Chapter
Ten

Sanding,
Scraping and Finishing

Finishing can be very involved.   I spend about 2-3 hours finish
sanding and scraping a harp.
Some builders will spend considerably more, a few spend less time.   Over time, I have found that touch
will often work better than sight for identifying areas that need work.   Here is the basic procedure I use
for surface preparation

80 Grit Sandpaper with Random Orbital Sander
- I only hit the areas with obvious glue sppots and significant roughness.   80 grit is way too coarse for
sanding veneer, so I don’t use it for sanding round back shells or
laminated soundboards.   I used
to be pretty stingy with sandpaper disks.
Now I rarely sand for more than 10 minutes or so before I change
disks.  Trying to sand with a worn
disk wastes a lot of time, and disks (in bulk) are not very expensive.    I carefully round all the
edges, paying close attention to the tactile points – the parts most
frequently touched by the harpist.    This includes the corners
the sound box, and all the square edges on the neck and pillar.

120,
160 Grit Sandpaper on a random orbital Sander – I sand
most of the harp with these two finer grits, carefully inspecting for scratch
marks left from the last paper.  I
usually wipe the hard wood areas with a wet rag to raise the grain and identify
any glue spots or glue haze before sanding it with the 160 grit paper once
again.

Scraping
– I carefully burnish a fine edge on the scraper and scrape down all of
the surfaces, working to remove any last burn or machine marks on the
harp.  Again, I use my fingers more
than my eyes to inspect the harp at this point, working to ensure all the
surfaces are uniformly smooth.

Finishes

For 10 years I
built furniture and boats.   I
liked Bartley’s gel finishes, Deft Brushable Lacquer or Behlen’s
Master Finish ®.  They can work
well if you have experience with them.
The purists really frown on polyurethane, but I think it may be suitable
if you expect the harp is going to have to live in a rough environment.

What you do will
depend on one’s personal preferences and how these fit with the clients
desires.   Some folks like a highly polished, glassy
finish.  This will require filling
the grain on many woods.   I like
the instrument to look like it was made from wood, and don’t usually fill
the grain.  Many of the harp woods
(hard maple, cherry) do not take stains as readily as oak or Mahogany, and I am
really quite reluctant to stain a harp for my clients.

The largest
problem I had with all of these finishes had to do with their drying time and reparability.   Most of them take several hours to
dry, and even with a separate finishing room, I had to spend a lot of time
sanding out dust motes that had settled into the finish.

I can recommend
two different finishing systems depending on the work area and tools the harp
builder has available.  Padding on
six to eight coats of the alcohol based shellac is the the simplest in terms of
tools and material needed.  I will
describe that first.   Spray lacquer
requires more equipment and a dedicated finishing area.

Padding
6-8 coats of an Alcohol based Shellac

I started using
this system after hearing Howard Bryan (A pedal harp restoration expert working
out of Richmond, Virginia) extol its virtues.   You can mix your own spirit based
varnish from fresh shellac flake, pure grain alcohol and other additives.   I found it was easier to buy fresh
pints of Behlen’s Violin Varnish®.   It dries to the touch in a mater
of minutes.  I can finish the harps
right in my shop if I put a drop cloth down on the bench and let my air filter
run for 15 minutes.   A full
description of this technique is included below.

Finishing kit:  Counter clockwise from the top.  Behlen’s Behkol® Solvent and
Violin varnish®, a French pad tied off with a zip tie, printer paper, the
dispensing bottle, 220 and 320 grit sand paper, and a some samples of finished
wood.

The Alcohol based varnishes are really
easy to repair.   I used to
wonder why instrument builders and furniture refinishers dwelt so much on the
reparability of a finish.

Reparability is not just valuable for
restoring a harp that has been damaged in some way.   Every finisher is going to miss
one or two glue spots, lay on a finish too thick and have it run or sag.   A repairable finish allows me to
go back and fix those spots and blend them into the existing finish.  The job ends up looking as perfect as my
patience allows.

There is one drawback to traditional
spirit based varnishes.  Shellac is
a primary component, and shellac has a limited shelf life.   I order from a supplier that is
turning over their inventory at a good rate and store it in my basement shop
which stays cool throughout the year.   I know it lasts at least 10 months
under these conditions.   If
the varnish is old, or has been subject to heat, I would recommend trying it on
a sample to make sure it will cure.
Old shellac will not cure into a hard coat, and will remains
sticky.   Make sure it will
cure hard before applying it to the harp.

After reading a few books on rubbed
varnishes, I was thoroughly intimidated by the French pad technique.     If you can find an
expert willing to tutor you on the intricacies of the traditional technique and
method, great.  They work best on
flat horizontal surfaces, and my harps have a lot of  surface that isn’t flat or
horizontal.   I adopted a
simplified technique largely based on Howard Bryan’s advice to the harp
list.

Description of
the Simplified French Pad technique

-Tools and Materials

The varnish is applied to the harp with
mushroom shaped pad that is made from an old, clean cotton T-shirt.    The outer layer is an
8”x 8” square of cloth held in place with a rubber band or zip
tie.  When the pad is compacted and
formed, it should be about 2 ½ “in diameter and ¾”
thick.

