Steps for 2 fiberglass layers?

[Brian G]

What are folks' opinions on the steps required for laying up 2 layers of fiberglass?
Option 1. Place the 2 layers of dry cloth and wet out all at once
Option 2. Wet out one layer, allow to cure, then place and wet out second
Option 3. Wet out one layer, follow with addtional epoxy coating, then place and wet out second layer.

Thanks

[Glen Smith]

According to West System Option 2 would be the best choice if you apply the second layer after the epoxy on the first one has lost its tackiness but before it has fully cured. Of course, if you are using a blushing epoxy you must wash off the blush before adding the second layer.

Option 1 presents a greater risk of having bubbles in the cloth. Option 3 adds unnecessary weight.

[Juneaudave]

I've done both 1. and 2. I suggest 2 unless you have some experience with cloth and feel comfortable working with it. I would not try option 1, especially on the inside, but I might go for it again on the outside if I had a real slow epoxy like MAS slow. I would never do it with West 105/207 because I don't think there is enough room for error.

[Scot T]

For interest sake and to carry this question a little further, what about adding a second layer of glass/epoxy at a later date? For example, say the canoe has been completed but has not been varnished yet,. Although it may have sat for a few months, one desides that more strength needs to be added. Or perhaps the canoe has been used for a season and the varnish is to be stripped and another layer of cloth is to be added. What are the thoughts on these situations? Will the second layer bond sufficently strong with the first, even though it will be a mechanical and not a chemical bond?

[canoeblderinmt]

I started this new path in my life (building and paddling strip canoes) by buying Gilpatrick's book, which recommends two layers of cloth at once being wet out. I do believe that his is a more utilitarian approach to canoe building, the idea being to build a strong boat that you can use, not so focused on the aesthetics. That being said, I have followed this method now on two boats, and it has come out OK. I use Raka glass and epoxy, which tends to be pretty runny (thin) and wets out very nicely. I was worried both times about outgassing and not getting the weave filled, but using a squeegee to help push the epoxy through and then to remove excess epoxy from pooling and floating the cloth, it has come out OK. It is obviously a little faster than two separate coats, but that isn't really a good reason to do it. You might try a sample board both ways and see which is more comfortable for you.

Let us see some pics as you go,

Greg

[hoz]

I applied a 2nd coat of F/G to my Osprey a year after completion. My first year of hard use was leaving lots of scratches on the bottom. I sanded all the varnish off to the waterline and laid the F/G. I also used graphite and silica for the final fill coat. It added about 6 lbs to the boat.

It's been several years now and no delamination or failure.

[Jeff in Farmington, MI]

Brian,
As a first time builder, I used 6 oz glass over the entire exterior of my hull, plus a layer of 4 oz glass cover the "football". I thought the 4 oz glass would be a good compromise between added abrasion resistance and added weight. I placed the 4 oz layer under the 6 oz glass and wet out both at the same time, without a pre-coat. While the glass came out OK, it did take far more time than I expected to wet-out. This can be a real problem with West System epoxy, because it sets up comparatively fast. I have not used any other epoxy brands, but on my next canoe project (someday), I will likely use a thinner, slower, more forgiving epoxy.

I would recommend wetting out both layers at the same time. This is faster, easier, and probably stronger. However, make sure that you have an assistant to do your mixing. Also, consider one of the thinner epoxy brands which will wet-out faster.
By the way, the 4 oz football layer posed no problem during the process, and the boundary can not be seen on the finished hull (not even by me).

[Bassbug]

I'd like to follow up on this question. I have used all three methods - I don't like to use #1 as well as #2. I see more of the weave when I use #2 compared to #3 (but this comes with a weight cost). I think this might be that the epoxy did not fill all of the weave with two glass layers are filled together - but this is speculation on my part. I'd like to know if others builders have a more visually appealing result with #3, than compared to #1 or #2.

[Its Me]

Why wouldn't you just go to an 8 oz or 10 oz cloth? I am not sure why one would need two layers of 6 oz cloth on a 1/4 hull but if strength is what you are after and the double installation is a concern, why not just up your weave?

Either way you do it, that is a lot of epoxy that you are going to need.

[Jeff in Farmington, MI]

I decided to use a 4 oz cloth under the 6 oz cloth because I had found that the 4 oz cloth weave is virtually invisible after having been filled with epoxy. As you know, the 6 oz weave is visible when you get up close. I reasoned that the 4 oz cloth would not change the transparency of the finished glass, and it did not.

A heavier cloth has a thicker weave, and it will not be as transparent. As with paint or varnish, it is better to use multiple thin layers than one that is extra thick. Another canoe builder that I know experimented with a 10 oz cloth and was very disappointed with the result.

[Rod Tait]

Wetting out two layers at once is more difficult than two seperately. I use the second method in combination with # 3. In that, I mean that I put down the first layer, add two coats of epoxy and let fully cure. I sand the next day, clean up the hull and then add the second layer. This way, you have a smooth surface to add the second layer to. It takes more epoxy and adds a little more weight, but this is a small compromise compared to bubbles and discolouration in the two layers at once.

As for heavier cloth than 6? Most epoxies companies will not promise clarity on anything more than 6. And two layers of 4 with cross weave is exponentially stronger than one layer of 8.

There is also two schools of thought about putting the smaller piece over or under the full piece. If you put it under it is easier in not having to deal with strands and can be done in one lay up. However, with the full piece over top, there will be a small ridge between layers. When it comes to sanding the hull for varnish, you are more likely to cut into the full piece if you do not fully fill the weave in that area. And when you cut into the full piece, you compromise the integrity of the full sheet of glass, leaving you a weak area at the overlap line. I add extra layers underneath on the inside where sanding is minimal, and extra layers over top on the outside.

[Juneaudave]

I tried 9 oz and could not get it to wet out even after heating the epoxy.

[Brian G]

Thanks for the advice.
I'll go with option 2 as it seems to be a good compromise between margin for error and avoiding excess weight.
I'm a first-timer using 4 oz cloth, two layers on the outside of the hull for extra strength, and 1 layer each inside the hull and on the deck to limit weight.

[Jeff in Farmington, MI]

Brian,
If you are going to use two layers of 4 oz cloth, I seriously doubt that you'll experience problems during the wet-out process. The 4 oz cloth absorbs even the thick West System epoxy very easily. I would recommend that you try a small test panel using each method.
Either way, good luck, and happy building!

Jeff

[Dell Littlefield]

I suggest you do a little more research on this subject. This has been discussed quite a bit on this forum. My understanding is that if you want to add strength to the hull, you would need to put two layers inside versus outside. If you are going only for the abrasion resistance, the two outside would be appropriate.