Minwax Helmsman Cracking when dry.

[robj]

I'm refinishing some mahogany trim boards on a sailboat. They were installed 3 years ago. Originally finished with 3 coats of West System Special clear epoxy, then 3 or so coats of Minwax Helmsman Urethane spar varnish. They looked terrific.

Last year they were not refinished as still looked very good and had additional wax protection. This year I noticed some random lines that sort of look like cracking, but they were in the surface. really more like random lines and mostly in one area of the board.

I sanded the entire board with 400 wet or dry until smooth. Then with a green scotch-bright. Blew off dust with air, then wiped it down with thinner, then after dry wiped again with MEK. Then tacked it off.

I put a coat of Minwax Helmsman urethane on, thinned about 8-10%, with a good brush. Went on fine, no fish eyes etc, so I'm pretty sure the surface was free from contamination.

Next day the finish is covered with "lines"of  random pattern and random length, any where from 1/8 to an inch long. They are at random directions that bear no relation to the direction of sanding.

The boat is in the shop, with barely some a/c from a window unit, but it's been hot and humid here last few days. Inside the shop it's a little less than 80, and not as humid as outside.

I used a can of varnish that was a year old, but it looked fine, and had been sealed well. 

Humidity? Old varnish? Anyone else experience this?

I'll post a photo when back to the house.

Thanks,

robj

 

Edited July 27, 2016 by robj
add photos

[drzaius]

Looks to me like old surface scratches that telegraphed through the new finish. Are you sure sanding with the 400 took all the scratches out?

[Unknown craftsman]

Robj that's just weird, it looks like something touched the surface maybe you had plastic covering your work.

Or your brush was shedding bristles.

The only Minwax product I like is paste wax.The rest i stay away from.

[midtnwoodworker]

I agree with drzaius. Those just look like surface scratches that didn't get sanded out or filled in with the new layer of finish. I would sand back a little further and wipe down with mineral spirits to see if the scratches are still visible.

[Unknown craftsman]

2 hours ago, drzaius said:

Looks to me like old surface scratches that telegraphed through the new finish. Are you sure sanding with the 400 took all the scratches out?

Nice catch Drzaius, I also agree

 

Aj

[mat60]

And another vote for Drzaius.....I did want to say,,thats alot of crack but maybe next time.

[robj]

That was my very first thought , except the original "cracking" for lack of a better term was limited to one area at the end of the board and was much less extensive. That was about a 1'x6" area at one end. This covers the entire board.

I also did two coming boards that were about 2"x16' that did the same thing only very faintly. And there were no scratches or cracks in them. I'm back to age of varnish and or humidity. I bought a new can of varnish tonight and am going to sand and redo if it seems hard enough to sand.

Ive used the minwax spar varnish before with Good results and longevity.Practical Sailor did a long term (3years) exposure test of about 20 different varnishes including 2 part. Minwax scored not far behind the 2 part and demonstrated great value even compared to $50 a quart brands. Up until now I've had really good luck.  As you can see I'm taping and sanding around hardware as the board is through bolted with s bracket for a solar panel on top and access to the nuts is a real pain.