some glass doesn't wet out easily, and if your epoxy is viscous or cold, it won't wet the glass well before it starts to cure.

You'll also have to take extra care to squeegee out excess epoxy.

Some other builders probably do this differently. YMMV, etc...

JayBabina

Wed, 11/13/2019 - 08:08

Most epoxies have a time span (roughly) when you can add more epoxy to get a chemical bond. I always do a second coat etc. as soon as the epoxy is dry to the touch. No sanding.

The football is a term builders used to describe a piece of glass that is long and travels from the from to the back along the bottom only. I put this piece down and lay my full piece over it and wet out both at the same time. Knowing what I know now, I wouldn't even bother with it.

As John said: all glass doesn't wet out the same. I just use standard 4 oz and I ALWAYS wet out a sample on a scrap of wood to make sure it wets out transparent if I try a new brand. Look for some videos on using a squeege. You need to flatten out the layup and pull off excess epoxy once the glass is wet.

JohnAbercrombie

Wed, 11/13/2019 - 15:24

Jay-

Perhaps if a barnacle/sharp rock is going to scratch through one layer, it will go through two?

I'm getting started on a build right now and I'm going to try to keep the weight down, so I am thinking about just a single layer of glass.

JayBabina

Wed, 11/13/2019 - 15:58

The glass vs. epoxy misunderstanding has been debated for years on this site. Here's what I did. A bit neurotic but.... I took a piece of plywood about 2 x 3 ft and put of epoxy on one half and glass and epoxy on the other. Then a seal coat over the glass and painted epoxy also over the other side (epoxy alone). I put a few cement blocks on it and dragged it around the block with my car. Both sides had scratches everywhere but the glasses side was shreding apart and the epoxy alone side held up much better.

For strippers and our use, glass is a sheath, holding the strips and integrety of the boat together. Extra glass fabric is a vehicle to add more epoxy and also has additional holding power. But for abrasion resistance you are not gaining a huge advantage. More glass holds more epoxy and that's good. But glass itself is not an abrasion resistant item. Its better than cardboard etc. but the abrasion resistance is the epoxy.

If you wanted to cast a sheet of fiberglass (panel), glass fabric will allow it more bending strength then epoxy alone just like a fiberglass boat. Sorry for the long write but there's always this misunderstanding about glass fabric. 10 layers of glass fabric that is wet out holds a lot more epoxy than one layer and will have a lot more abrasion resistance.

I agree, Jay. A couple of extra fillcoats of Epoxy on the bottom will serve better as scratch resistance, as scratches can be sanded out with less likelihood of getting down to the glass.

I recently spruced up a boat before selling it. Scratches on the hull that looked quite serious sanded right out before I got down to the cloth, and after an overall rub down and revarnish there was no trace of them left.

for extra overall stiffness one would be better off using thicker strips. Even one mm would make a big difference. As it is, though, even with 5mm strips and only one layer of 4oz inside and out, the hull would be way stiffer than even a pure carbon single skin boat of the same weight. A slight give in the hull is actually going to reduce the severity of a scratch, as the impacted area can bend around the offending object slightly while the rest of the boat is supported by the surrounding water.

To reiterate, I think a single layer of glass, with say, two extra fill coats, on top of the necessary fillcoats needed to fill the cloth weave, on the bottom of the hull, would serve one better than extra cloth layers.

Et

bug_hunter

Fri, 11/15/2019 - 10:28

In reply to by Etienne Muller

Thanks again guys for sharing you knowledge/experience.

Look like it will be one layer of 4oz on all surfaces.  With a couple extra epoxy coats on the hull bottom.

With respect to the epoxy, in searching the web, there are a couple methods of application.  Pour and sqeegee, brush on and squeegee, and roll on.  What are your thoughts, and favorite application method?  From my inexperience, I think roll on would be the easiest to control.

Thanks again, and a Great Weekend to All!

JohnAbercrombie

Fri, 11/15/2019 - 11:38

It think it may depend on the viscosity of the epoxy, and pot life.

Very 'thin' and slow epoxies (MAS??) may be good with a roller.

I tried a roller with WEST and didn't like it. It lifted the cloth and was too slow, and wasted epoxy (in the tray and rollers).

I usually pour on epoxy and move with a squeegee, but it takes a bit of care to keep the dripping under control and cover the vertical surfaces. Ted Moores explains this method well in KayakCraft. I have a brush handy to dab on epoxy in dry spots.

Whatever method you use to get the epoxy on to the glass/kayak, the important thing is to remove the excess and get the cloth on the wood with no puddles or floating. KayakCraft or other books and online videos show this.

Etienne Muller

Fri, 11/15/2019 - 13:42

I like to apply the wetout coat with a tile grout squeegee. Fill coats I also pour on, then spread them around a bit with the squeegee, then roll them to flatten everything out, then tip them off along the grain with a brush. It sounds complicated, but is quick, and avoids wasted epoxy in the roller tray. The trick is not yo try to cover the whole boat in one go. I mix about a half to three quarters of a paper cup at a time. I like Mas Low viscosity with slow hardener, for wetout and fillcoats. At room temperatures it needs only about three hours between coat, but gives a fairly decent working time.

et

Tile grout squeegee