Taping for drips saves the frustration of clean-up later. Varnish over paint's not a big deal, but can be hard to remove without damaging the finish of the paint underneath.

I'd mask the paint before varnishing.

As for the 600 vs. 400... you might be better off using 320, it's not that much coarser than 400 and ought to be a little faster to get to the surface you desire. Using 600 when you can't find 400 certainly won't do any harm, but it doesn't cut very fast at all so the time you spend may be prolongued.

Is your Lowe's the only DIY store around? Most hardware stores will carry sandpaper in various grades also, even some automotive supply outfits. Might be in their paint departments but if not look in the tool section. Store where I work has hand-sanding stuff in the paint area, belts & other mechanical sanding stuff with the tools....

   Thanks spclark, I went ahead and used the 600 and had some good buildup on the paper. I made sure to keep it wet and it seemed to work OK. If I didn’t do a wellenough job wet sanding will it show up on the second coat? This is the first time painting with the Brightside Polyurethane paint, so not sure what to expect. My first coat I was very pleased with and the paint laid down nice and when tipped  out with the foam brush it looked like glass, hated to sand it but I know the second and third coats should look even better. I was afraid the painters tape would pull up the painted surface but felt like I need some type of barrier when varnishing.

   I'm about to varnish the deck of my Cheasepeke Double. I've never varnished before. Boat building friends are saying I should thin my Schooner Varnish. Do you agree? With what, if you do? How much?

Thanks!

Sam

PS: I'll be painting the hull when the deck is done.

Thinning the varnish is done to allow you to put on very thin coats that stay wet long enough to self-level and eliminate brush marks. Whether you need to do it or not depends on the temperature, humidity, the type of applicator (brush, roller, sprayer, etc.) and your personal technique and skill.

You can always experiment and see if you actually need to thin it. As long as you apply thin coats the worst that will happen is that it'll need a bit of wet sanding and another coat.

I'm assuming that you are using the varnishing technique described in the CLC Shop Tips. Ways to avoid the need for thinning are to:

1. Varnish first thing in the morning when everything is at its coolest. This also has the advantage that as the Sun rises you get lots of raking light that will help you spot defects. Heavy dew will alo take the dust out of the air overnight.

2. Reduce the area being covered at any one time to guarantee that you don't lose the wet edge. On my last varnish job (in 80+ degree weather) I only did 2 vertical strokes before switching to horizontal and I never lost the wet edge.

If none of this works out for you then you should consider thinning the varnish. And 2 things to keep in mind - no matter how bad it is, you can always wet sand it and try again on the next coat; and you would have to actively work at it to make a piece of varnished wood look bad from 10 feet away.

This boat has a "non-skid" deck where closing the garage door dumped a load of dust onto it while the varnish was wet. No one notices it until I point it out to them.

You're going to have a nice boat that will be the center of attention whenever you launch.

Laszlo

Sam,

How much thinner depends on the conditions again. The hotter it is, the more you'll need. Again, a little experimentation will show you how much. Add some thinner and try it on a piece of scrap wood. If it has problems flowing, add more.

As to what to use, that depends on the varnish. I've never thinned Schooner so I don't know what it takes. It'll probably say on the can.

Laszlo

   Thanks, Laszlo.

Glad I'm not doing it this weekend here in the Northwest with 100+ weather predicted. I won't be finished with entire sanding that soon. It will cool off again.

The Schooner varnish can only lists solvent for cleaning up - no mention of thinning....so I'll experiment - maybe on a bit of plywood.

Thanks.

Sam

   Schooner behaves differently on bare wood compared to epoxy coated. I've thinned it by maybe 10% on bare wood for the first coat or two but that was ages ago. All recent work has been on coated wood. I have used full strength. In hot weather I might thin it some just to keep it flowing better.  Like others have said there is always another coat to correct errors. And pour out just what you need into a cup for the next few minutes of work then pour more if needed. I like the StopLoss bags CLC sells for varnish. Keeps it from skinning over on the shelf and is easy to dispense. 
 

And I think you need more time than the can says for cure before sanding. If the fingernail dents the coat wait longer or if it balls up on the sandpaper stop and wait a day. 

   Answering one of your other questions, getting varnish on your paint should probbly be avoided.  No big deal is the paint is dark, but if a light color, you'll probably notice the yellow color of the varnish over the paint.  And varnish will yellow even more with age, so I say take the extra few minutes and mask of a line between paint and varnish.  And as standad pratice whether with pain or varnish, on the last coat if you can pull the masking tape while the paint/varnish is still wet but not runny, your edge will probably not have a noticeable line, it will naturally "soften."  If you pull the tap a little late, carefull use of your thumbnail run down the edge will help eliminate the masking line.