Subfloor for Resilient (Vinyl) Flooring

Resilient flooring seems like one giant piece of duct tape:  it will stick to anything.  Well, it can’t.  And that’s why choosing the right subfloor is pretty important before laying resilient flooring.

In case you didn’t know–and why should you?–resilient flooring is the oh-so-sensitive term nowadays for the more hated term, vinyl flooring.  Got that?  Moving on…

Concrete

Roughening a Concrete Floor Before Vinyl Floor Installation
Roughening a Concrete Floor Before Vinyl Floor Installation

Smooth, level, patched, and dry concrete subfloor can be used directly for resilient flooring.  No underlayment needed.

Plywood

Plywood Subfloor
Plywood Subfloor

Half-inch or greater underlayment graded for such use by the American Plywood Association.

Existing Vinyl Floor

Yes, You Can Put Vinyl Over Vinyl
Yes, You Can Put Vinyl Over Vinyl

Sorry, did I use the word vinyl?  I mean resilient flooring.

Clean resilient flooring on a good base can be used as the subfloor for new resilient flooring.

Do Not Use as a Subfloor

  • Wood floorboards
  • Particleboard
  • Hardboard
  • Exterior-grade plywood
  • Cement-based backer board
  • Asphalt tile
  • Rubber tile

Soundproofing for Laminate and Resilient Flooring

If there’s one thing that laminate flooring and resilient flooring can’t do, it cannot deaden sound very well.

Carpeting dulls sound (especially in conjunction with a nice, thick pad).  Solid hardwood does a great job of quieting things down.  Engineered wood flooring, too.

But laminate flooring is so thin and built on such a worthless base, that it does a crap job of slowing the transmission of sound from one floor to another.  Resilient flooring has no base whatsoever.  So, for these materials more than almost any other kind of flooring, you seriously need to think about your subfloor or underlayment materials.

Sound-deadening panels such as Georgia-Pacific’s Hushboard are available which normally are used for walls.  But Hushboard can also be laid down for flooring, in addition to minimum 19/32″ plywood or OSB.  Predictably, Hushboard is a fiberboard type of material, so problems can result if you try to install the stuff under or next to something that will sharply press on it, such as partition walls.

Installing Hushboard

Hushboard
Hushboard

Hushboard is an easy install with 5d roofing nails or type W drywall screws.  GP recommends a grid-like layout of fasteners every 12 inches, and a half-inch from the panel edges.

Then lay another 15/32″ plywood underlayment on top of the Hushboard.  It’s like a Hushboard sandwich.

You’re really building up the floor high–two plywoods, one Hushboard, one finish floor.  But I guarantee, this will bring down the sound volume a long ways.

Install Plywood Subfloor to Concrete Slab?

Q:  I’m wondering if I can install plywood subfloor right on concrete slab.

A:  It is likely that you can install plywood subfloor or underlayment directly on concrete, but it depends on your slab.

If the concrete slab remains high and dry all the time, and is perfectly smooth and stable, you can install the plywood subfloor or underlayment right on the concrete.

You’ll want to lay down a thin layer of mastic to bond a 6-mil (minimum) plastic sheeting to the surface.  First test the surface of the concrete to make sure that it really is dry.  If you’re feeling “old school,” you can use roofer’s felt.  Same thing either way.

Why Is Level and Smooth Such a Big Deal?

You may think:  Well, I’m laying down 3/4″ plywood (or whatever thickness) on this concrete slab…why does it really have to be perfectly level and smooth?  Because even small bumps and imperfections can throw off your plywood.  You’ll end up with raised corners that you valiantly try to smack down with your power nailer.  Or you may even have an entire side that won’t go down.  Small imperfections get magnified when you’re laying down the underlayment/subfloor sheets.

There are 2 solutions here:

  1. Fill in the gaps and smooth down the rises with a power grinder.
  2. Lay down a system of risers to elevate the plywood.

Laying the Plywood on the Slab

Plywood Subfloor on Concrete
Plywood Subfloor on Concrete

With the surface prepared and the vapor barrier in place, it’s time to lay out and fasten down the plywood.

