How determine existing finish?

[jay case]

Its a table top. Im doing a spot repair then steel wool the entire top and spray another coat of clear finished over the entire top.

What test can I do to determine the type of finish it is? I suspect being a table top it is a poly.

If I prep the prior finish surface with steel wool, and spray with oil based poly over it does it matter what the existing finish is?

thanks for any tips

[glenn bradley]

In a hidden spot, alcohol will soften shellac, lacquer thinner will soften most lacquers and I don't know if there is a similar test for poly. Howard A. will know; the guy's a wizard on this stuff.

[jay case]

thanks. I lightly ragged on some lacquer thinner and the finished rubbed off and was dark brown on the rag. Also I could scrap off the finish coat with a finger nail so was very soft. I think it must have been a stain mixed with lacquer and sprayed on?.
A pretty cheap table to begin with.

Can you spray oil based poly over lacquer or should I stick with lacquer for the table top finish?

[Phil Phelps]

thanks. I lightly ragged on some lacquer thinner and the finished rubbed off and was dark brown on the rag. Also I could scrap off the finish coat with a finger nail so was very soft. I think it must have been a stain mixed with lacquer and sprayed on?.
A pretty cheap table to begin with.

Can you spray oil based poly over lacquer or should I stick with lacquer for the table top finish?

Poly won't attack lacquer but I wouldn't do it. I'd go the pre-cat lacquer route.

[Chris Padilla]

In general, poly doesn't stick very well to any other finish...it even doesn't stick well to itself. I have had, so far, success with poly/varnish over shellac but make sure that shellac is roughed up good with some #0 or #00 steel wool...get it to a flat/satin sheen. Ask me how this is doing in a year or two....

[Howard Acheson]

>>> I think it must have been a stain mixed with lacquer and sprayed on?.

That is the way most factory finish is applied. That way they can use junk wood and apply the coloring almost like paint. It hides almost all the grain in the wood but any color can be created.

[jay case]

thanks all. What about Deft brushing lacquer? Its not pre cat. I dont even know what precat lacquer is. Does it have some properties that would be better then brushing lacquer for a table top?

[Tony Bilello]

If it is factory made piece less than 90 years old there is a great probably that it is lacquer.
What I normally do is use a good wax remover/cleaner on the entire piece. When you are convinced that it is clean, spray the top with a vinyl sealer. Wait a few hours for it to set good, overnight is better. The sand it and see if the sanding residue comes off like dust. Then scrape it with a knife. What you are trying to do is to remove the vinyl by sanding and scraping and checking to see that it comes off, but is not peeling off. If it dont peel off, then the vinyl sealer is compatable with the existing finish. Once you have established that, then go ahead and refinish with a pre-catalyzed lacquer.
Dont get too carried away with the scraping and sanding, you will know in a few seconds if the vinyl sealer is compatable or not.
Also, I would suggest you lose the steel wool and just use sandpaper. 120 grit would be good for testing.

[Scott Holmes]

Tony is spot on about the steelwool...

You will leave shards of steelwool behind that will be trapped IN your finish and eventually it will RUST IN YOUR FINISH.

[Howard Acheson]

Here is the best write-up and procedure I have seen on determining the finish.

http://www.hardwoodlumberandmore.com/TipSheets/WhatIsThatFinish.html

[jay case]

thank you. thats great. Ive not done the xylene test. Ill have to find that chemical and give it a try.

However, I have experimented by brushing some lacquer in a hidden area and it seems to adhear very well and leaves a nice smooth finish. So given that Im thinking I could skip the xyelne test since my preference is to spray with lacquer anyway.

thanks again

[Phil Phelps]

>>> I think it must have been a stain mixed with lacquer and sprayed on?.

That is the way most factory finish is applied. That way they can use junk wood and apply the coloring almost like paint. It hides almost all the grain in the wood but any color can be created.
When is the last ime you were in a furniture studio? You need a seeing eye dog. They don't want you to see too much.