Stephen Boulton, Technical Service Manager at F. Ball and Co. Ltd, advises on flooring installations where expansion and construction joints are present.

Movement joints and construction joints are an almost universal feature of buildings, particularly larger ones. Only in certain circumstances can these joints be covered with subfloor preparation products or floorcoverings without risking floor failure.

Expansion joints (building movement joints) are breaks that are commonly and deliberately incorporated into a building’s structure, including its floors, to allow it to accommodate stresses and strains exerted by movements as a result of heat, moisture and environmental forces. Where they are present in a building’s screeds, they are most often located at door thresholds, corridors and terminated construction zones.

Construction joints (day joints) are different. These lie at the interface between sections of a concrete pours. These joints are not normally designed to accommodate movement and often contain reinforcement.

Floorcoverings and subfloor preparation products that are installed over designed movement joints are liable to rupture. Not only will this look unsightly, but it can also present a health and safety hazard. For this reason, it is always advisable that a flooring contractor consults a structural engineer or site plans to find out what kind of joints are where.

DIFFERENT APPROACHES A flooring installation should be terminated either side of an expansion joint and a proprietary joint cover fitted – subfloor preparation products and floorcoverings should not be installed over the top. Movement joints are also usually filled with a flexible material, such as a polysulphide filler, which absorbs compressive forces without damage and also acts as a sealant, preventing an ingression of dust and debris, which could render the joint ineffective.

Only where construction joints that are designed to accommodate future movements are present in a subfloor, must floor preparation products and decorative floor finishes be terminated either side of the joint. The whole joint should then be covered with a proprietary expansion / joint cover.

OTHER JOINTS It is also worth knowing about crack inducement joints, which are cut into concrete screeds to encourage cracking, which is inevitable as the concrete curls/contracts over time. Floorcoverings can be installed over this type of joint. It is recommended that they are filled with an appropriate floor repair compound, such as F. Ball’s Stopgap 400 Repair, to ensure a perfectly smooth surface for the receipt of floorcoverings.

REFURBISHMENTS It is not uncommon to find that movement joints in subfloors have been covered by previous work when undertaking floorcovering installations that are part of a refurbishment. In this case, remedial work will be required to remove all


materials applied directly over and either side of the joints before work proceeds.

This is another reason why it is always worth checking the locations of expansion or construction joints – they may not be evident upon first inspection.

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