View Full Version : Hard wood floor over concrete?
03-10-2003, 11:05 AM
The title says it all. I've been interested in looking at how I might install some wood flooirng in our 1957 house. Under the carpet we have foundation concrete. Can I install wood over this (the concrete - not the carpet :))- is it good / bad? Is this somehting a do it yourselfer can do?
Danford C Jennings
03-10-2003, 11:39 AM
Yes, a wood floor can be installed over concrete. The type of wood floor determines the method...i.e. strip, plank, composition, etc.
03-10-2003, 11:40 AM
I work for a wood flooring manufacturer, here's what we suggest:
Below grade, I would not recommend a solid plank floor. If it is above grade, you can use the following system in order of install over the slab:
1. A single layer of 6 mil poly
2. A loose layer of 1/2" CDX Plywood
3. A second layer of 1/2" CDX plywood laid in the opposite direction, shot into the first.
This method has worked wonders for many of our clients. You may also want to check out the National Wood Flooring Association's website if you need more information, www.woodfloors.org.
Let me know how you make out.
03-10-2003, 11:48 AM
My only worry about doing this is that I'd be looking at an inch and a half of added floring over the exisiting level, wouldn't I? You can prolly already tell by my qestions and such that I know notin about this. The wife and I are thinking about the Pergo stuff but would MUCH RATHER GO WITH HARD WOOD. I understand that the poly is needed to keep moisture from comming through the slab and affecting the wood. Whats the point of laying down the ply sheets? Is this to give the nails for the flooirng somehting to bit into? Is there any other method that id be near as good that wouldn't raise the level of the floor soo much?
Thanks for the info!! :)
03-10-2003, 12:32 PM
I am curious about that inch and a half issue. You are transitioning from carpet to hardwood in this area? I know the logic behind two layers of 1/2" subfloor, and if you were to remove one layer you still would have a 1" transition, better but not great.
I would be suspect of laying polyethylene over concrete simply because of the potential for moisture coming from the slab and remaining there. I would rather use felt paper for a vapor barrier than plastic. To be sure, you could do a test, seal a 18x18 sheet of clear poly to the floor taped down (with duct tape) on all sides and leave it for a few days. Check to see if any moisture has made its way to the surface, you will see droplets on the inside of the plastic if so. You are in Cali right? Now would be a perfect time to do that. If no moisture, then you can use poly or felt paper.
There are several reasons for the CDX, or OSB. The floor will be colder and noisier than heck if you lay it over just the concrete. If you are using hardwood for the floor the subfloor will also allow for necessary expansion of the wood.
In terms of the transition, you could create an optical illusion by planing the hardwood, 1/32" at a time from an acceptable height (1/2"?) stepping up to a progressive inch, so you would need 32 board span (assuming the flooring pattern is parallel with the threshold and the situation of the room). I have never seen this done but it is a thought. You would loose the tongue and groove on the first 16 boards. Maybe this is a good idea, or maybe it is one that could end up in the "horror stories" bin? I dunno how else you would ease that threshold.
FWIW, and My two cents.
03-10-2003, 12:35 PM
I have seen people use 1/2" hardwood flooring (traditional t&g oak strip flooring). This gives you the same "wear" layer as the 3/4" hardwood. That could save you a little space.
Also, I wonder if you could skimp on the thickness of the first layer of plywood a tad. Also, remember that 1/2" plywood is a nominal thickness and that it is actually about 1/16" less than that. Even without skimping, you could be able to lay a floor that is approximately 1-3/8" (actual) rather than 1-3/4 nominal. With some creative sub-subflooring, maybe that could be less. This, of course, comes in the form of "brainstorming" advice and you should talk with a pro before heading down my route.
The only hardwood floors that I have put down myself were on top of solid/old plank subflooring and I used 3/4" t&g oak strips over 1/2" plywood. As far as the process of putting the floor down, it was a lot of fun once the subflooring was in. I had a blast slamming that nailer. The subflooring work was heavy and almost more than I could handle by myself.
