I talk to people all day long about wood floors and sanding procedures. But even the most open-minded DIY-er comes to me with many preconceived notions that are incorrect. And they hold on to these notions as though they were commandments. But what I find astonishing is how many people have the same misconceptions. Is some version of Typhoid Mary out there, spreading and repeating misleading information about floors?
I found a 1951 edition of the Better Homes and Gardens’ “Handyman’s Book” that explains a lot, but it doesn’t account for all these mistaken beliefs.
“I’ve run lots of construction tools; I’ll be able to just teach myself the drum sander.”
The drum sander is the single best, most efficient way to sand large areas of floor down to bare wood, but learning to run a drum sander is a lot like learning to run a clutch: it’s almost impossible to get the hang of it by yourself. In 15 years of teaching the drum sander, I have yet to meet someone who could feather the drum down smoothly enough on the first try to avoid leaving a dig mark, especially on the backward pass. Unless you have a place to practice where stop marks won’t matter, your practice flaws will become a permanent part of your floor.
Still worse, most first-timers think their technique is smooth and, unless corrected, keep using the same flawed technique and don’t realize it until after the first coat of finish is applied. Which is a little too late. If you don’t have the benefit of a coach, at least look for these signs of good technique. A properly feathered stop will look like the photo on the right.
If the endpoint of any of your sanding strokes looks like the photo at left, you are letting the drum land on or leave the floor too abruptly.
“Floors only need three grit cuts: coarse, medium, and fine, right?”
Nope. Floors need as many passes as it takes to make them clean, flat, AND smooth. On floors in very good condition, that may happen in three cuts, but those floors are the exception, especially if you are working with light 110v rental drum sanders or using a three or four-head orbital. The age of your floor, the type of wood it is and the amount of finish still remaining on it are all huge variables that can increase the number of grit passes up to six!
There are six grits available for floor sanding: 12, 16, 24, 36, 60 and 80. If your floor has old adhesive or paint, and you are forced to start at 12 grit, you cannot count that as your coarse pass and jump to 36 for your medium, then up to 80 for your fine. Here’s why - though the floor will be clean, it will be rough and visibly scratched. If you automatically start at 36 grit (no matter the quantity of old finish), followed by 60 and 80, you won’t have any sandpaper scratches, but you will still have old varnish clinging to the edges of your boards. So be open and ready to passing a few times more, should your floors need it.
“Oh, I don’t need an edger, I’m going to use my palm sander.”
Palm and belt sanders work great on surfaces that are flat. But as you can see by the photo at left, floors aren’t always flat. Little sanders may be easier to control, but they aren’t strong enough to grind down high spots. So any areas of the floor that are even slightly concave simply don’t get clean because light sanders like a palm sander can’t sand down that far. The result is clean wood where the palm sander could reach and lots of finish residue in the lower spots, even after hours of sanding.
The floor pictured on the left was not an old or neglected floor, and it looked flat before the project was started. This customer ended up renting a drum sander and starting at 36 grit to remove all the finish that was still clinging to the edges.
Be advised: edgers, contrary to popular thought, are an excellent choice.
In part two, we'll consider three more misinformed beliefs about floor sanding. Stay tuned!