| The floor looked completely different
after sanding.
Before applying finish, I carefully vacuumed the
floor.
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Ventilation:
Getting rid of the fumes is critical. I always use
some sort of fan in a window to blow the air out. If the
weather permits, I'll leave the fan going for a couple
of days.
Keeping the power cord above the floor is important. Read about a
quick tip to keep cords off the floor. |
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Applying Urethane:
There are 3 important concepts to applying urethane floor finish:
- It's important to maintain a wet edge. This means that
you should apply urethane in a pattern that progresses
across the room, like a wave travels across a pond.
- Always back-brush. Back-brushing simply means moving
the brush from the wet edge back into the wet finish. If
you stab the brush into the finish and then move it, you'll see
a mark where the brush landed. You won't see a mark where the
brush lifts off the surface.
- It's best to apply urethane by brushing with the grain.
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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.) |
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| This is an organic vapor respirator
which you can see I'm wearing in the photo above.
You need one of these. Years ago I would just
"tough it out" and endure the fumes. That's
not smart. I bought this mask when I started doing spray
finishing with urethane, and now I use it for all kinds
of smelly work.
It costs about $35 at Home Depot or Lowes, and the
replaceable carbon filter cartridge lasts a long time.
This is money well spent. |
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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. |
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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 eat out. 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. |
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There were some clusters of bubbles like
these. |
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| After scuff-sanding, the bubbles were
mostly gone. |
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Even though about 18 hours had passed
since I applied the urethane, I still got some urethane
build-up on the sandpaper. |
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| So I just stopped sanding every few
minutes and used a knife to pick off the
"scabs" of urethane. |
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When the urethane gums up the sandpaper, it's a sure sign that
the urethane has not hardened completely. When tiny
"rolls" of soft urethane appear instead of sanding dust,
it's even worse.
But I got lots of sanding dust, and no little gummy rolls. I
didn't see anything abnormal, so I went ahead and applied the second
coat of Varathane.
I've had this happen before when finishing wood trim, and I've
never had a problem with the second coat of urethane. But... it
could've been a different brand of urethane.
We Have A Problem...
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Even before the second coat had fully dried, I
knew something was wrong. The Varathane was full of
wrinkles. |
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After calling the Varathane customer service toll-free number
(1-800-635-3286), I discovered that I had applied the second coat too
early. The high humidity had slowed the drying process for the
first coat. When I applied the second coat, there was still
a chemical
reaction occurring in the first layer, and it affected the adhesion
of the second coat.
| So I had to scrape off the second
coat of urethane.
Even though I had 400 square feet of flooring to scrape,
it didn't take too long. Read
more about this problem... |
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Recoating Urethane:
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After the second coat (i.e. the successful
second coat), I used a random orbital sander with 150
grit sandpaper to scuff-sand the floor before applying
the third coat. |
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| It took about 20 minutes to sand each
room. There is a lot more dust visible after sanding
with a random orbital sander.
I swept the floor and disposed of the
sweepings outdoors. Then I vacuumed the floor
with a shop vac. |
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After vacuuming there was still some dust
on the floor.
To pick up every last bit of dust, I dampened a paper
towel with rubbing alcohol and wiped the
floor.
I found that the easiest way to apply the rubbing
alcohol is to use a small garden sprayer that can
be pressurized with a pump. |
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Imperfections:
This picture was taken after the 3rd coat.
That series of spots visible in the reflected light
is called "blush". Blush is a spot of
irregular sheen (shininess) visible after the urethane
has dried.
Preventing blush can be difficult. I believe this
spot was caused by the heavy coat of urethane forming a
small pool before it dried. Applying a uniform thin coat
of urethane usually prevents blush problems.
I also understand that blush problems can be caused
when an excessive amount of paint thinner is used to
dilute the urethane. |
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There were several areas with blush spots. I wasn't concerned,
since I was planning on applying a fourth coat. Applying another
coat of urethane always fixes the blush problem.
Fine Grit Fiasco:
When I sanded the third coat, I tried using 220 grit
sandpaper, figuring it might be better than 150.
220 seemed to work about the same, but the dust
was so fine that it caked onto the sander and the
dust collector cup. When I tried to vacuum up the dust,
it just stuck to the floor. And when I used rubbing
alcohol on a paper towel to wipe up the remaining dust,
I got a muddy mess. I kept finding tiny chunks of
dried urethane mud on the floor.
I think I'll keep using 150 or 180 grit sandpaper for
scuff-sanding floors.
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Last Coat:
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I decided to try applying the fourth coat
with a 4-inch brush. I was hoping that brushing the
final coat would reduce the overlap marks that I
got when I used the lambs wool applicator mop.
But I still got plenty of overlap marks. |
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Imperfect Finish:
Overlap Marks
I wish I could get a picture of overlap marks,
but they're difficult to see... you can't see them
unless you're looking at the right angle. Overlap marks
are visible as strips of floor with a different amount
of shine. You can only see these marks in the glare
of light that is reflected off the floor. Since cameras
record glaring light differently than the human eye, I
could not get a decent picture of these overlap marks.
These marks happened wherever I picked up the
brush or lambs wool mop at the end of a stroke. If I
could drag the brush over the entire length of the floor
in one continuous stroke, I would prevent overlap marks.
It's possible to get full-length strokes using the mop:
You apply the liquid and then smooth it out using long
strokes from one wall to the other. But sometimes the
geometry of the room prevents such full-length strokes,
unless you mop across the grain.
Urethane can be brushed or mopped across the
grain. If you're lucky the urethane will level out
before it dries, making the brush strokes disappear. I
cross-brushed a few small sections, but I could still
see some phantom marks in the finish... not ripples in
the surface but variations in sheen.
Perfection is hard to achieve. But the good news is:
You don't need perfection. Few people will notice the
irregularities in sheen, and after the rooms have been
used a while, the floors get scuffed a bit and all these
imperfections are replaced with small scratches.
Perfection can be achieved by spraying
urethane onto a surface, but that's not done on floors.
Spraying is
suitable for furniture refinishing.
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| The last coat, while still wet. |
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Final Results:
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This is the main floor bedroom after the
4th coat of urethane had dried. It looked much better
than before. |
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| The upstairs bedroom. Now the walls need
repainting.
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.
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More Imperfections:
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. |
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