Turned underfloor heating up too high

[Loz]

Hi,

 

Been having a bit of a nightmare with liquid screed poured 6 months ago, had it sanded at the month mark but took ages to get underfloor heating working - probably at 3 month mark.  Then turned it up couple of degrees a day until water temp was about 45 degrees and left it permanently on, tiler checked moisture level each week and was taking ages to dry out to the 0.5 mark.  Stupidly in last couple of weeks when really needed floor tiling started increasing temp of water a bit more each day to 65 degrees - I was unaware that was a problem.  When I turned UFH heating off sure enough a crack appeared (6 month mark) between the two heating zones.  Screed company came round and have been really good and said they should have put expansion point between two zones, lightly disced it out and poured resin in crack.  Tiler is using matting and putting some sort of special joint where crack is.  Problem is since then another crack has appeared in a strange place that no explanation for - has also now had resin put in.  Screed company says above 55 degrees something happens to screed and now really worried I have screwed up the entire floor.  Tiler is due to start Monday and is going to mat (Dural) the whole floor - should I be worried that long term going to have problems - to be honest not sure what other option I have.  Wish knew about max temp and also should have gradually turned it down rather than just switching it off, any advice greatly appreciated,

 

Loz

[markc]

Don’t worry, you haven’t ruined it. Better to learn now than crack tiles. Screed often cracks between rooms and doesn’t affect the floor. Tiler is doing right thing using decoupling mat.

 

[Loz]

24 minutes ago, markc said:

Don’t worry, you haven’t ruined it. Better to learn now than crack tiles. Screed often cracks between rooms and doesn’t affect the floor. Tiler is doing right thing using decoupling mat.

 

Thanks, thats what I was hoping other than the new crack that has appeared over weekend (UFH been off for 2 weeks) is in a place that can't be explained, I was kind of happy with the other one between the two zones/rooms but the new one runs off centre of wall at one end of the room no where near any entrances, screed guy had no idea why would have happened and just concerned that having had it up too high that more will start appearing after tiling,

 

Loz

[saveasteading]

1 hour ago, Loz said:

crack has appeared in a strange place that no explanation for

It can always be explained. I

f it matters to you, then show us a picture and we can try.

 

I am very surprised that the screed was not considered dry after 6 months. Was the area sealed off so that the air remained cold/ humid?

 

My guess (just for fun)  is that the 'unexplained' crack is an area of least resistance to the shrinkage that has happened everywhere, and the ufh is acting as crack control...so a place where the pipes are absent , or running the other direction.

[Loz]

21 minutes ago, saveasteading said:

It can always be explained. I

f it matters to you, then show us a picture and we can try.

 

I am very surprised that the screed was not considered dry after 6 months. Was the area sealed off so that the air remained cold/ humid?

 

My guess (just for fun)  is that the 'unexplained' crack is an area of least resistance to the shrinkage that has happened everywhere, and the ufh is acting as crack control...so a place where the pipes are absent , or running the other direction.

 

Thanks for replies, the floor was pretty much dry, the first couple of months from October there were no windows just OSB boards so was pretty damp and then probably took til February to get underfloor on, was reading 0.7/0.8 few weeks back when whacked the heating right up to try speed up last bit - thought would be bulletproof at this point.

 

Have included plan layout of ground floor - first crack in yellow appeared after turned heating off from 65 to zero ready for tiling, may have had a lucky escape as original tiler wasn't going to use matting and maybe that was an accident waiting to happen as is the joint between the two zones and two different rooms on join between new double height extension and existing single storey.  New tiler is going to line tile join up on crack and use some special joint there.  the new crack comes off existing external wall no where near any entrances or stress points, may have been shallower there and also there is no under floor loops for 50cm off the wall.  The UFH been off for two weeks and crack started last week and doubled in length over weekend.  Has now been slightly disced out and stitched with resin.  Concern is will any more appear after tiling and could the 65 degree heat compromised the screed - they screed company said a chemical reaction happens above 55 degrees which compromises it but couldn't elaborate.

 

Not sure if matting would have saved me from new crack given the additional measure taking on the first crack, guess not a lot I can do but any input might help reduce or increase stress and worry levels !

 

 

 

Loz

 

 

[Jilly]

I was worried about this too and still haven't turned my floor above 35 degrees and its been tiled.  Funny how this game plays with your stress levels. As a suggestion, would it hurt to design in extra expansion joints to mitigate the risk of new cracks? Our floor isn't large, so we've only got them at the the thresholds but they don't look very different from the grout lines. At least you know where to put them.

 

Walking round the B & Q warehouse I now notice their expansion joints! 

[Loz]

8 minutes ago, Jilly said:

I was worried about this too and still haven't turned my floor above 35 degrees and its been tiled.  Funny how this game plays with your stress levels. As a suggestion, would it hurt to design in extra expansion joints to mitigate the risk of new cracks? Our floor isn't large, so we've only got them at the the thresholds but they don't look very different from the grout lines. At least you know where to put them.

 

Walking round the B & Q warehouse I now notice their expansion joints! 

 

I guess just not sure where any new cracks could appear and think would look weird to have too many just in case as not a particularly large space, just really worried now that the new crack is the start of a nightmare (not been a lucky build so far) and can't see an obvious reason why it appeared where it did and then doubled in size despite it appearing and enlarging with UFH having been off 2 weeks, I really wish someone involve din build had mentioned not to turn it above 45, the screed guy said on his system you can't physically turn it up above 40 whereas on mine goes to 65, gutted as been painful so far and not sure whether to just gamble now and go for matting and tiling and hope for best, just can't face having to rip it up at later stage especially as tiling the entire ground floor,

 

Loz

[saveasteading]

3 hours ago, Loz said:

Walking round the B & Q warehouse I now notice their expansion joints

B and Q has little relation to a domestic situation.  On a building that size, if fairly modern, there will be a very big steel grillage near the middle.

