In some circumstances flooring installers are instructed to install bonded resilient floorcoverings over cover concrete movement joints. This could be in commercial or residential projects. The explanations below are to help avoid problems when concrete joint terminologies are not fully understood or where similar terminologies are used to describe the same or similar concrete joints.

Isolation Joints Frequently Called Expansion Joints

Isolation or expansion joints are designed to allow for the expansion and contraction and sometimes to stop curling or warping of new concrete slabs. All such movable joints must be cleaned of all construction contamination prior to the installation of resilient floorcoverings. According to AS1884-2013 4.2 General Installation Procedures Section (f) floorcoverings shall not be laid over structural expansion or construction joints. Expansion joint covers designed for use with resilient floorings must be used at all movable joints. There are numerous options available.

Typical rucking of a resilient floor covering installed over an isolation or expansion joint is shown below.

The next image is a typical worm crack showing through the vinyl. The cause is generally attributed to a feather finish type smoothing compound or flooring adhesive having been applied over and filling the crack. Due to the expansion and contraction of the slab overtime the compound or the adhesive is pushed out of the crack which forms a slight ridge and can be seen in reflected light situations. The effect of the ridge can cause premature wear of the flooring over that raised spot.

Construction Joints frequently called Cold Joints

Construction joints or cold joints are normally a stopping point between a finished slab edge and where a new slab is going to meet or have met. All such movable joints must be cleaned of all construction contamination prior to the installation of resilient floorcoverings.

Once again expansion joint covers designed for use with resilient floorings must be used at all movable joints.

Contraction Joints (Saw Cuts) frequently called Control Joints

Contraction or control joints are a widely used method to control random cracking in concrete slabs. This produces an aesthetically pleasing appearance since the crack takes place below the finished concrete surface. The concrete will still be cracked, which, is normal behaviour, but the absence of random cracks at the concrete surface gives the appearance of an un-cracked section. In most cases successful floorcovering installations over non-moving joints are achieved once prepared using suitable non-staining and rigid fillers and / or cementitious patching and levelling materials. Always follow the manufacturer’s recommendations for the use and application of those products.

It is prudent to note according to AS1884-2013, and the floorcovering industry best practices:

The surface of a concrete subfloor shall be thoroughly checked for the following.

Surface quality

(a) Planeness—When a straightedge 2000 mm long is placed at rest at two points 2000mm apart on the surface, no part of the surface shall be more than 4 mm below the straightedge.

(b) Smoothness—When a straightedge 150 mm long is placed at any position at rest at two points on the surface, no part of the surface shall be more than 1 mm below the straightedge.

(c) Soundness—The surface shall be without cracks, grazing, dusting, rain damage, spalling, efflorescence or blistering.

Forbo warranties and most manufacturers do not cover rucking damage or telegraphing of the concrete joints. Subfloor show through in the floorcovering as a result of concrete movement or moisture coming from the joints subsequent to the installation of resilient flooring is not considered a product fault or failure and is structural or from a building site related condition.

It may be difficult to determine if curing compounds, concrete densifiers/hardening compounds, or sealers have been used. Always conduct adhesive mat bond tests prior to the installation to determine the integrity of the flooring system, and adhesive bond. Imperfections such as chips, spalls, cracks, and joints must be repaired using suitable patching and levelling materials. Always follow the manufacturer’s recommendations when using and applying these products and question the builder or architect if instructions are suggesting to install over joints.

Should you have any questions please contact:

Peter Brack Dip.Teach.Tech.Ed.
Certificate IV in Training and Assessment TAE40110, Technical Services Manager – Australia / New Zealand
Phone: 0439 063 336
Email: peter.brack@forbo.com