So I'm ready to install about 800 sq feet of Engineered ½ inch distressed hickory on a concrete slab.

Questions (Please Help):

The contractor doesn't like the ideal of installing ½ inch flooring and prefers 3/8 inch flooring because: It is much easier to work with the thinner (more flexible) wood which adhesives to the floor better and is less likely to pop loose causing a void.

1. True?

The contractor would also like to convert my concrete floor to a ply sub floor (using whatever method contractors use for conversions - ply over concrete). He would then nail or stable the floor. I'm sure he said nail. He explained that cost wise it was slightly cheaper, easier to use this method (over gluing) but would raise the floor about 1.25 inch.

2. Does or will this make transitions to say...like the kitchen, laundry room and ¾-bath room (Same floor - ceramic tiled) look awkward?

3. Could someone please provide a link or picture that shows similar transitions...please. At least comments of what you have personally seen.

If not the ply sub floor method, he wants to use Bostik MPV Moisture Barrier on the floor prior to gluing the engineered wood. He explained that not only will this method help prevent future moisture seeping up through the sub floor but it will also help to level the sub floor.

I don't know about the leveling part....maybe it helps a little. But being in super dry Southern California....

(Mamma and the Papas, "It never rains in Southern California)....

4. Do I really need a Moisture Barrier over...or should I say under, the lifetime moisture warranty already on the engineered floor?

Look for another contractor! He's blowing smoke. Sealers and adhesives are NOT levelers. Slab needs to be FLAT before any work can proceed. Slab should be tested for MC before deciding on material and sysyem. He wants to nail/staple because it's cheaper and faster. Glue costs big bucks and for nail down guys (like me), is slower and the clean up is a drag. If you want 1/2", that should not be a problem. He is attempting to avoid the prep/flattening needed to lay it. I will say suggesting MVP is not a bad idea but you may not need it. The concrete needs to be tested before that determination is made.

I just pulled back a section of carpet to study my concrete slab. It is covered with a thick smooth white substance. It not paint. Can’t scrape it up with a finer nail. I can chisel a bit off with an ice pick.

What is this stuff…..if anybody knows?

Tried a simple test also. The white substance has ¼ to ½ inch gaps at the room boundaries like at the door way to the laundry and restroom. So I poured about 1 ounce of some water over the area.

Nothing. Or at least, not what I expected. The water pools and just sits there on the bare concrete and the covered part. Guess I was expecting the water to seep into the slab. Left the water on the slab for 15 minutes…and it is still there. A 1 once pool of beaded water.

What does this mean?

And will I, or the contractor have to scrape all this stuff off the slab before installing the floor?

RED FLAGS FLYING!!!


Your contractor is not versed in gluedown wood floors!!!!! He is trying to do what he knows... fasten down.

Find another contractor, as Gary suggested.


How far did you pull the carpet back?? This may just be paint from spraying your baseboards, unless it is all over the concrete completely sealing it.

That stuff has to go. It is a bond breaker. Bead blast the concrete to remove it, or the adhesive will not get a bite.

The concrete substrate needs to be flat, it isn't the 3/8 vs. 1/2 that causes hollow spots or for the flooring to pull loose. It is the lack of floor prep to bring the concrete surface to the strict flatness specs for a wood floor.

To install plywood over the concrete, he is going to need to flatten the concrete anyway, unless he is cutting corners. 5/8 minimum for the plywood over concrete for a fasten down.

That thick white stuff maybe a flour based patching compound like Vitex. Lino and carpet installers use that stuff all the time to level and fill voids. No good for under wood however. Needs to be a cementious compound like Ardex