Hi All

If you have in screed UFH over an area of 220m2 finished in limestone flags with decoupling layer, how the hell do you impliment expansion joints which are recommended every 40m2 in a lafarge pumped screed. I have seen the Schulter expansion joints but they all seem to be put in against a finished edge of screed. With a pumped screed this surely isnt poss? What am I missing? do you have to lay the UFH in a pattern that allows for these joints and then saw cut the joints? Any help greatly appreciated.

Ernie, personally I would phone Schluter and ask their advice. Here is their technical phone line. 44 (0) 1530 813396. Also worth checking out their website Movement Joints, Expansion Joints And Control Joint Profiles - Schlüter-Systems

Are you talking about the joints in the screed or the joints in the tiling.

If its joints in the screed they should run through all door thresholds and in between independently controlled heating zones.

If I can figure out how to post it these days I have a section drawing which might be of use.

Joints are NOT required in these screeds at bays of 40m2 however the rules which are laid out in BS8204 part 7 2003 will usually dictate that the bays are less than 40m2 anyway unless you are in a really big room. This bay size unfortunately is based on the use of cement based screed. The tiling standards do not deal very well with pumped screeds so I think manufacturers advice is needed. The need for joints in your tile face remain unchanged.

Additional joints may be needed if any areas exceed 20 linear meters long or with an aspect ratio of more than 8:1 e.g. long thin corridors or L shaped rooms.

Other areas for potential consideration are large conservatories or sun lounges where there is likely to be solar gain and areas where there are abrupt changes to aspect ratio. All of these joints are exactly the same as those which should be placed in any screed but unfortunately should and are are often significantly different concepts.

As you are placing the joints to take account of thermal movement they must full full depth and compressible. This means that they should be placed prior to the installation of the screed using preformed compressible joint formers. Schluter do one called Dilex DFP and there are others available from for example CCF merchants and I think Sheffield Insulations as well.

Where these cross over underfloor heating pipes they are very simple to cut over the pipes using a Stanley Knife although you can buy a special tool for the job.