3 questions about sanding between coats of varnish

[Andrew Helman]

The bus-boy wiping method with thinned P&L 38 didn’t work out for me (orange peel again and again), so I sanded it back and switched over to brushing for a thicker film to level out. Of course, I ended up with brush strokes and then wet sanded with 400 paper on a rubber backing block to level. That has left me with a surface that is generally smooth to the touch but which still has some shinier spots that do not feel different from the dull spots when you run your hands over them and some sand through where I was not careful enough.

1. Do I need to sand until there are no shiny spots left at all to avoid having marks show through successive coats, or is it sufficient if I can’t feel any difference between the dull and slightly shiny spots? I assume that I only need to sand it until it is completely uniform when rubbing out a top coat rather than leveling at this point--and it could be that I'm confusing knocking down brush marks mid-varnish with leveling when rubbing out.

2. Do I need to sand until there are no shiny spots left in order to have a level finish that will then lay down better with the next coat, or is it sufficient if I can’t feel any difference even if there is some slight shine here or there?

3. Will the bare spots from my sand throughs show in successive coats? I feathered them in the best that I could. If they are likely to show, then I’m just going to sand it all back and start over.

Thank you.
Andrew

[Prashun Patel]

The sand-throughs will disappear if you put on enough coats on top.

When leveling the surface, no, you don't have to remove all the shiny spots. The shiny spots are because the surface is not yet leveled; they're micro-divots. You put on more varnish precisely to fill in those divots. With more coats, the number of shiny spots will reduce.

[John TenEyck]

The busboy method never worked for me either. And brushing always gave me brush marks, just like you. I get good results with Arm-R-Seal by wiping it on with a blue paper shop towel. I put enough on the paper towel that the finish flows out of it easily, but not so much that the finish drips off. I wipe end to end, one or two strokes, just enough to put on a film with no bare spots, then move on. I don't go back over it after the panel is done - that just leads to streaks and grief. If you have enough finish on it will flow out on its own after a few minutes. I've never used P&L 38 but I believe you will have to add some mineral spirits to it to use it as a wiping varnish. Others have reported good results with it when used that way. After you are done sanding it flat I would apply the last two or three coats by wiping it on.

John

[Kent A Bathurst]

If your brush-on coats leave brush marks, it is not flowing out before it "kicks". Thin it down a bit. I have used P+L 38, but its been a while - - I assume I did it the same way as Wlox: thin somewhere like 10% - 15%. I never measure, I thin it until it flows properly off the brush.........properly is a subjective thing - I know it when I see it...

But then, I still give it a final sanding and end with 1 or 2 wipe on coats.............I use the J 10 method - I haven't mastered the busboy thing either.

[Andrew Helman]

Prashun, John, and Kent, many thanks. I'll move ahead with a couple of carefully brushed on coats with enough film to level at the end. Am I ok doing in-between-coat sanding at 600 grit? Keeps me from going to far. Should I use 400? 320? Is that irrelevant with an alkyd?

Thanks, guys. I really appreciate your help (and need this project to be over).

[Prashun Patel]

I agree with the other guys:

The issue isn't the sanding (all 3 grits are fine, and if you're applying successfully, you won't need to be aggressive with any of the grits).

Either thin and brush on your finish, or do as John and I do with the blue shop towels. If you shop towel it, don't sand until every 3 coats. Then too, don't over do it.

On a test board work on getting a smooth finish off the applicator. Properly brushed, wiped, or sprayed, you shouldn't have to sand that much. In fact, if you find yourself asking, 'hmm, that looks pretty good without sanding, wonder if I really need to sand.' then you've done it 'right'. I'm not being glib here. If I can do it you can too.

[Todd Burch]

My recipe for P&L 38… (I've actually been using it the last 3 nights, and have used it for years.)

I apply with a quality foam brush. I use JEN brand. A cheap poly foam brush is worthless. JEN brand has the stiffness you need for P&L.

A 2" brush works well. If you are using a quart can, a 3" brush is almost too big.

I apply fast, brush back and forth, sometimes even side to side, but my final pass is always with the grain and lightly tipping off. I try to go a full stroke, end-to-end, and when I can't, I "airplane land" on and off and I stagger my take offs and landings along the stroke path.

