When Movement Joints Go Wrong!
As sad Movement Joint fanatics we check out floors wherever we go. It’s always bad news when we see a failed floor. We want people to be happy with the installation so that they use tiles again - hopefully with our products.
The purpose of this section is to highlight what happens when basic rules are not followed.
The most common causes of failure are completely avoidable. These are: –
As sad Movement Joint fanatics we check out floors wherever we go. It’s always bad news when we see a failed floor. We want people to be happy with the installation so that they use tiles again -
The purpose of this section is to highlight what happens when basic rules are not followed.
The most common causes of failure are completely avoidable. These are: –
1. Placement.
2. Solid Bedding
3. Incorrect choice of profile
Placement – All movement joints must, yes MUST be placed directly over each other throughout the floor structure. A moments thought will see that if the purpose of a movement joint is to absorb movement, placing it anywhere other than where that movement happens is not going to help. Worse still, by bridging the area of movement with a rigid tile, (of whatever material), it is obviously going to crack at that point. A typical example of this error is where a fairly straight crack appears in the tiling, usually about 10cms or less away from where the movement joint is actually fitted.
It’s worth noting that straight cracks are usually caused by vertical movement in the subfloor at movement joints. Where “lightning flash” cracks appear this is normally caused by horizontal movement within the subfloor. Tiling early onto unstable surfaces such as green screeds can also cause this problem. Sometimes indicated where tiles “tent” or “pop” under compression.
Specifiers
To avoid the above it must accepted that it might be necessary to cut tiles to achieve correct placement. This is why we produce colour matched profiles to minimise the aesthetic impact.
Fixers
Miss aligning movement joints may save time in the short term but is the saving involved in cutting tiles worth your reputation?
Solid Bedding
Cracks can appear alongside perfectly placed movement joints. Typically these would be “half moon” in shape. This are due to a failure to ensure that the fixing flanges of the movement joint are fully embedded into the tile adhesive. All reputable suppliers of movement joints will stress the importance of this solid bedding. Not only is it needed to fully support the tiles at this vulnerable point but also to ensure that the extension and compressive forces within the floor are fully transferred through the supporting profiles to the flexible infill material.
A simple test for this fault is to take a £1.00 coin and use it to tap along the edges of the tiles alongside the movement joint. Where the tiles are solidly fixed the sound is dull. Over hollows in the bedding the sound will change to a sharper, clearer tapping. Invariably if the tiles are lifted for investigation this simple test has proved accurate.
Specifiers
Make sure that your fixing team are reminded that solid bedding is your absolute requirement.
Fixers
Fixers given the job of constructing movement joints must be competent and it must be understood that the rules regarding the open times of adhesives etc are followed. Planning and pre cutting of the tiles can avoid delays which cause bonding problems.
Incorrect choice of profile
This problem is in two parts both of which can affect the longevity of the tiled installation.
Size – the depth of the movement joint must match that of the tile and adhesive bed. Ideally the top of the movement joint should be slightly below that of the tiles. (1 to 2mm maximum). Under no circumstances should the movement joint be proud of the surface.
The movement joint should not be considered as a stepping stone for traffic. They are not designed accept these impacts and stress in isolation.
Typically the signs of an incorrect size would be – Too tall = impact damaged side supports. Too small = chipped tile edges.
Material – This is an example of over optimistic cost saving. Plastic Movement Joints have a very limited use in domestic and very light commercial areas. In ALL other circumstances please, please use a movement joint with metal side supports. They cost more but their performance is absolutely superior to plastic.
Metal side supports transfer movement directly to the flexible infill. Plastic supports will bend or deform.
Metal side supports provide good protection to tile edges against chipping, Plastic supports don’t!
The infill on plastic Movement Joints is prone to damage from impact and specifically from ladies high heeled shoes. The infill on metal based profiles is tougher and much less prone to this type of damage.
Movement Joints - Summary
Don’t take short cuts, use the right size, (ask us), and, unless it’s for a simple domestic extension use a metal based profile.
Now gasp at our collection of horrors!
It’s worth noting that straight cracks are usually caused by vertical movement in the subfloor at movement joints. Where “lightning flash” cracks appear this is normally caused by horizontal movement within the subfloor. Tiling early onto unstable surfaces such as green screeds can also cause this problem. Sometimes indicated where tiles “tent” or “pop” under compression.
Specifiers
To avoid the above it must accepted that it might be necessary to cut tiles to achieve correct placement. This is why we produce colour matched profiles to minimise the aesthetic impact.
Fixers
Miss aligning movement joints may save time in the short term but is the saving involved in cutting tiles worth your reputation?
Solid Bedding
Cracks can appear alongside perfectly placed movement joints. Typically these would be “half moon” in shape. This are due to a failure to ensure that the fixing flanges of the movement joint are fully embedded into the tile adhesive. All reputable suppliers of movement joints will stress the importance of this solid bedding. Not only is it needed to fully support the tiles at this vulnerable point but also to ensure that the extension and compressive forces within the floor are fully transferred through the supporting profiles to the flexible infill material.
A simple test for this fault is to take a £1.00 coin and use it to tap along the edges of the tiles alongside the movement joint. Where the tiles are solidly fixed the sound is dull. Over hollows in the bedding the sound will change to a sharper, clearer tapping. Invariably if the tiles are lifted for investigation this simple test has proved accurate.
Specifiers
Make sure that your fixing team are reminded that solid bedding is your absolute requirement.
Fixers
Fixers given the job of constructing movement joints must be competent and it must be understood that the rules regarding the open times of adhesives etc are followed. Planning and pre cutting of the tiles can avoid delays which cause bonding problems.
Incorrect choice of profile
This problem is in two parts both of which can affect the longevity of the tiled installation.
Size – the depth of the movement joint must match that of the tile and adhesive bed. Ideally the top of the movement joint should be slightly below that of the tiles. (1 to 2mm maximum). Under no circumstances should the movement joint be proud of the surface.
The movement joint should not be considered as a stepping stone for traffic. They are not designed accept these impacts and stress in isolation.
Typically the signs of an incorrect size would be – Too tall = impact damaged side supports. Too small = chipped tile edges.
Material – This is an example of over optimistic cost saving. Plastic Movement Joints have a very limited use in domestic and very light commercial areas. In ALL other circumstances please, please use a movement joint with metal side supports. They cost more but their performance is absolutely superior to plastic.
Metal side supports transfer movement directly to the flexible infill. Plastic supports will bend or deform.
Metal side supports provide good protection to tile edges against chipping, Plastic supports don’t!
The infill on plastic Movement Joints is prone to damage from impact and specifically from ladies high heeled shoes. The infill on metal based profiles is tougher and much less prone to this type of damage.
Movement Joints -
Don’t take short cuts, use the right size, (ask us), and, unless it’s for a simple domestic extension use a metal based profile.
Now gasp at our collection of horrors!
© 2007 Dural (UK) Ltd
