Tongue and Groove Flooring Over Concrete Slab
Q: What is your opinion on how to place tongue and groove flooring over concrete slab ?
Jack Flounders
A: Any time you are putting a wood floor onto concrete there are certain considerations and rules you will want to adhere to. First and foremost is that you should not put a 3/4″ solid floor over concrete. Also, keep in mind that you can not nail into concrete. The reason for these first two has to deal with moisture vapor being released by the concrete. With nail down applications, this would leave the wood vulnerable to moisture and beyond being very hard to find a proper nail that would not splinter the planks, it would then absorb moisture and would warp, buckle and more. With 3/4″ solid, it is naturally less stable than other types of flooring and is more prone to movement. As these floors expand and contract so much more than other floors, they can not be glued in place which is what would be required to install over concrete.
With those two out of the way, let’s look into what solutions are available for your project. Your best bet over concrete would be to look into floors which can be floated. For tongue and groove floors, this means only engineered flooring, and then when you are installing you will have to use tongue and groove glue to adhere the planks together (since you will not have a locking mechanism like the click-together floors). Floating floors, even those that require glue in the tongue and groove, tend to be far easier to install than doing a glue down method, which is the only other option here. Keep in mind that with a floating installation you will need underlayment and a moisture barrier. For underlayment, get something relatively dense so that your floor feels a bit more solid and has less spring when you walk over it. Since you intend to install over concrete you must use a moisture barrier to prevent the moisture vapor, which slowly off gases from the concrete, from getting into your flooring.
If you are looking at a floor that can not float, but is an engineered or 5/16″ solid floor, you can glue these floors down over concrete. In this case your adhesive will act as a moisture barrier, so there is no need to purchase an additional barrier. The biggest problem with glue down applications is that they are the most likely of the DIY installations to fail. The reasons behind this is that if a subfloor is not perfectly level and the adhesive is not cured properly before laying planks, then the entire process will usually fail. Typically I suggest allowing only a professional installer to do a glue down application as they are relatively complicated and quite messy.
So let’s sum up: For T&G flooring over a concrete slab you can only install engineered floors or a 5/16″ solid floor. Your best bet would be to find a floor which can be installed as a floating floor, but your other option would be a glue down floor.