Expert: Jamie Yocono - 8/10/2008

Question
Hi
We will be varnishing a brand new laundry plywood bench top with marine grade polyurethane.

I can never seem to get a smooth surface when I varnish, it always has small brush marks, and when i apply it i often get what I think are tiny air bubbles in it?  These bubbles seem to disappear as it settles/dries but I wonder it they contribute to the rough surface.

Between coats I sand with 240+ paper or steel wool and that helps.

Is there a trick or technique for getting a smooth finish?

I am not using any specific brush.  Currently its quite cold down here (New Zealand), got to ~10'C yesterday.

All advice appreciated

Andy C

Answer
Hi Andy,

I don't do a lot of varnishing, but I have some tips that might help.

First, you have to stir the varnish, not shake it. Shaking it will put bubbles in the varnish, so gently stirring it is a good start.

Next, I sometimes thin my varnish, just a bit, like 3/4  varnish to 1/4 thinner.  When it's thinner, it flows better. So those brush marks disappear better. Some people start with a full strength coat, then thin the second coat.

A dust free environment is important, obviously, as you don't want particles settling on the varnish.  

And as much as I resisted this because I hate spending $12 for a good brush... well, a good friend of mine is a house painter and I got a lesson about how much of a difference a good brush can make. So when I have something really important, I open my wallet and buy a good brush. Your can of varnish might tell you what the company recommends for that type of finish. I really resisted this, but I've since learned that a good brush can make a huge difference. Also, since I hate spending that much on a brush, I keep them for a long time. The older ones get relegated for jobs like staining or something that doesn't demand a good brush. Save the good brushes for your varnish work, and the older ones for junk work.

Sanding between coats really helps, too, as you mentioned. I generally use 400 grit between coats, and after my last coat, I rub the surface with very fine steel wool. Wipe the surface clean, and if you see any sanding marks, try a final rub-out of a paste wax. That really helps, too.

OK, I think all these tips combines should help a lot. Write back if you have more questions, I hope this helps.

By the way, here in Las Vegas, it's about 110˚F every day... quite a difference from where you are. Sometimes I miss those chilly nights!

Jamie Yocono
Wood It Is! Custom Cabinetry
Las Vegas, NV
Check out my wood blog: http://wooditis.blogspot.com/