  • You can either lay out the panels in “logical” fashion (that’s what I call it anyway); that is, sheets parallel to the wall.  Or, as some floor installers do it, you can lay out the plywood on the slab in diagonal fashion.  This diagonal layout has one benefit:  you ensure that plywood joints and floorboard joints never line up.  Personally, I think the diagonal layout is a pain in the ass.  Think of all that cutting!  But you’re welcome to try it…
  • At the very least, you do need to stagger the joints.
  • Space out each sheet with about 1/4″ gap between them and about 1/2″ to 3/4″ away from the walls.
  • Use your power nailer to drive three or four nails in the center of each plywood sheet.  Then 2 or 3 nails for each edge.

And that’s that.

Fixing Concrete Slab Prior to Installing Flooring

If you’re going to install flooring directly on concrete, then that concrete has got to be perfect.  You have no more flooring layers available to smooth out things before your finish flooring goes down.  So, you need to deal with cracks, depressions, and high spots.

And keep in mind that we’re not even talking about the surface itself, which needs to be absolutely clean, oil-free, stain-free, dirt-free, and sealant-free.  That’s a whole different matter…

Cracks or Depressions in Concrete Slab

One good thing about repairing cracks in the concrete is that none of this is visible.  It’s really difficult to repair concrete cracks and not see the repair areas.  Here, all you want to do is get the thing level and smooth.

  1. Use your ever-ready masonry chisel to chip away at the loose edges of the crack.  Anything loose must come out.
  2. Then, chip away at the bottom of the crack to form a (rough) inverted “V” shape.  This will help form a space so that the epoxy goes in…forms a plug…and then won’t come out.
  3. Clean it all out with a pressure washer or hose.  Shop-Vac the crack thoroughly.
  4. Fill the crack with epoxy patch designed for concrete.
  5. Trowel smooth.

High Spots in Concrete Slab

Concrete Floor Grinder

High areas in the concrete also need to be brought down.  Otherwise, you’ll be bowing out your flooring.  Theoretically, this can be done.  And that’s one of the benefits of laying ceramic tile:  it conforms to the shape of the flooring below.  After all, you’ve seen ceramic tile laid on all kinds of curved surfaces such as swimming pools; it can certainly lay down on gently undulating concrete slab.

But do you really want this?  Given an option between smooth and flat concrete, you’ll take the “flat” option.

About the only solution is to use a concrete floor grinder.  These are serious machines that rent out for $80 to $100 per day.  High cost, but you probably will not need the floor grinder for more than a day or two.

Is the Concrete Slab is Ready for Flooring?

If you’ve got a concrete slab, you’re in luck.  In a best case scenario, concrete slabs provide a (relatively) glass-smooth surface for flooring and are so stable that you should never have squeaks. But one thing to keep in mind with installing flooring directly on concrete is that concrete has a lot of moisture…and it retains moisture for a long time.

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.

Fix High and Low Spots in Subfloor

Dealing with bumps and depressions in your subfloor is your last chance to smooth things out (both figuratively and literally) before laying down the finish floor.

I like to talk a lot about the benefits of layering and how layering can save your butt (in other words, if you mess up this layer, there will be another, covering layer atop to cover up your mess).  So, you really have to make this one count, because you’re at the next-to-last layer.

High Spots and Bumps in Subfloor

If you need to bring down your subfloor, you can try either a hand plane or a power sander.  If you have a drum sander on hand, this can level out any bumps in the subfloor, but you need to have a steady hand to control this.

Actually, if you go overboard and gouge out some of the subfloor, it’s not the end of the world.  The gouges can be filled in…or if small enough, the finish floor may be able to bridge them, as long as you’re installing solid wood or engineered wood flooring.

If your subfloor is of the solid wood variety (i.e., not plywood or OSB), you can single out a floorboard or two that are creating the bump, and which cannot be easily sanded or planed down, then you can pop them out and replace them.

Have a crawlspace or basement?  Then you have access to the bottom of the floorboards.

It really doesn’t matter how ugly a job this is–you’re going to cover it up anyway.

