Hi All, what do you think?

[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.