Either solid wood flooring or engineered wood flooring can be fitted onto a concrete subfloor. Most concrete subfloor consists of a sand and cement screed mixture. Solid wood flooring must be glued down directly onto the screed, and engineered wood flooring can be either glued down or floated over an underlay without being fixed into place. Before installing any hardwood flooring onto a concrete subfloor, ensure that the screed is dry, firm and level.
Ensuring the concrete is dry
A concrete subfloor must be moisture tested with a concrete floor moisture metre before any hardwood flooring is installed. When testing for moisture, the relative humidity of the screed must be below 6% MC (Moisture Content). If using under floor heating within the concrete subfloor, it must have been running for at least seven days before moisture testing to ensure an accurate reading is given.
If the subfloor is an old concrete or screed floor and is not dry (according to a concrete floor moisture metre) then a primer can be used to seal the floor. It must then be re-tested for moisture before hardwood flooring is installed. If the subfloor is new screed then it is best to let it dry naturally, although there are products available to seal it. These products are not suitable to use with under floor heating so the floor must be dried naturally. To speed up the drying process heating systems and de-humidifiers can be used. However, be careful not to dry the screed out too quickly, otherwise it may crack.
Ensuring the concrete is firm
The screed must be firm and of good quality before any hardwood flooring can be installed. If the screed is poor quality and crumbling away, it is recommended that the subfloor is repaired properly before laying either solid wood flooring or engineered wood flooring.
Ensuring the concrete is level
The screed subfloor should be flat and level before any hardwood flooring is fitted. This can be tested using either a straight edge or spirit level. If the subfloor is not level, then a levelling compound should be used to smooth and level the subfloor. If a levelling compound is used then it will need to be moisture tested to ensure it is completely dry before installing any hardwood flooring (see above for more details).