This is used over a certain size of floor (2,000m2 as a vague memory.) elsewhere there are also multiple crack induce joists, which may have  a flexible filler.

At the big joint there is a complete break in the floor slab. Elsewhere the crack control mesh runs through the joints.

Don't concern yourself with that, except to note that it is 'a thing' that is taken seriously.

 

They are not expansion joints, but contraction joints as all concrete shrinks, and doesn't expand again unless it gets very hot.

 

All concrete shrinks , as yours has done. I don't know the science of your screed, but presumably the heat is forcing water out of the chemical structure that has been formed when the screed was hardening.

Water is taken in chemically as a part of the new material, and not all of it has to dry.

I'm just surprised this happens at your temperature.

 

The manufacturer should tell you why this has happened and if it will now be stable or expand again when cooling and perhaps taking water back into the chemical structure.

 

The drawing is excellent, thanks.

The yellow line could have been forecast, and there should have been a contraction joint near to that point, to control the crack to a nice straight line.

The red crack will not stop at mid slab, and the question will be whether it carries on until it meets yellow,  dives off at an angle to a door opening, or dissipates in multiple tiny cracks.

None are likely to be long term problems once they stabilise.

But I wouldn't be sure that have yet.

 

Notting nasty is going to happen, but there is a risk of tiles cracking if the floor shrinks or relaxes back to where it was.

 

 

 

 

 

 

[Jilly]

12 hours ago, Loz said:

 

I guess just not sure where any new cracks could appear and think would look weird to have too many just in case as not a particularly large space, just really worried now that the new crack is the start of a nightmare (not been a lucky build so far) and can't see an obvious reason why it appeared where it did and then doubled in size despite it appearing and enlarging with UFH having been off 2 weeks, I really wish someone involve din build had mentioned not to turn it above 45, the screed guy said on his system you can't physically turn it up above 40 whereas on mine goes to 65, gutted as been painful so far and not sure whether to just gamble now and go for matting and tiling and hope for best, just can't face having to rip it up at later stage especially as tiling the entire ground floor,

 

Loz

 

[markc]

Do you have a picture of the cracks? I’m assuming these are fine shrinkage ones and not big open movement cracks. I think the tiler is ars£ covering saying they will line tiles up with the cracks as I really don’t believe this is anything serious

[Loz]

9 hours ago, saveasteading said:

 

The manufacturer should tell you why this has happened and if it will now be stable or expand again when cooling and perhaps taking water back into the chemical structure.

 

The drawing is excellent, thanks.

The yellow line could have been forecast, and there should have been a contraction joint near to that point, to control the crack to a nice straight line.

The red crack will not stop at mid slab, and the question will be whether it carries on until it meets yellow,  dives off at an angle to a door opening, or dissipates in multiple tiny cracks.

None are likely to be long term problems once they stabilise.

But I wouldn't be sure that have yet.

 

Notting nasty is going to happen, but there is a risk of tiles cracking if the floor shrinks or relaxes back to where it was.

 

 

9 hours ago, saveasteading said:

Thanks for very detailed reply, I agree that not the end of the crack in red, the screed guy put a metal resin stitch at end but as you say can see that running to the original crack or to a doorway.  The screed guy didn't have any more info on what compromised meant due to the high temperature and can't find anything readily by googling.  The tiler is due to start Monday and due to several floor holdups can't delay any longer so guess going to have to go for the matting and hope for the best.  The matting literature does say can bridge gaps 1,2 mm wide but really worried the screed won't now behave as it should and the tiles will ultimately crack all over the place, I think I can see the very faint beginnings of a new crack parallel to the recent red one.  I appreciate I have screwed up but wish someone somewhere along the line mentioned the max temperature, all that was mentioned was not to turn it up too fast which I followed but I guess I did then not thinking turn it off dead from max to 0 ready for the original tiler without thinking.  After all the money and stress of the build which overall hasn't gone well gutted that could be facing long term floor issues as really didn't want cracking floor tiles, guess any that crack could then be addressed individually and hoping unlikely whole floor will suffer, many thanks for taking time to reply, much appreciated, Loz

9 hours ago, saveasteading said:

 

 

 

 

 

[Loz]

6 minutes ago, markc said:

Do you have a picture of the cracks? I’m assuming these are fine shrinkage ones and not big open movement cracks. I think the tiler is ars£ covering saying they will line tiles up with the cracks as I really don’t believe this is anything serious

Here are pictures of the cracks now repaired, the original one between the two buildings was about a 1mm and there should have been a joint there but the other new one (first picture) was less than a mm:

 

 

[Ian]

Just make sure your tiler is going to use a good quality decoupling mat under the tiles. Schluter's ''Ditra 25'' is very good and that's what I specified on my own self-build as well as on any of our commercial projects.

https://www.schluter.co.uk/media/schlueter_db_6_1_ditra_uk.pdf

[markc]

Looks worse because someone has attacked it with a grinder. Don’t worry about it and as above, decoupling mat will protect the tiles.

all screeds shrink, just slowly and there are thousands of tiny cracks a bit like crazy paving, you have just concentrated them into one spot. 
 

[Loz]

I was wandering if at this point most floors are covered over so cracks aren't seen, tiler is using a quality matting - has gone for Dural as has links to the technical guy, seems the alternative to ditra mentioned above - they do seem to be the two main players.  Many thanks for all replies, been really helpful