Random orbital 3-head floor sander. Detailed Article:

Refinishing Hardwood Floors
Part 2:
Removing Old Finish With A Random Orbital Floor Sander

 
In This Article:

Old oak flooring is sanded with a rental floor sander. Special attention is given to edges and low spots. Discussion of sanding strategy, progression of sanding grits and sandpaper usage.

Related Articles:
Skill Level: 2-3 (Basic To Intermediate) Time Taken: 3 Days

By , Editor

Start:

After the closet doors, heat registers, and baseboard had been removed, I went to Lowe's and rented the Varathane ezV floor sander. The ezV is a 3-head random orbital sander that uses 7-inch sandpaper discs, which cost about $5 for a 3-pack.

I also bought a large supply of sandpaper, so I wouldn't need to rush back to the store if I under-estimated. It's much easier to return unused sandpaper than to keep driving back for more. At the end of the article I'll explain how much sandpaper I used.

Before sanding, we vacuumed the floor.

 

We carried the sander upstairs and installed 36 grit sandpaper on the machine.

My friend Tod started sanding the floor while I worked around the edges.

This machine has two power switches: One for the dust-collecting vacuum and another for the sander motor. It's probably best to turn on the vacuum first, and turn it off last.

The ezV sander is truly easy to operate. It doesn't require any great strength to move around. It doesn't pull forward like a drum sander, giving you incredibly sore arms by the end of the day.

There is no special pattern to follow when sanding, but it makes sense to be systematic to be sure that all areas get the same treatment.

 

This was Tod's first time using a floor sander. He just started in one corner and ran the machine backwards about halfway across the room, then forwards to the wall.

To slide the machine sideways, he just raised the handle so the wheels lifted off the floor and set them down a couple of inches to the right.

 

In about 15 minutes, Tod had half the room sanded.

But it wasn't really that easy. That initial sanding had only scraped off the very tops of the slightly-cupped boards, and there were lots of narrow strips that still had varnish.

 

After about 2 hours of 36-grit sanding, many of the larger scratch marks remained, and also lots of low spots that still had varnish.

Some of the scratches and gouges appear dark because the wood had been stripped bare and allowed to weather, as well as collect dirt.

I had to make a decision... try to remove these marks with the big floor sander, which can be painfully slow... or use a small hand-held sander to focus the sanding efforts directly on the scratch.

 

A High Spot:

After some sanding, I could see a long spot that was being sanded heavily, and it was right next to a strip that was not being sanded.

I could feel a ridge in the floor, and when I pressed on the ridge the boards moved.

I pre-drilled a couple of pilot holes and drove in some 2¼" trim head screws.

After this, the board wouldn't move when I stepped on it.

 

 

Edge Treatment:

I used the small sander to reach the details around the doorway. I didn't remove the casing in these areas because I'm planning to remodel these rooms in the near future.

 

There was a strip of paint beneath the baseboard. While this may get covered up when the trim is replaced, I didn't want to take any chances.

Some of these paint lines were kinda high, which would take a lot of time to remove with the small random orbital sander.

 

This is a carbide-edged paint scraper, about $13 at Home Depot. Carbide-edge paint scraper.\

 

Scraping paint from hardwood floor during refinishing process. The easiest way to remove narrow lines of paint is to scrape them.

 

The paint lines almost disappeared with a little scraping.

 

On the end grain, I held the scraper at an angle. This didn't work terribly well, but it did remove the high spots.

 

Attention To Detail:

Near the ends of the boards there was a visible groove (a dark stripe about 4 inches from the wall) left over from the original drum sanding. This would take forever to sand with the floor sander.

 

Low spots visible in hardwood floor after initial sanding. After the initial sanding with 36 grit paper, there were lots of low spots visible, like these patches at the edges of the boards. All these boards have a slight crown, so the centers of the boards got sanded before the edges.

I could use the floor sander for a long time on areas like this, or I could just use another tool to reach into the "valleys".

 

To reach into the valleys, I used a 5" random orbital sander.

 

Portable random orbital sander technique for sanding low spots. The trick is to lean the sander by lifting the back side.

I used 40 grit sanding discs for fast material removal.

 

My Sanding Strategy:

The coarse sanding represents the vast majority of the time required to refinish a hardwood floor that is in poor condition. In my case, the coarse sanding used up perhaps 80 to 90 percent of the total sanding time.

The goal of coarse sanding is to:

  • Remove old finish
  • Knock down high spots
  • Remove nicks and scratches
  • Most importantly, create a reasonably uniform appearance that is not too splotchy.

The goal of sanding with 50 and 80 grit sandpaper is to simply remove the scratches left by the previous grade of sandpaper.

Since the coarse sanding consumes so much time (and sandpaper) it make sense to develop some technique. Some important facts:

  • Old floors have cupped boards.
  • Old floors have scratches and gouges.
  • There may be some high and low spots where boards have shrunk over the years.
  • Previous sanding was probably done with a drum sander, so there will likely be a groove at the ends of the boards.
  • When new sandpaper is installed on the random orbital floor sander, it cuts REALLY WELL. Deceptively well. After about 2 or 3 minutes the sandpaper wears down noticeably. It still removes wood, but not as fast as those first few minutes.

You could change the paper after 3 minutes of sanding and you'll be done quickly, but at 5 bucks per set of sanding discs, you're burning money at the rate of a hundred dollars per hour.

After 20 or 30 minutes of sanding red oak flooring, I found that the 36 grit paper still felt quite new. Yet it didn't work terribly well. I could continue using the sandpaper, but it made economic sense to change the paper even though I knew there was still life in it. I found that using the 36 grit paper for 30 to 60 minutes seemed to work best for me.

