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How to prep concrete for glue down flooring

Using glue is a nice and easy way to set up flooring. If you know what you’re doing, you can have your floor ready in about two days. However, if you have a concrete subfloor, to get the best results you also have to know how to prep concrete for glue down flooring.

Preparing the subfloor to receive the flooring is very important to get a high quality finish. If your subfloor is damaged and uneven, it can also make the flooring uneven. And it may also make it more prone to get damaged in the future.

There are different kinds of subfloors and methods of floor installation, and each combination has their own characteristics, so in this guide we will focus only on concrete and glue down flooring.

How to prep concrete for glue down flooring: a short guide

A good preparation of the subfloor is crucial to get good results after laying down your flooring. When using glue down flooring, this is especially critical, as the flooring will be literally glued to the subfloor. If the subfloor has problems, then so will the floor.

Follow the steps below to know what you need to do.

Step 01 – Dry it up

Reducing the moisture content of the concrete slab is very important to get a good finish. If the concrete is too wet when installing the floor, it can give you some problems down the road. The moisture can make the plies of engineered floors separate, can make hardwood warp, among other issues.

If the concrete slab is recent, make sure it is at least a month old, but between two and three months is better. Use moisture meters to keep track of how wet it is. Refer to the manufacturer guidelines for the boards and glue to know what the moisture level should be when installing the floor.

Concrete will always be a bit wet, so don’t expect it to completely dry out over the next few months. Getting it below the manufacturers’ specifications is already good enough to get a high-quality floor.

Step 02 – Make it flat

Making the effort to make the concrete slab flat is important to get good results, but most of the time it’s not enough. The slab may end up with some bumps and low spots during drying, and you’ll have to straighten them out.

You can leveltThe bumps using a concrete grinder or an angle grinder. And should also fill up the low spots, preferably with some material that dries faster than concrete. There are some materials specifically made for patching floors out there, and they could be interesting for your case. Just make sure they can withstand at least 3000 psi, so that they don’t give you problems later on.

Most manufacturer specifications require that the floor be flat within 3/16 of an inch along 10 ft. That is, the difference between the highest and lowest point in every 10 ft line along the floor should not be greater than 3/16 inches. However, check the manufacturer guidelines, as it may be different for each one.

Step 03 – Clean it well

To make sure that the glue will adhere well to the concrete, it’s important for the subfloor to be as clean as possible. Otherwise, the glue will adhere mostly to the dust and dirt and end up making the adhesion weaker.

If you had to patch the floor because of low spots, then wait for it to dry first. Then, clean up the slab without using water, otherwise you’ll have to wait for it to dry again.

Use a broom or a vacuum cleaner. Clean it as well as you can, to ensure you end up with the best possible results.

Step 04 – Acclimatize the boards

Steps 01 to 03 explain how to prep concrete itself for glue down flooring. However, after you finish preparing the concrete subfloor to receive the boards, it’s also important to prepare the boards to be laid onto the concrete.

Because concrete is always a bit wet, if you just apply glue and the boards minutes after cleaning the subfloor, you risk having the moisture ruin the floor anyway.

To prevent that, it’s recommended that you leave the boards laid out onto the concrete for at least three days before you start gluing them down.

This way, they’ll absorb the moisture and temperature in the room before you glue them down. This will prevent them from warping due to the struggle between the strength of the glue and the expansion due to temperature and moisture.

That does not mean you won’t need to add spacers to install the floor, though. It just prevents expansion during the first few days after installation, not expansion because of the different temperatures throughout the day and throughout the year.

How to prep concrete for glue down flooring: final thoughts

Preparing you concrete subfloor to receive the flooring may look simple, but there are a lot of things to account for. You have to make sure you’re measuring the moisture correctly, that you have the right tools, and that you do a good job of making the concrete flat and clean.

To ensure that you get the best possible results and don’t end up needing to scrap out the floor later on, get some flooring professionals.

We at Meta Flooring can do the job for you. Contact us right now and get a free quote! It’s the first step towards getting the house of your dreams.

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