Expansion Joints and Underfloor HeatingDural Movement Joints specified on public transport facilities

Public Transport facilities including airports, bus stations and rail stations all require tiled flooring that comply with certain aesthetic and functional standards to maintain a high customer experience. Clients expect their tiled flooring to remain crack-free for many years.

Consider the stresses a building is under during its life cycle, expanding and contracting in all directions. Imagine if the floors were sheets of glass, any slight movement and they would crack, break up or shatter.

A subfloor construction within a typical commercial building is commonly laid in sand and cement rafts in bays of approx. 6m x 6m. Each raft will take on average a full mm of depth per day to dry out and as they do they shrink in size. This natural drying time can be a problem if the project completion date is time critical.

All hard flooring moves independently by expanding and contracting at different rates so it is a requirement for flooring installations to have movement protection. Judith Mawtus from Dural UK ltd offers some practical advice;

A time saving solution to this problem is to lay decoupling matting directly over the subfloor. It can be put in place as soon as the subfloor is dry enough for a person to walk over it. Air channels in the matting allow the subfloor rafts to continue to dry out in a controlled way by preventing the top layer of the screed drying quicker than the bottom. This slow drying period leads to a stronger subfloor. The edges of the subfloor will curl upwards if the top dries quicker leaving an uneven surface.

Decoupling matting prevents the subfloor shrinkage and cracking from being passed into the newly laid surface tiles.

Tiling directly onto the rafts when they are not chemically dry and without matting will almost certainly cause random “lightening flash” cracks in the surface tiles and they could potentially “tent” or pop off the subfloor.

All subfloor rafts will move independently over time as buildings expand and contract horizontally and vertically. This is generally caused by ambient air temperature and below ground water table fluctuations.

If surface tiles are laid directly onto each subfloor raft and they bridge the gap between each raft a perfectly straight hairline crack would appear the first time any vertical movement occurred in the subfloor. The hairline crack would nearly always follow the line of the subfloor movement zone void on the surface tile.

To isolate this problem a movement absorber is needed in the surface tile directly over the subfloor movement void between each raft. This comes in the form of a Movement Joint. Bedded into the adhesive under the tiles the movement zone of the joints allows movement to occur in all directions and isolates stress in the tiles from one raft to its neighbour.

Movement Joints and decoupling matting are specified on all types of transport projects and other projects where there are large expanses of hard flooring, projects such as retail, commercial and large domestic dwellings.

Decoupling matting and movement joints are both designed to cope with heavy stresses and distribute them evenly between the subfloor and floor covering, they can also prevent conduction of noise from footfall and other bodies. Even floors subject to heavy stresses remain in better condition for longer when movement joints and decoupling membranes are specified.

Movement Joints are available in PVC, Aluminum, Stainless Steel and Brass. The advice from the experts is that unless cost is an overriding issue then PVC profiles are not used. They are a short-term solution and lack the durability that is needed for tiled flooring. Aluminium based profiles will adequately protect the majority of projects. Stainless Steel profiles however will provide the greatest strength and are the least visible due to the design of the profile, these are ideal for Transport projects.

It is advisable to use movement joints that are designed to exceed BS5385. For a seamless designer look they can be specified in any of the RAL colour scheme range and if a tile sample is sent to the MJ manufacturer then an exact colour match is achievable even if the tile has a speckled effect. This upholds the beauty of a seamless tiled flooring scheme.

Clients generally do not like movement joints because it is felt that they can be obtrusive and spoil the aesthetic appearance of their carefully chosen floor. An added complication is that a MJ has to be positioned directly above the sub-floor void between each raft. If the position of the subfloor MJ has not been considered at an early design stage then the MJ within the hard floor finish could end up running through the middle of the floor like scar. This will look ugly if the floor finish has a intricate surface pattern. In some instances however designers take advantage of the position of the subfloor MJ such as at Barnsley Bus Station. The MJ on the surface followed the grid pattern in the subfloor which created an affective geometric design so in this instance there was no need to try to hide them using Coloured Movement Joints.

By incorporating decoupling matting and movement joints into early design concepts, architects and contractors are given confidence that their clients will have seamless tiled flooring that will remain permanently crack-free.

Specifiers and installers know that movement joints need to be used to absorb the natural movements in the floor. Architects are required to specify products that are fit for purpose and conform to building regulations. They are advised to consider the position of the subfloor Movement Joints at an early design stage. Installers have a duty to provide good advice and workmanship.

Judith Mawtus says, “The first thing that we ask installers to do is to follow all of the correct installation procedures and guidelines recommended for each product and that the conditions of use are correct. We also stipulate that installers have followed good tiling practice and procedure (refer to The Tile Association for more information – www.tiles.org.uk). If these procedures are undertaken and subject to a Dural site visit inspection we will give up to a 10 year guarantee on the flooring installation. A normal flooring guarantee is 2 years.”

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