Moving in the right direction
Jason advises on flooring installations where movement (or expansion) joints 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. Here I’ll advise on flooring installations where they’re present.
Also called expansion joints, movement joints are spaces 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. The location of movement joints are normally pre-determined by the architect, and are usually placed in areas which will have a minimal visual effect on the overall finished project.
Construction joints are different. These lie at the interface between sections of a concrete base. Like expansion joints, they are sometimes designed to accommodate movements in a building’s structure, but not always. Construction joints that are not designed to accommodate movement and are confirmed as static with no further movement, can be treated as a normal subfloor.
However, if further movement does take place, then 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.
When it comes to installing floorcoverings where expansion joints are present, a flooring installation should be terminated either side 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 prevents ingress of dust and debris, which could render the joint ineffective.
Where construction joints that are designed to accommodate future movements are present in a subfloor, a metal upstand on each side of the joint, or similar proprietary system, needs to be carefully fitted so that it finishes sufficiently above the screed surface to allow for the specified thickness of the flooring and fitting can be carried out neatly and tightly, following this a suitable capping strip may be inserted.
It’s also worth knowing about crack inducement joints, also known as saw cuts, which are cut into concrete screeds to encourage cracking, an inevitable feature as the concrete contracts over time, to go in a particular direction. Once these and any other joints are confirmed as static by a structural engineer, with no potential for further movement, the installation of floor preparation products can then take place.
It’s recommended that crack inducement joints are filled with an appropriate floor repair compound such as F Ball’s Stopgap 460 Exterior Repair, or an epoxy repair system, such as Stopgap SRS mixed with kiln-dried sand, to ensure a perfectly smooth, static base, ready for the installation of floor preparation products and floorcoverings.
It’s 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, into 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.
For advice on subfloor preparation and floorcovering installation where expansion and construction joints are present, or any other project-specific query, you can contact F. Ball’s technical service department 8.30am–5.00pm, Monday to Friday.