Sanding between varnish coats

[Alan Peck]

What are the favorite grades of sandpaper, steel wool, etc. to use between coats of varnish?

[Lucky Luke]

My favourites: (for Epifanes or Spinnaker Yacht varnish), 220 wet between the buildup coats (Epifanes), 360 wet for the two or three finishing coats (Spinnaker).

[westinghouse]

If you go any finer than 400 you don't get a mechanical bite. Finish off with anything more coarse than 220 and you'll have scratches telegraphing through.

Sounds like you do nice brightwork Luke.

[nedL]

Remember, no steel wool(!) -unless you like lots of little rust stains showing up in the future. ;)

[Paulyboy]

What about what they call synthetic steel wool? I've used that for furniture that I use waterborne finishes on and it seems to work really well.

[westinghouse]

Synthetic steel wool, as in Scotchbrite pads? They rock. Red for rough work, grey and white for scuffing and fairing.

But they don't level the job the way wet sanding does, so you never get a mirror finish.

[Bruce Hooke]

Yup, as Westinghouse alluded to, part of the purpose of sanding is to take off the high points and thus level the surface. To do this you need something that will NOT conform to every bump and dip the way steel wool or its synthetic equivalent does. At the other end of the scale you don't want a really hard backing behind the sandpaper because it will cut through edges and similar places way too fast...

[JimConlin]

I'm very careful in sanding a first coat. Don't want to cut through stain or sealer. I sometimes use a scotchbrite on the first few build coats. My objective in that stage is just to scuff the varnish lightly and clean off the dust, twigs, bugs and birds that have gotten captured. It's not to level the finish. When maybe three coats from the end, i will level with 180 and 220 and go finer thereafter.

[Alan Peck]

The advice to sand the first coat very carefully to avoid cutting through the sealer/stain is very important. Don't ask how I know this!

Also, I like the idea of wet sanding. I just tried it and I was really surprised how much better the new coat of varnish looked.

[Figment]

Originally posted by JimConlin:
I'm very careful in sanding a first coat. Don't want to cut through stain or sealer. I sometimes use a scotchbrite on the first few build coats. My objective in that stage is just to scuff the varnish lightly and clean off the dust, twigs, bugs and birds that have gotten captured. It's not to level the finish. When maybe three coats from the end, i will level with 180 and 220 and go finer thereafter.Same here.

[Bruce Hooke]

Just be careful when wet sanding because it can be harder to see what's going on...

[Nicholas Carey]

Originally posted by westinghouse:
Synthetic steel wool, as in Scotchbrite pads? They rock. Red for rough work, grey and white for scuffing and fairing.

But they don't level the job the way wet sanding does, so you never get a mirror finish.Some people say that there's no point to the betwixt-coat scuffing at all if you recoat within 48 hours or so, because the film isn't fully cured: there's enough molecules that aren't fully polymerized to give a good molecular bond between the coats.

However, if you want to scuff between coats, 3M's maroon scotch-brite is the Way To Go.

And you're right, it doesn't level the finish because it doesn't remove much material (unless you really honk on it.) That is widely construed as a Good Thing: the point of the exercise is building film thickness.

Do 8-10 coats, scuffing with the maroon pad between coats (you might want to take a card scraper between coats for particulary egregious drips/sags/runs and/or the occasional critter that gets stuck in the varnish.

When it's good and ropy, block it out with 220 or 280 on a hard block and level the finish. Repeat as necessary. One or two finish coats with your Good Brush and Bob's-Yer-Uncle.

Another good reason for using scotch-brite-like stuff for this that because the stuff is so open it takes a long time to load (and when it does, you can wash it out with water and maybe a little dishwashing detergent, dry it out and likely reuse it.)

Here's some more info/specs on scotch-brite surface conditioning hand pads that I gleaned from the 3M web site:

