Sanding an old hardwood floor. Overview Article:

Refinishing Hardwood Floors
With A Random Orbital Floor Sander
An Overview

In This Article:

Baseboard and door casing are removed. The wood floor is sanded with a rental floor sander to remove all scratches and old finish. Four coats of urethane are applied.

Related Articles:
Skill Level: 2-3 (Basic to Intermediate) Time Taken: Too Many Days

By , Editor


NOTE: This article is a summary of 3 detailed articles on floor refinishing:




Maybe you've seen them. The young couple that just bought their first house. Lots of first-time home buyers purchase an older house, maybe something built in the 1950's or 60's. In those days lots of houses were built with hardwood floors. Perhaps the original floors were simply neglected, or maybe somebody installed carpet over the hardwood. Wood floors went out of style during the 60's and 70's.

Today everyone loves wood floors... and for good reason. Hardwood floors cost more initially but are cheaper in the long run. Carpeting harbors nasty allergens, and cats love to piss on it. But the best feature of a wood floor in simply the appearance. Beautiful... 'nuff said.

Maybe you've seen that young couple in Lowe's or Home Depot, salivating over new cabinets and appliances, picking up paint samples, checking out window treatments. Lots of young couples do all the work themselves. Their budgets are limited but their energy level is high. That's how you get ahead in this world... by working. Sooner or later... probably sooner... that couple decides to redo their hardwood floors.

Boy, are they in for a treat.

Hardwood floor refinishing falls in the category of do-it-yourself projects the average homeowner can probably handle. Hey, you've been reading my stuff... I do everything myself. Some home improvement publications advise you to hire a professional for everything except painting and cleaning. Not me. I'll show you what I did, and you can make your own decision whether to try it or hire it.

I recently bought a 1963-vintage sorta-kinda-Cape-Cod style house. It has red oak floors throughout, but somebody carpeted over half of it.

I refinished the 3 rooms with wood floors, measuring about 400 square feet. Sanding took three days, though I might have done it in two if I had a helper the entire time. I applied 4 coats of Varathane® oil-based satin urethane floor finish, which should have taken only 4 days, but I had some problems caused by humidity. I rented the sander on August 23rd, and I applied the last coat of urethane on September 3rd. Here it is, September 6th and the urethane has had three days to fully harden, so now I can use the rooms.

That's two weeks. I could have done this faster, especially if I hadn't messed up the second coat of Varathane. Do-it-yourselfers need to realize this is not a project that can be wrapped up in one easy weekend. It is possible to sand one or two rooms in a weekend, and apply the urethane in the evenings (or better... the mornings) of the following weekdays, and complete the project in one week, with a couple more days to let the floor finish fully cure.

Refinishing hardwood floors does involve some skill and a moderate degree of physical work. Mostly the work is just tedious. Carrying the floor sander up a flight of stairs should be done with a helper... this thing weighs about 120 pounds. Oil-based urethane makes a lot of odor, so the rooms need to be well-ventilated. Spring, summer or fall are the best seasons, but I've re-done floors in the winter, in Northern Michigan.

Winter can be a good time to apply urethane because the humidity is lower. The windows can be opened with a fan blowing the air out, but any return air registers in the rooms should be sealed up to prevent the fumes from being drawn into the furnace and spread around. It's best to wait for a couple of days of not-so-cold weather.


The Floors Before Refinishing:

When I bought this house, the hardwood floors were in really bad condition. I'd guess that these floors have never been refinished since the house was built in 1963.

This is the main floor bedroom/


The main floor bedroom, different view. The rest of the main level has carpet over the original hardwood floors.

The original varnish had become reddish-colored over the years.

I think there was more bare wood than varnished wood.


Trim Removal:

To gain access to the edges of the floor, I decided to remove the baseboards and door trim. Since I planned on re-painting the room, it made sense to remove the trim. I'll be able to paint the walls without masking the trim or enduring the tedious process of cutting-in. I can paint the trim a contrasting color... or I can replace it with a different millwork profile, which is the direction I'm leaning.

Since the paint appeared to be bonding the trim to the wallboard, I ran a sharp knife along the top edge of the trim to break this bond.

I almost always do this when removing trim on older houses.


I used two or three pry bars to remove longer sections of trim. I started at the easiest end, with a mini-prybar, and slowly worked the wood away from the wall.

I progressed along the board, trying to pry adjacent to the nails if possible.


I also removed the door casing.

I only needed to remove the side pieces to sand the floor, but I removed the top casing too.

This step could be omitted if the floor was carefully sanded around the casing. On the upstairs bedroom door I left the casing in place.

For more detailed information on the preparations for floor refinishing,
read Part 1: Preparations


Upstairs bedroom, before sanding.

I'm guessing that the previous owner had tried sanding the floor with a small hand-held sander, because each room had a patch of bare wood.

Note the fan in the window. This helps keep dust under control, and exhausts the fumes when urethane is applied.


This bedroom had dozens of major scratches and gouges in the floor. It looked like somebody had dragged furniture around with no attempt to lift it.

Beyond the bedroom door you can see another room. I call it the "useless room", because the stairs take up most of the area.


Before sanding, we vacuumed the floor to make sure there weren't any big abrasive chunks that would get caught under the sander and gouge the wood.


Floor Sanding:

I rented the Varathane ezV floor sander, which is a 3-head random orbital sander. It uses three 7-inch sandpaper discs, which cost about $5 for a 3-pack.

