Recognize this patch material?

Dave Nagel

This Year's Obsession
Hi all you helpful or curious canoe enthusiasts,

When I got this Canoe I think someone had started a restoration project on it. The canvas and the outwales were off and there were some patches on the planking. I am wondering if anyone recognizes what the patches are made of. How smooth do I need to get the patches before I cover it. I am also curious about the puddy over the tack heads on the planking. I have not seen it on any one else's pictures of their restoration. Anyone know what it is? is it original?



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If either the greenish patch material or the tack head covering putty is bondo, you might have a problem. The last time I used bondo on a car dent (many, many years ago) it was that kind of light green color. See the thread at which discusses problems with polyester-based filler materials (cracking, etc.).

Usually the hammer dent around tack heads are raised by wetting the wood, not filling the dent. I don't know what would happen when a filled dent gets wet, but I would be concerned that putty-pimples might rise up when the planking gets wet, as it surely will.
Looks to me like someone at some point had fiberglassed the hull. If you take a stock wood/canvas hull and glass it, the tiny dents at the tack heads are a problem. The cloth winds up suspended over the little craters, which don't want to fill with resin. The fabric gets saturated, but the result looks kind of like little patches of screen wire over the tacks. This is why the depressions at the tack heads have been filled, since once you fill them and sand them flush you can apply fiberglass smoothly over the surface.

I suspect the Bondo (grey-green stuff) was applied to spots where the fiberglass had later been peeled off and it took some wood with it. There are some epoxy-based filler compounds which are very stable in this type of application, though Bondo and other polyester-based fillers aren't generally a great choice for marine use.

This leaves the question of what to do about all these and I don't think there is a clear answer that stands out above the rest. A heat gun and something to pick at them with is probably the best way to soften and remove them, but most likely a very slow, tedious process. I don't know of any chemicals or strippers that will remove the stuff easily - most will just make the surface gooey. I think I'd tend toward leaving them as long as they're firmly attached, making sure they're smooth and canvasing right over them. There is certainly a little bit of risk that they may somehow poke out a little bit in the future, but I think I'd take the chance.

Before doing anything, I would be tempted to put the hull on sawhorses out in the yard, get out the garden hose and really soak it down well. Once dry, it might tell you how much the fills tend to lift, if at all, from the planking getting wet.

Looks like Bondo to me. Awful to remove. Forget about it. Cut out the planking ahead and behind the patches at the center of the ribs and replace with "new" old planking rescued from some other dead canoe. If you need some let me know, I saved a couple pieces from my wreck. It is not worth trying to remove Bondo. You'll only end up screaming and swearing and nursing burns and cuts.
I agree it looks like bondo to me too. I would consider sanding the entire hull to the top of the tacks. At that point I might varnish the entire outside of the hull before recanvasing. If there is still a lot of bondo, another choice is a coat of boat paint to cover the wood and what is left of the bondo. Experiment on the pieces you are likely to cut out any way and see what will give you a stable surface.Good luck.
In my humble opinion (and based upon actually having done it) trying to sand the hull down cleanly and evenly to any level is absolutely nuts! The only difference between that and soaking it in gasoline and striking a match is that it takes longer to wind up with a similar result. You would need to be REALLY good with a disk grinder or spend a tremendous amount of time long-boarding by hand to get anything that looks fair in the end. Planking wood is also fairly easy to break, so sanding away 15% of it's strength isn't such a hot idea either.

As I said before, I'm not a big fan of using Bondo on boats, but if it's decently attached, the chances of ending up with a nice wood/canvas canoe by smoothing it and leaving it are probably better than the chances of trying to remove it. If there are big, localized areas of it, then replacing small sections of planking as Splinter suggested sounds pretty good, but trying to remove all the little filled spots on the hull, especially by grinding it down is a formula for disaster. The boat that I ground down eventually needed a fairly massive fill job (epoxy & microballoons) to get it back to a nice, fair shape. What a pain in the butt! It's the yellow one shown here. move 016 copy.jpg
Did I mention the fiberglass mat looking stuff?

