Varnish

[Doug Canada]

I'm varnishing the outside of my cedarstrip hull this week.

Normally I wait 24 hours to sand and recoat.

Is there any advantage or disadvantage to re-coating before the varnish has dried for 24 hours?

Do you get a better chemical bond if the varnish is some what tacky?

I am itching to go for a paddle in it before it gets too cold, i.e., solid water.

How long should I wait after the final coat?

Thanks,
Doug

.

[pcford]

You can go it; for just a couple coats it would make much difference. If you you are putting on several coats you will reach a point where the coat will not dry for an extra length of time.

The volatiles have to gas off and if you cover them up with an another coat it just slows things down. As I said, with a couple coats, probably no big deal.

[Stephen Hutchins]

that works good with a high build varnish. I used to do 1st coat thined 50% then sand, 2nd and 3rd coat then sand and a fouth and final coat to look like ten coats. -works best with high temps. Just watch the third and don't sand until it's hard.

[Stephen Hutchins]

that works good with a high build varnish. I used to do 1st coat thined 50% then sand, 2nd and 3rd coat then sand and a fouth and final coat to look like ten coats. -works best with high temps. Just watch the third and don't sand until it's hard.

[Wild Wassa]

"Do you get a better chemical bond if the varnish is some what tacky?"

Perfect if spraying.

The optimum for the longevity of the paint is to wait until each coat has polimerized before moving onto the next. Then give a physical key and then wipe over with prepsol or equivalent before recoating.

"How long should I wait after the final coat?"

The optimum is about thirty days. I wait a week or two (if possible before handing a foil over). The first two days of curing is done under heat to speed up the process.

I have put varnished foils on the water four days after painting, with only two thin coats, with half a day between coats. Again, the first two days of curing was done under heat, at about 24-26C. The coats held up at the time but I know that the life of the varnish was halved. That was with a poly/oil blend varnish though.

With a traditional varnish I wouldn't consider not letting it cure properly.

Last Saturday morning, we sprayed a dinghy hull that the owner and I had worked on for ages. Four coats of enamel, only a couple of hours it took, all up. Using 43% thinner by vol. Twenty five minutes to tack off between coats, was fine and perfect. Curing was done in a booth at 24C. The tapes were razor bladed and pulled at about 24 hours. The boat was to be moved out of the booth first thing Monday morning, which would have been the minimum time before moving. The booth was leased.

Late Sunday afternoon I get a phone call. "We moved the boat." ... :confused: "You moved the boat?" "We had to." "You had to?" "I didn't want to wait until Monday. I didn't want to get up that early." The booth was leased and the owner didn't want to get up early on Monday to move the boat. After all the work we had put into the racing surface, getting up early was a problem. So he made an executive decision to move the boat 15 hours earlier than planned, it is his boat. Unfortunately the owner was not prepaired to wait just two days for the four coats of enamel to cure acceptably. Even then the boat was not trailable and needed to be stored for a week.

The conversation continued. "The surface felt dry." "Still soft was it?" "Yes." "What happened, did the paint shift?" "Yes, I've left two hand prints in the hull and the paint slid." My final reply was, "It felt dry? ... paint is like that."

The owner was warned.

Warren.

[ 10-18-2005, 08:03 PM: Message edited by: Wild Wassa ]