underfloor heating and tiling prep

[cabbie]

Hi guys we are in the about to have work starting on an extension and am now thinking of finished floors etc. Budget is such that I MAY have to tile the floors myself. I do have some experience but this would be the biggest thing I have done so far so hopefully you will be able to help with the prep.

Firstly if I can give you an idea, the total area is approx 60 sqm which is a hall going into an open plan kitchen / diner. there are different substrates, there will be a screed of approx 40 sqm with a depth of around 75 mm and the rest is suspended floor. There will also be a water fed UFH system in the entire floor space. For the floor I would normally noggin between the joist but the UFH requires the top 50mm From the top of the joist, firstly would there be any point in still nogging the between the joists below this point. Im not sure yet but assume the joists are 100 mm deep? Assuming this is ok I was going to ply with 18 mm board which is the thickness recomended by the ufh company. In view of the different substrates I was going to use ditra mat throughout but waodered whether this would be suitable for an UFH situation. I.e would the heat still get through as effectively? Does anyone have any experience here? Im also sure that I would need to install expansion joints where screed meets wood as ditra does not cover this? Also, does an expansion joint have to be installed where the tiled floor meets with the threshold of the patio doors?

Im hoping there will be enough money keft over to employ a tiler but I would welcolme your input as the more information I have the better.

Many thanks for your time and input

Cabbie

 

[nybor62]

firstly the screed is fine allow about 5-6 weeks drying time , what type of screed is it, as for the floating floor this is a problem not really good to tile on because of vertical movement , ditra will stop lateral movement but wont help with vertical
probs not what you wanted to here

 

[cabbie]

Thanks Nybor62 for the response.

Not sure about the screed yet presume the builders will lay a sand and cement screed. Is there one particular type preferable to another?

From what you are saying re the suspended floor, it is not adviseable to tile on suspended Floors? I was going to try to stiffen the joists from underneath somehow to minimise and vertical movement although it is a lot of work so if anyone has any ideas that would be good, and with the 18mm ply screwed every 100 mm along the joists I would have thought it would be stable enough to tile to.

We have tiled the upstairs bathroom with 18 mm ply over suspended floor without a problem (no ufh though).

Presume I would still need to prime back and edges of ply before laying ??

I am anxious now as the plumber has ordered the ufh already

Also with regards to wherescreed meets floor would ditra cover this or do I need to fit an expansion joint.

Once again, many thanks for any assistance.

Cabbie

 

[cabbie]

Hi guys is does anyone have any thoughts on these threads. Thanks.

 

[White Room]

You mention suspended floors, whats the make up of them or do they have joists which you class as suspended..

 

[Rich]

You seem to be on the right track. As long as you can get the timber floor deflection free then you shouldn't have a problem. Ditra is fine over UFH, Schluter say that it helps "spread the heat out". Still seal the back and edges of the ply and screw it down into the joists until there is no bounce. Stagger the boards and leave a 2-3mm gap between each board and be sure to use suitable adhesive and grout.

 

[cabbie]

Thanks whitebeam and Rich. In answer to your question whitebeam the floor is joists. Is this not a suspended floor. Sorry for any confusion!! Also re the rxpansion joints wher screed meets wood I understand ditto mat is not designed to accommodate this and that expansion joints must be installed exactly over the joints between screed and wood. We have a prob with that on as much ad when the house was extended previous the screed part meets the hoisted part as two L s if you follow so expansion joints would look awful. Just wondering if it was overkill on duress part to protect themselves. Im all for doings properly but sometimes circumstances dictate a break from the norm Does any one have any experience on this. particular are I mention above is tiled it was tiled onto a dry mix of sand and cement over EML with mo probs so far. Sorry for the length of the thread. Once again any advice is appreciated. Many thanks.

 

[cabbie]

Thanks whitebeam and Rich. In answer to your question whitebeam the floor is joists. Is this not a suspended floor. Sorry for any confusion!! Also re the rxpansion joints wher screed meets wood I understand ditto mat is not designed to accommodate this and that expansion joints must be installed exactly over the joints between screed and wood. We have a prob with that on as much ad when the house was extended previous the screed part meets the hoisted part as two L s if you follow so expansion joints would look awful. Just wondering if it was overkill on duress part to protect themselves. Im all for doings properly but sometimes circumstances dictate a break from the norm Does any one have any experience on this. particular are I mention above is tiled it was tiled onto a dry mix of sand and cement over EML with mo probs so far. Sorry for the length of the thread. Once again any advice is appreciated. Many thanks.

 

[Rich]

The expansion joint problem is one that comes up in every job where one has to be installed. It doesnt need to be a preformed joint, it can be a silicone joint and there are loads of colours of silicone that are suitable so you should be able to get one that doesnt look an eye saw but blends in with the tiles. My advice would be to add one, if you dont it might be fine and the decision is entirely down to you but it just causes a pain in the back side if you start getting cracks in your floor.

 

[afenteman]

in regards to the UFH, if you screed over 50mm liquid screed is sufficient, otherwise you can install 20mm battens insulated with rockwool and fit aluminium diffuser/spreader plates and the pipe fits into the grooves withiin the plates, this can then be cover with an 18mm board and then the floor covering of your choice. If tiling or using the ditra matting, it os fine for use with UFH but the adhesive MUST be flexible ! You shouldn't need an expansion joint where the tiles meet the patio doors, the flexible adhesive and grouts should be ok but it is worth using an antibacterial silicone in that area which should stop any moisture getting under the floor and they usually prevent the growth of mould too.