Peculiar filler cracking

[mccloud]

The canoe was re-canvased and filler applied late October 2010. Canvas and filler came from Rollin. The canoe hung indoors to cure for several months, never froze. When the weather warmed up a bit it was moved into a carport where filler was sanded and two coats of high fill primer applied - sanding in between, and fine sandpaper at the end. This brand of primer has been used on several other canoes with no problems. When ready for paint it was hauled to a shop for spraying. At this point the filler had been on for at least 7 months. While waiting in the paintshop, several cracks developed in the filler, beginning at the gunwale and extending down about 3 or 4 inches, most of them within 2 feet of the points. Cracks are nearly straight, i.e. not zig-zag. If you inspect a crack closely and feel it, there is a small ridge along both edges of the crack. Nobody that I have talked with has ever seen this sort of cracking problem. It kind of looks like what would happen if the filler had expand and when sufficient force developed, it popped up along a 'stress line'. The paintshop is not air conditioned, and it does get warm in eastern Maryland during July/August. Has anyone seen this kind of cracking before? What is the cause? I don't want it to happen again, but don't know what to do to prevent it. For lack of a better idea we intend to carefully sand down to the canvas and at least prime if not lightly fill prior to paint. Thanks for the help. Tom McCloud

 

[Dave Wermuth]

I've had it happen with purchased filler and I think that your plan to fix is a good one. I suspect that the filler needs to be rubbed in really well and if it builds up too thick it can crack over short time. I've noticed some old canoes with lots of coats of paint have the alligator cracking going on and I wonder if there is some distant correlation to filler cracking.

HOWEVER, this too-thick-and-not-rubbed-in-well-enough theory is just a guess.

 

[goldencub]

Tom - I would think you should contact Rollin directly with your cracking problem. I think he would be quick to give you some possible explanationsand ideas of how to proceed. Al D

 

[Rollin Thurlow]

Tom did contact me but I was not much help. I thought I had encountered just about all the problems with oil base filler that there could be but this one is a new one to me. I've had some more time to think about it but I still don't have a good feel for what is going on with the filler and canvas.
For right now I would have to say the best solution would be the sanding and smoothing but I have no good idea on the source of the problem.

 

[Dave Wermuth]

I have a theory. I wonder if the application process can affect result? If the filler is put on too thick without being rubbed in well enough, would it crack?

 

[mccloud]

One gallon of filler was applied by hand all at one time. But I've noticed that when you're working with a canoe upside down on saw horses, it's easy to 'short change' the sides - the bottom where the filler lays tends to be heavier than the sides, where gravity is working against you, and on the canoe with the cracks the sides have a relatively thin filler coat.

Attached is a digitally-enhanced photo showing the cracks. The edges of the cracks are actually raised just a bit. The canoe is upside down, the gunwale being at the 5" mark, so as you see, these are long cracks. Tom McCloud

 

[Dave Wermuth]

Have you done anyting with the project? I think I'd sand pretty course, prime about 3 or 4 times and then paint about 3x. I had this happen with Zinsser watertite once and with Bill Clements filler once.

 

[mccloud]

Several of the cracks have been sanded down. I photographed a couple which have not been touched yet. But obviously it concerns me that because we don't know the cause of the cracking, it might occur again even after painting. That would not be a good thing. Tom McCloud