How to Fix Wood Flooring to a Concrete Slab

How to Fix Wood Flooring to a Concrete slab

Article Summary: Fixing wood flooring to a concrete slab need not be a difficult task. This article looks at what’s involved and the steps you should take to ensure a good job. As always, it’s a matter of “proper preparation” that makes an average job into a great job.

How to Fix Wood Flooring to a Concrete Slab

If you really like the look of hardwood flooring but you have a concrete slab, don’t worry – you can still have a beautiful hardwood floor fitted. The biggest worry with concrete slabs is damp – moisture readily rises through the ground and eventually will move up and through your slab, but only if your builder hasn’t properly fitted a damp proof layer and your slab sits lower than the outside ground surface. I have lost count of the number of houses I’ve been asked to inspect for damp, only to find the owner has unwittingly raised the outside ground level. Usually this is for raised garden beds and such like.

Of course, if you have a basement and you want to fit wood flooring you should always test for damp first, especially if your property is over 15 years old. There is a better option for these types of areas, namely engineered flooring. The difference is that engineered flooring, because of the way it is manufactured, is able to withstand a greater degree of humidity and moisture than is real wood (actually, engineered is real wood, it’s just a man-made version).

There are a few steps you should take before installing any wood flooring, but these are especially applicable when installing over a concrete slab. The first is not to install until a new slab has had adequate time to dry out. There are numerous ideas of how long it takes for a slab to dry out properly. Rather than making a standard recommendation, say 3 months, why not hire or borrow a moisture meter? It could save you a lot of bother if you take this simple precaution first.

There is a cheaper, but less scientific way of testing for moisture by taping clear plastic over a small area of the slab and waiting 24 hours. If the plastic shows any sign of visible moisture, don’t fit the flooring. As I said, this method is less scientific and I would only use it if your budget is really tight or you can’t find a moisture meter.

The actual process of fitting a wood floor to a concrete slab is relatively straightforward. You have two options. After laying a damp proof membrane directly over the slab, you can either fasten strips (joists) of timber; these act as surrogate joists to which the wood planks can be fixed in the usual manner. Or you can screw down sheets of plywood.

Using marine grade plywood would be another barrier against damp – expensive but well worth it especially if you are using expensive flooring. Be aware of how much you will potentially raise the floor surface – it may be a lot more than you first think and doors, etc, will need to accommodate the higher levels.

Important – Before you fix the joists or sheets, check that they are level. If you notice dips in your slab, chock underneath the joists or sheeting until the surface is dead flat. This is very important, so please take your time with this step.

To fix the sheeting or joists to the slab, use screws. Please, never use masonry nails as I have seen done. Yes, they can be used, but unless you do the job properly, they will eventually come loose – and so will your floor. You can buy screws complete with their own plugs that fit by simply drilling a hole straight through the wood into the concrete. Push the screw and plug into the hole and use a drill to secure.

Fixing the actual floor to the sheeting or joists should be done using glue and suitable fixings. I like to staple flooring, and by using secret nails I can guarantee a flawless, tight finish. Don’t forget, before you fix your floor you need to let it acclimate first. Leave it in the room for several days before fixing to take up the humidity levels that it will live in.

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