How to Screen and Recoat a Worn Floor Finish

Why this matters

A screen and recoat is the cheapest way to make a dull wood floor look new and the job most likely to fail in the customer's hands a week later, when the new coat peels off in sheets under a chair leg or a strip of tape. The new finish has to bond to the old one, and anything sitting on the old finish, such as wax, an acrylic polish, a spray "restorer" or silicone from furniture polish, stops it bonding. The floor looks the same either way when the crew arrives. The only way to know is to test before committing the whole floor, which is why this card puts the tests first and the buffer second.

If the floor is worn through to bare wood or needs real sanding, it is not a recoat job; that is 'How to Sand and Refinish a Hardwood Floor'. Choosing the new finish is 'Hardwood Floor Finishes for Refinishers'.

The gate: four questions before any abrasion

A recoat is the right job only when the answer to all four is yes.

1. Is the wear only in the finish? Walk the floor in normal light and look at the traffic lanes, the front door, the kitchen sink and under the dining chairs. Dull, scratched finish over wood that still has its color is recoatable. Gray, bleached or darkened wood with no finish on it is worn through, and a recoat seals that look in rather than fixing it. Worn-through areas go to a full refinish.

2. Is there wax on it? Ask what the floor has been cleaned and treated with, then test. Mineral spirits are flammable: use a small amount on a cloth, with ventilation and no flame or pilot light nearby, and take the cloth outdoors afterward. A common field test: dampen a white cloth with a little mineral spirits and rub a small spot in a corner; a yellow or brown smear on the cloth suggests wax. A drop of water left on the floor for several minutes that turns the spot white or hazy also points to wax. No finish bonds over wax. A waxed floor needs its wax removed by the method the finish maker accepts, or a full sanding.

3. Is there polish, restorer or silicone on it? Acrylic floor polishes and "restore and shine" products sit on top of the finish and lose their bond under a new coat. Silicone from spray furniture polish drifts onto the floor around tables and chairs and makes new finish crater into small circles called fisheyes. Neither shows reliably on a simple test, which is why question 4 exists.

4. Does a test patch bond? Clean, abrade and coat a small patch exactly as the whole floor will be done, let it cure, and run a tape adhesion test. This is the only answer that covers what questions 2 and 3 cannot see.

Step 1: Patch and test, in more than one place

Pick at least two patch locations: one in a high-contamination area (the kitchen near the sink, around the dining table, by the front door) and one in a quieter area. Each patch is about 2 ft by 2 ft. Do Steps 2 to 5 below on each patch only, with the same cleaner, abrasive and finish planned for the floor, and leave them to cure for the time the finish maker states before testing adhesion.

The tape test. With a sharp blade, cut a small cross-hatch grid through the new coat in the patch, press the tape the method or the finish maker names firmly over it, and pull it off sharply. ASTM D3359 describes the cross-cut method and how to grade it; the finish maker states what counts as a pass for its product. Generally, a pass removes little or no new finish at the cuts. Flakes pulled off in squares, or a sheet lifting with the tape, is a fail, and the whole floor would behave the same way.

Why two places. Contamination is local. A patch by the window passes; the area under the dining table, where chair-polish overspray has landed for years, is where the floor will peel.

Step 2: Clean with the finish maker's cleaner

Clean the floor with the cleaner the new finish's maker specifies for recoat prep, or its prep system, and let it dry fully. A generic cleaner can leave its own residue, which is one more thing between the old finish and the new one.

Step 3: Abrade the whole surface

Run a buffer with a sanding screen or abrasive pad of the grade the finish maker names, along the grain, overlapping passes, until the whole surface is evenly dulled with no shiny spots left. Hand-abrade the edges, corners and under toe kicks with a pad. Some finish makers sell a chemical abrasion system instead of screening; follow its own steps if you use one.

Why every inch. The new finish holds by gripping the scratch pattern in the old. Cut through the floor, a screened area and a missed one look like this:

          screened, evenly dull   missed, still shiny
 new coat ======================  ======================
          \/\/\/\/\/\/\/\/\/\/\/  ----------------------
 old      scratched: the new      smooth: the new coat
 finish   coat keys in, holds     rests on it, lifts
          ----------------------  ----------------------
 wood     | | | | | | | | | | |   | | | | | | | | | | |

Hazards. A buffer has strong torque and will swing sideways if the handle is lifted or dropped suddenly; start it with the handle at hip height and both hands on, and keep the cord behind you. Screening dust is fine old finish, so run dust extraction, and where it cannot be controlled, use respiratory protection under a written program per 29 CFR 1910.134 (applied to construction by 29 CFR 1926.103).