If there was a spot that needed extra sanding, I would run the machine over it during the first three minutes after new sandpaper was installed. After new sandpaper is installed, the machine makes an odd noise... it sound like a bunch of seals wrestling. I call it the "squirmy" sound. Arf arf arf. When the sound stops, the sander performance drops noticeably.

Sanding with this machine gets boring. If you hold a drum sander in one spot for too long it will bore a hole all the way to the basement, but this random orbital sander is completely different. I discovered that I could let the sander sit in one spot and it didn't make a huge divot in the floor. All that happened was the floor got warm. After 5 minutes in one spot... maybe 10 minutes.

Well that gave me an idea. Since there were lots of small spots that needed sanding with the hand-held random orbital sander, I positioned the floor sander where the wood needed a lot of sanding and just let go. I got down on my knees and used the small sander to touch up the low spots that the big sander couldn't reach. I used the 5" sander to remove the gouges and scratches while I monitored the big sander. That machine seems to have a mind of its own. It can linger in one spot for minutes on end, or it can wander away. My two-sanders-at-a-time approach definitely worked faster and was less tedious.

This machine was running when I took this picture.

 

A couple of seconds later, it had moved. By itself.

Just don't leave it running unattended.

 

More Sanding Strategy:

When I use a hand-held sander and the sandpaper begins to wear down, I can get better sanding performance by simply pressing down harder. When the sandpaper gets slightly worn, I think the granules are just skating over the surface, unless you force them to dig deeper.

So I tried the very logical thing... I pushed down on the floor sander. I just pushed on the handles, or the motor. Guess what happened? The machine worked better... I could tell because it began to make that "squirmy" sound that it makes when new sandpaper is installed. And I could hear the motor slowing down, like it was actually being forced to work.

As the sandpaper wore down more, the squirmy sound went away. Unless I applied more weight. For a few brief moments I sat on the motor, using my feet to navigate the sander. I envisioned an improved floor sander that could be ridden like a lawn tractor. But... there is a cooling fan on top of the motor, just below the metal end cap. Sitting on the motor places a guy's.... a-hem.... family jewels... about 1/8" away from a fast-spinning shredder. Protected only by a thin, perforated piece of steel. No thanks.

I decided to limit myself to simply pressing down on the handles with my hands. While the machine performs better, I doubt that the manufacturer of the sander considers this acceptable. Being that close to the moving sanding heads may pose a risk of injury.

Warning:

If you try pushing on or adding weight to this floor sander (or any other floor sander) then you assume the risk of personal injury or damage to the machine.

For maximum safety, follow the manufacturers directions.

This description of my floor sanding technique is for entertainment purposes only. Do not consider this article to be any sort of instructions or directions.

 

 

Stain Removal: A Vain Attempt

Before refinishing there was this large black stain near the wall.

At first I thought it might be mildew, but a dab of chlorine bleach didn't remove it.

After some initial sanding, I applied some wood bleach, which contains oxalic acid, to the area. I waited and re-applied the wood bleach several times, but it did nothing.
I rinsed off the wood bleach and applied some phosphoric-acid-based rust remover chemical. It didn't work either.
After some heavy sanding.

While less noticeable, this stain just wouldn't go away.

I suspect this black mark is caused by rusted steel. Rust causes black stains in wood. Maybe a previous owner had a triangle-shaped plant stand with a steel base and spilled water got trapped underneath and rusted the base.

 

Notice the dark veins (red arrows).

I believe this happened when the varnish wore off and dirt filled the pores, turning the wood black. This is a consequence of not maintaining hardwood floors.

Heavy sanding removed a thick enough layer of wood to make the dark grain disappear.

 

Notice dark grain in the center of the photo. This is another example of dirt getting into the open grain because the finish had worn off.

Heavy sanding removed the dark-striped grain.

 

At this point I was done with the coarse sanding.

 

Changing Sandpaper Grades -
What To Look For:

Before sanding with a finer grade of sandpaper, it's important to vacuum the floor to pick up the chunks of abrasive that break off.

After a few minutes of sanding with 50 grit, I noticed the sander was leaving some larger scratches, and there were small rocks on the floor from the 36 grit paper.

You can't rely on the sander's built-in vacuum to suck up all the loose grit.

This is the scratch pattern from 36 grit paper. I sanded with 50 grit until marks like these were gone.

The only way I could see these marks was under a very bright light.

 

I used the Fein Multimaster to sand the corners.

Of course, this could be simply done by hand.

I used one or two packages of 50 grit sandpaper for each room. It took about 30 to 45 minutes of sanding to remove all the scratches from the coarse sanding.

Then I vacuumed the floor and switched the sandpaper to 80 grit. It took one package per room, and about 30 minutes of sanding to remove the barely-visible scratches left by the 50 grit. I couldn't see any scratches from the 80 grit. 

 

Sandpaper Usage:

I used A LOT of sandpaper. To sand 3 rooms, totaling about 400 square feet, I used:

  • 16 packages of 36 grit sandpaper.
  • 4 packages of 50 grit sandpaper.
  • 3 packages of 80 grit sandpaper.

The sandpaper still had some life left in it. I saved the partially-worn sanding discs to be used for hand-sanding other carpentry and woodworking projects.

 

Continue To Part 3: Applying Urethane

Or Read:

 

More Info:

Tools Used:

  • Varathane ezV Floor Sander
  • 5" Random Orbital Sander
  • 2" Carbide Paint Scraper
  • Detail Sander (Fein Multimaster)
  • Vacuum Cleaner
  • Bright Light, Portable

Materials Used:

  • 7" Sanding Discs, 36, 50, 80 Grit
  • 5" Sanding Discs, 40 Grit
  • Trim Head Screws, 2¼"
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Written September 6, 2006