to fill or not to fill

Craig Johnson

Lifetime member
I am ready to start preparing the outside of the hull before canvassing and have some gouges from removing tacks. I have noticed in some photos others sometimes fill these, Is this recommended and if so with what? My concern is that it might eventually come loose and wind up making bumps under the canvas. Thanks


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Steam them out.

You might want to give this a try. Take a wet rag and squeeze a little water out on the dents. Let the water soak in a little bit. Then cover the dent with the wet rag and put the tip of a hot iron (clothes iron) over top of where the dent is. The iron should be set to the hottest setting that it will go. It should sizzle and let off a little steam. The water and steam in the fibers of the wood will expand the fibers back out to their original shape (Or close to it). I've actually seen the dents higher than the surrounding surface at times. It's the same idea as hot water on hammer blooms after clinching nails just a little more spot specific. It won't get rid of tears in the wood fibers, but it will be covered anyway. I've used this with my students for years with varying degrees of success. It might save having to use filler at all.

Sweat out the dents and hammer blossoms with hot water and a towel. Sand the hull as smooth as you can after drying. It's the high spots and bumps that will show after canvasing, so try to fair those out as best as practical. Most minor dents will be "bridged" by the canvas, the bigger ones can be filled and faired.
This would be a much higher quality filler if you're looking for a pre-formulated one or worried about fills eventually shrinking and popping out or trapping moisture in and around the dings.|10918|12212|309318&id=11580

Just about everything that Bondo makes is polyester resin/styrene-based and that brings with it most of the pitfalls of using polyester resin on wood - mediocre adhesion and sealing capabilities, eventual moisture intrusion, possible shrinkage over time, etc. The Watertight filler does cost more, but it's very easy to mix, easy to sand and epoxy resin-based, which is generally much better on wooden boats (sticks better, seals better, doesn't shrink). It usually has much longer shelf-life as well. I have some that I've been using for about ten years.

If you happen to have epoxy resin on hand, or want to buy some, you could also mix your own high-quality filler using resin and microballoons. If not, it's probably easier to just but the Watertight. In general though, it's a pretty good idea to avoid any products with polyester resin in them on wooden boats, as their track record isn't very good.
I agree with Tod on the epoxy thing.

If you don't have micro ballons fine wood dust works well and matches color beter.

I used mahagany dust from a disc sander mixed with marine epoxy to repair
this mahogany rail tip that had a piece of wood missing.


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Much better. It's an epoxy compound like the Watertight. We're nitpicking here and obviously the boat won't self-destruct if a few tiny polyester fills fail, but the best chance of a fill staying put and sealing well is if the bond of the filling material to the hull exceeds the grain strength of the wood. Cedar, being light and soft, doesn't have high grain strength, but even so, many of us have at one time or another seen big hunks of polyester/fiberglass peel from a cedar hull cleanly during restorations. Had they been epoxy/fiberglass, they would likely have taken wood off with the glass. That's the kind of bond we want with fills, just to insure that little loose bits floating around under the canvas are something that we never have to worry about.