Repairs: floors and flooring

Timber floors

The most common types include:

• timber ground floors on traditional sleeper walls;
• traditional suspended timber joist first floor/upper floors;
• floated floors, i.e. a timber deck faced onto a concrete base or similar; and
• unventilated suspended timber basement floors (older properties).

Concrete block-and-beam floors

This method of construction is very similar to a traditional suspended timber floor but incorporates a series of inverted T concrete reinforced beams that are infilled with concrete blocks before screeding over.

It is unlikely that you will be carrying out the detailed design of a concrete block-and-beam floor. Most manufacturers can supply you with the necessary specification and construction information for their particular version of the product, including beam strength calculations for Building Control submissions/approval. Despite the perceived strength of concrete, beams can be overloaded, so you do need to ensure that you have provided sufficient information about:

• the position of any partition walls; and
• any extra loads being applied (e.g. from floors above, the roof, or any lintels which pick up openings, spans or loads from elsewhere in the building).

You will also need to ensure that the beam positions are marked out correctly (e.g. on the adjacent wall) so that they can be referenced after the floor screed has been laid, and partitions correctly aligned on them.

The concrete is rather more resistant to decay from condensation than timber would be (certainly in the absence of contaminants or incompatible ground conditions), but it is still appropriate to maintain a sensible air gap under the floor and to ensure there is adequate ventilation to prevent the build up of condensation. Any form of suspended timber floor or concrete floor will offer advantages, particularly on sites which are very out of level. The concrete suspended floor also presents the opportunity for incorporating insulation beneath the screed.

Building Regulations requirements are changing rapidly (especially regarding energy conservation, and the control and minimisation of acoustic transmission), so the specification of this type of floor can become increasingly complex. Early dialogue with the manufacturers and suppliers is strongly recommended so that a cost/specification can be considered at an early stage.

Concrete wide span beams require similarly careful treatment.

Reinforced concrete floors

These are probably most commonly encountered floors in commercial premises, and incorporate a traditional steel reinforcing mesh within a cast concrete floor.

This floor type can also be subject to overloading, and it is extremely difficult to assess what the original load-bearing characteristics of the floor would have been. Sometimes you need to break open a section of the concrete in order to examine the depth of the reinforcing bars or mesh and to consider the size and dimensioning of the reinforcing material before an accurate assessment can be made of the floor's load-bearing capacity.

In theory, the trend towards paperless offices and more electronic communications implies less loading on modern commercial floors. However, the need to store large quantities of material to avoid litigation in the future could risk overburdening the floor slab.

Repairs or modifications to this type of floor are best specified by an appropriately experienced building surveyor or structural engineer, but you need to be in a position to consider the implications of this.

Ground-supported floor slabs

Essentially this means the concrete is cast directly onto the ground.

Some form of damp-proof material needs to be incorporated, but this is a frequent cause of failure. Older solid floors may have no damp-proof membrane at all; many have perforated membranes because of sharp rubble in the hardcore base.

Early damp-proof membranes would have incorporated a brushed-on layer of bitumen. This would have probably also been painted around the wall perimeters to coincide with the main damp-proof course. Conveniently this solution would have also created a low-friction area helping the floor to settle down inside the perimeter walls.

Magnesite composition flooring

Occasionally you may come across 'magnesite composition flooring' (sometimes known as 'jointless flooring'). This is a combination of magnesium oxychloride together with a bulking agent (typically sawdust, but a number of other products were used, including asbestos).

The floor generally has an ochre yellow tint but could also have other colourings. It suffers dramatically if it becomes damp. Although primarily used in commercial premises, this floor type is sometimes also encountered in domestic properties. Prevalent in the 1920s and 1930s, it was used in a few cases until the 1950s.