</font> Scotch-Brite Light Duty Cleansing Pad 7445 (white), finest flavor. grit equivalent: 1200-1500.</font> Scotch-Brite Wood Finishing Roll 7745 (gold), similar to steel wool grade 0000. I couldn't find a grit equivalency for this stuff.</font> Scotch-Brite Ultra-Fine Hand Pad 7448 (gray), similar to steel wool grade 00. grit equivalent: 800-1000.</font> Scotch-Brite General Purpose Hand Pad 7447 (maroon), similar to steel wool grade 1. grit equivalent 360-400.</font>There's coarser stuff, too, but you probably don't want to go there for your brightwork:
</font> Scotch-Brite Production Hand Pad 8447 (maroon), similar to steel wool grade 2</font> Scotch-Brite Blending Hand Pad 7446 (gray), similar to steel wool grade 3</font> Scotch-Brite Heavy Duty Hand Pad 7440 (tan), similar to steel wool grade 4</font>3M also runs another product line, called Multi-Flex that looks to be much more flexible and conformant to oddball surfaces, so depending on what you're varnishing, it might be the ticket.
</font> Scotch-Brite Multi-Flex Abrasive Sheet A ULF (gold), similar to steel wool grade 0000</font> Scotch-Brite Multi-Flex Abrasive Sheet S ULF (gray), similar to steel wool grade 000</font> Scotch-Brite Multi-Flex Abrasive Sheet A VFN (dark maroon), similar to steel wool grade 0</font>I'm not sure about the grit eqivalencies for the Multi-flex line, but a call to 3M Coated Abrasives Central at one of
</font> 800-742-9546 (lower 48)</font> 907-522-5200 (Alaska)</font> 519-451-2500 (Canada, eh)</font> 808-422-2721 (Hawaii)</font>will probably set you right.
And all this stuff is, I believe, all available in roll form as well as the more usual sheet form.

[Cullen T.M. McGough]

Originally posted by Alan Peck:
What are the favorite grades of sandpaper, steel wool, etc. to use between coats of varnish?You didn't mention if this is a first-time varnish, or a seasonal re-coating. I don't know about other people, but that makes a difference for me.

1st time wood, I like to spend AGES sanding the wood to absolute fair surfaces, working my way up through the 3M grades. (80-120-150-220-320) If it's a really nice piece of wood, I'll take a razor sharp scraper for the final pass. This really brings out the woodgrain pattern.

For each additional coat, I'll scuff with 220 or 320. (Let's be honest, not all varnished surfaces are equally visible.) I find that if you have patience, using 220 or 320 grit and your hands (not a block) can give the best surface. But don't rush.

Even more important, is properly cleaning off the dust after sanding, and re-varnishing in a DUST-PROOF area. (Each mote of dust that touches that wet surface breaks some surface tension.)

Also, filter your varnish to strain out impurities and try to resist working out of the can.

If the wood is old work, and you're just slapping on a re-coat, hit it with 180 or 220 and have at it. Heck, people pay good money for patina.

[Ed Harrow]

Two comments:

One, use the search gizmo and see if you can find Bob Cleek's treatise on applying varnish. Excellent, the usual superb deal from Bob.

Two, get yourself a copy of Rebecca Wittman's book Brightwork.

[Paul Scheuer]

Dust control and brush cleaning are as important, maybe more so than the abrasives. I'm also big on tack rags.

Some time ago I came across some plastic coated heavy "butcher paper" that I use to make tents over the work to keep the airborne stuff off the wet varnish. Clean cardboard does the same thing.

All molecular theory aside, I scuff lightly with a scotch brite pad between every coat during the build up, leveling and finish. I believe it makes a better bond and helps to minimize runs and drips by some surface tension mechanism that I don't fully understand.

I also cut the first and last coats about 50%.

For leveling, after sufficient build coats, I use fairly agressive paper, with a light plywood backing board and a very light, careful touch. You can actually see the "mountain tops" turn into platos, then level out.

No one has mentioned rubbing/buffing with wool.

[Bob Smalser]

Learn to sharpen and use both thick and thin card scrapers, and you can do away with much of the sanding of both raw wood and the sanding required to level out those first thick coats of varnish.

My best fine scraper used lightly on the varnish coat followed by a scuff-up of any hollows left with Scotchbrite can do a superb job much more quickly than sanding.

And some really crisp woods like H Mahog can often go from the belt sander with 120 grit to the card scraper straight to the sealer coat of oil or varnish.

http://www.woodcentral.com/cgi-bin/readarticle.pl?dir=smalser&file=articles_410.shtml

[westinghouse]

Paul, you mean a wool disc and a buffer? That's voodoo man, you have to walk this really fine line between heating up the product (a combination of product cure time/conditions and thickness) and getting the scoring out.

If you're gonna do it, though, I suggest the Makita variable speed set at two (reducing sling to zip, keeping the job cool and making that splendid growl) and 3M Perfect It Rubbing Compound #06062 followed by the Perfect It Machine Glaze #06064. I know this works for catalyzed polyurethanes, but I don't know about varnish. You'd want the stuff fully cured because if it is soft at all the grain telegraphs through with the heat of polishing and the job is wasted.

