SOF Kayak Fabric Coating Test
 By Steve Schmeck  -  { Back to ManyTracks Home }

[ See July, 2020 Update ]

Introduction:
I conducted this test in mid-March, 2017 in response to some difficulties incurred when coating the covering material on a Skin-on-Frame kayak in the spring of 2016. The fabric used was 10-oz. polyester, plain weave, obtained from Dyson, Baidarka & Co. (Product #10PE64). After the first coat of oil-based porch enamel was applied I noticed that the surface was quite rough - similar to how a piece of wood might look with water-raised grain. I lightly sanded the kayak with 220-grit sandpaper and recoated it with the same paint. It became obvious that the sanding, though it did help on flat areas, did not totally get rid of the 'raised grain' effect. In fact, where I sanded through to the fabric along the keel and chines, the surface was rougher than before the second coat was applied.

Since I had enough of this fabric left to cover another boat I contacted George Dyson via e-mail explaining the above problem. George replied that he had another builder contact him with a similar situation and suggested that perhaps one way to reduce the roughness would be to singe the fabric by passing a propane torch (with a spreader tip) lightly over the surface of the material. This is often done successfully before painting canvas covered boats.

I made up a 36" x 9" test panel, ironed it to tighten the fabric then divided the panel in half horizontally. I covered the top half, fired up the propane torch and passed the flame at a shallow angle over the exposed fabric. All went well but I learned that you have to keep the flame moving and especially not linger at the edges.  This is a pretty risky process and as George said in his e-mail "... I guess you can understand why anyone would be cautious about giving out instructions saying "go over your fabric covered boat with a blowtorch."

I divided the panel into five sub-sections and gave each a light coat of  the indicated finish. There was a significant difference in the smoothness of the five panels. I have summarized my not so scientific findings below. I then divided each of the four painted panels in half vertically, sanded the right half lightly with 220-grit sandpaper and recoated the sanded areas. On the varnished panel I chose to see what would happen if I just recoating an area without sanding so I divided that panel into three sections.

      

The photos and enlargements pretty much show the surface texture of the five panels but the real test is to run your fingertips over the surface. My rankings and recommendations are based on both visual and tactile impressions.

Ranking the panels, smoothest to roughest after first coat:
1 - Panel #1 (Varnish)
2 - Panel #2 (Alum.)
3 - Panel #5 (Waterborne)
4 - Panel #3 (Red)
5 - Panel #4 (Porch)

Notes:
1) Singing definitely did make a big difference; all five panels were noticeably  smoother on their lower half.
2) The various finishes seemed to make an even bigger difference in smoothness.
3) In all cases sanding failed to improve the surfaces; at least with just one recoat.

Conclusions:
First of all, I do like using this fabric. It has a tighter, more even weave than some lighter weight polyester fabrics and handled well on the kayak I made for Sue last spring. It is considerably easier to stretch onto the boat frame than the 13-oz. fabric I used on our Dory.

If you are going to use this fabric to cover a skin-on-frame boat, I'd recommend making up a test panel or two and trying out the actual finishes you are considering. I was somewhat disappointed that this test didn't produce any revelations so that I could make a specific recommendation for a coating. One note; the two highest ranked coatings were the thinnest (lowest viscosity). Perhaps thinning the first couple of coats of any coating material would work. 

The singeing was interesting but I think it might be difficult to evenly singe such a large surface. That said, I still might try it on the deck where it would be relatively easy to skim the flame over the surface. When I use this fabric I plan on using either the varnish or, for a opaque finish, the 'aluminum' Rust-Oleum as a primer. I believe that several light coats of either of these materials would work fine. I plan on following my own advice,  making up some test panels, and applying multiple coats just as I would on the boat.

UPDATE - July 14, 2020

A fellow skin-on-frame builder, Stephan Ross, had some serious wrinkling problems when skinning his Dave Gentry Shenandoah Whitehall.  He documented this on the Duckworks Facebook Group. Here is what his hull looked like after the right half was painted with one coat of Rustoleum Topside Marine Paint; rolled on and dried overnight:



There was an extensive discussion on the web; What happened? How to fix it? Etc., and Stephan conducted several tests on the other side of the hull before stripping the fabric off and starting over. The test that provided an answer was to use the same type of paint but in a spray can vs. being rolled on. It worked!

His conclusion was that the problem came from too thick of a coat on that first layer. He subsequently re-covered his boat and sprayed it with spray - lots of spray cans of paint - but felt that he could have just as well thinned the paint in the can and rolled / tipped that first coat. All other coats were applied direct from the can with very good results. (Thank you, Stephan!)

Since conducting and documenting my paint test I have been noticing an increased number and size of wrinkles on all of my boats - especially on the Expedition Rowboat, but also on the Chamberlain Dory and Mobjack kayak. Conclusion: Any of my future SOF boats will be primed with a thinned coat of varnish or paint.

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Please feel free to contact me if you have any questions or comments regarding this test.