My beachfront rental unit had a worn-out carpet that needed to
be replaced. I decided that a wood parquet floor would look
better, be easier to take care of, and make for a fresher,
brighter space. The unit sits on a concrete slab mere steps
from the water, so the wood flooring would have to be protected
against potentially high moisture levels.
With a concrete slab, the two big issues are always moisture
and surface condition. I had planned on gluing the parquet
directly to the concrete — until, that is, I discovered
the 1950s-vintage composition tile and asphalt adhesive under
the carpet (1). Asphalt adhesive on concrete is as bad as it
gets; it’s best to hire a professional to do the removal
or to cover the mess with plywood. I opted for plywood.
With wood flooring, an uneven subfloor will cause variations
in the finished surface, but those variations won’t be
noticeable if they’re gradual enough. The wood-flooring
industry standard for subfloors is a gradual change of no more
than 3/16 inch along the length of an 8-foot straightedge. If
you’re laying plywood underlayment over concrete, the
concrete needs to be leveled or variations will telescope
through the plywood.
I would normally use a planetary grinder (a concrete grinding
machine with counter-rotating disks) to grind down the high
spots. However, I prefer not to grind old floor coverings
because they may contain asbestos. Instead, I filled in the low
spots with 15-pound felt, folded to the depth needed at each
Dealing With Moisture
The next step was to measure the slab’s internal
relative humidity (RH). The rule of thumb when measuring slab
moisture is to drill at least three holes for the first 1,000
square feet of floor, then an extra hole for each additional
1,000 square feet. The holes should be drilled where you expect
the most moisture to accumulate — near a doorway where
rain might blow in, near a plumbing wall, or wherever you
observe leaks. In a standard slab-on-grade, the hole depths
should be 40 percent of the slab thickness.
I measured the RH with a moisture meter I developed for my own
work and sell to the trade. Its 3/8-inch-diameter sleeve fits
in a 7/16-inch hole and has electronic sensors for measuring
temperature and RH. Unlike the sleeve on other meters, this one
isn’t wrapped in plastic, so I can get a much quicker
reading once the test holes are prepared — a real plus
when doing a floor under schedule pressure. After drilling each
hole and vacuuming out the debris (2), I taped over the hole
with an impermeable packing tape and let it sit for 24 hours so
that the readings would reflect conditions in the slab rather
than in the room.
If the internal RH is 75 percent or less, you technically
don’t need a moisture barrier, but I always use one
anyway, just for insurance. Since this particular slab is
directly on grade, within 100 feet of the ocean, and only 3 to
4 feet above sea level, there was no question that I would use
one. The moisture test indicated a moisture content well over
80 percent, so that sealed the deal (3).
If I had been gluing the parquet to the concrete, I would have
applied a brush-on moisture barrier directly to the concrete.
But first I would have done an absorption test, which involves
putting drops of water on the concrete. If the water beads up
instead of spreading out, the surface is not absorptive enough,
and I’d need to use a grinder to remove the sealer from
the surface, then retest.
For this job, though, I laid down a 6-mil polyethylene vapor
barrier, then covered it with 1/2-inch CDX plywood, fastening
the plywood to the floor with 1 1/2-inch concrete nails to
provide 1 inch of penetration (4). I used 1/2-inch plywood
— rather than 1/4-inch or 3/8-inch — because it was
stiff enough to need just a nail every square foot (for a total
of 32 nails per sheet). The thicker, stiffer plywood also
bridges over minor surface imperfections.
I installed the plywood at a slight angle to the room’s
walls to ensure that no lines in the parquet floor would be
parallel to any lines in the subfloor. That way, expansion or
contraction of the plywood won’t open up gaps in the
The finished floor would be 12-inch-by-12-inch parquet squares
made from 5/16-inch-thick by 2-inch-wide strips of white oak.
Each square consisted of six strips laid side-by-side and held
together with two pieces of masking tape (5). Because the
flooring would be held in place by adhesive, I only needed to
keep the parquet squares assembled long enough to get them in
place. Working at the site, I used my Festool saw to cut the
strips to length; it doesn’t splinter, makes near perfect
cuts, and can be connected to a dust-collection vac (6).
I began the layout by determining the room’s focal
points. In this room I wanted the flooring to be parallel to
the longest wall, so I snapped a line 24 3/8 inches away from
that wall (two squares plus a 3/8-inch expansion gap), then
snapped a second line perpendicular to the first and the same
distance away from the adjoining wall (7, 8).
The adhesive has to be spread on a clean, dry surface. Had
this been old plywood I would have given it a light sanding,
but since it was new, vacuuming was enough.
Installing the Parquet
The adhesive, filler, stain, and finish used on this floor are
all made by Bona. (I always avoid using products from different
manufacturers on the same job; they may not work well together
and it will typically void the warranty.) We used an adhesive
that allows the floor to be wet-laid (older adhesives had to be
left to dry for a bit before the floor was put down), and we
spread out only as much as we could reach over — about 30
to 36 inches at a time. If you have a two-man crew, one person
can spread and the other can place the flooring.
Using a notched trowel (9) ensures that the right amount of
adhesive gets spread out on the surface. I laid the squares on
the adhesive (10) and pressed them firmly in place (11, 12),
starting at the layout lines and working across the floor
toward the opposite corner. So that I didn’t trap myself
in the corner, I left an unfinished strip at each wall. This
allowed me to work my way from the back wall and eventually out
the door without having to step on the freshly laid
It’s a good idea to occasionally lift a tile after
pressing it into the adhesive, just to make sure that the
adhesive is covering the entire bottom. If it isn’t, that
means the adhesive surface has started to skim over.
