Hi All,

I live in Phoenix, AZ, have a 35 year old home, and am going to install 3/4" aztech cherry hardwood over the concrete slab.

My plan is to lay out 6 mil polyfilm, fasten 3/4" plywood to the concrete, roll out the 15 # felt, then nail the hardwood flooring down.

I have some questions about the details of the installation procedure.

1. The slab is pretty flat, but there are a couple of areas that need to be taken care of. Would it be better to flatten the floor before laying down the plywood, or can I use felt paper on top of the plywood to shore up the low spots?

2. I've read in one place that I should install the plywood at a right angle to the hardwood flooring direction, but I've also read that the plywood should be installed at a 45 degree angle (that really sounds better to me). Anyone have any comments?

3. I plan to fasten the plywood every sqft with a powder-actuated fastener. What length of fastener should I use?

4. Can I use the concrete fastener with the washer built in (more holding power), or will it stick out too much?

5. Someone recommended liquid nailing the plywood down in addition to fastening. Is this a good idea, and how can I do it when there is polyfilm between the plywood and concrete?

6. At this time I only plan to lay the polyfilm over the concrete. Phoenix is pretty dry and so is my slab, so it doesn't seem that an additional moisture barrier (other than felt over plywood) is required. What do you think?

7. What's better for my area, stapling or nailing down the flooring? I thought about nailing even though staplers seem to be more popular.

If anyone has any experience with this type of installation in a desert area like Phoenix, and tips would be greatly appreciated.

Thanks!
Jason

Hi Jason,
As a flooring contractor for 25 yrs and a member of the NWFA, I'll answer your questions to the best of my knowledge.

1) It would be better to flatten the slab before your plywood so the plywood will not have voids underneath.
2) 45 degrees is prefered but will take more time and material.
3) I am not a fan of this method. Experience has shown me that the fasteners will work loose over time. I prefer to glue and nail.
4) Don't use washers on the nails. It will interfere with your flooring and stick up above the surface of the plywood substrate.
5) There are various ways to accomplish this. Forget the poly film. Here are two ways that will work well.
a) Install cheap sheet vinyl flooring over the slab using a full spread multi purpose adhesive. Cut your plywood into 2x8 sizes and lay on a diagonal. Gap the seams at least 1/8". Use Franklin Advantage urethane adhesive to glue the plywood to the vinyl. You will be full troweling the adhesive with a 1/4" square notched trowel. After that, you can hand nail 1&1/2" masonry nails in the plywood 12" oc and wherever you need to suck it down flat. Hand nailing works better and you'll have less spalling. Use a 2lb. short handle sledge.
b) Instead of sheet vinyl, use Bostik's MVP and their Best urethane adhesive to glue the plywood down. Taylor and Franklin also make similar moisture barrier systems. Whatever moisture barrier system you use, use the same brand of adhesive. Costs very so shop around. Cut your plywood as instructed above and nail the same. If you don't want to hand nail, then use the powder activated nailer (Hilti, Remington, etc.).
6) 15 lb. asphalt felt is NOT a moisture barrier. It is a vapor retarder. Without a moisture barrier UNDER the plywood, you risk having complete failure. All healthy concrete will emit moisture in the form of vapor. It just a matter of how much and how fast. A moisture meter or calcium cloride test will help you determine that. Highly recommended. No real pro would install over concrete without testing it first.
7) Stapling or using cleats: either or. Whatever you want. Staples hold somewhat better; cleats allow the floor to expand and contract better. The key is maintaining a consistant RH and temp year round with the HVAC system. This will minimize expansion and contraction of the flooring.

Good luck!

What happens to the poly moisture barrier, if you poke holes all in it fastening down the plywood to the concrete?

Kind of defeats the purpose of the moisture barrier, now doesn't it.


Asphalt mastic!!! It is in the industry standards!! Why skip it if your going to use poly and fasteneres?

Gary's instructions for using MVP and Best adhesive, from Bostiks is a sound solution, just costly compared to poly and plywood. Adds about $2 a sq.ft. to the installation costs.

The problem I see with asphalt mastic is true asphalt flooring mastics are not available anymore. One must use asphalt for roofing. Now this is smelly, SLOW drying and flammable. Talk about slow drying. In the 50's when they glued 3/4" parquet directly to concrete slabs, they used asphalt. Then spread it over the entire floor and came back the next day to start the install. That black goo gets everywhere. Better use some shoes you plan on throwing away. It's basically like resurfacing a blacktop driveway. I'm not a fan of it. Yes, the newer adhesives cost more, lot's more. However, the ease of working with them makes up for it, IMO. Now, I should have mentioned a third option. The floating subfloor. Jason, you could do that as well. As far as cost, every system should be cost analized and then determine which is right for you based on need and cost. I think with the cost of plywood going up after the hurricane, a floating Kahrs floor will start to look alot more attractive.

Antioch California? I'm a graduate of Liberty Union High School and resided in Brentwood. Loved it out there before it got too populated.

NWFA/NOFMA calls for roofing mastic to seal slabs, but Gary is right... darn stuff is a mess..

Yep, Antioch, CA. Sure has changed! You know those all those orchards? Gone! Now track after track of houses. So you traded earthquakes for hurricanes, heh? At least the temp is similar. Perhaps even warmer here. Enjoy Florida!

Thanks for the feedback.

Gary - I also lived in Antioch. Actually I grew up there. The population was about 45,000 when we moved there and I think 70,000 when I left to go to college in Phoenix in 1992. Most of my family is still back there so I even visit every year. Definely warmer here

Back to the flooring - the reason I was going to use only poly film, is this excerpt from http://www.nofma.org/installation1.htm

""

So it seems that according to the NOFMA it is okay to just lay poly film right down on the slab in an area like Phoenix where the annual rain fall is light to moderate.

NOFMA also recommends the powder actuated nailer.

That said, I called an NWFA listed installer here and asked how they install. Reply was with asphalt mastic and tapcons to secure the plywood.

So what's the diff between NOFMA and NWFA, or do both recommend the same thing and you guys know that's not good enough from your experience? Or am I saomehow taking thier NOFMA's instructions out of context?

BTW - I already have 20 sheets of plywood and 600sqft of hardwood flooring sitting in my living room so there's no switching to engineered now. Plan was to have the subfloor layed before the flooring came in but week after week of travel killed that plan...

Thanks again for all the info!

Hey Jason,
Another Antiochian! To your flooring questions.
I am aware of what Nofma and the NWFA say. And those methods are a SUGGESTED approach. However, experience has shown me that the powder activated fasteners will work loose to some degree over time and then you will have a subfloor that is loose and flooring becoming uneven. If you want to try that approach, go ahead. I'm just warning you to be prepared to to remove boards to fix the subfloor at some point in time. Tapcons would be much better but very time consuming and have you priced those little gems? Can you say expensive? AS far as the NWFA and NOFMA, they are not the same. Nofma is a much older association and deals with oak flooring primarily. The NWFA is an international organization the deals with ALL aspects of wood flooring and all species. The NWFA is more inclusive whereas NOFMA is more specialized. But much of the info and suggestions regarding installation and finishing came from NOFMA originally as the NWFA is fairly young, comparatively. Most experienced installers recommend and rely on what they know works. Sometimes, our recommendations are overkill BUT necessary in this litigeous society. We have to warranty our installs and can't afford failures. My suggestions stand. I know these work and will hold up to the test of time. Good luck.