03-10-2003, 12:52 PM
Jered is that double plywood method mentioned in that link you provided? I'd like to read up on that, but the concept of plywood over concrete slab has always been a big No-No for me, Now I am an old dog, but I'm always looking for new tricks :)
Danford C Jennings
03-10-2003, 07:43 PM
Well, if you want solid hard wood flooring, you will have to deal with the inch and a half transistion, regardless if you use 1"x2" sleepers or the 2 layers of ply. I will also add that 15lb felt is not used as a vapor barrier. It's used to allow the bottom of the flooring to breath and it helps to eliminate squeeking. You'll need 4 or 6 mil poly for the vapor barrier.
The other alternative is to go with a hard wood composition, Bruce, Mannington, and others sell it in thicknesses ranging from around 1/4tr to 3/8ths. These composistion floors are tongue and groove, have a hard wood veneer, and can be put down with mastic or they can "float". The mastic acts as the vapor barrier, on floating floors you'll still need to lay down poly, then the poly foam that comes with the flooring, which is about a 16th in thickness, they'll also provide the glue and T&G blocks for installing the floor. If it were me, I'd go with the hard wood composition... [link:http://forums.woodworking.com/cgi-bin/dcforum/dcboard.pl?az=read_count&om=3451&forum=DCForumID9|Click here] to go to an ongoing discussion on hard wood floors in the "I'm New to Woodworking..." folder. FWIW.
03-11-2003, 09:40 AM
You said what I meant regarding the 15lb felt. I am very skeptical about running poly over concrete that may have moisture. Why potentially create a larger problem? I would be driven to deal with the moisture potential first, or am I missing something here?
Nice thought about using the sleepers.
Danford C Jennings
03-11-2003, 09:52 AM
I think you're missing something.....The vapor barrier prevents moisture problems, since concrete is porous. The sleeper "idea" is not mine, it's a standard practice. When sleepers are used, the strips or planking are blind nailed directly into them, since there is an air space, felt would not be used...FWIW.
03-11-2003, 10:50 AM
If anyone is interested, I have a PDF file (it is fairy large), that I would be more than happy to email to anybody. It is the tech manual for a product I use regularly in my poly coatings business. It holds a hydrostatic head permanently as well as neutralizing alkali salts. Works wonders. Just let me know!
03-11-2003, 11:19 AM
I am familiar with the use of sleepers, I just forgot about them.
Ok, here is the deal, if a person does the test like I described above to check moisture coming from the slab, and moisture does end up being present, then the exact same conditions will exist under the poly under the wood floor. Now, what I am saying/asking is that if you have mosture emitting from the surface of the concrete, is it a wise idea to create a situation where the water/dew, has no place to go but to either sit or seep back into the concrete eventually causing damage to the slab? That is why I would remediate the moisture issue, if present, before I would simply install a poly vapor barrier? If you did a test spot and it looked like the inside of a shower curtain in the morning, would you do what you described, laying poly on the floor prior to installing...whatever?
Learn me sumpin' Dano! :7
Danford C Jennings
03-11-2003, 01:26 PM
If there is water/dew seeping through the slab, then is wasn't put in properly nor would've been the foundation. Without going into an indepth disertation on soil mechanics, a slab in residential foundation work has to be on top of a minimum 4" of compacted sand. If, and only if, the current slab is 4" thick on top of a 2" thick sub-slab with a vapor barrier between the two and the sub-slab has 15lb felt between it and the sand could a vapor barrier be eliminated. In reality, the actual moisture isn't detectable by the naked eye unless you put your hand on the concrete for a couple of minutes, when you remove your hand you'll see it's print. This is also why most building codes around the country require that pressure treated wood is to be used where ever it comes in direct contact with concrete, otherwise the wood would soon rot from absorbing moisture.
I'm unaware of any "moisture issue" that pertains to this discussion but, in answer to your last question, if I had the kind of moisture problem you describe I'd sell the house and move. ;)
03-11-2003, 02:13 PM
Good reading all - THANKS!!