You’re getting too far ahead of yourself and need to
spread less adhesive before laying the tiles.
When laying parquet, I continually sight down the lines to
make sure they are running straight. Since there will be minor
imperfections in the blocks, you need to be able to make
adjustments as you go. Leaving very small spaces between the
blocks provides enough wiggle room to make these adjustments.
The gaps can be filled later. It’s also important to
periodically confirm that the diagonals are aligning.
It’s best to use a string for this so you don’t
disturb the surface.
I left a 3/8-inch expansion gap between the floor and all
walls. Anything bigger wouldn’t have been covered by the
1/2-inch-thick baseboard. Besides, if a wood floor swells
enough to push the perimeter more than 1/4 inch, the adhesive
is going to fail. Even a fairly elastic adhesive — like
the one I used here — can’t stretch more than 1/16
Once all the parquet squares were installed, I gave the
adhesive time to dry by letting the floor sit overnight.
Filling and Sanding
With the adhesive dry, the next order of business was to fill
any gaps between the squares (13). I used a Bona filler made
specifically for filling unfinished white oak floors;
it’s porous enough to absorb stain. It also dries
quickly, so after I pushed it into the cracks with a flat
trowel (14), I could immediately start sanding.
I sanded most of the floor with a 200-pound Bona
professional-grade sanding machine. It connects via a hose to a
large vacuum with a HEPA filter, which makes for a dust-free
job. I started with coarse grits and worked to fine.
Sanding parquet is different from sanding strip flooring. The
wood grain in adjacent parquet squares runs in opposing
directions, so if you sand along the layout lines you will be
sanding half the squares with the grain and half against it.
This can leave perpendicular scratch marks that show up through
the finish. To prevent this, parquet is typically sanded at a
45-degree angle to the layout lines (15). As usual, I sanded
the perimeter of the floor with an edging machine (16).
After the sanding was complete, I used a floor buffer fitted
with a double-sided paper disk to blend the sanding patterns
together. There are two advantages to using a double-sided
disk: It’s stiffer than a single-sided disk, so it does a
more even sanding job; and the abrasive on the back creates
friction between the disk and the fiber pad on the buffer,
preventing the disk from slipping around. Which grit to use
depends on the depth of the scratches left by the big machine.
Here, I did one pass with an 80-grit disk, then finished up
with 120-grit. I used a random orbit sander with the same grits
around the perimeter of the room.
Applying Stain and Finish
I use a fast-drying stain — Bona DryFast —
that’s made for wood floors and doesn’t leave lap
marks like other stains can. A lot of guys apply stain with
rags, but I don’t like crawling around on my hands and
knees; instead, I used a technique here that I’ve relied
on for years with great success. I cut a piece of carpet to fit
the disk on the buffer, poured some stain on the carpet pad
(17), then used the buffer to spread the stain out on the floor
(18). It’s faster, quicker, and uses less stain than the
Whatever method you choose, don’t pour stain directly on
the floor. It can accumulate in small gaps in the wood, where
it can’t easily dry, then bleed back onto the surface
overnight and mar the drying finish.
To stain up against the walls and in spots where the buffer
wouldn’t fit, I used an applicator wrapped in a rag (19).
I stood on a couple of pieces of carpet so I wouldn’t
leave footprints in the stain — or track stain everywhere
else. Then I put a dry carpet pad on the machine and buffed the
entire floor to remove any excess.
Although the stain dries in three to four hours, I let it sit
overnight just to be sure. Then I tacked the surface with a
special microfiber dry-tack cloth made for use on floors
— its stickiness is provided by the structure of the
fiber, so it doesn’t add any chemicals to the
I topped the stain with Bona’s Naturale, a two-part
water-based finish (20) being careful not to
mix more than I could use in two and a half to three hours. The
finish has to sit for 15 minutes before it’s used. Bona
provides a strainer you insert into the opening of the finish
container to remove any small globs that slough off the
interior of the container.
I poured the finish on the floor in long, straight lines, then
spread it with a roller specifically made for floors. The
roller has plastic disks on each end — I call them
training wheels — that ensure a consistent finish
thickness (21). The finish works best if used at the
recommended coverage rate of 300 to 400 square feet per gallon,
and the roller helps ensure this coverage. When rolling, I
overlapped the last line a bit to make sure the finish blended
together. We cut in around the perimeter with a 10-inch-wide
Padco paint applicator attached to a wooden handle. As with any
finish application, I needed to maintain a wet edge to prevent
lap marks when the finish dried, which made it important not to
cut in the edges too far ahead of the roller (22).
The label on the can of stain says to use two coats, but I
prefer three. I generally wait a minimum of four to six hours
between coats, which means I can put one on early in the
morning and then come back later the same day for the second.
Because this is a water-based finish, low temperatures and high
RH can extend the wait time between coats.
By the way, the trick to working with this particular kind of
finish is to not watch it dry. It won’t look right an
hour or two after application, but it’s self-leveling and
will level itself out nicely over the course of the drying
The final coat also needs a minimum of 24 hours before being
walked on. If possible, wait seven days before putting down any
rugs, as they’ll restrict airflow and keep the finish
from drying properly. If you must put furniture down, do so
extremely carefully, without dragging it across the
Howard Brickman is a wood-flooring contractor and
consultant in Norwell, Mass.