Tips for Tackling Floor Sanding

sanding down hardwood floors with a standing sander
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Sending hardwood

Sanding hardwood floors is an essential part of many remodel jobs. Here is some expert advice on where to start, how do minimize the mess, and which tools work best.

prepping the room for a sanding job
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Prep the room

Some of the prep work is obvious, like removing all the furniture and covering doorways with plastic. Here are some steps some people often don’t think of:

  1. Cover or plug air grilles to keep dust out of ducts. Turn off the HVAC system at the thermostat; less air movement means less dust traveling around your house.
  2. Remove or wrap up all window coverings and any art on the walls (unless you want to clean them later).
  3. Remove doors that open into the room. You can’t completely sand under doors, even by opening and closing them.
  4. Raise low-hanging light fixtures; just tie two links of the chain together with wire. Otherwise, you’re guaranteed to bump your head...repeatedly.
  5. Nail down any loose boards with finish nails.
  6. When you’re sanding, nail heads will rip the sanding belt (which costs money) or gouge the sanding drum (which costs even more money). So countersink all nails by at least 1/8 in.

rental tips for floor sanders
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Rental tips

You’ll need two rental machines: a drum sander to sand most of the floor and an edger to sand along baseboards. Here are some tips:

  1. Rent from a flooring specialty shop rather than a general rental store. You’ll get expertise at no extra expense.
  2. Measure the room. Knowing the square footage will help the crew at the rental store estimate how many sanding belts and discs you’ll need.
  3. Prep before you rent. The prep work will take longer than you think. Don’t waste money by picking up the sanders before you’re ready to use them.
  4. Get a drum sander that uses a continuous belt or sleeve, not one that requires you to wrap a strip of abrasive around the drum. That’s tedious and often leads to chatter marks on the floor.
  5. Think twice before you rent a flat-pad sander (aka “orbital” or “square-buff” sander). Sure, they’re easier to use, but sometimes they’re just not aggressive enough to bite into finishes or hardwoods.
  6. One critical feature: Choose a sander that has a lever to raise and lower the sanding drum. That makes graceful stops and starts easier—and reduces gouging.

Change belts open
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Change Belts often

Using dull belts is a strategy you’ll regret. Here’s the problem: After the floor finish is gone,  you can’t see whether the sander is doing its job. So you keep sanding. The machine is raising dust and everything seems fine. But the dull paper isn’t cutting deep enough to remove the scratches left by the previous grit. And you may not discover this until you put a finish on the floor. A dull edging disc is even worse, since it won’t remove the ugly cross-grain scratches left by the previous disc. Even if paper feels sharp, it may be beyond its prime. So the best way to judge is by square footage covered. One rule of thumb is to change the belt after sanding about 250 sq. ft., and edger discs are spent after about 20 sq. ft. That varies, so ask at the rental store, or check the specs on the belts or discs.

Edger Education
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Minimize swirl marks

The edger is basically a sanding disc mounted on a big, powerful motor. A simple tool, but not so simple to use. Here are some tips to help you master the edger and minimize the inevitable swirls left by the spinning disc:

  1. Follow up each phase of drum sanding with edging. After you’ve drum-sanded at 36-grit, for example, edge with 36-grit.
  2. Place a nylon pad under the sand-paper. This cushion minimizes gouges and deep swirls.
  3. Replace the sandpaper when it’s dull. Dull paper won’t remove swirls left by the previous grit.
  4. At the end of the job, lay a flashlight on the floor to highlight any leftover swirls. Then hand-sand them out with 80- or 100-grit paper.

A warning to woodworkers: You’ll be tempted to edge with your belt sander, but even the biggest belt sander can’t cut half as fast as an edger. You’ll also be tempted to polish out swirls with a random orbit sander. But beware- that can over-polish the wood so it won’t take finish the same as the surrounding wood. Hand-sanding is safer.

Don't skip grits
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Don’t skip grits

The initial coarse grits remove the finish and flatten the wood. But that’s not enough. You need to progress through every grit to polish off the scratches left by the previous grit. On most jobs, the sequence is 24-36-60-80 for coarse-grained wood like oak. Scratches are more visible on fine-grained wood like birch or maple, so add 100-grit to the list.

Scrape out corners
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Scrape out corners

When the sanding is done, use a paint scraper to attack spots that the machines can’t reach. A sharp scraper will leave a super-smooth glazed surface that won’t take finish the same as the surrounding wood. So rough up scraped areas with 80- or 100-grit paper.

Clean up between grits
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Clean up between grits

Sweep or vacuum the floor before you move up to the next grit. Even the best abrasives throw off a few granules while sanding. And a 36-grit granule caught under a 60-grit belt will leave an ugly gash in the floor. Wrap the vacuum nozzle with tape to avoid marring the floor.

Screen the floor
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Screen the floor

After you’ve finished with the sanders, the floor will look so good that you’ll be tempted to skip this step. But don’t. “Screening” blends the edge-sanded perimeter with the drum-sanded field and polishes away sanding scratches. You can do it with a rented buffing machine or with a sanding pole (like the one used for sanding drywall). Either way, the abrasive to use is 120- or 150-grit sanding screen (again, just like the stuff used on drywall).