I had the exact same problem with the one and only canoe that I filled with Zinzer. The blisters went away with time but since then I’ve had a real bear of a time with the paint cracking, soft spots and other nasty issues especially along the bottom of the canoe. Even stripping the paint off and re-painting did not do much to cure the problem. Zinzer was the only unusual component in my restoration routine thus rightly or wrongly it gets the blame. In other posts I’ve commented on these problems concerning Zinzer so I won’t get too much further into it here.
However, I will say I don’t think this product is really able to do what we are asking it to do. I know some have had good results with it but I’ll stick my neck out and suggest that “luck” has played a big part in that success. I’m not that lucky so my second gallon is going to refinish my basement wall…where the stuff belongs. IMO.
I've just looked up the ingredients (at least the main ones) in Zinzer Watertite--- Limestone, Petroleum Distillates (most likely mineral spirits, which seems to be in many non water based paint products these days), Quartz, Titanium Dioxide (white pigment), fungicides and Portland Cement.
If you compare that with the common basic canoe filler recipe as can be found in the WCHA pages
http://www.wcha.org/build_restore/filler.html which has the following ingredients--- Boiled Linseed Oil, Mineral Spirits, Enamel Paint, Japan Drier, Spar Varnish and Silica (a major component of Portland Cement).
One thing that pops out to me (and as Gil suggests) is that the ingredients in the Zinzer are heavy on the "stiff stuff" (for lack of a better word at the moment). There seems to be little to add flexibility to the product and reduce failure (cracking) as the canoe and canvas move. In the tradition filler there is a good combination of hard and soft ingredients as well as a significant portion of oil based products to enable flexing, stretching and so on of the filler so as to reduce any tendency to crack or fail.
As to the “-Filler recipes have historically been highly guarded secrets.” I agree that there is that air of mystery when it comes to the canvas filler. There seems to be that in many disciplines for one reason or another. In musical instrument varnish (which I am more familiar with than canoe fillers) each luthier from before the time of Stradivarius until today had/has his/her own “secret recipe”. Over the years and after lots of research I’ve come to believe that they are all variations on a theme…a little more of this or a little less of that. In the end they are all basically the same recipe….I suspect canvas filler falls into the same boat, so to speak.
Oh, by the way…don’t ask me for my secret varnish recipe. I don’t know. I have three monks, scattered throughout the world, unknown to each other and each with their own components of the 130 ingredients in the recipe…oh wait, that’s Chartreuse…
