Experience coating wood on the DS

[GreenLake]

Here's a brief summary of my experience with varnishing the wood on my DS. I've not tried everything, but I thought it might be useful to just capture in detail what I tried and how it fared.

My experience with PU on floorboards is negative so far, after several attempts. (I used water based PU without cross linker). The varnish tended to fail near the nail heads, and progressively from there. I've also had frequent and unpredictable problems of flaking (where one of the varnish layers looses grip on the layer beneath it). This despite having re-applied the PU according to schedule from the bare wood.

The PU is very hard, so it otherwise holds up well against scratches, but it is brittle, so when the wood cycles, it cracks. To remove it, heat works, or sanding with a coarse grit. Ideally something below 40.

Coamings and thwarts: similar results. The coaming edges would rub off to bare wood from use, so I had to reapply varnish there each season. Some years, but not others these maintenance coast would flake off.
Failure around the screw heads were difficult to fix.

Tiller held up better, but I had used an insane number of coats (15?). These finally failed after several years.

After all this, I switched tactics.

My latest attempt for coamings and thwarts has been to follow System Three's method for clear finish of outdoor wood, which is based on varnish over epoxy.

Last year I appliet 4 coats of their satin water-based PU with crosslinker on coamings and thwarts over 4 coats of their ClearCoat epoxy. After one year, there's no sign of failure anywhere, not even localized. No damage to coating along the top edges of the coamings either.

This has encouraged me to do the tiller the same way earlier this year. Instead of using multiple coats of ST3's ClearCoat (a very thin epoxy), I applied their laminating epoxy, for the second and third coat, which builds up faster. Applied during the "green" interval. Finished with 4 coats of crosslinked PU, all applied during the no-sanding interval.

If results continue to be good, I'll do the floorboards the same next time I get to them.