Got plywood or OSB subfloor that is warped or bumpy and can’t be sanded down?  Then either screw the thing out or pry it out and replace it.

Low Spots and Depressions in Subfloor

Floor Leveling Compound

Some flooring, such as solid wood or engineered wood, can bridge small depressions.  Any depression that is more than 3 or 4 inches wide is, in my opinion, too wide.  It’s not the depth of the depression that matters; it’s the width.

Floor leveling compound is made for just such a thing.  Spread it on, trowel it smooth.  Guides often tell you to sand it smooth–but what’s the point?  As long as it’s level, you can forgo the sanding.

When you have depression that are three or four feet in diameter or more, it’s the joists that are the problem.  You need to get access to the bad joist(s) and replace or repair.  Sometimes a joist will be bowed simply as a function of aging.  This type of joist can receive wedges on top to bring the level up.  While it’s probably fruitless to try to straighten out these warped joists, you can most certainly sister them and prevent them from warping any more.

Should I Use Subfloor Adhesive?

Q:  I’m laying down subfloor and everything I read says to use adhesive with the subfloor.  Now, I don’t remember this from years past.  Is this a new-fangled thing that completely blows…or should I consider doing this?

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
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
Applying Subfloor Adhesive - Copyright Liquid Nails

Why Stagger End Joints on Subflooring?

Subfloor installs directly on top of floor joists.  Subfloor, along with those lower joists, is the only support for your floor covering.

It is often said that the end joints–or corners–should fall in a certain staggered pattern.  Is this true?

Best Answer

Yes, you should favor staggered ends for our subfloor.  But if you happen to have existing subfloor that is not installed this way, you may want to consider leaving it in place.

Because

Staggering your subfloor end joints should be done because you cut in half the number of problematic corners that converge at one point.

Avoid This:  End Joints That Form a Cross

Plywood Subfloor Layout Incorrect

Do This:  Stagger Subfloor End Joints

Plywood Subfloor Layout Correct

Staggered formation is just like brickwork.  Bricks are laid out in a staggered formation for a good reason:  it’s structurally stable.  In fact, you don’t want this kind of arrangement with any kind of building material.  Drywall is another application where you never want to have these corners meeting up like a cross.

It’s the same with subfloor.  Staggering the corners makes for stronger subfloor, and a better and smoother surface for your floor covering to rest on.

While staggering is correct, exactly how incorrect is a non-staggered formation?  Short answer:  it is twice as incorrect.

With unstaggered joints, you have 4 corners converging at one point.  When you stagger the joints, now you have 2 corners plus the straight edge of a board converging at one spot.  By staggering you have cut the number of potentially weak corners by 50%.

Non-staggered joints will not result in the immediate, or even long-term, self destruction of your flooring because:

Tongue and groove subfloor also means that subfloors are stronger than ever.  T&G means that subfloor boards do a better job of “locking” together than regular plywood.

 

How Thick Should Wood Floor Underlayment Be?

An underlayment is the “meat” in the wood flooring sandwich. Top is the finish flooring; that is, the wood flooring that you see and walk on. Very bottom is the subfloor (okay, well the floor joists are at the very very bottom…). Between the subfloor and finish floor is the underlayment.

How thick should the underlayment be?  What kind of materials should be used for underlayment?

Underlayment Thickness and Material

It all depends on the condition of your subfloor.  If you’ve got a nice, perfectly smooth subfloor, you may not need any underlayment.

But if you have a problematic subfloor, your underlayment will be anywhere from 1/4″ to 1/2″.  You can even install up to 3/4″ thick underlayment…or thicker…depending on your needs.  Really, the sky is the limit.

Problem with installing thicker and thicker underlayment is that you shoot yourself in the foot–you’ll have problems with making transitions from one floor to another.

Plan on installing the flooring everywhere (i.e., no transition problems)?  Then you’re still dealing with transitions to the outside.

The most common material for underlayment is good old plywood.  Or you can install what is called Oriented-Strand Board, or OSB.

Oriented Strand Board - OSB
Oriented Strand Board - OSB