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Bob Perkins
08-07-2006, 08:34 AM
Hi All,

I'm in the process of varnishing the deck of my runabout.

I'm using Interlux Schooner varnish - reduced a little and sprayed w/HVLP.

So far so good.

From what I've read - I should sand w/220 grit between coats to level the varnish - remove the grain, etc..

Problem is the sandpaper just clogs up - even after waiting a few days.
Anyone else try to level varnish build this way?

I've switched to the green *scotchbrite* type sanding pad and they seem to work better - but the scratch pattern is not as heavy. Should I stick with them?

Just wondering what others are doing.

Thanks!
Bob

Ken Hutchins
08-07-2006, 08:41 AM
I would just wait longer to sand and use 150 between coats except maybe 220 for just the last coat. Are you using a ROS or sanding manually with a block? ROS works the best.
Another option would be to use wet or dr paper, sand wet, but I don't like sanding wet on any wood, ok for metal work.

Bob Perkins
08-07-2006, 09:16 AM
Hi Ken,

Thanks.. I've used both with same results (actually - using an inline sander to keep scratch pattern w/grain). I'll give the heavier grit a shot.. but I need to build up more finish first. I'm doing the Scotchbrite manually - good for about an hour - then I need a break.. whew...

JimConlin
08-07-2006, 09:55 AM
If the prior coat is young enough to gum up when sanded (#180), I think the next coat will soften it enough to bond without it being scuffed up and you only need to remove the larger dust, bugs, etc. that have sought immortality in your varnish. OTOH, if it's firm enough to sand cleanly, you need to scuff it well. Don't worry about flattening it until you've built the thickness you want to end up with.

Lew Barrett
08-07-2006, 10:25 AM
To avoid scratch reading through the finish, you really should sand with 320, especially the final coats. 220 is too coarse for a show finish. Some go to 400 grit for the last coat. By the last coat or two, you are really just keying the surface; the big leveling should be done before then.
Gumming up on the paper is a common occurance, and means you need to rest the finish more. A complete cure can take weeks, but after having laid down a few coats, it's not out of line to take a rest for a week or even more to allow everything to harden up.
Usually, I only use scotchbright to hit low spots,or really hard to sand areas, not for an overall key.
When sanding between varnish coats, it is important to scuff everything to an even "white" with no gloss showing anywhere. Unless you do that, the finish will be lumpy and uneven. It can't be said frequently enough: the more care you put into your prep, the better the job.

Nicholas Carey
08-07-2006, 12:35 PM
Lots of techniques for sanding between coats...

What we do is just scuff between coats with a maroon scotch-brite pad. Really egregious drip/runs/lumps might get some careful attention with a razer sharp cabinet scraper.

We build up 4-5 coats and let it get lumpy -- the point is to build film thickness. Then we level it with a hard wood or rubber sanding block with P-220 or P-280. The last couple of coats, of course, get much more gentle treatment.

You might want to consider, when choosing your sandpaper whether it's CAMI (US graded) or FEPA ( ISO/European ) graded. The grading rules and grit sizes differ. CAMI defines the grit by average particle size (mesh) and FEPA uses statistical tests for quality.

For instance, FEPA P-180, a "macrogrit", the rules are that no more than 3% by mass of the grit can have a particle size larger than 90 microns, and at least 94% must be larger than 53 microns. FEPA P-220, a "microgrit", the rules are that no more than 3% can be larger than 75 microns, at least 50% must be in the range 50.0 to 56.0 microns, and at least 94% must be larger than 45 microns.

Consequently, FEPA graded coated abrasives offer a more consistent grit size than does CAMI graded coated abrasives. Most coated abrasives manufacturers in the US are moving to FEPA grading.

You can tell FEPA-graded sandpaper because the designation printed on the back will be prefixed with a "P". It won't say 22O, it will say P-220.

Also as the grade gets finer, the differential between CAMI and FEPA grading gets more pronounced. FEPA P-80 runs about 197 microns whilst CAMI 80-grit runs about 192 microns. Moving up the scale, FEPA P-320 is about 46.2 microns; CAMI 320 is about 36 microns. Moving even further up the scale, FEPA P-2000 and CAMI 1000 are roughtly equivalent at about 9.5 microns each.

Ostensibly a given CAMI designation is finer than the same FEPA designation, but CAMI allows for much higher variance in grit sizes and a higher proportion of grits larger than the designated grade. Consequently, this can an inconsistent scratch pattern -- you get a much more consistent scratch pattern from FEPA abrasives.

The higher proportion of larger particles in a given CAMI grade and result in larger/deeper scratches that will take longer to remove with the next finer grader of paper. You tend not to have that problem with FEPA graded paper.

Bob Perkins
08-07-2006, 03:47 PM
Thanks everyone.

I think you all have helped me put it together.

Scuff it up when I have only a few coats and build up film.
Sand smooth once hard for a level finish (150/180/220 grit or so..)
Add a couple more coats for good measure and use 320/400 in between.

