How to Prepare a Substrate for LVT Flooring

Preparing the substrate is one of the most important parts of fitting LVT flooring. It may not be the part you see once the room is finished, but it has a real bearing on how well the boards sit, how securely they click together and how the floor performs over time.

All of our Luxury Click Flooring ranges at Topps Tiles use click-fitting systems and come with integrated underlay already attached. This makes installation more straightforward, but the flooring still needs a dry, clean, stable and level surface underneath it.

This guide explains how to prepare concrete, screed and timber substrates for LVT, SPC flooring and real wood veneer flooring, including the flatness and moisture checks needed before fitting begins.

What Is a Substrate?

The substrate is the surface the new flooring sits on. In most homes, this will be concrete, screed or a timber subfloor.

Our click-fit LVT is laid as a floating floor. The boards lock together but are not glued, nailed or screwed to the surface below. This means the substrate must be firm and even enough to support the floor across the whole room.

Dips, raised areas, damp patches or movement underneath can all cause problems, as boards may rock or sit unevenly, which would lead to click joints being put under strain and gaps appearing over time.

What Condition Should The Substrate Be In?

Before fitting LVT, the substrate should be:

Dry

Clean

Stable

Level

Free from loose material, residue and contamination

Brush or vacuum the full area before you begin, and remove anything that could prevent the boards from sitting properly, including dust, debris, paint, varnish, wax, oil, sealants, solvents, sand and old adhesive. We also recommend that you walk over the floor and check that it feels solid, as loose areas, cracks, dips, raised sections and movement should all be dealt with before any flooring is laid.

Why Does The Substrate Need to Be Level?

Click-fit flooring relies on the joints being aligned and locked together correctly. If a board is sitting over a dip, part of it may be left unsupported when pressure is applied in that area, and a raised area can have the opposite effect, forcing the board upwards and putting pressure on the joint.

The permitted variation depends on the flooring range:

For SPC flooring, the substrate should have no more than 5mm deviation over a 2m length and no more than 2mm unevenness over a 20cm length.
For real wood veneer flooring, the substrate should have no more than 3mm deviation over a 2m length and no more than 2mm unevenness over a 20cm length.
For Pronto LVT, the level variation should be no more than 5mm within a 3m area.

Use a suitable straight edge to check the floor in several directions. Pay particular attention to doorways, edges of the room, old repair patches and joins between boards, as these are often where uneven areas show up.

Any sections outside the stated tolerance will need to be corrected before fitting.

Preparing Concrete and Screed Substrates

It is important to make sure that the concrete and screed substrate is sound, dry and level before being deemed as suitable. You should always check the surface for cracks, loose or hollow areas, damage and any remaining contamination.

If you notice any cracks, these need to be repaired with a suitable compound. For SPC and real wood veneer flooring, cracks in concrete must be repaired and should not be wider than 5mm or deeper than 2mm before fitting.

Before you move on, make sure any old adhesive, paint, oil, wax or sealant has been removed from the surface. If the substrate is rough, damaged or outside the permitted level tolerance, you may need to use a suitable levelling compound to create a firm and even base.

It is also worth checking the moisture level before fitting begins. Concrete and screed can look dry at the surface while still holding moisture underneath, so readings should always be taken and recorded before installation.

Preparing Timber Substrates

It is essential to ensure your timber substrate is structurally sound. We recommend checking the entire floor carefully, as the centre might feel stable while the edges and corners are loose or hollow. Any damaged, creaking, or unsecured boards must be repaired, screwed down, or replaced before fitting your new floor.

Make sure all screw heads sit slightly below the surface, and check for any raised edges or uneven joins between boards that need to be corrected.

Wooden subfloors should be overboarded with a suitable sheet material in line with the manufacturer’s instructions. This creates a smooth and stable foundation for your LVT.

Once the preparation is complete, brush or vacuum the area thoroughly to clear away all dust and debris.

Moisture Checks Before Fitting

Moisture readings should be taken before fitting over concrete, screed or timber, and it is good practice to keep a record of the results.

For SPC flooring, moisture levels must not exceed:

12% for wooden substrates
2% for concrete substrates
0.5% for anhydrite screeds

Where SPC flooring is being fitted over underfloor heating, moisture levels must not exceed:

1.5% for concrete substrates
0.3% for anhydrite screeds

For real wood veneer flooring, moisture levels must not exceed:

12% for wooden substrates
2% CM for concrete substrates
0.3% CM for anhydrite screeds

Where real wood veneer flooring is being fitted over underfloor heating, moisture levels must not exceed:

1.8% CM for concrete substrates
0.3% CM for anhydrite screeds

Do not fit the flooring if the readings are above the stated limits. The substrate will need more time to dry or further preparation before installation can begin.

Can You Fit LVT Over Existing Flooring?

LVT should not be installed over soft surfaces such as carpet, existing PVC flooring or similar materials. These do not give a click-fit floor the firm support it needs. Other existing floor coverings may also need to be removed if they affect the level, stability, height or moisture conditions of the room.

Do not rely on appearance alone, as an old floor can look reasonably flat while still hiding movement, softness, loose material or trapped moisture underneath.

Do You Need Separate Underlay?

No. All of our Luxury Click Flooring ranges have integrated underlay already attached.

A second layer should not be added unless the fitting instructions for the exact product specifically say otherwise. Extra underlay can make the floor too soft, interfere with the click joints and lead to movement once the floor is in use.

The flooring should be laid directly over the correctly prepared substrate.

Preparing for Underfloor Heating

LVT, SPC and real wood veneer flooring can be used with suitable underfloor-heating systems, provided the product guidance is followed. Heating elements must be covered with an appropriate screed or overlay before the flooring is installed. The heat needs to be spread evenly across the floor, and the surface temperature must not exceed 27°C.

Moisture limits can be lower when underfloor heating is present, so the correct readings for the chosen flooring must be checked carefully.

Underfloor heating should never be used to force-dry a damp substrate. The base must be allowed to dry properly before installation.

Need More Help?

A properly prepared substrate gives LVT flooring the support it needs. It helps the boards sit evenly, reduces unnecessary strain on the click joints and gives the finished floor a better result.

Always use the fitting instructions for the flooring range you have chosen, as tolerances and installation requirements can vary. You can also visit your local Topps Tiles store for advice on preparation products, fitting tools and finishing pieces before you begin.

How to Prepare a Substrate for LVT Flooring

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How to Prepare a Substrate for LVT Flooring