Addition of inside fiberglass layer after 9 years?

[mayday]

I built a 16' wood strip Prospector model canoe nine years ago using RAKA 127/350 epoxy with a 6oz sheet of fiberglass on each side. I LOVE THE CANOE! I have taken it ito BWCAW several times, paddled solo, dual, and with three persons plus gear. Nine years alter of hundreds of miles, plenty of rocks, stumps, and other hidden gems, I have now noticed many cracks in both the wood strips and fiberglass. So I have been thinking....I might want to add an additional "football" layer on the inside hull and use the RAKA blend. This will in theory strengthen the canoe hull from the inside, which in my opinion would be stronger than on the bottom (aka outside hull).

So, what do you all think? Will this work without delaminating? Or should the second layer be on the outside/bottom?

Jeff Wadley
Maryville, TN

 

[Todd Bradshaw]

It would need to be on the inside, where its tensile strength can help strengthen the hull against flexing and cracking. If you already have cracks in the wood and inner glass though, you're still going to wind up with only one good layer in the bottom, which is not very durable, as you have already seen. A new layer is not going to "fix" the broken stuff, just reinforce it to an extent.

A new layer on the outside adds virtually no reinforcement in this way. It would add a thicker abrasion barrier, but on impact the outer glass just flexes. By the time its "strength" comes into the picture, the inside of the hull would have shattered.

Assuming that the inside was varnished to protect the epoxy from UV (which it should have been) the ability of the new resin to bond well may hinge on how much of the varnish you can remove. Epoxy is pretty sticky stuff on a variety of surfaces, but ideally laminating is best done with no foreign materials between the layers of resin. Remove whatever you can, scuff up the inside surface with sandpaper (without cutting deeply into the glass cloth), apply the new fiberglass and hope for the best is about all you can do.

 

[mayday]

That was my though process as well. The Helmsman Spar Varnish has been reapplied a couple of times and I can remove some of that. I wish I had known about applying either a second inside layer or a heavier layer when I first crafted the canoe. Oh well, I think I will probably add a second football shaped inside layer and try to stay off rocks and stumps! By the way the Helmsman product and the Schooner Gold products are awesome UV protectors! I use the Schooner Gold exclusively on my wood canvas restorations. I love the golden tint once it is applied to white cedar!

 

[Dan Lindberg]

Jeff,

Thanks for posting this, as it re-confirms my initial belief that the std 6oz/1/4"/6oz layup is not strong enough for canoes that are not babied.

When I built mine 10-12 years ago, during my research I found many owners who had similar or worse failures with the std layup. I did the 2 layers (in and out) in the football thing and had a heavy canoe. Then after more research, learned that 6 oz might not be the best glass to use. At the time, a guy in Ok was getting beat up pretty good for expressing his contrary ideas. Hint, multiple layers, thinner fibers and tighter weaves are stronger.

Anyway, if I was going to repair it, I'd only add glass to the football. I'd clean it good, maybe even carefully use chem stripper to remove as much finish as possible, then a good sanding, no finer than 100 grit, and then I'd put down 2 layers of 4 oz satin (or tight weave) cloth, using a low viscosity NON blushing resin. ( I like System 3 but there are others.)

Dan

 

[Todd Bradshaw]

Two layers of 4 oz. might be a good solution. George was a good composite engineer and built some nice boats, but it was his attitude on other stuff and toward people that got him tossed off of most of the forums (eventually being arrested for hanging the neighbor's dog in his front yard in particular was the final straw). He was building single kayaks using 1/8" strips with three layers of 3 oz. cloth on each side, and I don't think anybody was complaining about his boatbuilding skills. It was basically revolving around layups that had the highest possible glass fiber to resin ratio, and thus maximum strength.

There are some marine strippers that state specifically on the can that they won't attack fiberglass, and if you plan on preserving the existing glass and using chemical stripper, you need to be a little bit careful about your stripper choice. The blushing or non-blushing thing really makes no difference here. Whether you saturate the cloth layers both at once (lightest and strongest per ounce) or one after the other as soon as the first one has stiffened enough (maybe more controlled but uses more resin) any blush will simply float up through the resin to the surface. It can later be washed off in a couple of minutes with water before varnishing. Blush on epoxy construction is generally such an easy thing to deal with that it's just not worth getting all up tight about. If your epoxy blushes, just wash it off. In most cases, you would be wise to wash the epoxy surface before your next step to rid it of contamination anyway - whether it is blushing epoxy or not.

 

[Dan Lindberg]

Todd,
You are a master of the understatement. I hadn't heard about the dog before, I dropped off the boards when I discovered W/C.

Blushing or not, ya, I know it works fine and is easily dealt with, I just don't want to.

"his attitude on other stuff and toward people that got him tossed off of most of the forums (eventually being arrested for hanging the neighbor's dog in his front yard in particular)"

Dan
who's not nearly the teacher that Todd is

and are you going to be at the Assembly this weekend?

 

[Todd Bradshaw]

No, we've been making multiple weekend trips up north to fix up my family's place near Rhinelander this summer (paddle or fish maybe two hours if you're lucky and do construction fifteen hours per day the rest of the time) and this weekend we'll stay home and work on stuff around here.

Once in a while back in the day, I could get into a good technical discussion with George, and he was really doing some neat stuff - but you had to filter out a whole lot of nasty attitude. I can certainly be blunt and abrasive at times, but George was the hands-down prize winner and it really hindered his participation. That, and the fact that he guarded his knowledge closely and would tell people that they would have to pay him for more information. I figure that you can't take it with you, so you might as well give as much of it away as possible before you go. The modern generation tends to be kind of scary, paddling around in stubby 9' kayaks and cheap plastic canoes from Wal-Mart. A huge percentage of these folks may never paddle a really good boat (or a long enough one) in their entire lifetime and won't know what they're missing. It's our job to remind them, encourage them and preserve the heritage of great boats, as most of you are well aware.