Model Forum / Radio Controlled / Water Models / September 2003

I'm not a modeler (although I have some interest in building a R/C
iceboat -- any other R/C iceboaters out there with ideas?) .. but I
DO do a lot of varnishing -- about 60 square feet each winter, as
I put a couple of coats on the coamings, hatches, etc., for my
"big boat".

I know it's against the common wisdom, but here goes.

0. Prepare the surface. Sand with ... well, I use 220-weight paper in
a lovely random-orbital sander, but for model work, I think I'd
go with 320 paper for the final sanding, or maybe 400. Get the wood
as smooth as you can.

1. Go ahead an put on a couple of quick coats, thinned with whatever the
varnish maker recommends. Don't trust your grand-dad's recipe for a
"great thinner that just uses vinegar, gasoline, and bit of mayonnaise."
The folks who made the varnish WANT to make it look good, and have spent
time on the chemistry, I promise. Make sure you get good coverage, and
there's no dust or hair or drips, but don't sweat over the beauty of the
job. One thing that'll happen with most woods when you apply the varnish
is that the grain will swell a bit, and your sanding work from part 0
will be partly negated. That's life.

2. Sand it down until you have a matte finish that is as smooth
as you want the final finish to be. The idea here is that you have
a possibly slightly rough wood surface (from raised grain), covered
by a layer of varnish that's thick enough to fill in the low bits, and
whose upper surface you have now polished to the sort of smoothness that
you want. Random-orbit power sanders (for large-scale work, anyhow) are
amazingly good at this.

3. Now your job is to put on a few more fairly thin coats that'll build
up to a decent thickness for weather- and abrasion-resistance, and give
a nice gloss. Amazingly enough, you can do this pretty well without
ay more sanding to speak of: you apply a coat, and when it's almost dry
-- dry enough that your finger leaves no fingerprint, for instance,
unless you hold it there for a few seconds, but still wet enough that
you can smell the varnish  -- you apply the next coat. The idea is to
have something that's still got some "solubility" left -- the old
surface gets partly dissolved by the solvents in the newly applied
varnish, allowing some cross-polymerization between the two coats -- but
for which the stuff that needs to evaporate from the lower coat is
almost all gone. In winter, working in a basement that's about 67
degrees F, I find that between 18 and 24 hours seems about right for
the Interlux "Captain's Varnish" that I use.

-----

How do you apply it? Well...I like to use foam brushes. Not badger-hair,
or anything like it. Just foam. I use the high-density brushes sold by
Jamestown Distributors; they have wood handles. The Home Depot sells
far cheaper, less-dense brushes with red plastic handles, and those
are awful. I take a throw-away plastic cup and hold it over the open
varnish can. I dip the brush in the can until it soaks up some varnish,
then lift it up and over the edge of the cup to let it dribble into the
cup. Repeat a few times. 15 dips of a 2-inch brush gives me enough
varnish to coat about 30 square feet. You may be doing only a few square
inches, but still take several dips -- you don't want the varnish drying
in your cup.

If you've done this right, the might be a small drip down the side of
the cup -- wipe it up! -- but no drips on the can at all, so you
can replace the lid and get a good seal again. Also, there will be very
few bubbles in the varnish that's in the cup. (Don't get tempted to
press the brush against the side and squeeze  the varnish out in a hurry
-- you'll get tons of bubbles.)

How do you apply it?

Step 0: wipe everything down with a rag, and vacuum everything as well.
Make sure that there'll be no one walking in the room overhead for a
while (or rig a plastic sheet over your workspace) so that dust won't
fall from the ceiling. Just before varnishing, wipe down the surface
with a tack-cloth to get away any dust particle or hair.

Step 1: What about the VARNISH, eh????

Well, I take the wet brush and dab it gently onto
the board I'm working on in several places that are perhaps separated
by about 4 or five inches, and are aligned with the grain. I'll draw a
picture: dashes are grain, and xxxxx's are the blobs left by my brush
tip.

--------------------------xxxxxx---------------------------------------------
---xxxxxx------------------------------------------------xxxxxx-------xxxxxx-
-----------------------------------------------------------------------------
------------------------xxxxxx--------xxxxxx---------------------------------
-----------------------------------------------------xxxxxx------------------
--------xxxxxx------------------------------------------------xxxxxx---------
------------------------------------xxxxxx-----------------------------------
----xxxxxx---------xxxxxx-------------------------------------------xxxxxx---
-------------------------------------------------xxxxxx----------------------

(view with fixed-width font). That's for a board that's about 10" wide
and perhaps 3 feet long.

Now, working across the grain (i.e., top to bottom) I brush the varnish
out over the board. Imagine if I started at the first blob up above and
drew it downwards..after a few inches, the varnish is starting to run
out...but it's replenished by my encountering another blob .. and then
another. I work along the whole board -- maybe applying a few more blobs
if necessary -- and then look at it with a bright hand-held light and
check for spots that might be "holidays" -- little missed bits. I work
these over by brushing with the grain.

Perhaps at this point there are some bubbles from all that brushing,
although I move the brush quite slowly -- perhaps 2" per second -- and
by the time I'm done with a couple of feet of board, a lot of the bubbles
will have risen to the surface and have popped. (That's an advantage of
working in a cool place -- it takes longer for the surface to start
drying, and there's a better chance for the bubble to burst.)
So I take the brush ... and holding it very lightly, I just DRAG it over the
surface, but WITH the grain. The only pressure is the weight of the
brush or a TINY bit more. The idea is to let the brush tip break the
bubbles that are there, and perhaps to help make any ridges be
grain-aligned so they'll be less visible.

Once more I check with the light. If there is a hair anywhere, I go
ahead and pluck it out, leaving a frightful mess, and then work over
the mess with the foam brush gently, trying to level it and reduce
bubbles. Again, cool environments are good -- more time for things like
this.

Once everything looks good, I leave the room, shut the doors (reduce air
circulation and dust), and come back 12 hours later to check.
------------------------------
For the next coat: a new cup, a new brush, a new portion of the
tack-cloth. To do 4 coats on both sides of my coamings takes me
just about a week. Live with it. You can probably manage to
spray the stuff with Japan drier in it, etc., and do it all in
two hours, but unless you've got an amazing work-space, I wouldn't
try it. Just live with the time it takes.

------------------------------

A last bit of advice: get some wood that's similar to the stuff in the
model and use up a half-dozen brushes and cups trying to get a decent
surface one it BEFORE doing the model.

Best of luck,

John Hughes