Buffing and Polishing Polyurethane

Suggestions for buffing a poly finish to a high gloss. October 19, 2013

Question (WOODWEB Member) :
Has anyone tried wet sanding with Naphta on a polyurthane surface? I was told using 800 grit, followed by 1000 grit, and then followed by hard and soft polish (auto polish - with a buffer) will give a the required mirror finish.

Forum Responses
(Finishing Forum)
From contributor J:
I have, but I used 2000 grit wet/dry (black) paper to sand it with and used water. Then buffer with a compound (polish same as a car finish). I have everything for that since I paint cars on a regular basis. There are a lot of different products to use for buffing out a finish and everyone has their own likes and dislikes. You need to get the sanding up to 1500 or above to begin buffing. The higher you take it the easier the buffing will be. Some folks even go to 3000.

From contributor F:
Most importantly though you need the finish to fully cure. Poly takes a long time to cure and for best results it should set up for several weeks. You also want it dead flat before you start wet sanding, so a lot of work before laying down the final coat.

From the original questioner:
It is not advisable to start polishing after four days of spraying poly?

From contributor A:

It would matter to know specifically what coating you are using or at least if it is a professional class coating requiring a catalyst to be mixed into the coating when using it and drying to the touch in minutes. Or would you be referring to a polyurethane varnish like Minwax that dries relatively slow like an hour or more before you can touch it?

From the original questioner:
I am using this poly for the first time. I have sprayed it today and the weather was around 27 C but all next week the temp will be 12 C.

From contributor J:
You can do it after a week if it's kept warm, but it's still soft. The longer you wait the easier it will be. Lacquer is much easier to polish out and quicker to harden. When I finish a wood top that I want a clear high luster finish I use an auto urethane, it takes an activator and is clear as water. It hardens up overnight enough to rub out. It usually takes two spray sessions, one to lock everything down and to seal it, then a second spraying after sanding the first one flat.

From contributor A:
That confirms the class of coating you have. I use a similar coating from a different manufacturer. While it could be polished out as your question states by virtue of its chemistry (flexibility) it may not be the optimum coating for that purpose. You can get decent results polishing them to satin or semi-gloss sheens but it would not be the coating to use if you want a mirror gloss finish. Harder coatings respond to polishing better to produce the brilliant gloss like you'd see on many new pianos. That said I would wait at least a week for curing before starting to level and polish. If you are new to polishing out a coating this way then you really must test your procedure for yourself on samples. The procedure you describe sounds reasonable, so give it a test and see what you get.

From contributor R:
Abralon pads on a random orbit sander with water or mineral spirits will get you close, but not high gloss.