Modern Hi-Tech Finish Using SilverTip Epoxy and Ilva 2 Part Urethane

This data sheet will help you navigate your way through using SilverTip Epoxy as a pore/grain fill and Ilva 2-part Urethane as a clear-coat finish.

Step 1: Surface Preparation

Your guitar should be sanded to 220 grit. What I do is sand the neck to 220 and the body to 180 grit. I then apply tape to mask off the bridge and fretboard extension and then sand the body to 220. If you don't do this just sand up to 220.

Remove all the sanding dust with one of three ways:

Blow it off in a spray booth that will capture the dust.
Use a vacuum to clean it if you are not working in a good spray booth.
Wipe it with a solvent like Naphtha.

Whatever method you use, I always wipe it with a solvent afterwards to highlight any areas that might need attention such as sanding scratches, dents, or glue spots.

Epoxy is not used on spruce, redwood, cedar and similar soundboards. You can use it on mahogany and koa top guitars, or any other open-grained hardwoods. It may be prudent to seal the spruce and other softwood tops with dewaxed shellac in case epoxy drips onto the tops. Epoxy left long enough will darken the wood.

Step 2: Applying SilverTip Epoxy

I switched to using epoxy years ago because oil based, and water-based fillers did not work that well. They either added unwanted color to the wood, shrank back or took too long to dry. Plus, it was always hard to wipe it or remove it in a way that left the filler in the grain. Epoxy is much easier and here is how I do it.

SilverTip epoxy is mixed typically in a 2:1 resin/hardener ratio, but that is hard to do for the small amount needed to use on a guitar, so I do it by weight.

I weigh 10 grams of resin and 4 grams hardener on a small, inexpensive scale and mix it well in a small cup that's sold for condiments. Mix it well, scraping the sides often. I usually mix it for a minute. With the guitar held in the StewMac Free-Hand holder or some other type of holder that holds the body up, I start with the sides, using 1" inexpensive disposable brushes. (Do not use the foam ones).

Starting with the sides, I brush epoxy onto the sides, staying away from the top. When I am done, I take a credit card or some sort of squeegee and pack the epoxy into the grain. I wipe the excess onto the back. I like to use applicators for applying window tint (see sources). As I get close to the binding, I just use my gloved finger to spread the epoxy with a little more control.

With the sides done, I use the rest of the epoxy and pack it into the grain of the back using a credit card or squeegee. I apply it first in a diagonal direction then switch to even it out. It does not have to be perfect because you will sand most of it off when dry.

One of the advantages of SilverTip is that you can apply a second coat, if necessary, without sanding, after letting the first application set up (usually 4-5 hours), but I have not done this personally. I just let it dry in a warm area.

The next day the epoxy is sanded back using 240-320 grit sandpaper. I use a random orbit sander for this, but you can also do it by hand. Sand until you see a bit of wood dust then stop. You should sand all the application marks for the epoxy out. On woods like cocobolo or wenge with deep grain, a second application of epoxy is advised. Do not over-sand, or you will remove the epoxy from the grain.

When you have sanded back the epoxy you may see a bit of un-filled grain, that's OK, you'll fill it with the urethane application. I wipe the surface several times with Naphtha to make sure I have removed any epoxy clumps or application marks. The surface should look uniform when wet with Naphtha.

Step 3: Applying 2 Part Urethane

I like to apply the urethane with my spray gun and a disposable cup system such as the 3m PPS®. But you can use any spray gun. The ideal atomization sets are as follows.

Turbine guns like Apollo or Fuji – 1.0mm atomizing set
Gravity feed spray guns – 1.3-1.5mm atomizing set. (if using the StewMac gun, it only comes with a 1.0mm so you may have to add more thinner to get it spray properly)
Suction feed (bottom) spray guns, non-pressurized – 1.6 – 1.8mm

You can mix the urethane by wight or by volume, it's a simple 1:1 ratio for both. I find that mixing around 80-100 grams of each yields enough for most guitar bodies and necks. Try not to mix too much, because any leftover is unusable. You can also mix smaller amounts and if you run out before the final days application, it's easy to mix a bit more up. My standard thinner amount is 20% but you can increase it or decrease it slightly as needed. Make sure you use the TZ4223 slow thinner in warm, humid weather.

Before spraying, make sure you have removed all the dust and other debris from sanding the epoxy. Use one of the methods mentioned previously. After a solvent wipe I use a tack cloth to pick up any minute debris. See the Sources for the ones I recommend.

I start with the neck because it's easier to make minor adjustments to fan width and delivery of fluid. Then I spray the body starting with the sides and then I do the back and then finally the top. It's no different than spraying lacquer, except you don't want to double-pass or crosshatch spray, because that puts down too much. Remember Ilva Urethan is about t 3 times the volume solids of a typical lacquer, so you do not need too thick a coat.

Day 1 Spray - I spray 3-4 coats in a day waiting 45-60 minutes between coats. If you follow this schedule, you will get "burn-in" of the urethane (fusion of the coats). If you wait too long or the urethane has started to thicken, its best to mix up fresh stuff. A thickened urethane won't burn into the prior coat.

Let the finish dry overnight. If it's cold, use a small heater to keep the area warm where the guitar is drying.

Day 2 Spray – Sanding Back and Spraying

Sand back the urethane the next day using 320 grit. You don't need to wet sand. This is one of the best features of urethane, it sands easy. Sand the clear finish back until all the grain is gone and there are no shiny spots. Then inspect by wiping with a solvent.

As you sand back, any binding gaps, pinholes or large pores will catch the sanding dust and show up. Blow out the white dust and use Glu-Boost FillnFinish® with their accelerator to correct these problems. Wipe the surfaces with Naphtha and it should look like a dead flat, matte surface.

Then I use a tack cloth to remove any debris that is left and spray again, just like Day 1 spraying, waiting 45-60 minutes between coats. Do not apply more than four coats.

NOTE: If the grain isn't totally filled, or you are sanding to the bare wood to level the finish, repeat the Day 1 schedule to build a better base for the final topcoats. As you gain experience with this finish, usually only 2 days of topcoat application are necessary

After spraying you can remove the tape the next day from any areas that you may have used it. I wait 4-6 days before leveling and polishing the urethane, but if you want you only must wait 24 hours to get a satisfactory gloss.

Leveling and Polishing

After 4-6 days, I level the finish with P800 – P1500 Eagle Super Assilex, and progress though the grits to P-2000 - P3000 using Super Bufflex. I then use a stationary buffer using Medium, Fine and then extra fine. You can use a foam polisher and liquid polishes as an alternative.