Hi All, what do you think?

[Walenut]

Hi All,
First can I congratulate you all on excellent forum loads of information and a wealth of experience. I have spent some time scouring the posts and think I have answered most of my queries but I will detail my job and hopefully clarify to myself any remaining points.

Firstly I have self built a large extension on my house so have a certain level of expertise. I have done a moderate amount of tiling in the past but I am in no way an expert and I would be paying for a professional if I hadn’t run out of money due to the fact that I have now well and truly had enough of building J

So the job in hand, I have a kitchen, conservatory & wet room floor to tile 33m2 in total, these are all on the same level and running into each other apart from the kitchen to the conservatory which is separated by an oak timber thresh-hold set in the screed which secures by-folding doors.

The screed is fibre reinforced Truscreed at a depth of 50mm over wet UFH; this is bonded to a 150mm concrete slab which is then over 100mm Celotex then DPM. (I am assured by Tarmac & the UFH supply company that this level of screed fully bonded to a slab is an acceptable construction method for wet UFH at this depth, fingers crossed)

I will be tiling the kitchen & conservatory floor with a 330mm x 500mm porcelain tile in a stretcher bond pattern and thought it would look nice set at 45º instead of square to the room.

The screed, now 5 weeks into drying out, has some hair line cracks in various places which are what I expected to a certain extent. An additional problem is that it will be difficult to commission the UFH system as its going to be fed by a new condensating boiled which has yet to be installed in the garage and with the current weather I’m reluctant to start ripping out the old back boiler.

I am assuming that best practice would be to lay an uncoupling membrane prior to laying the tiles on a full bed of adhesive but I am now really struggling for height so I would welcome any suggestions. Reading the forum I am also assuming that an expansion gap will have to be left around the perimeter 10mm? I can cover this with the skirting & kitchen units, plus a silicon bead where the tiles run into the hall timber floor & to the timber thresh-hold to the conservatory.

I will be using a flexible adhesive (chemical set for porcelain?) and grout but I am uncertain about the difference between single or two part adhesive & the best amount of gap to leave for grouting, I know you have a poll running but any suggestions for recommended manufactures of either are welcome. I’ll also buy a wet cutter for the tiles.

I was also going to ask about the wet room but I think that I’d better leave that for my second post! I was going to run the same tile into this area but I don’t think this will work due to the size of the tile and the fall of the floor, 10mm’ish?

I hope all that’s not information overload and look forward to reading any comments,

Happy New Year,

Walenut.

 

[Dan]

Welcome to tilersforums.com | Tile Forums | Tiling Forum!

Hi Walenut and welcome to tilersforums.com!

 

[david campbell]

:welcome:to the forum!

i think you are very much on the right track using the uncoupling membrane,epansion joints should be inserted about every 5m over larger area,the difference with 2 part adhesive compared to single part flex is that it's mixed using a latex additive allowing for more flexibility(a kind of rubber adhesive)

 

[The Legend; Phil Hobson RIP]

Hi, Walenut, and :welcome:I think you have answered most of your questions yourself. I think the decoupling membrane is a must. My choice of adhesive would be Mapei, Keraquick with latex plus. But every one has their own favourites. Good luck. Keep us posted

 

[diamondtiling]

Hi Walenut and welcome.

Put some pictures up for us to see your floors/wet areas, they are a tremendous help when giving out information.

 

[jay]

hi as above also check that tiles are flat first( place tiles face to face and see if all four curners are the same) most tiles in that shape tend to bow up in centre may cause trouble laying landscape:8:

 

[Perry]

this is one done at 45 deg random bond made it a lot easer not had much to do with underfloor heating but thought you were meant to turn it on first to let it expand then turn it off and tile it ? but something like pesalastic would be a good idea rather than ditra

 

[mikethetile]

hi and welcome walenut

i would use two part

and the skirting will cover the expansion at edges but at 12mm it will just cover

good luck

 

[Hawkofeagles]

Hi Walenut and :welcome: to the forum

 

[Diamond Pool Finishers]

sounds like your on the right road mate!! :welcome:to the forum and pic's would be nice as you go along mate or of the finished job

 

[DHTiling]

Hi walenut and welcome...

I'm afraid you deffo need to commission the UFH even if using the uncoupling membrane..

The membrane might not cope with the amount of expansion when you turn the heat on..and the last thing you want is a failure..

 

[Ajax123]

Depth of sand cement screed bonded to concrete substrate should be a minimum 50mm to meet BS. It could be argued that this depth starts from the top of the underfloor heating pipe and with a sand cement screed I would certainly expect 65mm but I am seeing more and more installations where the rules are bent and the depth shaved. The hairline cracks are probably simple long term drying shrinkage although they may have been exacerbated by early age drying shrinkage due to lack of curing.

