After a thorough search of the discussions on this board, I'm wondering why the majority of people say either glue or float an engineered wood over concrete. Why is laying plywood over the concrete and then nailing or stapling not an option, or is it?

My situation: I'm using an engineered hand scraped maple that is about 5/8". I'm a little leery of floating the floor because of everything that I have read about the "bounce". I am equally leery about gluing because I'm not sure how exactly flat the slab is and because using glue also seems to be more difficult and cost more. The manufacturer says all three methods are ok.

Any help is appreciated!

Thanks,
kc

Nothing says you can't do it.
Engineered's were made to go directly over the concrete, so there would less expense, and difficult height gains, where there were and still are, concerns for a solid.

I took a look at plywood prices at the local DIY store and it looks like it would be about the same price as the materials needed to do floating job. I'm not concerned with the height gains, I have 12ft ceilings (or should I be?). Am I missing something here? Does anyone have any recommendations? Thanks!

Some height sensitive situations are kitchen remodels where raising the floor too high can cause problems for dishwasher clearence under the countertops, or you may have to trim a bunch of doors. You also want all the different types of flooring in your home to be as close to the same height as possible.

To add to already good suggestions and tips, another consideration is this. The more complex a floor "system", the more pieces/components that can fail. Your engineered floor was designed to be glued directly to a concrete subfloor. That is the best way to install that floor. You're concerned about the slab being flat enough. Just putting plywood over it does not solve that problem. The slab still needs to be flattened before putting plywood down as well. And the plywood should be glued as well as nailed (unless it's floated). So, why not just glue your engineered floor down? Moisture test your concrete first. Look, it's right in the instructions. I have yet to find a set of instructions that did not address the correct way to install the floor.

I am in no way a pro, just wanted to say that we glued my engineered wood floor and the concrete was in no way flat. That is what he glue helps with it can and will fill in those areas that or to low. Also it cost use about $800 more in glue, what would your cost differnence be with plywood and glue?

Very confused - Glue or Nail???

It seems like the cost is about the same for gluing or using plywood and nailing, about $500 - $700.

I read somewhere that gluing has the highest failure rate and it also takes longer to install. I know that engineered wood was made to be able to glue it to the concrete, but isn't nailing it down a superior method? So if the price is comparable why would you not use the plywood?

If I glue, then should I use a moisture barrier or does the glue also serve as an adequate moisture barrier? If yes, then what and how should the moisture barrier be applied?

Thanks,
kc

We have glued and the glue has a mosture barrier. I do think that it is far BETTER than nails.

There is only one wood adhesive that I know of that is a one application, moisture barrier, also. That is STAUF 960. All the others have a membrane that is troweled or rolled on, before the adhesive application.

For a SOLID wood floor, I would say probably. However, you are installing an engineered plank. That floor would be better installed by gluing directly to the concrete subfloor.



I think if you factor in the correct way to install a 3/4" plywood subfloor, you will see it is less money to directly glue your engineered plank floor down. See which adhesive the manufacturer recommends and will warranty the floor for. Some have proprietary adhesives one must use and those can be expensive. But your flooring may not and simply recommend various good ones. Shop around. I did a simple math and came up with this. Assuming you get 40 sq.ft. installed per gallon of adhesive. And the adhesive can be had for $25.00 per gallon. It will cost you $125.00 to install 200 sq.ft. of flooring. That comes to 63 cents a sq.ft. for adhesive. 3/4" plywood is nearly $30.00 for a 4 x 8 sheet. That is 94 cents a foot right there, not including any moisture barrier, nails or anything else. So, gluing it down will be less money and make for a more secure install, if done properly.