Peter Coombe Mandolins and Guitars
A modern brushed varnish finish for music instruments
by Peter Coombe
I have been using a varnish finish on my mandolins ever since I first started in 1994. Varnish can mean many things, but this article refers to a finish that polymerizes rather than drying via evaporation of a solvent. Most guitars are finished with nitrocellulose lacquer, a very well-known solvent based finish. I did use nitrocellulose lacquer on my early guitars, and was reasonably satisfied with the finish I was getting, but hated the smell. Then I ran out of nitro and was quoted at least 6 weeks delivery for a new batch by the supplier. That was a problem. I really needed to get a guitar finished soon, so decided to finish it with the varnish I was using for mandolins. What followed was a surprise. So many positive comments were received about the varnish finish, that the end result has been no more nitro. This made the other half (and also probably the neighbours) happy because she hates the smell of nitro solvent, and I don't like having the smell in my workshop while the nitro cures. If you can smell it, you are breathing it and it is not doing your health any good. So, the products and procedure outlined in the following have been tried and proven for mandolins and guitars.
The varnish product I use is Target Coatings EM2000, which is an Alkyd resin based varnish in a water emulsion, and I brush it. Alkyd resin based oil paints have been around since the 1920's so it is nothing new, but Alkyd resin in a water based emulsion is new. Some American mandolin makers also use EM2000 on their mandolins, but they spray rather than brush. Why this product? It works better for me than any other varnish I have tried, and I have tried many. No finish is perfect, all have advantages and disadvantages and it is a matter of what your priorities are. I have outlined the advantages and disadvantages below to assist readers to decide if it is worth trying.
No toxic solvents - major advantage. The solvent is water so no strong smell in the workshop as solvents evaporate. You don't need a respirator when brushing. The only real hazard is exposure to dust when sanding. Don't breathe in the dust, but then don't breathe in wood dust either. Don't get uncured EM2000 on your skin, and if spraying still wear a respirator, but there is not a problem when brushing.
Can be sent through the post because it is non-flammable.
Since it is a polymerizing finish, shrinkage is negligible so can be buffed before it is fully cured.
Easy clean up with water, particularly if brushed.
Can be brushed, sprayed or wiped.
Since the solvent is water, you don't need to worry about humidity when applying. It is like a water based paint. Avoid hot dry days because it dries so fast it is difficult to maintain a wet edge, and don't apply if the temperature is less than 10deg Celsius.
Fast drying time. Touch dry in a few minutes, recoat after 1 hr. Dust and insects are not a problem. Full polymerization takes 5 days, so start to complete polymerization (after pore filling) only takes 5 days. Hand buffing with Micromesh can be done the next day after the last coat has been applied.
Absolutely no bluish haze as occurs with most other water based clear finishes.
With age it turns a light amber colour, which gives the instrument a warm vintage glow. Some may consider this a disadvantage, but I like the amber colour.
It is a very flexible finish that will never crack or graze.
Goes on very thin. My varnish finishes are less than half as thick as I was spraying nitro. I have measured it at 0.003 inch.
Is compatible with shellac. It will stick to shellac, and you can French polish on top of EM2000. However, bear in mind that the alcohol will soften EM2000 and you will need to wait a few days for it to harden up again after French polishing. Only French polish after it has fully polymerized (5 days). French polishing can be used to remove witness lines.
Easy to repair. One would expect that since it is a polymerizing finish it would be difficult to repair, but in practice I have found that not to be the case.
On necks it feels much better than nitro, especially if French polished.
Target Coatings do supply a crosslink product that can be used to toughen the finish but I don't have any experience with this.
My ears tell me that my best sounding guitars are finished with EM2000. They sound slightly warmer and looser than nitro, but the difference is not huge.
Not available in Australia, and Target Coatings do not ship international. This may be enough to rule it out for some, but it is easy to get if you set up an account with a freight forwarder such as shipito.com. Shipping costs from the USA are expensive, but it is well worth it.
Not as hard as Nitro. It tends to dent on soft woods, but small dents can be steamed out.
Not as forgiving as nitro.
Since it is a polymerizing finish, witness lines can be a problem. However, this problem pretty much goes away if the procedure outlined below is followed. If you do get witness lines they can be made invisible with French polishing.
It does have a shelf life. Discard if older than 12 months. Like all oil varnishes it will go off if exposed to oxygen.
It is not a pore filling finish. You will need to pore fill woods with pores prior to using EM2000. EM2000 gives best results on well prepared surfaces that are completely flat and smooth.
