porc's and grout cracking on ditra on screed - TilersForums.com

[m3fitter]

First problem i've ever had with a floor ??

2 new build 5 bed houses / ufh underscreed hep spaced at 100mm with wall stats measuring air temp only
screed 6 weeks old
primed with acrylic
ditra'd flexible benfer rapid
solid bed trowel flexible benfer rapid fixed 3mm joint / 600x600 porcelanosa rectified x 90 m2
flexible grout 2-12mm

in both plots the same cuts have cracked twice, where ie: in cupboards there is no ufh, ie: half the tile is hot and half cold
All i can see is that due to expansion of the hot part of the tile, it has cracked ?
but why has the grout cracked all over 30m2 of the kitchen ??
never felt tiles as hot anywhere.. as floor heats to max until desired air temp is reached, is this right ??

 

[Ian]

How soon after laying/grouting the floor was the heating turned on? And was it brought up gradually?

 

[Ajax123]

Ditto...

 

[m3fitter]

hmmmm exactly... i was told it was.. but if you think about it, how could it, as boiler is controlled by air stat, not floor probe.. was told by plumbers they had balanced the valves ?? ( WTF is that ) the tiles are unbelievably hot !

 

[DHTiling]

You can still crank up to high temps with an air stat.. i would be looking at this issue as fault.

 

[Ajax123]

With underfloor heating the maximum recommended surface temperature of the floor should be 27degrees c. Your hand will new rally be around 25 to 30 degrees c (body temperature is 37.5) so at best the floor should feel luke warm or tepid. If the tiles feel hot then the floor is far too hot and the tiles are cracking due to thermal issues. The flow temperature should be controlled by mixing valves in manifolds to give a constant flow typically with sand cement screed of 40 to 45 degrees c. This will maintain a room temperature of around 23degrees. It does this by miing water from the boiler with cooler returnwater from the heating system and should be preset to a maximum temperture (typically 40 to 45 as already stated) with anhydrite this temperature an be much lower (around 30 to 35 degrees c) The air temperture thermometer is simply to call for heat when the room gets colder. It will not (assuming its all working correctly) call for a flow temperature higher than the maximum that the manifold valves are per set to.

 

[m3fitter]

This floor heats to max until, the air temp is reached, i believe this to be the problem, ie: the floor was never gradually heated 1 degree a day, as this system does not operate in this way...
I know it is not a workmanship problem or a materials problem, as same faults on same tiles in both plots, as i set both 90m2 floors out the same as they were a mirror image of each other, and when the ufh is turned off, the cracks dissapear, which suggests expansion and contraction issues that exceed extremes products are capable of, i believe these floors are operating at 50-60 centigrade to achieve an air temp of 24 c, and then the boiler shuts down and the air temp drops.. surely this not correct ? how can i measure the temp of the floor acurately ?

 

[warmadmax]

there are infra-red thermometers you can get that read surface temp.
this sort of thing -

i'd also check the temp of the flow pipe from the thermostatic mixing valve, it should be limiting the max temp and is probably "adjusted" too high.

 

[Ajax123]

cracks opening on heating and closing on cooling means a serious problem caused by the floor trying to belly upwards due to thermal expansion. This wil be the result of one of, or a combination of, two things. first thermal expansion and second lack of facility for movement in the form of movement joints.

have you put any movement joints in your 90m2 of porcs??

 

[bugs183]

This may sound odd m3 but i've seen plumbers fit underfloor heating circuits in the same loop as radiators. Maybe if the floor is getting really hot they may have done the same. As Ajax says the floor shouldn't feel hot at all.
It's a long shot but there are still plumbers and electricians that don't understand these systems at all.