Step 4: Vacuum and tack

Vacuum the floor, the baseboard tops and sills, then the floor again. Tack with the dry cloth or microfiber the finish maker names. Dust left on the floor becomes grit in the finish.

Step 5: Apply the compatible finish

Apply the finish the maker lists as compatible over the existing type, at its coverage and with its applicator, working with the grain and keeping a wet edge. For solvent-based finishes, shut off and extinguish every pilot light and ignition source in the area before opening the can and keep them off until the vapor has cleared as the SDS describes; then relight each per its appliance maker's instructions and confirm it lights and stays lit, and one that will not stays off for a qualified gas technician. Lay finish-soaked rags flat outdoors to dry or keep them in a water-filled closed metal can.

Worked example: one house, two answers

The house. A kitchen and dining area of about 300 sq ft and a front hall of about 120 sq ft, all 3/4 in solid oak finished eight years ago. The hall meets the kitchen at a doorway where the boards butt a header board, a natural break line. The customer cleaned with a spray mop and, every few weeks, sprayed polish on the dining chairs.

Question 1, wear. The kitchen and dining area: dull traffic lanes and fine scratches, all in the finish; the wood kept its color. The hall: a gray, bleached patch about the size of a door mat just inside the front door, worn through to bare wood. The gate splits the job. The hall goes to a full sand and finish per the refinish card, stopping at the header board. The kitchen and dining area stay a recoat candidate.

Question 2, wax. The mineral-spirits cloth came away clean in two kitchen corners, and water drops left for several minutes stayed clear. No wax.

Question 3. The customer named the chair polish, so a silicone concern went on the sheet.

Question 4, patches. Patch A by the sink and patch B under the dining table were cleaned, screened and coated, then left the 24 hours this product's maker gives before adhesion testing. When the finish went on, patch B showed a scatter of small craters, the fisheye sign. At the tape test:

The fix. The finish maker's guidance for silicone and polish contamination called for its stronger cleaning step before abrasion. The crew re-did patch B with it beside the original patch: no fisheyes, and the tape test lifted nothing. That passed patch decided it. The whole dining area got the stronger cleaning, the kitchen got the standard cleaner, and then both were screened and coated together.

The care sheet names the chair polish and asks the customer to apply it away from the floor, since a recoat is only as good as the next coat's chance of bonding.

What changes the answer

• A factory-finished floor. Many prefinished floors carry a very hard factory coating with aluminum oxide in it, which screening barely scratches. Some finish makers sell a system for recoating it, often with a bonding or adhesion-promoting step, and the floor maker may have its own instructions. Without one of those, the patch test is likely to fail however well the floor is cleaned.
• Changing finish type. Going from an oil-modified finish to a waterborne one, or the reverse, is allowed by some makers over a fully cured, properly abraded coat and refused by others. The new finish's maker decides, and the patch test confirms it on that floor.
• A floor recoated several times. Each recoat adds film. Past some point the film starts to look plastic and to chip at board edges, and the honest answer is a full sanding back to wood.

How to check you got it right

• The test patches: each passed the tape test after the stated cure, and any failed patch was redone with the corrective step and passed before the floor was coated.
• The floor: after full cure, a cross-hatch tape test in an inconspicuous spot, such as inside a pantry, using the same method, lifts no new finish. The result goes on the job record.
• The look: standing in the room's normal light, an even sheen across the floor, no fisheyes, no shiny unabraded spots showing through, and no lap marks along the grain.
• The break line: where a recoat meets a full refinish, as at the hall header board here, the change happens at a natural line, not mid-room.

References

• ASTM D3359, standard test methods for rating adhesion by tape test
• 29 CFR 1910.134, respiratory protection
• The finish maker's recoat instructions and SDS, which govern cleaners, abrasives, compatibility, cure time before testing and ignition controls
• See related: How to Sand and Refinish a Hardwood Floor; Hardwood Floor Finishes for Refinishers; Sanding Machines and Grit Sequences