I've done that on these:
http://www.pronauticyachts.com/PacMar_65_table6.htm

edited to add: wool pads get dags, I like the 3M foam pads #05729 But really, I'm just a chowder.
Eli

[ 02-03-2005, 12:58 AM: Message edited by: westinghouse ]

[Paul Scheuer]

I have used the bonnet on a buffer with buffing compound. That was the winter that I varnished the piano. You're wight, it's a fine line. What I had in mind above was a light rub with a wool rag, somewhere between "dry enough to handle" and fully cured. It seems to take off the microscopic airborne stuff.

[westinghouse]

Thanks Paul, I've spent hours hunched over the DA machine wondering how varnish polishes. Sounds like it's just what I suspected. I'm gonna have to try it sometime.

Now that wool rag thing, that's brilliant.

Eli

[Duncan Low]

Westinghouse-
I have done some varnish polishing on my boat and it comes out very well. First, make absolutely sure that the varnish is dry ( 2-3 weeks.) I then wet sand the area(s)with 4000, 6000, and then 8000 grit sandpaper using a random orbital variable speed sander at the lowest setting. Once that is done, I had apply 3M Finesse-It to the areas sanded and wipe that off with flannel cloth. I then apply Meguire's #3 Anti swirl stuff and polished that off with a woolen bonnet on the random orbital variable sander and foam rubber pad at about the 5 setting(around 3000 rpm). My results have been excellent and I have actually used this method after applying the final coat of varnish.

[Todd Dunn]

I varnish quite a bit (almost every day). I am able to achieve an acceptable finsih (i.e., glass smooth) after 5-7 coats. Basically I don't sand at all for the first three coats. I apply the first three coats quickly, pretty much as soon as the surface is tack free. Then I let the surface cure thorougly for 3-4 days and sand quite aggressively with Norton 3X 220 grit on my random orbital sander. After that I hand sand wet with the grain after each coat using 3M SiC 400 grit paper on a rubber sanding block. I sand and recoat every 48 hours. When I achieve a flat 100% varnish surface I spray the finish coat on. This method produces pretty nice finishes.

[westinghouse]

Duncan,
I think using the micro grits with the low speed sander is underrated.

Eli

[ 02-03-2005, 08:40 PM: Message edited by: westinghouse ]

[Alan Peck]

After four or five coats I am getting a nice mirror smooth finish, except I am having a problem with what appears to be very small bubbles.

I think that perhaps the varnish is too thick and that traps the bubbles?

Any thoughts

[westinghouse]

Small bubbles (like a blush of pinholes) are a pretty good sign the finish kicked on top too quickly. It's too thick, or the worksite is too hot.

Gotta sacrifice a chicken for that one, IIRC.

Seriously, you might get lucky and only the last coat has the offending bubbles, but I have often had to sand down to sealer or bare wood (depends on the quality of the chicken, I guess).

Eli

edited to add, that's a problem I associate with catalyzed products that flash. I've never seen it in one part varnishes. Unless it's actually bubbles and not pinholes, in which case the same culprits are at work, but a good sand and recoat should do the trick (save the chicken for the barbecue)

[ 02-04-2005, 01:38 AM: Message edited by: westinghouse ]

[alteran]

I used to get very very fussy about this and that on varnish and on polishing a FG hull too.

As I get older I've realized that almost no one but me knew the difference in a PERFECT job and a pretty good one unless it was still in the shop with lights all around and no water or skyline or babes to look at to distract ones attention.

The satisfaction of doing a PERFECT job can be worth a lot the "doer" but unless the boat is going to be on display I doubt that anyone else is going to notice much difference and if the boat is being used that PERFECT job is not going to be perfect very long.

The truck I drive to the shop has never been washed and looks like hell, my social truck is always polished. Both have peanut shells on the floor.

smile.gif shrug smile.gif

[Paul Scheuer]

On Al's theme, "The girls all get prettier at closing time". Keep trying until you need to go sailing.

The "bubbles" might be contamination from the brush. Father in law had a jewler's eye loupe (he was a very picky painter) that he used to show me the cylinders of dry varnish that were coming out of the brush that I thought I had thouroughly cleaned.

[steadybrook]

I use LeTonkinois Varnish oil,no sanding between coats,great product.

www.steadybrooksaddlery.ca (http://www.steadybrooksaddlery.ca)

[Hwyl]

Originally posted by Alan Peck:
After four or five coats I am getting a nice mirror smooth finish, except I am having a problem with what appears to be very small bubbles.

I think that perhaps the varnish is too thick and that traps the bubbles?

Any thoughtsYou're not stirring your varnish are you?

In hot climates (he longingly remembers) you can put the varnish can in the fridge before use.