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How to Lay Hardwood Flooring on a Slab of Concrete

how to lay hardwood flooring over top of a slab of concreteYou may have considered hardwood flooring for your home, but have concerns about installing it on top of a concrete slab versus a sub floor system. This could be because you have heard stories about the hassle involved with this process with the old ways of installing and also problems caused by moisture. While it is somewhat more difficult to install hardwood over concrete than a wood subfloor, it is not impossible.

Check out the wide variety of hardwood flooring available for installation over concrete by clicking HERE!

While you may have an idea of the type of hardwood floor that you want to put down, before purchasing anything you first need to decide how you are going to install it. You may choose to go with the route of the traditional 3/4″ hardwood flooring, or choose instead to go with the newer varieties available in engineered and click-lock flooring that feature a layer of hardwood on top.

How Hardwood Floors Were Previously Installed

An older method, known as the “sleeper method” involves applying a layer of mastic to the cleaned slab surface and then fastening 2′ x 4′ pieces of lumber on their side on top of top of the adhesive. A layer of polyethylene film or tar paper is then laid on top of the lumber as a moisture barrier. Care must be taken not to puncture this layer, as that would allow moisture to reach the hardwood flooring. The next step is to nail the hardwood flooring down.

how to lay hardwood flooring over a slab of concreteThe problem with this method is that it adds an additional 2.25 to 3 inches to the height of the room, which could interfere with existing exterior doors, installed cabinets, or fixtures. Because of this reason, in addition the potential of a mess with the mastic, this method has been phased out by flooring professionals over the years.

A former method used was to glue or nail hardwood directly to the moisture barrier laid on top of the concrete slab. The problem with this, however, is that you are running the big risk of your flooring warping or popping up from moisture. It is in wood’s nature that it will expand and contract according to moisture conditions. Thereby, this method is rarely used and is definitely not advisable.

Choosing an Installation Method and Type of Floor

You will need to be clear on which method you are using before choosing flooring because different types of flooring need different types of installation. The following methods do have some pros and cons associated with each, so if you are undecided which to choose, it is best to consult with your flooring supplier.

A method that has been gaining popularity has been to install a floating subfloor that consists of two layers of plywood (3/8″ each) that overlap and are attached to one another by short fasteners such as staples.

This layer is placed on top of a layer of polyethylene film or tar paper that acts as a moisture barrier. The hardwood flooring can then be nailed to the subfloor. With this method, you will only be adding about an additional 1.5 inches to the height of the floor.

how to lay a hardwood floor over a slab of concreteIf you want to avoid the work of installing a subfloor, you can choose to go with real wood engineered flooring. The advantage to this type of flooring is that it consists of several layers, with the top layer being real wood that can be refinished in the future. The additional layers are glued together with their grains in opposing directions, which helps to minimize expanding and contracting from humidity.

The flooring pieces are then glued together on top of the moisture barrier laid on top of the concrete. You will need to install shoe molding around the perimeter of the room to cover the expansion joints between the flooring and the wall and existing molding.

For those who want to totally avoid using glue, the click-lock system is for you. Similar to the engineered flooring, the planks are made of several layers with the top one being real wood. This type of flooring will float on top of your concrete slab and will allow for the natural expansion and contraction of the wood.

You will, however, need to take the additional step of installing cushioned underlayment on top of your moisture barrier layer. You will also need to secure the floor in place with molding or quarter round.

Purchasing the Necessary Materials and Tools

Now that you have decided on the type of installation and flooring you are going to use, you need to purchase all the materials you will need. You will need to measure the room you are planning to put the floor in to get the square footage you will need to know for purchasing the correct amount of flooring, moisture barrier (tarpaper or polyethylene film), and cushioned underlayment or plywood if needed. Be sure to purchase the appropriate adhesive or nails that are recommended by the flooring manufacturer for use with the flooring you choose.

how to lay hardwood flooring on a slab of concreteA good rule of thumb is to always purchase at least 10% more than what is needed for the flooring, even if it requires you to purchase an entire extra full box of flooring. This could save you a headache in the long run, especially if your flooring is special order, you make a bad cut, or in the event of a damaged piece in one of the boxes. It is also advisable to put away some of the extra in the event a piece is damaged in the future, then you can pop out the bad piece and easily replace it.

