Time Remove Varnish/Epoxy?

[Brent Newsome]

After pulling my sail boat out of the water this past fall for winter storage I discovered a "large" (2" by 4") water blister under extending from the bottom of the rubbing strip down onto the main hull exterior. I popped the water blister - not wanting it to freeze or extend further. I suspect that water worked its way under the rubbing strip and under the finish.

I've also noticed some chipping and degredation in the varnish/clear epoxy above the rubbing strip which needs to be re-varnished or cleaned up.

In addition I've been known to be slighly less than practiced bringing the boat alongside, and this year I put a rather nasty scratch in the finish which removed a piece of the varish and epoxy about 8 inches above the water line.

On top of all this, the varnish on the hull seems to be considerably yellowed compared to some new applications I put on the deck-house and toe rail this past summer. Also, the rubbing strip has gone very dark, and above the rubbing strip there are some pretty dark spots which I think are from from water getting under the varnish.

The boat is Mahogany (Central American) and in the few spots where I've "removed" the varnish the wood is a nice dark/red orange.

My challenge to the wood finish experts out there, is all of this enough to justify striping all the varnish & epoxy off a 31" boat and revarnishing? Does someone have a secret they'll share for "spot repairs" to varnish/epoxy?

If you were going to redo this boat would you do the epoxy/varnish combination, a two-part poly-urethane, or just multiple coats of varnish? Opinions on effectivenes of Epifanes products for this type of job are solicited.

For those interested, she is a 31' Storebro Sea Eagle built in 1964 in Sweden (Hull #149 for the yard). Mahogany over White Oak Frames. In great structural shape, in need of cosmetic finishing interior and exterior, and new DC wiring all in due time. This is a great boat that I want to restore the cosmetics too and keep sailing for another 40 years.

http://www3.ns.sympatico.ca/brent.newsome/boat1.jpg

[JimD]

Brent, I failed to make expert for another year in a row but since the experts have all gone to bed...my little sloop is fiberglassed/epoxied and top coated with 2 part poly clear coat. Its in the garage now for winter maintenance and when I took the chainplates off the wood under them is noticably darker despite the fact that polyurethane is supposed to block UV. Perhaps Chemist will grace us with his appearance and offer his comments.

I don't know much about varnishes but I searched the web once and found that a varnish must contain certain ingredients to be truly called a varnish. What sort of chemical soup you might end up with layering epoxy/polyurethane/varnish I wouldn't hazzard a guess. I would think if you have abnormal dark coloring in local areas only its due to water penetration. Is the wood spongy like its rotten? If I read your thread correctly you had to pop a water filled blister?
jimd

[Bob Cleek]

Brent, my man... you might want to read what I just posted about varnish under paint... LOL

Bottom line, keeping varnish on exterior mahogany is masochistic and keeping varnish on a mahogany hull is self-flaggelation! LOL Mahogany is a bitch to keep varnished. The main problem (you mentioned it) is that mahogany fades in the sun. Mahogany that has been varnished for a while will go straw yellow. So much for that deep reddish brown that looks so good on Chippendale furniture... which lives indoors. There is no solution for this... short of staining... and even then, you won't get it evenly colored until it is too damn dark.

As for varnishing... (assuming you live with the fading phenomenon... which is fine), if your varnish is lifting, there isn't much you can do about it. It has to be stripped to bare wood and relaid. This happens usually when water (Moisture from a crack in the varnish film even) gets into the wood below the varnish. The sun heats it up and it expands and contracts and the bond between the wood and varnish lets go. This is always the cause of varnish blistering and peeling. Happens most often at a joint of some kind where it works and water gets in.

You can patch varnish, but it isn't finestkind. Sand out the stripped patch and feather the edges. Build up the new spot to the same thickness as the original. Then sand a larger area, fairing the new into the old. Go down to a fairly fine grit, like maybe 440. Then take a fine spray rig or airbrush if its a small area, and lay a fine thin finish coat or two, blending into the surrounding area. Live with the result. It won't be the same as stripping the whole thing and doing it right from scratch.

BTW... enough said about laying CPES under ALL varnish. It will prevent/delay about 99 percent of the blistering and water intrusion problems. Look it up in the index here. Get a copy of Whatzername's Brightwork book. Rebecca something. It's as good as they come... except that she didn't know about CPES when she wrote it... does now!

[JimD]

440 grit? Mr C, you have a very keen eye! smile.gif
jimd

[thechemist]

Originally posted by JimD:
Brent, I failed to make expert for another year in a row but since the experts have all gone to bed...my little sloop is fiberglassed/epoxied and top coated with 2 part poly clear coat. Its in the garage now for winter maintenance and when I took the chainplates off the wood under them is noticably darker despite the fact that polyurethane is supposed to block UV. Perhaps Chemist will grace us with his appearance and offer his comments.

<snip>Ahem!

*Grace*

Not all "Polyurethanes" are created equal.

"Polyurethane" is a polymer of urethane linkages between different sorts of molecular arrangements, and a mixture of stuff [we paint chemists call it a Formulation does whatever it does depending on what is in it and how thick or thin it accidentally ended up being applied by the applicator.

UV absorbers are expensive, and one can put a tenth of a percent [worthless, but it meets the legal requirements for saying it's got some of that in there] to perhaps one percent [plausible] to perhaps ten percent [too exp3ensive to be affordable] in a polyurethane-containing product and you get what you get and the manufacturer won't tell you.

Film thickness is important. Too thin a film and the best stuff will let enough UV through to do damage.

The right kind of UV absorber and antixoidant is also important, depending on what exact molecular structure one uses in a formulation. This information is acquired by aging outdoors for a year or two, and examining the results.

Management will want to market it immediately, where the paint chemist will want to make another series of test formulations based upon results of aging the prior set for a couple years, and the set before that, and time-to-market and the economic cycles of a society often dictate what ends up on the shelf.

Required company profit margins that particular year cause management to dictate to manufacturing just what allowable raw material costs are allowed to be, and you get what you get.