sorry for another question on this topic. i've been reading alot of posts on this topic, but wanted to ensure what i am doing is correct.

i actually have 2 questions. any help would be appreciated.

1. i'm currently in the process of installing 3/4" plywood onto the concrete slab. i didn't add a vapor barrier under the plywood, but plan to have 15 lb asphalt felt installed on top of the plywood (btw the plywood and actual hardwood floor). from what i've read, a lot of installs had the felt under the plywood. would the install i did cause any moisture problems? this is being installed on-grade.


to install the plywood, i used a urethane adhesive. i didn't cover the entire surface of the plywood, but placed the glue in each of the corners and one right in the center. i then used a ramset to nail (1.5" nail) the plywood to the concrete.

also, the concrete seems to be painted already, but i'm really not sure if this was painted with a vapor barrier.

because i've been researching and seeing diff methods, i wanted to see if this install will have any problems in the future or if is this correct??

2. i spaced the edges of the plywood 1/4-1/2" from the edges of the room. but i didn't add that much space btw the sheets itself. in some cases, they are butted next to each other. because of this, do i need to re-cut the plywood to allow for some spacing between the sheets?

again, i understand this has been covered in the past, but wanted to ensure what i have done so far is correct.

thanks!

IMO, you may certainly have problems with your subfloor for the following reasons.
1) All concrete slabs need to be checked for moisture content prior to installing any wood on them. It doesn't sound like you did that.
2) If you are planning on nailing a solid wood floor to that 3/4" plywood subfloor, you should have installed some form of moisture control mechanism under the plywood. Either a vinyl floor or a moisture controller like Bostick's MVP.
3) Before you proceed, get a moisture meter and get an accurite reading of your plywood. If anywhere exceeds 12% MC, you've got problems. Ideally, the readinigs should be between 8 to 10% MC.
4) You should have gapped the plywood panels. You will need to go back and add some space between them using a circular saw. 1/8" is MINIMUM. 1/4" is preferred.
5) Even if the MC readings are OK now, they may not be 6 months from now because you are on grade and have no moisture control in place. I'd recommend an engineered floor that can be stapled, glued or floated. A solid wood floor will probably fail within a year.

gary

thanks so much for your response. i'll be sure to run all these by with the person. again, i'm new to this and had been observing the process.

it seems the concrete was previously treated with a gray paint like substance, however, this wasn't done by me. prior to the hardwood, the previous owners had carpet/padding tacked to the concrete. since the carpet was directly on the concrete, would this indicate that the had used a vapor barrier already?

i'll do the moisture test to get an accurate reading of the moisture.

i'll go-back to check the spacing between the panels as well. may need to pick up a circular saw and control the depth (since it's 3/4" and i don't want the saw to hit the concrete) of the cut to ensure the spacing is at least 1/8". in most cases, there a space, only a few areas where the plywood was butted next to each other.

be sure to use a carbide tipped blade.

thanks for the posts.

will going back to add gaps now in between the panels cause add'l harm since they have already been glued and nailed down?

EDIT: Sorry this is an above grade install. not on-grade as i mentioned above.

joe

Quite simply, no. Carpet does not need any form of "vapor barrier", whereas, wood on concrete does. Who knows what was painted on and what it was for? IMO, this is an excellent situation for a floating wood floor.

gary - thanks for the follow-up!

before continuing, i'm doing a DIY test to test for moisture, given the electronic meters are quite expensive. i'll see if i can look for a less pricey one. again, this is above grade, so i'm hoping all is fine. if not, i'll start to lay down the polyethylene layer

after the test, i plan to re-cut in between the plywood to allow for more room. the edge spacing is fine.

i was actually looking into solid wood, but i'll research floating floors based on your advice.

You cannot lay polyethylene vapor retarder OVER your plywood. To do so will trap moisture in the plywood, causing premature rot. You are supposed to use 15 lb. asphalt felt, which will allow the moisture to disapate (diffuse) at a slower rate. Moisture testing is a must when installing wood over concrete, whether it is below, on or above grade.

gary - thanks.

oh, i wasn't at all planning on laying the polyethylene vapor over the plywood. i'm using asphalt felt over the plywood.

i used DIY to test the moisture and didn't see any real indications. i wanted to start laying the polyethylene layeer under the plywood for the areas i have not finished laying down plywood yet, which is a majority of the area.

thanks again for your help