Screed too thin?

[Vera16]

Hi, new to this site. I am renovating on older property and have installed a solid floor in the old part of house and new extension (concrete base + 150-200mm celotex + UFH + screed). I'm worried about the screed as it has cracked near the door. Apparently this is normal when a large door is installed but I measured the cracked part and it is only 30mm. Difficult to guage the depth of the rest of the floor (although measured less than 50mm in another part) but I'm worried....should I be?

 

Also the screed appears to have large aggregates in it. Is this normal?

[Mr Punter]

Sand / cement screeds (which you have) are normally 60-80mm.  Liquid screeds are 40-60mm.  Either one is fine with UFH.

 

30mm is too thin.  Are the UFH pipes embedded in the screed?  How are the levels at doorways etc?

[Temp]

Thinnest I've ever seen recommended was 40mm but that was with an UFH system that meant the 40mm was all above the pipes.

 

Screed can crack where two rooms meet at a doorway. This is due to the screed in each room shrinking towards its own centre eg pulling apart at the door way. So that crack might not be due to the thickness but 30mm isn't enough.

 

What's going on top? Tiles - risky. Carpet - who knows. Engineered wood flooring - probably ok if thick enough (eg >18mm).

[Pocster]

7 minutes ago, Temp said:

What's going on top? Tiles - risky.

Decoupling Mat for sure 

[Vera16]

I can’t see the depth in the doorways but one has a big crack across it. I called Building Control and they said 65mm minimum. The builder will probably argue it’s only the edge which is not deep although I can’t see a reason why that should be so. Other concern was the insulation was rocking a fair bit before screed went in. So now I have an unstable 200mm insulation base with a ‘too-thin’ screed layer on the top.

 

Yes the pipes are embedded. 

[Vera16]

Engineered wood on top. But I would like the UFH to work as it should i.e. have something to heat!

 

How bad would it be to rip the whole lot up? To be honest the whole thing looks like a dogs dinner in any case. I’m disappointed. 

[Temp]

I very much doubt having a thinner screed will make any difference to the UFH. What pipe spacing did you go for? On a renovation Id recommend a close spacing as they can need more heat than a new build. 

 

 

 

[Cpd]

How level is the area ? Did you get the correct up stands put in ? Do you have some better photos of the whole area before the screed went in and after ? I am no expert but it might help people give better advice.

[Vera16]

Before and after. Upstands are in. And edging strip although coming out in places.

Edited June 15, 2021 by Vera16

[Declan52]

On this pic there is Def something wrong with the ufh pipes. You can see they aren't sitting flat with a very noticeable bump. Was there subfloor beneath the insulation not left flat and smooth.

 

 

Get a hammer drill and drill through the subfloor at this point. Going by the pics you should be enough away from any ufh pipes. If this is 30mm then it's up to you. Digging it all out will damage the ufh pipes though which will need redone. 

How much height is there between the floor as it sits now and the bottom of the door. If you have 30mm you could rough the floor up with a hammer and bolster,apply a primer and put more concrete on it. You can also use self leveling compound that has fibres in it for this depth. 

 

[Dave Jones]

the builder has buggered up the build-up so there isn't enough height for the correct amount of screed.

 

block and beam + insulation + screed =  325mm this has to sit on blocks (which sit on conc)  and doesn't work brick so they have to bed them up. not many know how to do this properly so don't bother bedding up the blocks and you end up with a FFL 30-40mm less than it needs to be as you have found out.

 

[Vera16]

The sub-floor is not beam and block it is a concrete slab. I think a lot of the issue is with the insulation layer. It was VERY rocky when I walked over it which likely explains the lumpy appearance. I did question this at the time time but was told the screed layer would stabilise everything. I wanted to tape it but there was so much movement in it I'm not sure the tape would have held. There were also some large-ish gaps. I really should have put my foot down at this point (but it gets tiring complaining about every single thing).

 

5 hours ago, Declan52 said:

Get a hammer drill and drill through the subfloor at this point. Going by the pics you should be enough away from any ufh pipes. If this is 30mm then it's up to you. Digging it all out will damage the ufh pipes though which will need redone. 

 

 

This is a good idea. 

 

There isn't a huge amount of room under the door frames for extra layers. 

Edited June 15, 2021 by Vera16

[James Newport]

Where did the 30mm piece of screed come from in your pictures?

it looks as though it slopes a bit in front of those chipboard doors, but it’s difficult to tell from the photos.

A metal ruler pushed down in the gap between wall and screed till it touches concrete or insulation might let you gauge the depths at strategic points around the floor

 

[Dave Jones]

28 minutes ago, Vera16 said:

The sub-floor is not beam and block it is a concrete slab. I think a lot of the issue is with the insulation layer. It was VERY rocky when I walked over it which likely explains the lumpy appearance. I did question this at the time time but was told the screed layer would stabilise everything. I wanted to tape it but there was so much movement in it I'm not sure the tape would have held. There were also some large-ish gaps. I really should have put my foot down at this point (but it gets tiring complaining about every single thing).

 

 

This is a good idea. 

 

There isn't a huge amount of room under the door frames for extra layers. 

 

so where did they stop the insulation ?

 

Was it 75mm below finished floor ? From what you have found it sounds like 30mm below finished floor.  Either way the buildup of the floor is wrong. What does building control have to say?

 

150mm insulation doesnt work brick.

Edited June 15, 2021 by Dave Jones

[Vera16]

Building Control said 65mm minimum. I asked if they check this and they said it’s difficult ?

Edited June 15, 2021 by Vera16

[Declan52]

5 minutes ago, Dave Jones said:

 

so where did they stop the insulation ?

 

Was it 75mm below finished floor ? From what you have found it sounds like 30mm below finished floor.  Either way the buildup of the floor is wrong. What does building control have to say?

 

150mm insulation doesnt work brick.

150mm is perfect for brick. 2* 75mm (65mm brick + 10mm motar) 

[Vera16]

The insulation is 200mm in this room.

[JFDIY]

Bit late now, but if the boards rock you can either use lots of thinner layers that will accommodate it, or cut them once laid into a union jack, to allow them to flex to the base floor.

 

Cemfloor can go thin, think you'd get away with 40mm  ( or 25mm cover over ufh pipes)