Re-surfacing the filler


Enthusiastic about Wooden Canoes
I restored my WC canoe and I'm not happy with the finish. It feels/looks like fine grained sandpaper. I applied the filler as directed, smoothed it by hand as directed, sanded as directed but couldn't get it as smooth as others I have done. I thought maybe the paint would smooth it a bit. Four coats later it is better, but not as glass smooth as I would like it to be.

My question is this. Can I sand it down to the filler - almost to the weave and re-fill it and hopefully get a better surface or do I have to re-canvass it and start over with a virgin surface?


Did you use primer between the filler and the paint? ...because smoothing out small surface irregularities and leaving a super smooth surface to paint over is pretty much the function of the typical high-build marine primers. Primers are certainly not always required before painting, but a high-build version is designed to go on fairly thick and sand down easily, removing unwanted textures and small surface defects in the process to make a great base for painting over. I would try to sand down to the filler (not into the filler, and a small amount of well sanded paint left here and there probably won't hurt anything). Then prime it, sand until fair and smooth and then paint. It's that old "prep work is 90% of painting" thing. If you are seeking a really smooth surface, don't rely on the paint alone to generate it, as it is probably not going to happen. Your pre-paint surface needs to be smooth with just a little bit of tooth for a good bond, and your paint can may specify what grit they want you to sand to for best adhesion.

There are lots of good primers. This is just one of them.
I don't often disagree with Todd, but this time I will. On one first canoes I restored for a customer, circa 1987, I used a sandable primer. After 2 coats of primer, sanding and painting, the canoe was quite smooth. Unfortunately, the canoe was used in an acidic lake, and the primer absorbed water and the paint blistered rather dramatically. I called Jack McGreivey, and he said" Welcome to the canoe restoration business. sandable primers have microballoons, and will absorb water. I sanded the hull rather dramatically and repainted-- at my cost of course. I have never ever used a sandable primer again.

Wet sand with 320, paint; wet sand with 320, paint; wet sand with 320, paint; etc. until it is smooth enough.
Gil’s wet sanding technique is spot on. It’s about the only way to fair traditional filler because of the hard silica in it.
I wet sanded the first couple of canoes that I restored. Lots of messy work. Wet sanding paper needed, but they came out fine.
For the canoes I’ve restored since making it my full time work, I’ve gone the primer route. After somewhere north of 175 canoe restored, I’ve never had a paint issue due to primer. Im not sure what primer Gill tried 34 years ago. An internet search on marine primer with micro balloons came up empty. I’ve been using Pettit EZ Prime. I actually usually use three coats with sanding in between. It gets better with each coat, but still needs a minimum of four coats of enamel to get the finish I like.
I suspect any high build marine primer would be fine, but one I distain is Total Boat Topside Primer...gummy. Need xylene for clean up and thinning.
As with so many things in the crazy canoe restoration world....., your mileage may vary.
There are no microballoons in the primer I suggested. The fillers are Titanium dioxide (a common white paint pigment) and powdered limestone. The reason that microballoon fillers tend to be somewhat porous and often pinhole is because sanding them cuts open the tiny phenolic spheres at the surface, leaving little craters. Some paint will bridge the craters, but paint is too thick to soak in and fill them. Heat from the sun can pop the paint film over the craters and cover your entire surface with pinholes. Likewise, water can get into the craters and lift the paint. A sanded microballoon filler should always be overcoated (usually with epoxy resin) before painting. If you don't, you are going to have problems. Microballoons can be a very handy product to have available, but an awful lot of the people using them never took the time to study their use before blindly diving in. I would avoid any microballoon-filled paint product. I don't consider most paint film strong enough to seal the balloons. I've even seen two-tone paint jobs over microballoon/epoxy fillers where one color pinholed like crazy and the other color had none. One color just had stronger paint film than the other, or heated up less in the sun.

Note: You will notice that many or the paints and primers that we use on canoes are listed as "topside only" or "above the waterline only". This is so that sailors don't leave boats painted with them in the water for extended periods (multiple days, weeks, months, etc.). If they do, these paints are likely to peel if submerged. The typical use we put canoes to (in the water when paddling and stored out of the water) is not a problem.

Here is the composition of the Pettit primer I suggested. Look microballoons!

IMG_3538.JPG OK, I know everybody does it differently. And that's ok you have to stick to what works for you. Here's mine. After the filler dries, sand with 150. One or sometimes two coats of Interlux precoat primer. Of course sanding most of that back off. 150-220 grit. Than 3 coats of good marine paint. Roll and tip. Brightside, Epifanes , Pettit ... In between coats of paint I sand with maroon scotchbright pads sometimes the finer white ones. I have never wet sanded. Always comes out nice, smooth like glass. Yes sometime I have a screw up but 95% of the time it works great . :)
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The filler sanding step is my least favorite. I am not happy with a final finish full of imperfections in the filler. I find that there is a very fine(and frustrating) line between acceptable filler smoothness and breaking through into the weave. Especially on a hull that is not completely fair and may have some high spots. I agree with other posters that high build primers like Interlux Pre Kote are the way to go to get that final, very smooth substrate for the paint. But, sanding the filler enough, but not too much is so frustrating. I have mentioned before, that I wonder about avoiding the extensive filler sanding by using some sort of marine, sandable surfacing putty to better fill the filler imperfections and avoid the dreaded weave break through. I have a canoe that Jerry Stelmok built that was surfaced with some sort of bondo-like material. It is brick red and can be seen under the paint if there is a chip in the finish. I have had no blistering or paint adhesion problems with this boat.

Oh, and using semi gloss paint really helps hide any finish imperfections.
Thank you all for the great responses. We are getting warm enough to start thinking about painting projects. Your words of wisdom are much appreciated.