I mix equal parts of varnish and Behkol®
solvent in a half pint “squirt bottle”.  My bottle was originally used for
dispensing saline solution for contact lenses.   I drilled the hole in the cap to
1/16”

I use a Q-tip to apply finish into
nooks and crannies, and I store two pads and Q-tips in an a discarded Sour
cream container (with a tightly sealed cap) between uses.    The layer of cloth on the
outside of the pad will wear through after applying three or four coats of
finish, and I replace it with a new square of cotton.   The tools to apply the Violin
Varnish cost pennies at most.
The Varnish is $19 per pint (in 2005), and the Behkol runs another $9,
but that is enough to finish three or four harps.

-Method

Finish is applied to the pad then the
pad is used to apply the finish on to the harp.   It takes a couple of tablespoons
of finish to saturate the pad the first time you use it.  The first three of four strokes are made
in a circular motion to distribute the finish evenly over the area.   I use the pad to move finish from
areas that are puddling, sagging or running to areas that are dry.  Within 8-15 seconds most of the alcohol
has evaporated and the finish will become tacky.   The final strokes should be made
before it begins to tack up and are linear, along the grain.

Because the finish dries rapidly, I
usually limit the area I am finishing to a square foot. When I am ready to move
on to a new area, I renew the pad with a squirt of fresh finish.

It takes me about 25 minutes to apply
one coat of finish to a five octave harp.    At that point, the first
area varnished will be dry to the touch, and I will put on a second coat.    Invariably there will be one
or two spots where glue dripped onto the wood, or excess varnish pooled, ran or
sagged.   I will jot the
location of these flaws spots on a notepad (“glue spot, right hand edge
of shell, by the middle sound hole”) so I can scrape them down to bare
wood after the first two coats of finish have cured.

It takes four or five hours for the
varnish to cure hard enough for sanding.   I take care of any flaws, then
sand the entire harp with 220 grit paper.
The object of this sanding is to remove any surface roughness – no
more than the top 30% of the finish.
Do not sand the finish off to bare wood.

I brush the sanding dust away with a
shop brush and tack cloth and apply two more coats and let them cure for
another 4 hours (or overnight) before sanding the parts with 320 grit
paper.

At this point I am getting a pretty
good build on the finish.
I will apply 1-3 more coats, “sanding” in between coats with
copy paper.   This paper seems
to cut about as well as 500 grit sandpaper.  As you rub the finish, the paper will
take on a sheen, at which point you will need to change to a new fresh sector
of the paper so it will continue to abrade and smooth the finish.   Copy paper loads up a bit quicker
than real sand paper but is much cheaper.

I pay special attention to the string
rib and the side of the neck that will be under the strings.  If I get the finish I want in these
areas, I can proceed with mounting hardware and stringing.  I can return at my leisure to touch up
any areas after I have strung the harp.
It takes about two weeks for the harp to start holding its tension
before mounting levers, so I have ample time to inspect the harp and identify
and correct any blemishes.

After the finish has cured two days, I rub
out the entire instrument using Behlen’s Deluxing Compound.    It is a lot like the rubbing
compound used for car finishes.   It removes any dust motes, and
gives the finish uniform semi-gloss sheen, leaves a light coating of wax on the
surface of the instrument.

Target
Coating’s Water Based Ultima Spray Lacquer (USL)

After Asking
Larry Fisher to explain how he got his incredible finishes, I found that many
Luthiers have been adopting the Target Finishing System.   It is a water based finish, but replicates
many of the best qualities of a nitrocellulose lacquer.  Spraying requires a larger investment and
more set up time than shellacking but once I had invested in an HVLP spray rig,
a proper respirator and set up a ventilated clean finishing area, I found that
I could get a smoother, deeper gloss with less effort.   Here is the process that I
use.  You will be able to find several
other variants (that involve more steps and work) on the Internet.    They may result in a glossier, thicker finish,
but I think this is one of the best for the effort invested.

1. First I lay on
two coats of the Alcohol-based shellac.
It may be tempting to skip
this step and start with the Target Coating’s USL, but I find the result
has that grayish-blue tinge that many water-based finishes suffer from.  The amber tones of the shellac warm the
finish and seem to give the instrument better depth and clarity.  After the finish has cured for at least 5-6
hours, I rub it down with the grey 3M pad and wipe off any sanding dust.

2. I screw an eye
hook in the top of the sound box and use twine to hang the sound box and the Neck/pillar
from overhead hooks while spraying.    I find it works best to hang the pillar
from a bolt in the foot and spray it upside down.  To spray the top of the neck (now facing
the floor), simply grab the dowels extending from the knee block to swing the
neck into a vertical position.

3. I spray on four
coats of USL, with each coat spaced at least an hour apart.

4. After the paint
has cured for three days, I sand and level it with 400 grit paper.  A fully cured finish takes about 8 days
(depending on the temperature and humidity in your shop).  Several instrument finishers have found
tha the enters this nicely sandable state at about three days.  Before that, it tends to gum up the sand
paper.  After four days, the finish gets
much harder to sand.  Thoroughly
wipe off any excess sanding dust.

5. I spray on four
more coats of USL, with each coat spaced at least an hour apart.

Now, at this point many of the violin
and guitar finishers go through two or three more sanding (800 grit) and spray
painting cycles.  I think that may
be overkill, and will usually let it the finish cure the full 8 days, then rub out
the finish with Behlen’s Deluxing Compound.

Copyright ©
2007, Rick Kemper

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