Preparing An Old Wood Floor For??Heavy Duty Pro Satin Polyurethane


We have hardwood floors that have been covered for 40-50 yrs( probably since new) They are clean, no marks and the color is beautiful. It looks as thought they do not have poly on them. Can we clean them then put poly on rather than sand etc….?




Dear Ron

I hope by now you have read the full second half of the cleaning article (FREEEE), and know just what finish is on the floor. But just in case you either didn’t read it or didn’t understand it I will review this before we go on.

You can use various solvents to determine just what generic type of finish it is. The first solvent to try on the finish is alcohol. Use rubbing alcohol that you find at the drug store. Apply a few drops of this in a inconspicuous spot and observe. If, in a few minutes, it starts softening the finish and makes it sticky, the finish is shellac. This is the least durable of all the film type finishes so that may be why you are having problems washing the floor. A lot of people start waxing these shellac finishes and in order for this test to work you will have had to remove the wax with mineral spirits or paint thinner first.

The next step is to apply a few drops of lacquer thinner on a different area and watch this. If the finish is a lacquer or a water based finish, the lacquer thinner will start to soften it. Unless the floor has a pale look to it and has been resanded in the last 15 years, it’s unlikely that it is a water based finish. To prove if it is a water based finish apply a few drops of toluene or xylene and if the finish softens it’s a water based coating, and not a lacquer finish. If you find that none of these solvents affect the finish, you then have some sort of reactive finish, polyurethane varnish being the most common used on wood floors for the past 30 years. There are other reactive finishes but for the sake of maintenance and recoating it really doesn’t matter.

You will need to re-coat the floor with the same or similar floor finish, so tell me if I didn’t guess correctly, that’s it’s a varnish. Once the finish is determined and the floor is well cleaned, prepare several small areas, prep by light sanding of the finish, and apply a small 6″ area of finish. If it’s poly let cure for two weeks, razor cross hatch the test spot to the bare wood, apply duct tape and rip it off. If more that 20% of the test finish comes off, you will have to just resand or simply continue paste waxing the floor. A new coat of any film finish just will not stick to this floor.

So Ron, I’m betting that the floor finish will turn out to be some sort of reactive finish, a floor varnish, and even a early version of polyurethane varnish (which was invented in the 1930’s. That means you certainly can recoat this finish with a similar finish, and I would personally recommend the Heavy Duty Pro Satin polyurethane by Fabulon. That’s the stuff I use every day.

But the prep is the main thing. First you have to make sure there is no oil, wax or silicone containing furniture polish on the floor. It’s always worth a look under the kitchen sink or basement storage area, to see if there is any old dried up cans of any of these materials. Again back to the article:

It is most important to determine if the floor has been waxed. This may be not so easy to see. A lot of heavily waxed floors have fooled me. Take a piece of extra fine steel wool and wet it slightly with water. Rub it on various areas that you think may have been waxed. Paste wax will show up as a light gray smudge on the wool. Also water drops left on a waxed floor will turn white after about 15 minutes. Paste wax can be removed with a rag wetted with mineral spirits or paint thinner, and will show up on the rag as a dirty film.

To tell you the truth Ron if I find a floor that has been paste waxed, I would never attempt to apply ANY new film finish on it, no matter how well I cleaned it. Instead I would just continue to de-wax it once a year, and apply another coat of liquid paste wax, and buff it to a nice satin shine. Let me know if this is the case, and I will tell you ALL about waxing floors. But I will be gone fishing until about May 15 so a follow up would have to wait until then.

Water based acrylic waxes like Mop and Glo will be harder to dissolve and generally need an ammonia based wax stripper to remove them. Most of these acrylic polishes will give the surface a patchy, dirty appearance when they start to wear off. You can test for these types of waxes by mixing a tsp. of water with a tsp. of household ammonia, then add a drop of liquid detergent, into a small cup. Apply a drop of this mixture on a clean area that you suspect has this acrylic wax and wait 5 minutes. If this type of wax is present the spot will turn white. You can only remove this wax with an ammonia based mop stripper. The Cleaning Center ( makes a Mop Stripper that will remove the most stubborn acrylic type wax, without introducing too much water to the floor.

If you find NO presence of either wax you can remove any other contaminants from the wood floor by spraying a small area at a time with odorless mineral spirits and using a white nylon flat non abrasive scrubbing pad (found at the grocery stores) and scrub the still wet solvent a blot if all up before it dries with paper towels. Do the whole floor systematically not skipping any area. You can also wash the floor with a pH neutral cleaner, but be sure to rinse it off. But if there are any spots in the floor that have an unsound finish (as described in my article) you’d better stick to the solvent for cleaning. Any unsound areas that have turned gray, will need to be sanded down to the bare wood and touched up with at least two coats of poly.

Let the floor dry free of solvents overnight, and start by screening the floor to provided the small scratches needed for polyurethane to stick to it. Rent a floor maintenance machine and use a 100 grit screen to do this task. Run the buffer in both directions never stopping in any spot, just a nice easy back an forth motion. Go with the run of the wood, then repeat again against the run of the floor boards. This assures you that all low spots on the floor will have the finish well scratched. Next, get on your hand and knees and scuff sand the floor in all the areas that the buffer couldn t reach. All along the edges.

One you have a 100% scuff sanded finish, and it feels as smooth as a baby s behind, you can start cleaning up. Vacuum twice again, with your industrial vacuum. Get into all the corners of course. Now you can tack rag the floor. I use white lint free rags (yes you can get lint free cotton rags at most big box stores , expensive but worth it). Choose the most lint free in rag in the box, and wet it well with paint thinner. In this case paint thinner is just right, it dries at just the right rate for cleaning the floor. Fold the rag in a long narrow bundle and using both hands on your knees wash the floor in a back and forth sweeping motion as you crawl backwards.

Allow the solvent to completely dry up, and then BRUSH on a coat of polyurethane according to the direction spelled in great detail in my “How to Apply Polyurethane Without the Bubbles”. You just need to apply one single carefully brushed on coat.