- Introduction
- Tools, required materials and tips
- Renting the proper equipment
- Tips and tricks before you begin
- Choosing the initial grit
- Sanding 101
- Operating a floor sander
Which sandpaper should I begin with?
In order to remove an old finish, the starting grain of your sandpaper should be the one that is the least aggressive possible while still allowing the finish to be completely removed, all the while leveling the floor as much as possible. In general, 36 grit is a good starting point, but this may vary depending on the type of finish you're trying to get rid of. Therefore, testing 36 grit beforehand will help determine the ideal grit type to start your project. If you believe your floor is in great condition, attach 36-grit sandpaper to your sander and sand a test surface, approximately 4 feet by 4 feet (or 1.3 meters by 1.3 meters). Try to sand an area of the floor where damage, grooves, scratches, etc. are particularly noticeable, following the direction of the wood grain. Once it's done, turn off the sander and carefully inspect the freshly sanded area. If it's nice and clean, even at the edge of the boards, then you have determined that you will need to sand gradually starting at 36, to 60, 80 and then to 100 or 120 grit. However, a few exceptions apply here:
- A brand new hardwood floor that has never been finished, if it is in very good condition, probably does not need to be sanded by with a 36 grit abrasive. In this particular case, starting with 60 grit abrasive paper might be more suitable.
- In addition, if your floor was factory finished, there is a possibility that it might have been finished with a high abrasion resistance finish made from aluminum oxide, which may be difficult to remove initially if using coarse grain. Finishes designed for high abrasion resistance are usually removed more easily by starting sanding with a finer grit (80 or finer, ceramic-based), and then starting again with a coarser grain (36 -> 60 -> 80 -> 100/120). The finer grain initially will allow for an easier removal of the aluminum oxide layer on the surface, and then allow the coarser grain progression to sand much more efficiently.
On the other hand, if the freshly sanded 36 grit test surface is not completely free of defects, then you will have to use an even more aggressive sandpaper to start with. In this case, find a new 4ft by 4ft area on your floor and sand with 36 grit, but this time maneuver the sander against the wood grain, followed by another pass, this time in the direction of the grain. Sanding perpendicular to the wood grain removes the finish and eliminates material more quickly. Again, carefully observe the freshly sanded surface. Is it satisfactory? If so, well done! You have determined that you will need to start with a 36 grit abrasive, sanding perpendicular to the wood grain, then follow the wood grain with the same abrasive, and move on to 60, 80 and 100 / 120 grit.
If the result is still not satisfactory, you will have to use a more aggressive sandpaper and repeat the steps below, until you find the combination that gives a satisfactory surface after sanding with 36 grit paper. If you are convinced that your floor is in very poor condition, you can start immediately with 24 grit, especially if you are using an orbital sander running on 120v, since it will be much less aggressive than a belt sander plugged into the 240v outlet
Note that if the floor was covered with old paint, shellac or wax, it will be important to move the sander quickly with as little pressure as possible in order to minimize heat production, as too much heat will liquefy these old finishes and could damage the sanding equipment, in addition to quickly stuffing the abrasive. In addition, if you sand a floor that has been stained a very dark or very light color, there is a possibility that the color will remain in some areas where the wood is softer or in small cracks, because the stain will have penetrated deeper into the wood fiber. In this case, you will need to sand using a more aggressive / coarse grit over the entire surface to remedy the problem. Finally, on old floors that have been repaired with filler, fragments may lift up during sanding, due to the movement of the floor during the restoration work.
Can we skip steps in certain cases?
Skipping sanding steps may seem like an easy shortcut to save time and money, but it's not necessarily a good idea. Much depends on each specific situation, and without experience it is risky to do so. Unless you are a seasoned professional with a lot of experience, skipping sanding steps is generally not recommended. If you do so, you might run into some issues. For example, if the previous sanding grit (e.g. 60 grit) left sand marks that you did not correct and you jump straight to 100 grit by omitting the 80 grit pass, you will need to spend a lot of time trying to remove these grooves with paper that is too fine for the job at hand. In addition, the paper will quickly jam with dust before it can really attack the surface and previous blemishes.
According to Sylvie Plasse, a technical specialist in abrasive systems and methods for Abrasives JJS / Sia Canada, the only step where you can technically skip a sanding grit without worry is during the initial sanding. If a hardwood floor is new and appears uniform and has never been finished beforehand, it is possible to start directly at 60 grit rather than starting at 36. Luc Pelletier, at MC Crystal, a flooring specialist, has a similar, albeit slightly nuanced, approach: "As floor sanding pros, you can quickly tell with a quick visual inspection if a grit can be skipped, say 60 to 100 (skipping 80), but a rule to always keep in mind is to NEVER skip more than 1 grit". Keep in mind that professional hardwood floors sanders always use very powerful belt or drum sanders, so skipping a sandpaper grit can save time in some cases. For a neophyte with little experience and a 110v orbital sander? This could prove to be counterproductive, especially if you overestimate the quality of your sanding and don't do a thorough inspection between each step. In short, it's up to you, but you've been warned!
Work in two sanding zones per room
The surface of the floor to be sanded should be divided into two parts of similar length. It is also important to ensure that you do not start or end a sanding pass on a highly visible surface whenever possible. Once one side of the room has been sanded with a specific grit, rotate the sander in the opposite direction and repeat the process on the remaining part of the floor. The sanding of the second part should overlap the first part for a width of 2 to 3 feet in order to even out the result. In order to avoid creating a trough where the overlap occurs, be sure not to stop the sandblaster in the same place on each pass.