My guess is that whilst you are told it is bonded it is not fully bonded as this would invlove mechanically preparing the subslab using a scabbler or enclosed shot blasting. My guess (based on what usually happens) is that the screed has simply been placed in direct contact with the concrete. This is classed within BS as Unbonded (some call it partially bonded but this term is not covered within the standards) This being the case the minimum depth should be 65mm.

Unless it is fully bonded to the concrete slab it cannot be considered as acting compositely with the slab and therefore cannot be considered a part of it.

If underfloor heating is placed within the screed NO floor coverings should be placed unless the heating is comissioned. If there are already hairline cracks in the screed these may widen and lengthen on heating.

An uncoupling membrane would help with this but may not cope entirley depending on the level of expansion. Additionally it will not cope with vertical movemen such as may occur if the screed begins to curl which can also be associated with the action of underfloor heating.

There should be joints within the screed to reflect independently controlled heating zones and through all door thresholds. If these are not placed then, again, an uncoupling membrane may help but is not a guranteed method of overcoming the issue.

Drying is also an issue here as the 50mm screed drying will be impeded by the 150mm concrete slab. The overall drying time will be goverend not by the screed (which is a modified screed and so is reasonably fast drying) but by the concrete.

I have to say that Whilst I have seen this method of construction and whilst it may be mechanically adequate is probably not the best way to have built it where underfloor heating is being used. The heating will need to warm the whole screed and concrete slab turning it into a big storeage heater - not the most efficient way to heat a floor have but there you go....

All that said Truscreed is a good material in terms of durability to abuse because of it's relatively low water cement ratio which improves the strength performance.

I think uncoupling is a must but I would not tile until the heating has been turned on and run.

 

[Ajax123]

Oh by the way :welcome:

 

[White Room]

Hi and welcome

 

[Walenut]

Fantastic response many thanks, I have took everyone’s advice and spent the day under the floor plumbing in the UFH, now up and running.

In answer to Ajax, the idea of the UFH on top of the slab is to bring the thermal mass into the building; it needs to be heated differently to screed on insulation methods and to what I understand is the system used more in colder countries as you say like a big storage heater.

The system should work on an extremely low heat, it comes on at the start of the season and stays on until the end of the season & utilizes night set back; this is particularly applicable in my case as there is usually someone in the house all the time as we’re shift workers. I’ll let you know if it works J

I’ll try and get some pictures up & I’ll also check the tiles for flatness.

Again many thanks for your replies.

 

[Ajax123]

Fantastic response many thanks, I have took everyone’s advice and spent the day under the floor plumbing in the UFH, now up and running.

In answer to Ajax, the idea of the UFH on top of the slab is to bring the thermal mass into the building; it needs to be heated differently to screed on insulation methods and to what I understand is the system used more in colder countries as you say like a big storage heater.

The system should work on an extremely low heat, it comes on at the start of the season and stays on until the end of the season & utilizes night set back; this is particularly applicable in my case as there is usually someone in the house all the time as we’re shift workers. I’ll let you know if it works J

I’ll try and get some pictures up & I’ll also check the tiles for flatness.

Again many thanks for your replies.

Will you use the floor for coooling in the summer as well.

Never wuite convinced by the Thermal Mass Storeage arguments co I can't work out in my head how you maintain control over the heat release. e.g. if the store is warm and the weather unexpectedly improves or vice versa can you get a fast enough response. I did do some development work a few years ago on thermal stores using anhyrite screed due to its thermal properties. the storeage units were 1 cubic meter laminated in layers with heat transfer pipes in each 50mm layer....never really came up with a market though....

 

[Colour Republic]

Have you connected the UFH to the old system tempoary tails?

 

[Walenut]

Have you connected the UFH to the old system tempoary tails?

This seems like one of those questions that's going to lead somewhere you don't want to go.... :yesnod:

Yes?

 

[Walenut]

Will you use the floor for coooling in the summer as well.

Never wuite convinced by the Thermal Mass Storeage arguments co I can't work out in my head how you maintain control over the heat release. e.g. if the store is warm and the weather unexpectedly improves or vice versa can you get a fast enough response. I did do some development work a few years ago on thermal stores using anhyrite screed due to its thermal properties. the storeage units were 1 cubic meter laminated in layers with heat transfer pipes in each 50mm layer....never really came up with a market though....

The system should work well for cooling in the summer especially as I have a south facing garden with conservatory but I would need a decent heat dump somewhere.

I did deliberate over anhydrite screed but over such a small area it was difficult & expensive and I thought tiling would be an issue, may have been the way to go though as I'll need a decoupling membrane anyway.

The response time should not be to much of an issue as the system should work at a lower temperature than screed on insulation, virtually just warming the kitchen floor, wet room has an additional radiator & the conservatory has electric fan heater for rapid heat.