What Subfloor Can You Lay Rubber Gym Tiles On?

The question of the subfloor is almost always asked after the question of thickness, when it should come first. It is the existing floor that decides whether the tiles are laid loose or bonded, whether a levelling compound is needed, and sometimes whether you should change thickness altogether. Here is what each type of subfloor imposes.

Three conditions that apply to every subfloor

Whatever is already on the ground, it has to be flat, clean and dry. Those three words translate into concrete checks:

• Flat: check with a two metre straightedge. A thin tile follows the defects underneath and makes them visible; a thicker tile hides them better.
• Clean: dust, laitance and old adhesive residue prevent bonding when tiles are glued, and make tiles migrate when they are laid loose.
• Dry: a recent screed must have dried, and a floor subject to rising damp must be treated before, not after.

Subfloor by subfloor

Concrete and screed

This is the simplest case and the one the tiles are designed for. Loose laying is enough on an area closed in by walls or machines; bonding becomes necessary in circulation zones and on large areas. On a new screed, respect the drying time before covering it.

Ceramic tiles

Laying over existing ceramic tiles avoids an expensive removal, and it works perfectly well provided the tiles are properly bonded. The point to watch is the joint: a hollow or wide joint eventually draws itself on the surface under a 10 mm tile. Two solutions: a levelling compound, or a 15 mm tile, which tolerates irregularities better.

Timber floors, upper floors and mezzanines

The real question is not the tile but the load: a strength area adds the weight of the machines, the plates and the users. On a timber floor or a mezzanine, the load capacity is verified before the covering is chosen, with the project manager or the structural engineer. On an old or slightly unstable timber floor, a polyethylene film between the two protects the wood from residual moisture and prevents wear through friction. Once that point is settled, the issue becomes acoustic, and an acoustic underlay laid beneath the tile is what treats impact noise transmitted to the space below.

Underfloor heating

Rubber is an insulator: the greater the thickness laid, the lower the heat output of the system underneath. Underfloor heating installation guides cap the thermal resistance permitted for floor coverings for exactly that reason. In practice a thin tile can remain feasible where a thick one is not, but that is not decided from a general table. Tell us the type of underfloor heating and the thickness you have in mind before ordering, and compatibility is checked case by case.

Outdoor ground: soil, gravel, compacted fill

A rubber tile is not a self-supporting covering. Laid directly on soil or on grass it follows the deformations of the ground, separates at the joints and traps moisture. A stable, free draining base is required, compacted gravel or a concrete slab depending on use. For a permanent outdoor installation, use products intended for it: our outdoor sports flooring is designed for UV, frost and water run-off. In all cases allow a slight fall for drainage, because water standing under the tiles eventually degrades the base.

Damp and rising moisture

This is the point that causes the most trouble in garages, basements and older buildings. Because rubber has low permeability, moisture rising from the subfloor stays trapped: odours, adhesive failure, degradation of the subfloor. A simple test gives a first indication. Tape a square of plastic film to the floor, sealed on all edges, for 24 to 48 hours. If there is condensation underneath it, the floor is emitting moisture and the problem must be dealt with before laying.

What the subfloor changes in your quotation

• Levelling compound: a line item as soon as flatness is not there, and often cheaper than moving up a thickness over a large area.
• Loose or bonded laying: the subfloor and the size of the area decide this, not preference.
• Underlay: useful on an upper floor for acoustics, or to make good a slightly irregular subfloor.
• Thickness: an imperfect subfloor pushes towards a greater thickness, which changes the price per square metre.

Frequently asked questions

Can rubber tiles be laid over ceramic tiles?

Yes, if the tiles are well bonded and the floor is clean and dry. The point to watch is the joint: a hollow or wide joint eventually shows through a thin tile. A levelling compound or a 15 mm thickness solves it.

Can they be laid directly on soil or grass?

No. A rubber tile is not self-supporting: on soft ground it deforms, separates and traps moisture. A stable, free draining base is required, compacted gravel or a concrete slab, or products designed for outdoor use.

What about underfloor heating?

Rubber is an insulator and reduces heat output as thickness increases. Compatibility is checked case by case according to the type of system and the thickness planned, so state both before ordering.

How do I know if my floor is too damp?

Tape a square of plastic film to the floor, sealed on all edges, for 24 to 48 hours. Condensation under the film means the subfloor is emitting moisture, which must be treated before laying or it stays trapped under the rubber.

Do I need a levelling compound?

As soon as a check with a two metre straightedge reveals pronounced defects. Over a large area, levelling often costs less than moving up to a greater thickness intended to hide them.