Fillers Again


Inquiring Mind
I bit the bullet and finished what I'd started as some sort of reasoning behind filler formulas which I'd put aside unable to decide whether it was worth anything to finish it!

So I put it up with the intent to broadcast what I learned and hopefully others may find it informative.

It's at:

(It rambles a bit, but so do I!;))
Good Job...

Hey Dennis,

Maybe a little wordy but ya know what? I loved it... You took a controversial subject and broke it down into it's components and threw away all the garbage. Boy, if I didn't know better, I'd say your close to using the "Scientific Method", eh...

The only suggestion I would make is with your recommendation. Put it in a box or table like the other breakdowns and list the materials, quantities, etc. so there is no doubt about your final recommendation.

Good job, CYA, Joe
great research, very interesting. now about this part " it'd be interesting to mix up a batch and see what happens, eh?" you go first we'll be right behind you. i'm not sure after weeks of building and the cost of canvas i'd be willing to experiment on my new canoe. i'm not sure how you could test this out inexpensively.
Filler Research

Just to echo the previous comments, great job on this research!! This has really helped me to understand a little more about the great mystery of fillers. As stated previously, it would be very interesting to me if you would summarize your research into one or more possible filler recipies that follow from your research - perhaps someone out there will have the courage to try it out - or - even better - devise a scheme to test your new formulas(s) somewhere other than on their new canoe. Thanks again for your work on this.
Very impressive research. It is interesting to see the indivigual components broken down to such detail but as Dennis points out the interaction of the indivigual components may produce different results than expected. A case where 2 plus 2 may not equal 4.

It would take academic reseach to the nth degree to come close to a quality filler. But I think most of that research has been done in the field. Think of the thousdands of back yard builders, semi-professional builders and professional builders and also most everyone of them has conducted some kind of research trying to make a better filler, yet even today we come back to the old recipes. While I think the pursuit of the goal is worthy, I doubt if the traditional fillers can be improve IF your limiting the research to traditional materials. Once the research is opened to modern materials the chemical mix becomes many more times complicated. Once again the research in the field continues on many levels and has produced some good results for specific uses but once again the traditional fillers for the traditional canoes still seems to work the best.

One reason academic research is hard is because it is difficult to tell what is going to happen in the shop. The areas that jumped out to me were the positive comments concerning the turpentine and the lead.

I have had good results using turpentine but the odor is so overpowering it becomes a major problem. The paint thinner works just as well and the odorless thinner is a pleasure to work with compared to the turpentine.

The lead may make the best filler not just because of its drying and mold killing agents but because it is strong, adheres well, abrasive resistant and it is extremely flexible. Cement can do most of that but it fails the flexabity test. The silica can do most of what the lead does with some of the flexibility and it is not so toxic to the user.

The lead can certainly be used on the canoe without any real harm to the environment. The real harm comes in the mixing and sanding of the filler when the dust is in the air. Using the correct respirator still would not be much help because the dust would be in the air and in the shop and over time it would accumulate. I have no doubt a person doing one or two canoes could do it safely but if your doing it over years, thats a different problem. The lead kills brain cells and I really don't have any extra!

I've had enough promising filler experiments that I have had to eat, recanvas, redue and lose time and money on. I would love to have a faster drying, stronger and flexible filler that will last thirty years but i don't think I'm going to find it!

Thanks for doing this research and posting it to us.

And yes, please take it a bit further and purpose a couple options for folks to try.

One bit of feedback, concerning your discussion about silica and clay. You should research this a bit. I don't remember much so take it for what it's worth.

I took a couple pottery classes years ago and it was driven in that when the clay is fired, it has to reach a certain temp or it doesn't melt and form "glass". The process was that after forming the clay, it had to slowly dry for several days (or more), to have as much water is gone as possible, then it was slowly fired up to temp. (if it had too much water, I think it would break?) When clay was "dried" it was still porious, after firing, it was not porious and would hold water.

If I'm remembering this correctly, the following statement wouldn't hold, and without the correct heat, you don't get the clay to form to glass.
"Using a kiln is just supplying a catalyst, just like using a two-part epoxy, and its hardener"

I had always "assumed" (ya I know) that the oils acted as a binder and the silica just acted as "hard stuff" in the dried mixture, similar to cab-o-sil or other fillers in epoxy.


I'd say quite worthwhile. It is a bit over my head but this one thing seems to me to be valuable. That filler needs to cure. The cedar breathes so the filler can cure from inside and outside? But if I varnish inside and outside before canvassing the cure time may be slower and more prone to blisters?

Does that sound right?
Dave Wermuth said:
That filler needs to cure. The cedar breathes so the filler can cure from inside and outside? But if I varnish inside and outside before canvassing the cure time may be slower and more prone to blisters?

I can only answer theoretically now, remember...

It seems that if I sum up my long-winded piece:

The blisters would seem to be caused by evaporating solvents being trapped under the oil film as it polymerizes. The use of Japan drier actually encourages the outer layer of the filler to seal first and thus hampers the evaporation. The use of a through-dryer/drier like lead (or others) would probably not initially solve this problem by itself, we'd have to use less solvents to start. That's why I mention adding solvents "to taste".

I'm not sure if varnishing the outside of a canoe would have any effect one way or another, but I'll think on it...(as you've probably noted, I do a lot of thinking...for better or for worse!)

But this doesn't explain a question I asked earlier which I re-phrase now:

"Why would blisters form on the outside rather than on the inside?" Granted we can't actually see that they're NOT on the inside, but these things should take the path of least resistance and if evaporation can't easily pass through the filler to the outside, why wouldn't it just evaporate inwards?

It may be that for all intents and purposes, the top-drier seals solvents in by sandwiching them between the outer filler/air interface and the filler/planking interface and just the pressure of the canvas against the planking is enough to force the evaporation outwards...

Here's a thought:

If anyone has a spare hyperbaric chamber sitting around their workshop, I'll bet they could stick a newly filled canoe in there and pressurize it with oxygen and cure a canoe in no time!
"Why would blisters form on the outside rather than on the inside?"

Because the blisters are forming in the paint (or rather, in the paint-filler boundary), as a result of a variety of interactions between the canvas, filler, paint and water.
Purpose of filler

Just so I'll understand all the details in this thread I would like to make sure I've got the basics covered.

While using the traditional canvas, the purpose of the filler is to:
- waterproof the canvas
- add abrasion and tearing resistance
- prevent canvas rot(lifespan of 15-20 years)

Also, the filler needs to remain flexible and does not bond the canvas to the planking.

The -ideal- filler would do all this, will cure in a week, not too expensive and would not require an environmental decontamination suit to apply...

Anything else ?


Louis Michaud
I think this thread, the basic body of it, should be transferred to the knowledge base.
interesting thread. clearly enough written that it can be followed after too many glasses of wine. the interesting problem with wooden canoe fillers is that so far, no-one has be able to come up with a one-size fits all recipe. There are a bunch of interesting compromises

- weight ( do we really need to add 5-10 lbs of sand and clay to our boats? ),
- sandibility( latex can be evil ),
- beaver dam drag over toughness ( doesn't puncture ),
- beaver dam drag over slickness (doesn't catch - hard is slick, but hard is brittle ),
- time to finish ( are you really patient enough to wait 2 weeks ),
- quality of finish ( my goal is no leaks, but really, most folks like fresh varnish )
- mildew resistance
- how hard do you have to work to make your boat look like furniture...
- how hard do I have to work to keep my boat afloat...