It may seem that sealed concrete is a perfect surface to lay down finish flooring.  What could be cleaner and less porous than concrete with sealant on it?

Well, as it turns out, sealed concrete is not the best surface…

Find Out – Is the Concrete Sealed?

Dip your fingers in a cup of water and sprinkle some drops onto the concrete slab.  Does the water bead up?  If so, it could be that the concrete is impregnated with oil or some other substance that repels water–in which case you still need to thoroughly clean the thing.

But if water beads up all around the flooring, you’ll know it’s been sealed.

How to Remove Concrete Sealant

Your finish flooring adhesives actually need a porous surface in order to bond well; slick does not do the job.  There is no substance that I know of that will allow you to blister and peel/scrape away concrete sealant, in the manner that you might strip paint from woodwork.

Your only option is to rent a concrete floor grinder at the rate of around $80-100 per day and roughen up the surface.

While some concrete experts may disagree with me–and hey, they’re the experts–my take on the matter is that not every single square inch needs to be thoroughly blasted away.  As long as the majority of the concrete surface is exposed, that’s enough for your flooring adhesive or mortar to “take.”

Sure, it may be tempting to grab just any old nail in your shop and start pounding away, but in the case the wages of sin are high:  nails popping up through carpeting and even laminate floor; floor squeaking; and general homeowner misery.  So, spend two minutes and get this one right.  Getting the right kind of nail and spacing these nails correctly very much fits in with my idea of how to remodel.

Type of Nails

First, you’ll be using ring shank nails.  Do not even think about using any other type of nail, because ring shank nails are designed to stay in place.  Loose nails and wood-against-wood friction are the two main sources of floor squeaks.

But this goes beyond mere wood squeaks.  You do want your floor securely fastened, don’t you?  I thought so.  Then use ring shank nails.  Ring shank nails are perfectly designed for floor installation.

Size of Nails

Ring Shank Nail - Note the Ridges?

Pick up packs of 3d ring shank nails.  These are 1.25 inches long and can be used for underlayment that ranges up to 1/2 thick.

If you so happen to have thicker underlayment (3/4 inch or more), then use 4d ring shank nails.  These are 1.5 inches long, plenty long to drive through that over-sized, over-thick underlayment.

Nail Spacing

Now, here’s the part that sucks.  Nail spacing?  You basically need to pepper that underlayment board everywhere, and by everywhere I mean:

• On the edge:  3 inches apart
• In the main area of the board:  6 inches apart

One saving grace of using those thicker underlayment panels (1/2 inch thick or more) is that you can cut the spacing in half.  So, for example, edge spacing would be 6 inches apart, and so on.

Huge concrete projects retain moisture seemingly forever.  Hoover Dam supposedly is still drying out and cooling down from its pour over 75 years ago.

If the tape doesn’t hold down the plastic, then the concrete might be too dirty…or too moist even to hold down tape.

Back to the residential world, how do you know if the concrete slab is ready for flooring?  Moisture is your biggest culprit, so do these things:

• Well, first of all you’ve got to wait a good three or four days.  Concrete will not be dry before then.
• But after that 3-4 day waiting period, you can tape a square of clear plastic to the surface of the concrete.  The plastic doesn’t have to be very big–maybe two feet square.
• Now, tape down the entire perimeter of the plastic with duct tape.  Make sure it’s down good and tight.
• Wait 24 hours.
• If you come back and find fogging, beads of water,or any evidence of moisture on the inside part of the plastic, it’s not time to install flooring yet.  Wait a day, then tape down the plastic again.

A:  Nice, but not necessary.  Call me lazy, call me cheap, but I think you can get by without subflooring adhesive.

I agree that subfloor adhesive is a cool little addition to your new floor.  There are two main reasons why you might use subflooring adhesive:  1.)  if you’re afraid of the floor squeaking; 2.)  If you need an ultra-stiff floor for some special reason.

Gosh, what kind of “special reason”?  You tell me.  Is a piano room?  Plan on installing a 1 ton floor safe?  Is this your personal ballroom?

I really can’t imagine why you need to squirt subfloor adhesive–because that’s extra work for very little return, and we don’t like that.

Subfloor Adhesive

Now, if I had hired a builder, I would damn well make sure they used subfloor adhesive.

