What happened to this varnish

[FSS172]

About 10 years ago as I removed deck hardware in preparation for a refit I put all the hardware, fasteners, etc in ziplock bags. The staysail and jib blocks were in stored two each in two bags. I just unpacked them for refinishing and the first three were in the same shape that they were in when I bagged them. This is the fourth along with the bag it was in.

http://www.dickinson.edu/departments/drama/public/block.jpg

The varnish on one half of one side looks as if it's been sitting in stripper, or something. It's darkened, and part of it's partially dissolved into a gummy goo. At the edge of the deteriorated area, the finish is bubbled, blistered, and seperated from the underlying wood but still intact as a film. The other block that was in the bag didn't have anything like this. There is no residue of any kind on the inside of the bag. It is, or was, Z-spar Captains varnish on cherry.

Any ideas about what would do this?

Jim

[imported_Craig]

Possibly it was damp on that side when it went into the bag.

[ssor]

Plasticizers and sunlight will do that.

[Jay Greer]

This is not unusual. Varnish on stored parts seems to last longer in a breathing container but out of sunlight. A friend just discovered thirty three teak shelled Merriman blocks at a garage sale. They had been in a cardboard box for some twenty years. Most were only in need of a light sanding and a few coats of fresh varnish. Others had developed a case of the cruds and aligator skin as the one in your picture. The bad ones were on top of the pile where sun and poluted air could give them a double whammy. The bearing grease gassing off is also suspect.
JG

[ 12-19-2005, 09:02 PM: Message edited by: Jay Greer ]

[Wild Wassa]

Although I can't tell exactly from the small photo, I'm 'guessing' that the amount of oil in the bottom coats was richer than in the top coats.

Excess oil from the foundation coat has sweated out. The oil (which is the binder for the paint) has come to the top ... oil doesn't dry, not during our life time anyway, so it is always there to do this, if the less oil rich coats, are the top coats. The block could have been oiled before painting as well, as it has a real old linseed oil look, rather than just a varnished look.

The less oil rich coats should be the foundation coats. With the oil, increased slightly (or the solvent reduced slightly) per coat, as you paint your way to the top. This technique is called 'thick over thin' or 'fat over lean'. The lower coats will draw the oil from the top coats into them. The top coats will start to crack when they have become oil deprived. So what has happened is the reverse, in the case.

Oil based paints and varnish are special (if protected from UV). Oil bases stay flexible for longer than other paint bases. An oil based paint should not dry in our life times. The paint oxidizes, sets, hardens and then polymerizes but does not actually dry. These are not individual stages within the curing of oil based materials but overlap during the curing. Moisture and mildew from condensation could have played a part, by keeping the top coats soft. Mildew likes to feed on the oil.

Just scrape off the goo, a bit of anti-mold (if mold is there which is most likey) then re-coat, no real drama.

Warren.

[ 12-20-2005, 04:12 PM: Message edited by: Wild Wassa ]

[Concordia..41]

Another guess: Ever been working on something, maybe sanding your way down a toe rail, and knocked over something? Solvent, lamp oil, linguini in clam sauce, etc.?

Well...ever been refinishing something and had one spot adhere fiercely and an adjoining spot practically fingernail scrape?

Hummmmmm....if you could only remember where on the bare toe rail that clam sauce landed :D

Sometimes it's as much about Murphy and life as it is science..... ;)

[Bob Cleek]

Odd thinks happen when stuff is stored in an "air lock." Those of us who build models face a common problem when models are kept in glass cases. The metal castings, if made of lead based alloys, will not hold paint. The lead oxydizes. I've read that this occurs due to chemical reactions from the paint and whatever in the airtight environment. Leaving a breathing hole solves the problem. Who knows why exactly. Another job for the Chemist... were he around!