Just a lil background - I will check for moisture and will prolly end up going with a composit simply cuz I don't think we can afford the full cost of a nice hard wood :(
We actually live out here in Tucson AZ - total rain is something like 2" per year and our average humidity is around 10% most of the time. Our house sits nice in high on a thick foundation and I'm not too concerned about excessive moisture - but I will definately check for moisture under the slab - would hate to find out theres some water problem but better now than later.
03-11-2003, 03:22 PM
Ah Dano, the answer I was looking for. Although I didn't know for absolutely sure, I was hoping you would say that it isn't typical for moisture to bleed through the concrete to the surface. I have on one occasion, however seen moisture seep through after taping a 14x14 piece of poly on all sides down to the concrete floor checking on it the next day and finding it like a little greenhouse. Which in that case I would never seal it up and install wood flooring. So we were saying the same things really that if there is moisture you deal with that first and not simply seal it in with poly?
Thanks Dano my friend, this has been very informative!
03-12-2003, 10:45 PM
I would love to know about such a product. I'm involved with a project to re-do a hardwood-over-concrete floor that failed due to moisture problems.
My email address: email@example.com
You need to learn from other people's mistakes. You'll never have enough time to make them all yourself.
03-13-2003, 11:00 AM
Gotta a reply form the website Dano listed - Thanks!!
Here it is
Take a look at the engineered wood floors. They are multiply but topped
with real wood in various species. Many can be sanded and refinished 1-3
times and all can be screened and recoated forever.
Another option, on concrete slab, is a solid wood parquet, which can be
glued direct or a thin real wood such as Bruce's 5/16" solid strip - Natural
Good advice - I didn't know that you could actually sand composites! That makes me think that they had a relatively thick top layer. My main concern/worry was that if it got nicked youd instantly be able to tell it was a laminate. Cuz of the height issue I think I've decided on the composite route. I'll be posting info on it down the road. Now its time to start saving :)
03-13-2003, 11:23 AM
>If anyone is interested, I have a PDF file (it is fairy
>large), that I would be more than happy to email to anybody.
> It is the tech manual for a product I use regularly in my
>poly coatings business. It holds a hydrostatic head
>permanently as well as neutralizing alkali salts. Works
>wonders. Just let me know!
Sweet! Your timing is perfect. I am in the process of installing a Mannington wood floor over concrete, and would like all the info I can get on possible waterproof coatings.
I also have a problem with a section of 120+ year old (1.5 foot tall, then all brick) fieldstone foundation that leaks. Fixing it properly is unfortunately not an option at this time, so I am looking at any treatment that may temporally solve the problem.
Just some of the joys of living in a building built in 1903, on the foundation of a building built in 1885.
03-13-2003, 12:44 PM
I also have a leaky foundation. Aren't old houses a blast!
Besides the obvious fixes of routing storm water away from the foundation and re-grading pretty much an entire yard, I am also looking into a product mentioned in my local newspaper after our big floods. I don't recall the name, but it is a sealant for foundation cracks that swells in the presence of water. I'm not certain that it is what I need, but I'm looking into it. If you are interested, let me know and I'll dig up the info that I have so far.
03-13-2003, 01:13 PM
This product is not water reactive, but alkali reactive. It grows crystals in the form of a glass within the structure of any cementiuos(sp?) material. It is completely permanent also. The guys I buy from waterproof concrete water tanks for munucipalities from the OUTSIDE.:o
03-13-2003, 02:45 PM
Concrete will retain its original moisture indefinitely. A "fun" experiment is to find an old chunk of concrete and take a torch to it. Make sure you have a full face shield, gloves and a heavy shirt. Steam, with no place to go is a very effective explosive.
I have always used "pea" gravel for the base layer of a structural slab. Compacted sand allows water to more readily wick because of the tightness of the grains. Pea gravel minimizes the granular contact and reduces wicking.