What is the recommended substance to use when refinishing a baby grand in gloss black? (i.e.Paint, lacquer, etc.?) It is already a gloss black, but wasn't sanded well enough to give a smooth finish. We're sanding it down to make it smooth, but not stripping the full coat off. I don't know what the finish is on the piano already. Any suggestions?

Modern polyesther finishes are nearly impossible to strip and re-finish. Sanding down a poly finish to smooth it will give you a piano that no finish will stick to over the long haul.

How about some more information. Was it already refinished? If so, how long ago? If it was refinished it likely was NOT polyester. Polyester is not usually done except by factories for a myriad of reasons.

You can take a little lacquer thinner to an inconspicuous spot and see if the finish softens.

If it was a lacquer finish you could go over the top with lacquer or polyurethane but only if the existing finish is well adhered to the wood, (unless you don't mind doing it all over again). If in doubt, strip.

If it IS polyester, lacquer thinner will not soften it, nor would acetone. Polyester makes a fabulous base coat for overcoating with lacquer. Nice and stable. It should be sanded first for adhesion, but that goes along with leveling the existing surface.

If it is polyurethane you are stuck with polyurethane for recoating unless you strip first. Applying lacquer over urethane will result in BAD things happening followed by stripping the finish.

In any case, I never trust an existing finish and prefer stripping to bare and clean wood.

Dale has good advice - BTW, does the piano have to be gloss? A Satin black is far easier to do and hides many defects. I suggest sticking with a satin finish. The underlying finish may not be a good base, given it was not properly done in the first place. Like Dale, I don't trust an existing finish - covering one up could lead to problems.

Dale Fox:
Yes the piano was already refinished. It is a 1928 Hobart M. Cable baby grand. I don't know how long ago it was refinished. I'm pretty sure it is lacquer that's on the piano. I'm confused about "polyester" finishes. I've never heard of that. I thought polyester was a fabric. I know of polyurethane. Is that the same?

Bob:
Yes the piano has to be gloss. I've never liked satin finishes. But it's what the customer wants too. I'd like to go with a red or white gloss myself.

Polyurethane is totally different, and not compatible. Urethanes are elastic- great for kitchen chairs, not for instrument finishes.

Polyester is a polymer of the PETE chemical plastic resin- used for soda bottles, fiber glass, and yes polyester suits.

Your nitrocellulose lacquers are made from nitrated cotton, sawdust, etc.
Acrylic lacquer is made from acrylic resin, tough like enamel.
Traditional lacquer is made of poison oak oil, beetle juices, etc.

Not sure about a couple things here. Poly urethane is another form of urethane. Longer chains when chemically bonding? Why would urethane not be suitable for piano finishes? It's been used frequently for just that. Most modern urethanes are classed as poly's now. Urethanes are for the most part synthetic varnishes. Many are water based in that they are 60-70% water in formulation with acrylic polymers, glycol ethers, polyurethane and nonionic polyethylene mixed in proprietary formulations along with small amounts of other solvents to help them bond with previous layers of applied finish.

polyethylene is used for wrapping food and other commercial film purposes. HDPE (high density polyethylene)is used for popular items like milk comtainers. It should not be confused with polyester which is commonly used as fiberglass resin, bondo and polyester threads in clothing. Fiberglass is made of glass, not polyester. Polyester resin is the bonding agent for the glass fibers on boats and corvettes.

Shellac best fits the last category as being made from beetle excretions. Never heard of the poison oak oil ingredient, though I'd not be surprised.

Polyester resin is what all those glossy pianos from Asia, Europe and Haverhill, Massachusetts are covered with. It can be buffed at high temperatures without melting and has virtually no organic solvents to gas off. It is also used as a base coat for lacquer on some pianos where a satin black finish is desired. Black polyester looks grey when sanded to satin so lacquer is applied over an existing base of non-softening polyester on some pianos in order to achieve a satin finish on a solid base.

Maybe you can straighten me out on what I have wrong. I don't know all the chemistry, which I've probably just proved.

Wow. Now I feel really confused. ha-ha I think I am just going to play it safe and go with a gloss black lacquer finish. Sand it down, spray on several light coats and ba-da-bing.

Polyester (polyethylene terephthalate, PET or PETE) is not usually done outside of factories because it must be sprayed at a high temperature.
I've heard polyester accepts topcoats of either nitrocellulose lacquer or polyurethane varnish.

The polyurethane is not recommended for soundboards because of its elastisity- this can absorb vibration and shorten your sustain, including instruments in the string family. It is sometimes used for the case finish- although I prefer the formality of lacquer, and that lacquer works well with shellac, whereas polyurethane isn't chemically stable with lacquers. Especially important for the case, because of polyU's water content, you are increasing drying times, whereas solvent lacquers flash dry much quicker in between coats. A Poly-u coat's final cure time would be about 2 months, whereas lacquer would cure in 2 weeks. I think polyurethane is a fraction of the cost of nitrocellulose- making it more economical for the refinisher.

Poison Oak/Ivy (Rhus toxicodendron diversilobum) secretes a blackish oil called urushiol, to which 85% of us are allergic. Cut a poison oak branch in half and the black oil will dribble out- and permanently stain your clothes. I think it was the earliest of the lacquer varnishes in Japan.

Polyester can be sprayed in a normal shop environment.

Axon Corp has a very nice product.

Problem in a small shop is the mixing.
In factory settings, the mix occurs at the gun.

Recoat time is critical, it is short. And as you add coats, it gets shorter slightly.

In a small shop, you mix what you will spray and then quickly clean the gun before it sets.

Minor temp differences in the shop can be accounted for by adjusting the amount of promoter you add.

In my experience, small shop, I prefer NOT to spray in hot weather. Material cures too fast. Too much risk of things like trapping wax in the cured finish.

Polyester is very friendly with lacquer and polyester sealer is used under lacquer by many manufacturers when the end result is a satin rub look.

Probably the 2 greatest reasons polyester resides in manufacturing mostly, is the strict working requirements and it is very toxic until cured.

There may be air quality control issues that restrict the use of polyester finishes in some areas.