You mneed to determine what the exising finish actually is forst.

Lacquer was very common, and not that hard to overcoat or repair defects.

Varnish was rarely used post war since the drying time was very large.
Lacquer can be dust free in minutes, and dry in hours (minutes if baked).

You first said varnish, then asked about poly.

While there are poly varnishes, real varnish does not contain poly.

What brickeyee said is correct---knowing what finish is present is necessary.

If lacquer thinner dissolves part of the finish, it is lacquer and can be simply hand sanded and new lacquer applied. However, applying lacquer is better done when sprayed on. Applying with a brush can be problematic.

If the finish does not react to lacquer thinner or alcohol(for shellac), the finish will need to be sanded to even out the dings and scratches and new varnish applied.

Polyurethane contains plastic. That causes defects to be almost impossible to spot repair. Non poly varnish is more easily spot repaired since the lack of plastic allows better feathering and blending.

Thanks Mac.

Do I need actual lacquer thinner or can I use something I have around the house already, like MEK? I'd hate to add to my solvent collection unless absolutely necessary! :)

Oops. Yep I switched from "varnish" to "poly". I would probably use a polyurethane varnish but what's on there is probably old school varnish if it's varnish at all which I guess it probably isn't.

If I have lacquer and want to use polyurethane, does all the lacquer need to be removed?

Thanks again!

Many nail polish removers contain acetone.

I have never tried MEK as a thinner for lacquer. Might work, since it can be an ingredient in some lacquer recipes.

I have no idea about overcoating lacquer. I just never tried it.

"Applying with a brush can be problematic. "

If you want to add lacquer use Deft Clear Wood Finish.

It is a lacquer suitable for brushing.

You DO need a VERY good brush.

'Badger' is about the best for lacquer work.
Around $30 or so.

If you use gloss you cam rub it to any sheen you want.

Thanks for the recommendation. Is lacquer durable enough for daily abuse? (I know that's hard to say!)

When recoating lacquer, does the base finish need to be sanded smooth? Will the phone number gently embedded in the finish fill in or does it need to be erased first?

Thanks!

" Is lacquer durable enough for daily abuse?"

It is not all that resistant to alcohol or warm water, about like all the furniture you have had for a long time.

It is much more resistant than shellac.

"When recoating lacquer, does the base finish need to be sanded smooth?"

Depedning on how deep the impression is it wil fill in with more lacquer layers, it is just a quaestin of mow many.

I would make sure the surface was completley clean (mild soap and water, then a wipe down with paint thinner) and a light sanding with around 300 grit wet-or-dry paper (dry is adequate here), then wipe with paint thinner again to remove ALL the sanding dust (if you leave a tiny bit behind it will melt into the new coat IF it is lacquer dust ONLY).

One great advantage of lacquer is that new layers melt into the old forming a single homogenous thicker layer.

It may take multiple coats to get any build since even brushing lacquer is less than 15% solids.
The other ~85%+ is solvent that evaporate, quickly.

Thanks for the details, B.

Turns out it's been varnished on the top, and not as well as I'd thought so I think I'll have to strip it.

Any tips for stripping varnish (that is probably over lacquer)? Or perhaps I should leave it as is until my kids grow up and and THEN refinish it! Hmmmmmm...

"Or perhaps I should leave it as is until my kids grow up and and THEN refinish it!"

Might be a very good idea.

Depending on the type of varnish it can take some potent chemicals to remove it.

Varnish hardens by oxidation and/or polymerization (depends on the exact chemical type).

Once it is cured it is no longer soluble in the carrier that was used (water or petroleum based based).

Newer types are often easier to remove than some of the old stuff.

Sometimes the only thing that can attack and soften older varnish is methylene chloride (the old standard 'stripper' main ingredient).

Used outdoors with adequate ventilation by a healthy person it is not that much of a risk.

Used without adequate ventilation by someone with any latent hear tissues it can be very dangerous.

It behaves similar to carbon monoxide and ties up the hemoglobin in blood (binds better than actual oxygen) that carries the oxygen you need, making it unavailable to your body.

A heat gun and a good scraper would make short work of it.

You can cover lacquer with varnish. I have done it many times...back when I was entranced with the ease of applying Deft...and then discovered how fragile it is. Sand it well ( after cleaning all traces of grease and shudder...silicone furniture wax.
And also I have added coats of varnish to old....after, of course cleaning very well. If you actually have chips in the varnish you will need to rub them out before applying the new coat. If it's into the wood, you may have to do a little artful stain work with an artist's brush to match the chips. And you can put oil based poly over well dried varnish ( or paint for that matter).
Actually if a finish is well dried...VERY well dried...you can coat anything with anything else. I have coated 2 day old oil paint with lacquer and it blistered down to the wood....acted like paint remover! But I have coated well dried paint and varnish with lacquer ( carefully as the lacquer will dissolve what's underneath...so gentle with the brush) Shellac with lacquer and with varnish and with poly.

Thanks all!

While the tabletop itself is apparently varnished, the legs, apron, etc. as well as the matching chairs seem to have the original lacquer so I think I'm going to be doing every darn thing suggested here on one part of the set or another.

Eek. :)

"You can cover lacquer with varnish."

that deepness on exactly what kind of varnish.

It is not universally true.

The only way to know is to try in an inconspicuous spot and see what happens.