Thanks for all your input All advice and opinions are welcome, I think quantity breeds quality.

The pictures did not come out as good as I would have liked by the time I shrunk them down. They didn't show there is some mesh in the patches that looks like fiberglass cloth. The patches are really more of a gray and I don't see any hint of green. My guess was it was an epoxy. It is very hard, it will be tough to feather the edges if I sand it.

Sounds like putting it out in the rain (no need to use a hose here in Western Washington) would tell me if it is bondo, if it swells I would need to dry it out then seal it or remove it, probably along with some of the planking.

The stuff that covered the tack heads sands easily I can get it off without taking off much wood. Then I think I can pick it out with something like and awl, man, that's a lot of tack heads. At least it will keep me out of the fly shops.

Any opinions on being able to seal it if it is Bondo? How hard would bondo be? could I scratch it with a nail?
The Bondo itself isn't likely to swell or even absorb a noticable amount of water. Bondo is simply polyester resin (the resin used to make most fiberglass boats, and in this context, it could be considered virtually waterproof) mixed with ground-up mineral fillers until it becomes a thick paste. Substances like talc and fumed silica are commonly used for filler. The danger from getting this boat wet is more a matter of the possibility of wet wood swelling around the fills and "popping" the bondo out of the craters. At that point, you might have little lumps of hardened Bondo pushing outward on the canvas or floating around between the planking and the canvas. The other possibility might be big chunks of fill coming loose and no longer doing the job of filling the holes they were slathered into, and/or losing whatever structural strength, stiffness, etc. it might have been providing to a damaged and filled section of planking.

Polyester resin doesn't stick particularly well to wood and the more filler that is added to it, the worse the bond and lower the peel strength of the patch. The suggestion to hose down the boat to see what happens is more to see if the wet, swelling wood is going to pop any of the fills loose or cause them to stick out - thinking that it's better to find this out before applying new canvas than after spending time and money re-canvasing the boat. I'm not really expecting much to happen if you do wet down the hull as Bondo is pretty inert and wood doesn't swell all that much, but it's probably worth doing just to be sure things will stay put when the boat eventually gets wet.

"Bondo" is actually a trade name for one particular, and very common, brand of automotive body putty. There are plenty of others out there. They range in color from white to black, grey, blue, green depending upon what brand they are and their hardness (and sandability) varies dramatically depending on what that particular brand or type uses for filler (silica is hard to sand, plastic powder fillers sand easily, various minerals and blends fall somewhere in-between). The screen is a tell-tale sign that they purchased an automotive body-filler kit (comes in a cardboard can with some body putty, hardener for it, small chunks of screen, sandpaper, etc.). The screen is included in the kits for bridging small holes (like rust holes in fenders). It provides a little bit of structure for the putty to stick to as it bridges the hole and acts to some extent like re-bar to help strengthen the suspended blob of putty. The person who patched your canoe must have decided that if the screen would strengthen a fender patch, it must be worth doing on a canoe as well. You can also tell whether it's polyester or epoxy by smelling the sanding dust. Polyester (auto body putty) dust smells like styrene (plastic model cement). Cured epoxy dust generally has very little odor.

In reality, even with the screen, it's pretty weak stuff. If you suspect that the filler in any given spot is in any way being used for structural strength, it's probably worth removing and replacing with wood. If it's just filling a small dent at a tack hole, on the other hand, and things don't seem to move if the surrounding wood gets wet, then the only real reason to remove it is because you don't want it there. It's unlikely to ever cause a problem and sanding it flush, canvasing over it and forgetting about it is most likely going to do just fine. The truly suspect areas are the big fills and those are the ones where you want to spend your time.

Anybody remember a product called "Rock-Hard Water Putty"? My dad had a can of it when I was a kid - a can about the size of a small oatmeal can with a tan and maroon label. It was some kind of water-based, air-dry filler putty, maybe casein-based. Anyway, it's one of the only tan-colored pre-manufactured fillers I can ever remember and it wouldn't surprise me if that's what the stuff in the tack head dents is. It would be about the proper vintage for an old canoe and something about the way it was putty-knife-applied reminds me of it.