New cement based screed cracked

[BobS]

Our Cemfloor screed was poured on Friday over UFH (75mm screed, UFH, 100mm PIR, concrete slab). Went to check it today and there are a number of large cracks, about 1.5mm wide. The main ones of concern are around the doorways as they are ovals that look like the threshold of the door is now separated from either side.

 

Would this be considered normal shrinkage cracking?

[nod]

Quite normal 

[LA3222]

Is that normal? I thought 'shrinkage' cracks are up to 0.6mm wide. 1.5mm wide is Double that - I may be wrong though?‍♂️

[Pocster]

19 minutes ago, nod said:

Quite normal 

+1 and across a doorway , typical . I have the same 

[SteamyTea]

I am interested in what causes this cracking.

Is it just too much water in the mix, or the wrong temperature, or even the wrong mix of aggregates.  Or maybe the UFH pipework causing a stress raiser.

I can understand that a very large slab may have problems, why they put in expansion and contraction joints.  But most houses are not huge in the scheme of things.

Edited December 19, 2021 by SteamyTea

[nod]

It’s just shrinkage 

I normally put an expansion joint in all doorways 

Or at least cut a line across the opening with my trowel 

[Pocster]

3 minutes ago, nod said:

It’s just shrinkage 

I normally put an expansion joint in all doorways 

Or at least cut a line across the opening with my trowel 

Decoupling Mat for certain if tiling floor 

[Temp]

We had exactly same issue except the cracks propagated through the stone floor on top. I've posted on here a few times about it and recommend an expansion gap (aka deliberate straight crack) at doorways.

 

16 minutes ago, SteamyTea said:

I am interested in what causes this cracking.

 

As @nod said its just regular shrinkage. Pretty small percentage if you think about it. Just 1mm over the span of a room. Near impossible to avoid. 

[nod]

3 minutes ago, pocster said:

Decoupling Mat for certain if tiling floor 

Yes 

 

Many years ago we used to lay chicken mesh over pipe and crack points like doorways 

[SteamyTea]

18 minutes ago, Temp said:

Just 1mm over the span of a room. Near impossible to avoid. 

I grew up in a place with concrete roads, don't remember any cracks like this in them.

Mind you, the surface was not flat, was more a load of semi-circular ridges.

Edited December 19, 2021 by SteamyTea

[Temp]

The issue is there are two areas of screed that meet with a narrow  strip at the doorway. Bit like a figure 8. The two areas shrink towards their own centres which puts stress where they meet. If the whole floor had been screeded as one before the internal walls were built it probably wouldn't be an issue but that's rarely possible. Here is what ours looked like. The doorway runs top to bottom with no actual door fitted.

[dpmiller]

Our screeders put a submerged foam joint at every doorway.

[SteamyTea]

15 minutes ago, dpmiller said:

Our screeders put a submerged foam joint at every doorway.

That's interesting, can you pop a sketch up please?

[dpmiller]

this kinda thing, just a foam strip with an adhesive base

 

https://www.amazon.co.uk/Screed-Dehnfuge-Dehnfugenprofil-Self-Adhesive-Base/dp/B00SYVO71A

 

but they were all cut down to be about 3/4 of the screed thickness. Screed can flow over during the install and then  it leaves a weak zone for any movement.

[bassanclan]

I went round with an angle grinder and put a clean cut in the concrete across thee doors as soon as the concrete had got just hard

[SteamyTea]

6 minutes ago, dpmiller said:

this kinda thing, just a foam strip with an adhesive base

 

https://www.amazon.co.uk/Screed-Dehnfuge-Dehnfugenprofil-Self-Adhesive-Base/dp/B00SYVO71A

 

but they were all cut down to be about 3/4 of the screed thickness. Screed can flow over during the install and then  it leaves a weak zone for any movement.

Neat idea.

What do they do if UFH pipes are going the the doorway, just cut notches out to go over the pipework?

[dpmiller]

Yes indeed, just a wee notch.

[Mr Punter]

Including crack control is a really good plan.  Even better if you can place it centrally under the door and start the tiles either side, with mastic instead of grout but I think once it is fully dry you could get away with filling the crack and tile straight over.

[nod]

1 hour ago, SteamyTea said:

That's interesting, can you pop a sketch up please?

I normally use a  100 mil strip of double wall and trim it off afterwards 

It helps if there’s a straight break across the doors 

We refuse to tile if there is no break across the doors 

[BobS]

Thanks all for the replies. Controlled cracking sounds like it would have been a good idea.

 

I am wondering if there is an issue with both sides of the door cracking and creating a small island in the centre that could become loose over time. Or are they only surface cracks?

 

 

[Barryscotland]

I was just away to post the exact same issue, our cemfloor was poured about 7 weeks ago and today two large cracks have appeared in the hallway. I asked the Screeder about expansion joints before he poured it and his reply was none needed with cemflooR over 160m2. Good to hear it’s not a major issue though, just not so good aesthetically as it is going to be our finished floor until we’ve saved up for flooring 

[Adsibob]

On 19/12/2021 at 13:48, Temp said:

Near impossible to avoid.

Will touch wood, we’ve managed to avoid it, so far at least. Our screed was poured on 11 October, no cracks yet. Not sure how my builder set it up, though he did use a couple of courses of engineering brick for the bottom of the only wall that divides two areas of screed and also line every wall with foam, but I think that’s standard.

[Temp]

Yes we have no cracks anywhere except where the screed in two rooms meet at a doorway. 

[epsilonGreedy]

On 19/12/2021 at 14:40, Temp said:

 

 

Nice floor finish, what sort of ££ per sqm would the material cost be?

[Jilly]

Our screed has smudged over the doorway cracks, which I now know were put in deliberately, episiotomy-like. As I don't have an angle grinder, and there UFH pipes under the doorway, does anyone have any suggestions? Maybe just walk on them to crack them before the tiles go down?! And will use coupling membrane.