It will not "pop" the grain well if applied direct to bare wood. It needs to be applied on top of shellac or some other material that pops the grain.
Can of Target Coatings EM2000 full gloss. Don't use it direct from the can. Decant enough to cover one instrument at a time and keep both well sealed. Dilute the decanted part with clean water. Use up to 20% water. The actual amount of water needed will depend on the prevailing temperature and humidity so some experimentation is required.
High quality brush. I use a high quality artificial bristle artist brush, but you will need to experiment with brushes to get the best brush that works for you. As with all finishes, practice on scrap first. Good brushing technique is required. As with all water based finishes, don't try and "fix" problems, it will usually self-level nicely if you leave it alone. Practice bushing technique on scrap.
Non clogging P400 sandpaper.
Pore filler. I use Aqua Coat Clear Filler which is available from LMI in the USA. It is a clear pore filler, water based and works reasonably well when applied with a rag, although does require more than the recommended 2 coats for best results. Practice on scrap. Other pore fillers will probably work fine, but I have only tried Aqua Coat and West Systems epoxy. Target Coatings do offer a pore filler, and I used to use it, but they have changed the formulation and it is no longer clear.
Plastic polish such as Meguiar's Mirror Glaze #17 and Meguiar's Mirror Glaze #10. Available from LMI in the USA.
Note that EM2000 has a completely different chemistry from nitrocellulose lacquer, so the techniques you might have learned with nitro don't work. Do not wet sand EM2000. Wet sanding with water is guaranteed to ruin all your hard work. Always dry sand, and always dry buff with Micromesh.
The procedure outlined below is entirely done by hand. No spray gun, no powered buffing wheel is required yet a superb professional standard finish can be attained.
Sand the instrument down to P180.
Wipe with a damp rag to raise the grain.
Once dry, sand with P400 and remove the sanding dust.
Brush on a coat of dewaxed shellac. This is the time to get anal about scratches. You will miss some sanding scratches, so remove all scratches, gaps, tool marks etc. now because it will get progressively more and more difficult to remove scratches. Use different angles of light, different light sources etc. to see the scratches. Get them all out now. Sand with P400.
Brush on 2 more coats of dewaxed shellac, sanding between coats to remove any raised grain.
Pore fill. I pore fill with Aqua Coat as a matter of routine. Even with woods such as Sassafras or Myrtle, almost invariably there will be a wood with pores used as bindings that need pore filling. Obviously, when sanding the pore fill, try not to go overboard and sand through the shellac.
It is best to brush all the EM2000 in one day. This minimises the risk of witness lines. As a polymerizing finish, if there is too much curing between coats, successive coats don't burn into each other and that can cause witness lines. You can complete all brushing in one day (recommended), but you need to start early and finish late. If that is not possible and two days are necessary, time it so the level sanding step happens to the overnight curing coat (i.e. the 5th coat).
Brush on 5 coats of EM2000, allowing 1 hr to dry between coats. Light sand between coats with very fine sandpaper to remove any nits. Allow the 5th coat to dry for 2 hrs or overnight.
Dry sand with P400 to level the finish.
Brush on at least 5 coats of EM2000, allowing 1 hr to dry between coats. It might take more than 5 coats, sometimes 6 or 7, but you should be getting a reasonably good looking level finish now. If not, wait overnight and level sand again with P400, followed by another 5 or 6 coats of EM2000. It is important not to sand aggressively during the last 5 or 6 coats or you will get witness lines. It is not unusual to need to do two level sandings on Spruce tops to get them completely flat and smooth. Back and sides will depend on how good your preparation is.
Allow to dry overnight. Any longer and you will be sweating a lot when buffing, and it is much harder to get a good level shine.
Dry buff with Micromesh, starting with 2400 and working through the levels down to 12000. This is the hardest part of the whole procedure, especially the first step with 2400. The first step removes the brush marks so is the most critical step. 2400 is likely to take about half of all the time of going through all the levels of Micromesh. Once finished with 12000 it should be looking really good. This is when witness lines (if any) will show up. They can be removed by French polishing, or start again via another level sanding and another 5 coats of EM2000 (recommended). French polishing can be tricky and may create more problems than it cures so I usually only use it for small witness lines.
Wait at least 5 days (from last coat) for the varnish to fully cure.
Polish with Meguiar's Mirror Glaze #17 followed with Meguiar's Mirror Glaze #10. Be careful with #17, it can be a disaster if the varnish has not fully cured. Try on scrap first. #10 is safe, even if not fully cured and if the finish is already good, #10 is enough (and safer).
You can now put the bridge on and string it up.