I sand with either 220 or 240 stearated paper (the white stuff). I sand fast and only work the nibs. While I try not to have holidays, sometimes I do. A raking light with help find those as you go.

I apply 3 coats in 3 days. Each coat dries faster than the previous. Sanding of the first coat is always the worst / most lengthy. Especially if you have used an oil based stain. This is because the varnish will pick up the stain on the first coat and mix with it. Even the stearated paper will gum up some.

Sanding the second coat, you watch for "color" on your paper if you have stained. Finding color on your paper is bad when sanding the second coat.

After the third coat is applied and dry, ditch the sandpaper and get some #0000 steel wool and some paste wax. Apply the wax with the steel wool. Paste wax will cure a multitude of sins. It will hide any shiny divots and blend / hide any holidays. It also warms the piece up some, gets rids of any nibs and provides a consistent feel, no matter how poorly you applied the varnish.

That's my recipe, and I'm sticking with it.

[James Tibbetts]

...."While I try not to have holidays"....

Never heard this before. What is it?

[Todd Burch]

A holiday is a dry spot on your workpiece where you failed to apply varnish. I learned that term when I read the book "Understanding Wood Finishing" by Bob Flexner. One of the best woodworking books I've ever read.

[Brian Tymchak]

......I use the J 10 method - I haven't mastered the busboy thing either.

OK, I gotta ask - busboy? J10? never heard of 'em. (but pretty much a finishing novice) Can I get a little help on these, please?

And I was gonna ask about "holidays" but James caught that one.

Thanks!

[Scott Holmes]

The wipe on varnish technique is very simple and very easy. Wipe it like the kid wipes the table at the burger joint. All you want is damp wood. No shiny spots, no puddles, etc. It should dry in ~45 minutes then another coat, repeat for 3 coats per session. I would not use any sandpaper until you've done at least 6-9 coats.

[Todd Burch]

Wipe it like the kid wipes the table at the burger joint.

How about a better analogy? Seriously. I'm envisioning a table 1/2 missed with crud still there, leaving what they did wipe, sopping wet. Or, were you just referring to the sopping wet part?

[Prashun Patel]

Having struggled with this, I can say that the analogy is a good one with respect to the SPEED. The problem with wiping varnish is going back over and over it again after the initial wipe. Overworking it is what (for me) causes swirls and issues.

Wring your shop towel out, and polish the piece quickly and completely. Then walk away. Just as the burger kid doesn't overthink it, so neither should you.

[Andrew Helman]

Ok, a short update with photos, in case it is of interest, and a question about air bubbles at the bottom of this. Here is what I started with last night. https://drive.google.com/file/d/0B3O...ew?usp=sharing You'll see the sand throughs I previously mentioned.

I followed Scott Holmes’ advice in the brush care video (and some other advice; thanks, Scott!) and thinned the P&L 10% with true non-odorless mineral spirits and brushed the stuff on. It laid right down. There were some bubbles, but I blew on them to disturb the surface, and they mostly popped. I didn’t want to tip off much because it lay so flat after brushing on. FYI, I got most of the way down the board with one dip in the varnish over the already-sealed areas—a 90-inch run—and then had to reload.

Here’s a link right after brushing on while wet. https://drive.google.com/file/d/0B3O...ew?usp=sharing

Here’s a link to a few shots from this morning when dry. There are a few dust nibs, a dead bug, a few air bubbles to snap open, and a few errant brush strokes.

https://drive.google.com/file/d/0B3O...ew?usp=sharing
https://drive.google.com/file/d/0B3O...ew?usp=sharing
https://drive.google.com/file/d/0B3O...ew?usp=sharing
https://drive.google.com/file/d/0B3O...ew?usp=sharing

Question: With air bubbles that didn’t rise enough to the surface, what do you think of scraping through to get to them and letting the varnish fill that back in? Seems better than letting a bubble stay in the finish. I suppose I could sand.

Thank you,
Andrew

[Brian Tymchak]

Ah, thanks guys. .. Bus Boy, should've picked up on that...