It is also advised that you purchase the flooring a week in advance of the installation and place the boxes flat in the room where it is to be installed. This will give the wood the opportunity to adjust to the humidity and temperature conditions of the room before installing and will help avoid expansion and contraction after the installation.

If you have existing carpeting on your floor, invest in a heavy-duty utility knife with heavy-duty blades and a roll of duct tape for reasons that will be explained later. Also, be sure to purchase a package of face masks to help prevent breathing in the dust that has accumulated for years under your carpet.

A table saw will come in handy for easily making long cuts and speedier short cuts. You will also want to have a coping saw for odd cuts and a miter saw for cutting molding if needed.

Another good idea is to get yourself a pair of knee pads or a kneeling pad to cut down on some of the pressure on your knees. Many flooring suppliers offer a kit that can be very useful, as it includes rubber shims to provide proper spacing between the wall and the new floor during installation and a rubber tapping-block for use with installing click-lock flooring.

Floor Preparation

You will need to strip the floor area down to the concrete. If you have existing carpeting, you are going to have to pull it up from the floor. You will first want to carefully remove the existing molding from your walls and set it aside if you plan to reuse it. To make the job easier, slice your carpeting straight through the padding underneath into manageable lengths, roll both together, and then secure with the previously mentioned duct tape.

how to lay a hardwood floor on top of a slab of concreteOnce the carpet is up, you will need to sweep up all the accumulated dirt and dust that was underneath it; hence, the suggestion to use a face mask. You may find that some of the carpet padding has adhered to the concrete, so you will need to scrape that up also.

Once all the debris has been cleared, you will want to inspect the concrete for any holes or evidence of mold.

You can fill any holes with concrete patch and allow it to dry thoroughly. If you find mold, make sure that you do not have a leak coming from an external wall, but it may just be there from a past spill. The mold can be removed by washing the concrete with a water and bleach solution. You must allow this to dry completely also before installing the hardwood flooring.

Moisture is the Enemy

how to lay a hardwood floor on a slab of concreteIt cannot be emphasized enough that you must allow your concrete floor to completely dry before installing your floor. Even though you will be putting down plywood or just a moisture barrier according to the method you plan to use, you still do not want to chance having moisture trapped below your floor.

Once the concrete slab is completely dry, you can then lay your moisture barrier. You will want to lay longer strips in the direction of the longest measurement of your room. Be sure to overlap the pieces and secure with duct tape to each piece.

If you will be installing a subfloor of plywood, this is when you will install it. If you are installing click lock flooring, you will now also lay down the cushioned underlayment in a similar manner to the moisture barrier. However, do not overlap but lay flush and tape the sections together.

Time to Lay down that Floor

You will start laying planks down at the longest wall of the room. Be sure to stagger your planks. Depending upon your installment method, you will either be nailing or gluing your boards to the installed plywood, gluing your engineered flooring, or snapping or tapping your click-lock flooring in place. It is advisable to work from several boxes of boards to blend in any possible variations of color.

how to lay hardwood flooring on top of a slab of concreteIf you are gluing your hardwood or engineered flooring, you will want to firmly press the boards against one another to ensure there are no gaps and clean up any oozing of glue from the top of the boards with mineral spirits. To make sure your boards do not slip while installing, you can apply blue painter’s tape every couple of feet to hold them together as you work. It is easiest to lay a length of section first and then fill in any areas that require cut pieces.

Once you have finished installing all the boards, you will want to walk over the floor to ensure that the flooring is laying flat and has made contact with the concrete or subfloor if installed. With this done, you can now install your molding to either hold your floating click-lock floor in place or cover the expansion joints created with the engineered flooring.

Today, with new advancements in the types of flooring and installation methods available, you too can have beautiful hardwood floors in your home even if you are on a concrete slab foundation. If you are a do-it-yourselfer comfortable with doing this type of project, you could easily accomplish this job in one weekend. You may want to view videos that are available on YouTube or on DIY Network’s website to determine if you are up to the task.

There’s no better time to start looking for new hardwood flooring for your home than NOW!

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