NOFMA Tip Sheet: Refinishing a Wood Floor
Why would a customer want to refinish a floor? For the older floor: to replace finish that no longer has a recoating option; to change the color or look; to follow a repair or allow a repair to occur. For the recently finished floor: to replace a problem finish; to repair sanding mistakes; to repair a damaged area.
The job begins with a review of customer expectations. Does the customer want to merely improve the appearance of the floor or does the customer want a blemish-free floor? Depending on the age of the floor and previous abuse a nearly blemish free floor may not be possible. Customer expectations will determine options for sanding and finishing and if the customer needs to modify their expectations with the selected choices.
Issues that Affect Refinishing
Wood species - In FCI July-August 05, we talked about staining or not staining certain woods. If the flooring is maple, staining may not be a finish choice. Unusual species may not be available for repair.
Abuse - Scratches, dents, pet stains, water stains, carpet pad stains may all require too much sanding to completely remove. Options are to replace and/or repair the board(s), or not to completely remove them. If the decision is to not completely remove the dent, stain etc., an understanding should be reached on the expected look after finishing. Pet stains in particular are a problem if the discolored area is not replaced. They can be muted if the flooring is to be stained.
Cupped or crowned floors - The cause of these issues should be determined and remedied before refinishing, otherwise they may return. If they are permanent conditions then sanding flat is a primary option.
Loose flooring - This can affect the quality of the sanding operation and/or finish performance. Waves, chatter, and uneven stain/finish application can result. Also, too much flooring movement can result in the top coated finish flaking or pealing along board edges. Options include fastening through the face or face nailing; or fastening from the underside if accessible. Again, what are the expectations; a loose floor most often cannot be completely cured. Also, a seal and wax system can be a great option to prevent finish flaking where most of the movement among boards cannot be eliminated.
Original finish - If the flooring was originally sealed and waxed, a new surface finish may not properly adhere so the option is to stay with the original system. If a surface finish is applied the customer should be advised of the possibility of pealing, then the question becomes "Are you responsible?" Also, if the original finish is white or very dark extra, sanding may be required to remove all of the existing finish.
Determine how much sandable surface is present. Check the thickness of the top groove lip. The limit for 3/4-inch flooring is when the thickness of the groove lip is near 3/32-inch after sanding is completed, and then only if the flooring has little or no movement among boards. Too much movement will crack the groove lip. For thin flooring and engineered flooring with a much thinner top wear layer, the groove lip is even more fragile. If movement is present top nail/screw and/or screw from below. Most of the movement must be eliminated for surface finish to perform; otherwise, a seal and wax system is a good choice.
Check areas that have been abused and repair/replace as discussed with the customer. If the floor has been covered by carpet or vinyl, the abuse may not be discovered until the floor covering is removed. A re-evaluation may be necessary once the floor covering is removed. Remember, a repair is should not be noticeable from a standing position.
For repairs, choose pieces with a similar grain pattern. To repair holes, use plugs with similar grain, acclimate new wood to existing conditions and chose filler that matches the wood color. When face nailing pick the open grain to hide the filled nails. When filling gaps, clean the gap then fill completely from the tongue up. Don't fill large gaps or gaps where the boards move. Instead, shim or sliver large gaps.
After the repair, the object is to remove the old finish and flatten the floor. Start by sanding on an angle of 30 to 15 degrees with the direction of the flooring. Use the grit necessary to remove 70-80 percent of the finish,. With an old floor it may be necessary to use a very coarse grit to start, 30, 24 even 20 or 16, if the finish loads the sand paper rapidly. Remember, for the coarser grits more passes will be required since you can only skip one grit level to get to the next pass. Again, know the conditions and explain to the owner the required extra work before proceeding in order to cover the cost of the extra time and materials. Also, we are not in the sanding dust business, so sand only with the grit necessary to do the job correctly. Don't be the one who has over-sanded the flooring and caused a premature replacement. The flooring should last the life of the home and can be refinished 6 to 10 times with normal wear and quality refinishing techniques.
From this point the finishing operation is generally the same as with a new site-finished floor.
A new floor that requires a refinish because of finish or sanding problems: the customer is often concerned that a high percentage of the life of the flooring is lost. If the floor is flat and not marred with excessive sanding dips or drum stops subsequent sanding should remove only the finish and minimal wood, generally less than 1/64 inch. So, depending on how much material was removed initially, the floor will have lost little of the overall life with a proper refinish.
Engineered Flooring: be careful. A refinish can yield great results with careful sanding if the flooring is flat and has minimum over-wood and under-wood. Start with a medium or fine grit, 50, 60, or 80 grit. Even with a 1/12-inch thick wear layer one refinish is certainly possible. But that is not the case with an uneven, rough floor, or one that has been abused.
Refinishing a factory finished solid wood floor: the 15-, 25-, 50-year warranties don't cover abuses that result in scratches, gouges, pet stains, planter stains, etc. When the abuse becomes obvious and the bare wood is exposed, refinishing becomes an option. Most of these floors have some kind of edge modification, a bevel or round over, to which a finish has been applied. Finish must be removed from these edges in order to have a clean surface for the new finish. Extra wood will likely be removed during sanding; it depends on the depth of the edge modification as well as the extent of over-wood/under-wood. Sanding off the new finishes with the wear additives can also be difficult. Sand paper dulls quicker so more is required. You would think the coarser grits would remove the finish more efficiently. This may not be the case, if you have difficulty removing the finish and don't want to put a deep scratch in the floor that you have to remove by extra sanding passes, try using a finer grit, 60, 80 or 100. Once most of the finish is removed, the regular sanding and finishing processes can be completed.
Communicate with the customer. Determine customer expectations and whether or not they can be met. Offer options if the situation will require modification. Assess existing conditions, repair as necessary, particularly where movement is present in the flooring. Begin the sanding process with angle cuts. Think out side the box with special conditions such as sanding a factory finished floor with a fine grit to remove finish. Complete the sanding and finishing in a professional manner and both you and the customer will be pleased with the results.
The photos included with this article are a refinish of a 1930s, 9-by-9-inch, 3/4-inch solid, bevel edge, factory finished, waxed, parquet that had been covered by a glued down carpet. The floors had significant abuse, gouges, divots, water damage, uneven areas, nails and screws, and wide gaps. A small area was repaired along a wall line where the floor had been patched. The customer had very low expectations and was planning to replace the carpet. Her directions were for a minimum cost refinish and if the results were not presentable as an office, carpet would be installed. The flooring was sanded and stained with two coats of a penetrating oil finish, and waxed. The results were far beyond the customer's expectations.