Hard Bottom paint

[David Satter]

Has anyone used hard bottom paint over new canvas and filler. Sometimes people leave the large square stern canoes in the water to long. So I'm wondering about a few coats of hard bottom paint over the filler, from waterline down of course. I wouldn't think there would be any issues. Putting bottom paint over say brightside or enamel paint might be a little overkill.

 

[Todd Bradshaw]

Are you thinking about something that is an anti-fouling hard bottom paint, or one which has no anti-fouling properties like the Pettit Racing Bronze? The anti-fouling versions are not completely waterproof. The copper content they contain (which can be as high as 50% of their total weight) slowly dissolves out. In the case of most of the hard paints or vinyl ones, this leaves them somewhat porous as well as eventually ineffective against marine growth. In the case of ablative bottom paints, the whole shebang slowly dissolves away, saving you from the dreadful job of eventually having to remove old hard bottom paint (been there, done that, can still taste that crap, won't do it again). Brightside or similar enamels will not be protected from blistering or peeling from prolonged immersion by painting over them with bottom paint. It's another one of those classic scenarios where the weakest layer of a multi-layered construction represents all the strength you can get out of the entire thing. I've never left a filled canvas boat in the water for days on end, but I suspect filler doesn't have much better resistance to eventual water damage than oil-based paint does.

In terms of resisting water penetration, the closest you can come to completely doing so is epoxy resin with a barrier coat additive, like aluminum flake powder added. This can be home formulated or purchased ready to use. It takes about ten mils of thickness to get serious protection, which can add up to five or six thin rolled-on coats which are then sanded smooth. If you ran your finger down the side of the hull, you could just barely feel the thickness difference where the epoxy layer starts. In this day of high tech stuff, the aluminum flake powder barrier coat additive is kind of refreshingly simple. Any moisture which might try to work its way through the epoxy will also have to zig-zag around the tiny aluminum flakes.

 

[David Satter]

Todd, yes I was thinking of hard anti-fouling paints but your right there's no real water barrier to keep water from reaching the canvas filler. Though I'm looking at two part epoxy high build bottom paint. There's a few out there and they claim to put a good water barrier in them for water intrusion. Sea Hawk is one. Just not sure how they will react with the filler. I'll look at the aluminum flake also. I do a lot of big square stern canoes and boats with canvas and some customers always leave their boats in for weeks no matter what I tell them. Thanks.

 

[Todd Bradshaw]

The real focus of the issue may be the ability of the filler to survive being wet for long periods of time. Even if totally sealed from the outside, it is still going to pick up water through the cracks between planks, soaking into the canvas. I don't know how much wetness it can survive on a more or less continual basis. If I felt reasonably certain that the filler wouldn't fail, and I wanted some antifouling capability on a canoe, I might use a paint like VC17. It's only 17% copper, so it has somewhat more modest fouling protection than others, but it is super thin and very slick - feels like a Teflon frying pan. It has a copper color when new and gradually turns a dark grey with age (looks kind of like a smooth-sanded graphite stripper bottom). It dries in about two minutes after being rolled on and it is so thin that multiple layers don't build up to some sort of thick mess that you have to sand off every few seasons (one of the most miserable jobs in all of boatbuilding).

VC17 is essentially a vinyl antifouling paint, so it has a strong solvent base and you would want to test first to see if it attacks your filler. With a barrier like the epoxy/aluminum flake home mix, or Interlux Interprotect (a ready to use version) the VC would be isolated and the filler protected from the outside moisture.

https://interlux.com/en/us/boat-paint/primer/interprotect-2000e

I eventually switched from hard, solvent and epoxy based bottom paints to a water-based ablative called Hydrocoat, vowing never to sand bottom paint again. It rolls on like latex on a wall, has good antifouling power, barely smells and gradually removes itself so you never need to sand off old dead paint. It would also work on a canoe and is one of the best at also being able to be stored dry for long periods without losing its effectiveness (a lot of antifouling paints won't do that). My only gripe on a canoe is that it wouldn't be terribly pretty - dull colors and looks like flat latex house paint. So you wouldn't want much of it showing, maybe just an inch or two above the waterline.

Brightside (dark green) and Hydrocoat (red) over barrier coating of WEST epoxy and aluminum flake powder.

 

[David Satter]

Thanks Todd, I'm thinking of a barrier like possibly Interprotect and then a couple of coats of anti fouling. I like Pettit vivid , nice bright clean colors, I've used it before. These people use the boat hard with an outboard. I'll do a test spot of the barrier first on the filler. As long as the filler is hard and dry I think the barrier coat should adhere well. I hate bottom painting. I try to stick to small boats/canoes that fit in my shop and I can move around myself.