I'm also going to wet sand and polish per/ Dannenbergs Book. for final finish.

Now back to varnishing... :eek:

Dave Gray
08-07-2006, 04:08 PM
Nicholas, thanks for your discussion on the sandpaper gradings. I had wondered what the P stood for on some of the sandpaper I have bought. Now I know.

Nicholas Carey
08-07-2006, 04:56 PM
I think you all have helped me put it together.

Scuff it up when I have only a few coats and build up film.
Sand smooth once hard for a level finish (150/180/220 grit or so..)
Add a couple more coats for good measure and use 320/400 in between.

I'm also going to wet sand and polish per/ Dannenbergs Book. for final finish.You'll probably want to level it long before you get ready to put on the finish coats. For a great job, you'll probably want 12 coats of varnish -- if you don't block it out 'till all 12 coats are on, you'll have a lot of work to do.

FWIW, foam brushes are great for building up (though I'm sure some will disagree), but they're cheap and they work well. You'd spend more on thinner to clean a conventional brush than the foam brushes cost. And you lay down a thinner coat with a foam brush, a good thing IMHO.

Anyway, more than one way to skin a cat, varnish a boat, etc. All of them perfectly valid.

For the finish coat, it's hard to beat the Epifanes oval brushes or Hamilton Namel-Var oval brushes. They're expensive, but great brushes.

Lew Barrett
08-07-2006, 07:44 PM
Just to help make Nicholas' point (that some will disagree) I don't like foam. I have my reasons, and named them before, but to the point, I'd just as soon use a good cheap chip brush for build coats and then switch over to better brushes (and/or roll and tip if possible) with better brushes as I approached the end. Twelve coats is good, fourteen is better, and so it goes. The point about the Hamiltons is that a good brush will hold more material and unload more evenly than a cheap one (or foam).

JimConlin
08-07-2006, 08:12 PM
Because of my poor skills with them and my lack of discipline about cleaning them, i've never gotten good or comfortable about varnishing with good bristle brushes. The foam brushes, by themselves, lay down far too little material. The method at has worked best for me is foam rollers, followed by tipping with a foam brush. If I'm doing 'build' coats at tight intervals and am not obsessive about the cleanliness of the tools&materials, i'll sometimes cover the roller pan and roller with aluminum foil and put in the fridge or freezer to save the whole business over to the next day.

Mea culpa...

Nicholas Carey
08-07-2006, 09:00 PM
J...I'd just as soon use a good cheap chip brush for build coats and then switch over to better brushes (and/or roll and tip if possible) with better brushes as I approached the end.Chip brushs work, too (they're cheap enough to toss, too.)

I just gets tired of having to pick chip brush bristles out of the dried varnish :D

Lew Barrett
08-07-2006, 09:14 PM
Chip brushs work, too (they're cheap enough to toss, too.)

I just gets tired of having to pick chip brush bristles out of the dried varnish :D

I flick 'em out as I go along and get the benefits (the ones I believe that I perceive;) ) of an even and better coat with less holidays, but, as I think I have heard you say, your mileage may vary! You know where I get my chip brushes; same place you buy your foam.
Another inexpensive (but I wouldn't necessarily say "cheap) option are the "ProForm" brushes that are now showing up at the usual sources. These are decent cheap brushes that don't actually meet my usual requirements but I like them anyway. More than just a really great chip brush, they are not natural bore bristle, but rather some kind of synthetic fiber, which I normally avoid but in this case seem to work really well. They are densly packed, full brushes, with good quality ferrules so they don't shed much if at all especially if they have been teased a bit to start. The bristles are quite fine but of the right "flex" so they lay down and tip out nicely. Cheap enough to toss at the end of a day, but good enough to make you think maybe they'd be worth cleaning. So, another option then.

Bob Perkins
08-07-2006, 09:16 PM
I figure I'd put on 2-3 coats, then a leveling sanding - repeat until I get up to a point where the mirror finish starts coming into play.

Since I have an HVLP sprayer - I've been going with that for the large areas, and use the brush for the small ones. I think I'm finally starting to get spraying..

JimConlin
08-07-2006, 09:23 PM
The stuff shrinks as it cures. I f I have the luxury of time, i'll let the whole mess bake and harden before levelling it. It'll stay flatter.

pcford
08-07-2006, 11:31 PM
I'm Pat Ford, I do runabout restoration..a few quick notes.

Almost certainly, the problem is excessive humidity in your area....it's hanging up drying. I like to use Epifanes because you can add a little acellerator (sp?). Also, as you build up layers, the varnish below is still liberating vapor; this slows down drying of subsequent layers.

Never thought spray was worth it for runabouts. One final thing: Yachtsman Corona brushes are really quite good for build-up. They are quite cheap 3 or 4 bucks. Use 'em and toss. Use a good brush on final. Takes me a long time to clean a good brush.