This article was inspired by a question from Larry. He writes:
I have a question about a damaged finish on antique furniture. My wife’s cousin was cleaning her house and her 3 year old daughter was “helping”. Isabel, the helpful little youngster, sprayed Windex on a number of her mother’s antiques. The Windex, as I’m told, left white spots on the finish where it was sprayed. Being the only woodworker in the family I was solicited for advice. I know that ammonia based products can be used to clean shellac off of brushes and such, so my initial thought was that the furniture was finished with shellac. But, I’m not sure how ammonia affects other finishes such as lacquer and oils. I wouldn’t think that it would damage poly, but I’m 100% sure about that either. Are you familiar with this type of damage? If so, is there an easy/quick fix or does the finish need to be stripped? I’d appreciate any information you could give. Thanks a bunch. Love the web site and videos. They are quit helpful and informative.
Windex really isn’t good for any finish, so its best if you avoid it completely. So what are these white spots? In all liklihood, the water in the Windex is the cause. Water can create a hazy white spot of moisture that gets trapped below the surface. So, what can you do about it? Worst case scenario is refinish. And if these pieces really are antiques, I recommend consulting with a restoration professional before doing anything. On the other hand, if this is just family furniture for daily use, you can try a few things that may remedy the situation.
Before doing a repair, its essential to know exactly what the finish is. You can do spot tests in an inconspicuous area like the underside of an apron, table top, or leg. If the finish dissolves easily in lacquer thinner, you’ve got lacquer. If it dissolves in denatured alcohol, its likely shellac. And if it doesn’t dissolve in either, its probably a varnish of some kind. Check out this video where I use this methodology to determine what the finish is on an old piece of furniture: Refinishing Pt. 2
If you know the finish is lacquer, you try to spray the surface with lacquer thinner. A good heavy coat will reactivate the lacquer and might allow the moisture to escape before it once again dries to a hard film. Another thing to try would be to spray a fresh coat of lacquer on the surface. This will redissolve the top layer of lacquer and might get rid of the white spots. If you don’t have an HVLP system, you can use a can of Deft from the big box store if you like.
Now there are also a few products on the market that claim to get rid of white spots but I don’t have much experience with them. In fact, I was just at Lowes yesterday and they sell a pre-moistened rag (probably some sort of oil), that you can wipe over the spots to get rid of them. For $5, its probably worth a shot. I have also heard of a weird trick using mayonnaise. Since mayo is pretty much oil, you can put it on the surface so that the oil soaks through the finish and displaces the moisture. But who knows if it actually works. And to be honest, I would envision you replacing your water stain with a more unsightly oil stain.
If the finish is shellac, you could try all the same things mentioned above, substituting denatured alcohol for the lacquer thinner. And if the finish is oil-based, you can try a light sanding with 320 grit followed by a light coat of an oil-based finish. Of course, feel free to try some of those off the shelf solutions mentioned above.
What solutions have you found for removing water spots?