HELP! I have made a new pair of 8 ft. Oars and after finish maching them I added two coats of neat epoxy with 6 oz. glass on the edges of the blades (25" long section). This is the third pair of oars I have made, this is first time this issue has bit me.
This pair is made from Doug Fir with Blk Walnut accent stripes in the blades.
So here's the problem, after the third coat of Epifanes High Gloss Varnish applied to the oars (no problems yet), the fourth coat and now the fifth coat also has a cracked finish on just the blades. The first two cioats were thinned 50% and 25% with a high quality thinner. For the third and subsequent coats I added additional Varnish to the left over varnish to increase the ratio closer to 100%. I guess it's approx. 80% varnish and 20% thinner.
Each coat was sanded w/ 220 grit sand paper after the previous coats were "cured" (24 hrs minimum).
The "cracked finish" is only only on the flat surface of the blades (both oars, both sides). The shafts are Ok, just like they should be.
The fourth coat was cured in the garage, minimum temp about 45* (was 60* during the time I applied the varnish and for 2-3 hrs after), So I moved them in the basement for the application of the fifth coat, min. temp 70*. Same result......
Anyone have any suggestions as to what I am doing wrong. Damn!
The only time I have ever had this happen (lacquer paint and varnish both do this) is when the previous coat dries on the surface but is still uncured underneath. Applying the new coat softens the "skin" and it crackles. In my experience this only has happened when I have tried to force dry the finish using a heat gun, putting it in the sun, next to a heater, etc.
I actually have intentionally done this to create patina with excellent results.
So how long should I let the varnish "cure" before applying the next coat, 48 hrs, 72 hrs, longer?
The two coats that "cracked" were cured 24 hrs. As recommended on the Varnish can.
Well, I mean everything you are describing sounds right. I'm doing a bunch of varnishing right now myself, doing the same thing you described... 50% thinned, 25% thinned, full strength, waiting ~24 hours between coats and steel wooling between coats
Is it possible that your conditions are force drying the outer "skin" and preventing the varnish under from curing? If you heat up the varnish when it is wet it can form a hardened skin preventing the varnish underneath from curing. Are you drying it near a wood stove or space heater or did you try to speed it up with a heat gun or anything like that?
I guess what I would do now is wet sand it with some 220 grit on a sanding block to try to flatten that finish back out, let it dry for 24 hours, wipe it down with some mineral spirits and try again. But if you start sanding and run into gummy stuff, quit and wait at least another 24 hours.
Hope this helps.
Your second paragraph is exactly what I did for the fifth coat and caused the cracking. I had some feedback from another forum and the advice given was to let it cure a few more days and take it back to the third coat and repeat the fourth. After that let it cure a few more days.
When I removed the fourth coat that cracked I sanded it and used a cabinet scraper to remove the gummy varnish, It seed to work Ok after I was able to sand it w/ 220 grit dry paper.
Also he stated: "Over a sealed surface (epoxy) you wouldn't thin varnish anymore than necessary to remove stipple and/or brush marks."
My real problem is I am committed to deliver the oars on the 12 Th. of March. Not too much time left, eh.
Thanks for your help,
Well, live and learn, right? Gotta just give it plenty of time to dry. Hope it all works out well.
Phil I`m thinking the wood was on the cool side before the varnish. Try warming up oars before varnishing.
The other thought was check with someone about thinner dry times. Most thinner/retarders can be bought for different speeds to compensate humidity, temps ect. The last coat of straight varnish will take the most time to dry, but the thinner should help the varnish to cure through the thickness.
Just a couple thoughts.
(Just for a posting fix, heres my fir/walnut oars you designed last year with the blades fully glassed and a couple coats of that Epifanes. Thanks for the help!)
Funny how things turn out. Seems like my memory has failed me having made this goof up. Anyhow thanks for your input.
PS: I received the oar locks today, thanks. I'll get back with you on them soon.
Just to show what has transpired over the last week. Here are the Oars and the third Picture is a close up of the crackeling problem.
So as explained above the "cure" is to sand the oars back to eliminate the affected varnish and then refiinish them with an additional coat or two. The oars have been sitting in my heated workroom in the basement now for 5 days and except for the sanding tinme will remain in the heated environment so the varnish has a few days to cure.
We'll see what happens, eh.
Well here's a final report on the status of the oars. They turned out just fine.
I traded them for a 7 1/2 Ft. 4 weight bamboo fly rod. I made the deal in January with a fellow I met a few years ago who is one of the top bamboo fly rod builders here in Michigan. He bought a new rowing skiff and needed oars. I made the offer and he accepted. I now am the proud owner of a beautiful bamboo fly rod and can't wait to get out on the streams and try it out.
Back to the varnish issue; After about 72 hours after the fifth coat of varnish cracked I sanded the oar blades back to the third coat of varnish. I had to use a cabinet scraper to remove some of the gummy varnish but they looked pretty good after sanding.
Now I don't have enough time to add two or three coats of Epifanes Varnish. So I purchased a can of Spray Spar Polyurethane from a local paint store. I sprayed six additional coats of this stuff on the blades. Each additional coat was sprayed on the blades after the previous coat was cured 1 1/2 hours. After 72 hours of cure indoors at room temp I buffed the blades with an automotive buffing compound (2000 grit). The poly was compatible with the Epifanes and they really turned out super.
Now here's a trick I learned a show, "Quiet Waters Symposium" held a couple of weeks ago at Michigan State University. There were a bunch of canoe, kayak and wooden boat builders there. Also a couple of guys that only built oars and paddles. One guys stuff was really beautiful, nice use of different woods, shapes and excellent workmanship. I asked him how he got such a beautiful finish on the oars. He told me he sprays on the last couple of coats of varnish. He takes his varnish to a local paint store and they put it in spray cans with the appropriate amount of thinner. He paid about 12 bucks a can plus the cost of the varnish and thinner. Kinda steep but I am sure he made up for it in the price of his oars. They were awesome looking!