Inqism-02: Chart the Direction

[Russ]

Just now getting around to grinding it down and and sure enough, it must have had a half inch of filler and about 30% was never bounded to the balsa core.

Hmm.... I didn't know there was balsa on our boats. Is this the case elsewhere?

[Inquisitor]

Just now getting around to grinding it down and and sure enough, it must have had a half inch of filler and about 30% was never bounded to the balsa core.

Hmm.... I didn't know there was balsa on our boats. Is this the case elsewhere?

I don't recall any mention of it before. And the few places I've cut into the lower liner there have been none. I want to say someone found some in an X in the transom area.

Its the first time I've run across it. I find, I didn't take a picture of it. But it was that end-grain stuff.

[NiceAft]

I believe Highlander, in response
To an X, owner mentioned Balsa in one of his posts.

It was in this thread.
https://macgregorsailors.com/forum/post ... 9&p=347317

[Inquisitor]

Yes. The oil-based spar urethane does darken with time. Like Kevin, I actually like that. I've never had it flake off, but it does have a finite life.

Looking forward to seeing how your polishing works out!

I was ecstatic about results. It had a nice consistent sheen everywhere and no nits. I prefer the oil rubbed finish to the deep gloss look and had that... then I polished too far in a few places. Total about half of sq-inch. Tried to sand down and found the compound had gotten into the grain. Total right-off. At least tracing and cutting a new piece was quick. First one took about five hours to cut, sand, fit, sand, fit... This took about an hour to cut, sand
and stain. Twenty-four hours and I can start the four coats of poly again.

Oh well. Try, fail, learn... rinse and repeat. Not sure if I'm subtle enough with the polisher to know when enough is enough.

[Inquisitor]

YouTube'd polishing polyurethane... first vid said he had 15 coats on it! Think I'll take a hard pass on that.

[Jimmyt]

Sorry you had to make a new panel. 2 coats isn't much depth to work with. i would go at it by hand - if you feel the need to. Maybe 0000 steel wool and a light hand polish with fine polishing compound.

15 coats would definitely give you some wiggle room for cutting and polishing. But, geez that's a lot of time...

[kmclemore]

A couple of thoughts...

- polishing... I’ve never used a machine to polish wood - I’ve always done it by hand, since it gives me the best control of cut and I never risk burning through, particularly on edges. And see if you can find some rottenstone and have a read on French polishing... it really is the way to go.

- film thickness... Yes, just two coats, particularly of the water based (which tends to go on pretty thin to begin with), is probably too thin to be polishing, I think. 4-6 coats should be plenty, IMHO.

- surface coating delamination (peeling/flaking)... as I noted earlier, using too fine of a paper between coats can definitely cause this. Don’t be afraid to use a fairly rough paper between coats. Those scratches allow the next coat to lock into the previous one, and without those scratches the new coat has nothing to grab hold of and can subsequently delaminate in service. If the paper you’re using leaves visible scratches in a new coat, go to the next finer for subsequent coats until you find the one that doesn’t. I find that 320 or even 220 works fine, depending on the thickness (viscosity) of the coating, and for a very thin water based coating the finest I’d ever go would be 400. (It’s also important not to sand your raw wood too smooth before starting the finishing process, too, and for the same reasons. A really slick, smooth piece of wood feels great, but it won’t hold a finish very well at all.)

- balsa use in the Mac... Yes, the Macs have wood core in several places, most notably in the overhead (cabin roof). I’ve never seen or heard of any rot problems though, but it wouldn’t really matter if it did. It’s only there to create boxed sections of fiberglass to increase strength and rigidity in the panel. The wood itself is not placed there for strength, it’s simply there to act as a form to create a strong box-tube shape in the fiberglass, hence balsa is used (it’s light weight and is easily and quickly shaped).

[Inquisitor]

The one I screwed up had four layers, all sprayed, with 220 grit sanding between. It was very difficult for me to tell if I had covered it well with the spray gun. Again a learning curve issue I'm sure. When I used the polisher, I got overzealous... more learning curve. My last attempt (still doing since its not getting warm enough to do it outside) has 3 coats, all brushed and sanded between, but I know its laid on thicker. I plan (have a few 50F+ days coming next week) to sand and spray the last coat. I certainly won't use the polisher again. Will look into the Rottenstone and French polishing.

Thanks.