Re-Polishing a Polyurethane Table Top Finish

      Re-buffing an existing glossy finish involves some tricky procedures. July 2, 2008

Question
I am working on a huge conference table. The client wants to keep the original finish but bring it back to the original shine. I believe the original finish is polyurethane. I first sanded the finish to remove the scratches. I started with an orbital sander with 320 grit sandpaper, then moved to 400 grit, 500 grit, 1000 grit, and finally 2000 grit. I also used lower speed rotation for the lower grit paper and increased the speed with every next grit, so with the 2000 I was at max speed. I'm now rubbing the finish with a high speed buffer/lamb wool. If you look at it from a distance, it is perfect, but when you come close to it, it is uneven - there are places where it looks cloudy and places where it looks good. Also, from up close you can see scratch marks from the sandpaper. Does anyone know what caused the problem and how to fix it?

Forum Responses
(Finishing Forum)
From contributor C:
If there are still scratches visible, they may not have been removed as you went to lower grits. Some were left behind from the previous grits. Cloudiness, on the other hand, might be from porosity of the coating being filled with microscopic particles from the compounds you're using. Are the areas milky white? Is your compound white? If not, then you should be able to get them out. If not, try using a black compound over them and see if that helps. Beforehand, solve the areas with naphtha or light mineral oil to help bring the white back out of the film.



From the original questioner:
Thanks. The cloudy areas appear milky indeed. By black compound, do you mean the dark automotive compound?


From contributor C:
Yes, unfortunately they don't make or sell Liquid Ebony anymore - so you will have to use whatever is available. Check and make sure this is the problem, as it could be something else. Without being there to see it I cannot say for sure.


From contributor D:
320 grit was probably too aggressive for this job. I would have started with 800 and gone up from there, or 600 depending on how bad the scratches were. You are seeing the scratches (probably from the 320) that you did not fully get out before going to the next grit. The only thing to do now to remove them is to either go back and re-sand those spots from 400 up, or spend lots of time with a buffer and a couple grades of compound. The cloudy/hazy spots might also be spots where you sanded through the topcoat into the sealer, thus the sealer is not buffing to a high gloss like the topcoat. You could also just sand the whole top with 320, clean, and spray a couple coats of polyurethane on the table to even things out and be done with it.


From contributor W:
Use a guide coat.


From contributor R:
Once you have expired your final sanding grit and you are ready to final polish your coating, you can use Liquid Ebony, which is an excellent product. It will yield you a most beautiful final finish on either a conference table or a set of cabinets. I have a gallon on hand for my own use but it is still available from many online sources by Googling "Liquid Ebony".


From contributor C:
That's good to know. I had tried many places and the last told me Clearbrite was no longer in business and they had tried to buy the formula but it was not for sale.

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