We started sanding the floor with 36 grit sandpaper.

The ezV sander is truly easy to operate.  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.


In about 15 minutes, my helper 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.


To fasten a couple of loose, raised-up boards, I pre-drilled several pilot holes and drove in some 2¼" trim head screws.

These high boards show up right away because they get sanded more than the surrounding floor.


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.


Edge Treatment:

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.

The easiest way to remove narrow lines of paint is to scrape them.


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.



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 took perhaps 80 to 90 percent of the total sanding time. The goal of coarse sanding is to

  • Remove the 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. For more information read the detailed article Removing Old Finish With A Random Orbital Floor Sander, which is part 2 of 3.


Notice the dark veins (red arrows). I believe this was caused by dirt that filled the pores and turned the wood black. Dirt got into the pores because the finish wore off and nobody ever bothered to re-finish the floors.

Heavy sanding removed a thick enough layer of wood to make the dark grain disappear. Then the wood looked just like a new floor being sanded for the first time.


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. The best technique is to shine the light sideways across the floor, and the scratches show up quite well.

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. Again, 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. 


Applying Urethane:

There are 3 important concepts to applying urethane floor finish:

  • It's important to maintain a wet edge.
  • Always back-brush.
  • It's best to apply urethane by brushing with the grain.


For the first coat, I used a "lambs wool" applicator to apply Varathane Oil-Based Satin floor finish.

(Normally I apply urethane in a more systematic, continuous pattern. I only did this for the photo.)

Applying polyurethane with a lamb's wool mop.

Note the organic vapor respirator. You need this. It uses a charcoal filter to absorb ALL the chemical vapors in the air you breathe.

In the upstairs bedroom, the only way I could maintain a wet edge was to brush across the grain.

So after applying a 3-foot wide strip, I used the mop like a push broom to "back-brush" the urethane.

The weather was cool and humid when I applied the first coat. I knew that the urethane would take longer to dry... no big deal. I finished up around 7:00 on a Saturday evening. Since the house kinda stunk, it was a good excuse to go out for dinner. I figured that the second coat could be applied sometime the next afternoon.

The Next Day:

After the first coat had dried I scuff-sanded the floor with 120-grit sandpaper on a pole-sander.


I also tried scuff-sanding the urethane with a 5" random orbital sander and 150 grit sandpaper.

I'm still not sure if machine-sanding is better than using a pole sander.

After scuff-sanding, I swept and vacuumed the floor.

To remove the last bit of dust, I wetted a paper towel with rubbing alcohol and gave the floor a good wiping.


I applied the fourth coat of urethane with a brush, just to see if the results would be any better than using a mop.


I would say that a brush is easier to control than a mop, because a mop often drools a trickle of urethane onto the floor, which needs to be spread around. Brush-applying urethane is certainly slower, but not as slow as you'd think. 

After the fourth coat, I let the urethane dry for 3 days before doing anything in the rooms. While the Varathane will be dry after a couple of hours, it takes about 72 hours to fully cure.


The End Results

After Refinishing:


Before Refinishing:

After   Before

Note how the floor has a red color in the "before" pictures. I think old-fashioned varnish becomes reddish over time. The re-finished floors have a warm, golden color. Oil-based urethane has a slight amber color, which I think adds the perfect touch to most types of wood.

If I had used water-based urethane, which adds no color at all, the floors would not have so much amber color. Maybe someday I'll try doing a floor with water-based urethane, but for now I'll stick with tried-and-proven oil-based urethane.

Imperfect World:

In spite of my careful cleaning, there were still some flaws in the final finish, such as this strand of hair. (It sure didn't fall off my head.)

Sometimes small specks of foreign matter can be scraped off with a fingernail. Mostly these little bumps will just get rubbed off from normal wear and tear.



What's Next?

Now the rooms are finally ready for the next step... repainting and trim replacement.


Discussion of Risks:

Refinishing hardwood floors seems like a low risk project. You might think your greatest risk would be from urethane fumes (preventable) or pulling a muscle lifting the floor sander (very possible). But this job came very close to being the most disastrous project I've ever undertaken. I almost burned my house down... and I never would've expected the reason.

It turns out that when Varathane is dry but not yet fully hardened, the sanding dust has an interesting ability to spontaneously ignite. That means it will heat up and start to burn without the need for a spark or flame. This is serious stuff, folks. Read more about my close-call.


Read The Detailed Version Of This Article:

Part 1: Trim Removal and Other Preparations
Part 2: Sanding
Includes discussion of sanding technique, sandpaper usage, etc.
Part 3: Applying Polyurethane
Describes some problems I encountered and explains how I solved them.


More Info:

Tools Used:

  • Varathane ezV Floor Sander
  • 5" Random Orbital Sander
  • 2" Carbide Paint Scraper
  • Vacuum Cleaner
  • Bright Light, Portable

Materials Used:

  • Sandpaper Discs, 7"
  • Sandpaper Discs, 5"
  • Rubbing Alcohol
  • Urethane
Related Articles:
Web Links:


Do you like this article ?



Project Archives:

Kitchen  |  Bath  |  Electrical  |  Plumbing  |  FramingRoofing  |  Windows
Doors  |  Exteriors  |  Decks  |  Finish Carpentry  |  Flooring  | Workshop

Search Page

Home    What's New    Links    Rants    Contact Us

Before you hurt yourself, read our Disclaimer.

Back To Top Of Page 




Copyright © 2006

Written September 6, 2006