Sanding and Rubbing Out Spar Varnish

Tricky problem: eliminating brush marks and restoring an even gloss to spar varnish after the piece is installed. April 19, 2011

I have a set of new curly maple countertops with 4 coats of oil based spar varnish applied to the tops (and 4 on the bottom). I applied this with an 8" pad about 2 months ago and was pretty pleased with the result.

Now the counters are installed and the under cabinet lights are shining on the surface. From the fronts of the counters they look great (looking cross grain), but looking down the length, the surface is less than satisfactory. I can see brush strokes from the paint pad and even some heavy buildup areas.

It seems to me I'm going to need to buff these out, but I haven't done much of that over the years. Mainly I spray with sanding between coats and then get a good clean final coat. Why I didn't do that on these I'm not quite sure. I had some reason at the time, but I doubt it was a very good one!

So what sort of buffing procedure should I use here? Micron paper in a random orbit? Perhaps a rubbing compound? I think a fair amount of material is going to have to be removed to get past the unevenness of the brush strokes. Is there likely to be a problem with going through the topcoat to a lower layer?

The varnish was a satin finish and I am happy with that. I don't want a gloss finish on a counter.

Forum Responses
(Finishing Forum)
From contributor N:
Varnish does not melt into the previous coat. If the finish is very uneven, you will have to sand the finish flat and apply another coat of varnish. Then you will be able to buff the top coat of varnish to whatever sheen you like. If you try to buff a rough varnish surface, you will burn through the topcoat of varnish and you will see the coats in layers.

Spar varnish is also a soft finish, which makes it difficult to rub out. To rub out a top that has a reasonably flat final coat, start with 400 grit and work through the grits to 800 or 1000. After that, switch to a buffer and automotive compounds (3M makes good ones) to bring it to the sheen you desire. Avoid compounds that contain silicone.

From the original questioner:

I just found this in the WOODWEB archives. Any comments?

"I have restored several wooden boats with marine (spar) varnish on mahogany. While it is true that spar varnishes are long oil (vs. short oil) and thus remain somewhat flexible, they can reliably be rubbed out. I would use 400 then 600 on a foam auto body pad, followed by 1000 grit paper.

Then I would use 3M Imperial Microfinshing compound followed by Finesse-It III, both on buffing pads. Incidentally, you should wait a long time prior to rubbing out spar finishes, as they continue to dry for weeks, leading to reverse sanding scratches after rub-out as the finish continues to shrink."

From contributor N:
The drying time is important; I forgot to mention that. You should be able to rub out a spar varnish, but not as easy or as well as a furniture varnish.

From the original questioner:
Can the sanding be done with a random orbit sander, or will that generate too much heat and create nasty problems? I would think this might need to be sanded by hand with a block.

From contributor N:
A random orbit sander should work fine. Just don't let it sit too long in one place. The buffer and compound will burn the finish quicker if you don't keep it moving. If you're going to try to do this with the counters installed, the buffer might not be a good idea, as the buffer and compound make quite a mess. Hand buffing is a tremendous amount of work.

From contributor M:
Sorry, but you have a few more problems. First, the only way to rub out spar is to first remove the brush damage, then remove the damage that the abrasives have done. Your final gloss will have nothing to do with the gloss of the finish that you started with, but the final sequence that you rubbed out with. It is also very hard to just stop at a lower grit of abrasive and have a uniform scratch pattern. If this is what you chose to do, I would sand out the damage, then wet dry from 400 grit through 1500 grit, heavy compound and glaze. Once you have a clean, scratch free finish, go back to 0000 steel wool on a board with very straight strokes.

Second, if this is on clear, no stain maple, your spar will turn yellow very quickly. Other problem is that when you rub out the surface to a low luster, you are increasing the surface area of the finish with your scratch pattern, which will greatly reduce the longevity of the finish.

My approach would be to sand out the brush strokes, mask off everything, cut your spar with acrylic enamel reducer (25%) and respray, then walk away!

From the original questioner:
Thanks for the detailed post. I've pretty much settled on your final conclusion as well, except that I really can't spray with the counters installed. I will experiment, but I think a good varnish brush for a final thinned coat after sand out should do the trick.

From contributor M:
Brushing is only going to give you the same problem. If you mask off well and shoot with a good gravity gun, the finish will lay down and dry to tack in about 4 hours with the acrylic enamel reducer. You also may try using a French polish process. Just cut the spar with a slow dry thinner and use a lint free pad.

From contributor R:
Here's another option. Roll the varnish on with a small foam roller and tip it off with a chiseled foam brush. Don't roll it on with vigor (reduces the likelihood of bubbles). An even pace with a wet roller will yield good results.

From contributor N:
A high quality varnish brush should give you a nice finish but will likely show some brush strokes. The amount of brush strokes will depend on your experience brushing varnish. As far as spraying varnish goes, I would try to avoid it, especially in someone's house. The sticky overspray will get everywhere and it does not spray well anyway. Varnish is made to be brushed. If you are looking for a perfect finish, it will have to be rubbed out, but you should be able to get a very nice finish if you sand it flat and apply a careful brush coat.