How dry is dry when it comes to varnish?

[bob winter]

I have decided to varnish the transom before I re-install it mainly because it will make for easer access in some areas. How do I tell if varnish is dry enough to sand between coats? If it is dry to the touch, is it actually dry? I want to start the re-installation this weekend but I don't want to screw anything up by trying to rush.

The weather here is Ottawa is not all that warm - low 20" C but thing are fairly humid with pop-up showers off and on for the last few days.

I'm working in my garage so no direct sunlight.

[Jay Greer]

Usually, once varnish is hard enough to no longer feel tacky, most often overnight under average conditions, it can be sanded. However, if the material balls up and clogs the sandpaper, it is still too green. Many times during the first stages of building up from bare wood, a process known as "hot coating" can be done. This allows for rapid build up. In dry areas as many as three coats can be applied in one day. This would be the max as too much hot coating can lead to a ropey surface. Varnish will continue to cure during its lifetime. Varnish that is completely dry is over the hill due to it's loss of skin flex. This phenominom occurs at different times depending upon the grade of the varnish used.
Jay

[Bob Cleek]

You don't have to wait as long on a thick coat if you use Scotchbrite pads to skuff up the surface between coats, rather than sanding. Sand well cured varnish buildup only to fair the surface a few coats before you are done. Many people sand so much they sand off the coat they just put on before applying the next. At the end of the day, they'll tell you they have ten coats and then wonder why it goes to hell in a couple of months!

[Lew Barrett]

All good info here. I'd add that if you have a curtain (what can I say? it happens), it may never fully dry until you sand it down. Cleek makes some good points. If it were Rebecca Whitman talking, she'd say it this way: Put on a good scratch between coats one and four, then sand hard at coat four, and scratch between five and seven, a good sanding to level, and put the last coat on. Easier said than done.

[David G]

All good info here. I'd add that if you have a curtain (what can I say? it happens), it may never fully dry until you sand it down. Cleek makes some good points. If it were Rebecca Whitman talking, she'd say it this way: Put on a good scratch between coats one and four, then sand hard at coat four, and scratch between five and seven, a good sanding to level, and put the last coat on. Easier said than done.

True about how slow a run or sag drys. I like to shave them as flush as I can with a sharp chisel or scraper. Sanding will ball up the uncured varnish and peel it off, leaving a crater where the thick leading edge had been - and leaving you to build it back up.


"Let us go singing as far as we go; the road will be less tedious" -- Virgil

[bob winter]

Thanks for the information, everyone.

At the moment I have three coats on and have not sanded so far. The first coat pretty much soaked into the wood. I put the thrid coat on late yesteday PM and it is sitll a bit tacky. There appears to be a dead beastie adhering to the surface so I guess this would be good time to do some light sanding. I will let things set up until tomorrow morning and give it a quick shot with the sander and some 220 grit. I am working on a horizontal surface so sagging isn't an issue, thank God.

Considering how ratty the transom was, I am quite pleased with results so far. The boat is a far cry from new but the transom looks pretty good. I just hope the installation goes OK.

[Lew Barrett]

True about how slow a run or sag drys. I like to shave them as flush as I can with a sharp chisel or scraper. Sanding will ball up the uncured varnish and peel it off, leaving a crater where the thick leading edge had been - and leaving you to build it back up.


I just finished a section of my boat and had a rough day at it. It was windy, I had the mix wrong, bad light, wrong glasses, whatever, but I varnished anyway, and got the full range of flaws. Sags, holidays, brush strokes and laps! No time to do it again before we go boating, but at least we'll go boating! What really frosts me is that I did a very careful job of prep. Speaking only for myself, I'll say varnishing for me is a bit like that. Usually I do fine, but every now and then, Oh Mama!

[Jay Greer]

When a sag "Maggies Drawers" occurs, I often will cut off the surface with a razor blade an we sand with 220 wet or dry paper and white gas, coleman lamp fuel.
Jay