Applying Subfloor Adhesive

• Squirting it on every joist in the central area of each subfloor sheet.  Bead should be about 1/4″ thick.
• Calculate about 65-70 linear feet per subfloor adhesive tube.
• Squirting the adhesive on every “end joist” (where two subfloor sheets meet).  But you’re saying, “How?  Subfloor sheets are supposed to have a gap between them, and if I lay down the bead in the center of the joist, then I don’t get it.”  Well, ignore the center of the joist, and instead lay down two beads where the edges of the subfloor will fall.
• If using tongue and groove plywood subfloor, squirt the subfloor adhesive in the grooves.

Applying Subfloor Adhesive - Copyright Liquid Nails

You have several types of subfloor and underlayment options available.  Let’s take a look, and I’ll do my best to separate the terminology.

Solid-Wood Subfloor

In modern home construction and renovation, the solid-wood subfloor isn’t seen very much.  If anything, this “subfloor” is the actual, finish floor of solid wood that the renovator has decided to lay over with another type of flooring.

Plywood Subfloor

Plywood has been used as a subfloor for quite some time now.  Plywood comes in 4′x8′ panels and is laid down in that size straight onto the joists.  The plywood is laid with its grain perpendicular to the joists.

You can’t just run down to Home Depot and grab any old kind of plywood.  The Half-Assed side of me says, “Yes, it probably will last,” but armed with just a tiny bit of information, you can certainly buy the right kind of subfloor plywood, and it’s like this:

Plywood is rated for certain uses.  In this image shown, the first figure refers to the ply’s rating on roofs; the second figure applies to floors.  So, ignoring the first number, we can see that this plywood is rating for flooring joist which are 24 inches on-center.

The Engineered Wood Association is a good resource for plywood ratings (apparently, we don’t call it plywood anymore?  Well, whatever…).

OSB Subfloor and Underlayment

Oriented Strand Board - OSB

OSB stands for oriented-strand board, and it works as both subfloor and underlayment (amazing, huh?).

Not to be confused with particleboard, OSB is serious stuff, and it’s bonded with resins that can even withstand exterior weathering.  In fact, OSB is often used for exterior applications.  OSB gets graded by the Engineered Wood Association, too.

Plywood Underlayment

If you’ve got a subfloor, but this subfloor is not smooth and flat enough for your finish flooring, you may decide to lay down plywood underlayment.  This plywood underlayment does not have to be as strong as plywood subfloor because it’s not such a structural material.

Particleboard Underlayment

Yes, underlayment only here.  Particleboard is not a structural material.  Wood chips are bonded together, and it’s nowhere near as strong as OSB or plywood.

Any kind of dust remaining on the surface of your just-sanded wood floors will mess up your sealing work.  Sawdust will make you nice sealing coat all gritty and bumpy and awful.  After that point, the only way to fix it is to…sand again.  And I’m sure you’re not especially keen on that, are you?

Vacuuming is Not Enough

Run a Shop-Vac across the floor, and call it a day?

No.  Use the Shop-Vac (and start with window sills, radiators, door molding, etc. even before vacuuming the floor) to get off the worst of the sawdust.  But that’s not enough.

Some floors installers will not recommend this, but you can use a very squeezed-out damp mop to pick up more sawdust.

Tack Cloth

Clean Floors with Tack Cloth

But the best thing in the world is called a tack cloth.  These are annoyingly gummy rags that you buy cheap at the local hardware store.  The gum feels like beeswax (because it is!) and feels a bit wet (’cause it ain’t), and that’s the cool thing.  It works like a wet cloth, but it’s not.

For a 400 square foot floor, I would buy a five or six packs of tack cloth.  Using the tack cloth will be your very final cleaning step.  Keep the floor clean!  Walk in sock feet!  And those tack cloths are worthless once they have picked up sawdust.  Toss ‘em out.

A small expense, but well worth it.

A: Yes, if your budget allows for it. Quarter-sawn wood flooring is considered a big deal (vs. plain-sawn wood).

Quarter-sawn wood flooring is superior to plain-sawn because of the way the saw bites into the wood.  Instead of sawing tangentially to the rings in the wood, the saw blade approaches perpendicular to the wood rings.

This is a big deal, because sawing tangentially to the rings gives your wood flooring planks more of the really soft wood that the tree produces between the rings.  And the tree rings are the hard part.

Sawing off quarter sections produces less usable planks, so the price is higher.

In this image, the plain-sawn boards are on the right-hand side.

Quarter Sawn Boards