Anhydritic screed problems

[Fluff]

Hi all

I'm wondering if I could get any advice on a problem I have with an anhydritic screed recently installed.

Story:

~ 10 days ago, we had a screed laid over UFH pipes. It was supposed to be Truflow B. I had my hands full and also had to leave the house whilst this went down.

...The next day, I found that

- 1) the screed hadn't been laid to the right depth

- 2) it's not level

- also 3) that there's very little moisture coming out of it subsequently.

- and 4) I also think that I have a laitance layer which I was not expecting with Truflow B. I could be wrong - is there a way to know for sure if I have or haven't?


Details:

- Floor area is approx 32m square (4.5 * 7)
- Construction is block and beam + membrane + 150mm kingspan on top + thin membrane + 15mm UFH pipes laid with typical clips. Screed depth required was between 51 to 65mm. Screed depth laid is probably around 25 to 40. In some places, I imagine there's only 10-15mm screed above top of pipes (and less above top of clips)

- The guys barrowed the stuff in from the delivery mixer. They didn't use tripods (which I think is unusual). I'm pretty sure they didn't do a slump test (which is probably not unusual) and to me, the stuff just didn't look as watery as I was expecting. They used a dapple bar, but not sure if they went "across and then down".

- Have checked it reading a ruler off a laser and it's higher at one end than t'other, by ~10 to 15mm (aswell as being insufficient depth).

- Have tried putting a membrane down on the screed in the hope of seeing a bit more water and there is very little sign of moisture under the membrane after couple of days - I imagined this should be chucking out water during the first week?


Ideas to fix:

a) Another layer of pumped screed - this would depend on actually finding someone (reliable) to do it.
My concerns here are that

• whilst each layer will have a strong 3D "crystalline" structure, the 2D interface between the two layers will be nowhere near as strong. The UFH will be in the lower layer and as the temperature goes up and down that will cause some expansion and contraction in the lower layer faster than the upper layer - which I guess is likely to stress the weak bonding between the two layers. I presume it will help to some extent if I create a mechanical key between the two layers, but not sure what form this should take (sanding vs really really deep scoring)? Also - at the end of the day, is it a big deal if the two layers separate? The heat is still gonna come through and I guess the lower layer is already floating (on the kingspan+membrane).
• That said, due to current screed not being level, in some places the second layer may be as thin as maybe 15mm - and I'm worried this could split if loaded.

b) Self-levelling compound.
It'll need to be one suitable to bind to anhydritic screed. I'm not sure how strong these things are and also, I understand they have a max depth of 20mm. It doen't really seem like the right fix and as far as I can see, the stuff is only available in 20kg bags - looks like an expensive fix.

c) Other options
Any suggestions??


Other stuff
- The floor for the most part will not take any unusual weight....except .....at one end, I'll be building substantial bookshelves off the floor (say 2.5m high by 4 m long)- they'll be fully loaded.
- I'm putting an 18mm engineered laminate wood over it, which would reduce any point loading of the screed.

Any suggestions/advice on best way forward to "fix" this would be very gratefully appreciated.

(or any suggestions about better places to find an answer to this question)

 

[Rich Midge]

@Ajax123 is your man! Though there's plenty of others with vast experience of anhydrite on here.

 

[Leory]

The screed installers sound like complete cowboys ! Hope you haven't paid !! Never seen anyone attempt to barrow liquid screed before what a disaster ! On a job I've just done we chose to leave some insulation lower those making some of the screed 20 mm thicker . Big mistake cost over 5 weeks in drying time ! It would be best to get them to bear the cost of starting again . Sorry for you pal .

 

[Fluff]

The screed installers sound like complete cowboys ! Hope you haven't paid !! Never seen anyone attempt to barrow liquid screed before what a disaster ! On a job I've just done we chose to leave some insulation lower those making some of the screed 20 mm thicker . Big mistake cost over 5 weeks in drying time ! It would be best to get them to bear the cost of starting again . Sorry for you pal .

Cheers Rich, Leory.

Yep, unfortunately they have the cash. (Aswell as a building project, we have a 6 week old baby, and a few other major things going on - It's difficult trying to keep a close eye on everything at same time).

The builder (my brother) has gone back to screeders about it and they have said they will sort it.... however that hasn't translated into any action after a week .....and also, I'm not sure if I want them back on site - I started feeling a bit uncomfortable on the day, when I was told that you could just "stick a membrane over an anhydritic screed and it will just dry itself" (!).

If there's a simple solution and the screeders will cover the costs, then I could live with that.

If there's a solution to this that requires a significant amount of expertise/skill/understanding of the issues, then I'd rather take the financial hit and get someone else in to sort it properly. - That said, it doesn't seem like there's many companies that want to supply flow screed to a small(ish) project?

 

[Kyle Knowles]

I think the first thing is u need to find out what exactly it was the barrows in coz that determines where to go and what to do . there are leveling compound specific for anhydrite screeds . who is doin your tiling ?

 

[Fluff]

I think the first thing is u need to find out what exactly it was the barrows in coz that determines where to go and what to do . there are leveling compound specific for anhydrite screeds . who is doin your tiling ?

Cheers Kyle

It was a liquid screed which they said was Truflow B. However, what looks to me like laitance on the dried surface suggests it might have been a different one. Whatever it was, I'm pretty sure it didn't have enough water in it - it looked too thick going down ...and it hasn't levelled. So it's definitely an anhydritic screed. It's probably Truflow B.

Yes - I've thought about just getting some gypsum-based levelling compound e.g. Anhylevel. (And as far as I can see there's SFA difference really between anhydritic self-levelling compound and anyhydritic pumped screed - same compressive strength, same key ingredient, same curing times, same drying times . ....Please someone tell me if I'm wrong). My main concern with Anhylevel or similar is that I've got 32 sq meters that is ~25mm too low. That's a hell of a lot of 20kg bags (63 by my reckoning - and I can't see it available anywhere in bulk) and no way to mix it all at once so we'd need to do multiple pours. I don't like the sound of this because it cures in under 3 hours - which means we'd end up creating stratified layers of the stuff which isn't gonna be great for its structural integrity. It just doesn't seem like the "right solution" for this kind of depth and area. Plus, it also has a max of 20mm depth in one pour.

Final finish is an engineered timber laminate - not tiles.

 

[Kyle Knowles]

@Lee@TileTown how much are you looking for a pallet of anhylevel ?

 

[Ajax123]

holy cow.... these screeders sound like they need to go back to being plumbers....

right. firstly truflow b is a bagged product and is a simple anhydrite screed premixed with kiln dried sand. if it was deliverd on a lorry it was most deffinitely NOT truflow b. it is likely that it was just truflow which is the premixed version. the requirement is that there should be 25mm over pipes so its too thin. the required depth of 51 to 65mm is slightly deeper than needed but is better than too thin.

as for moisture coming out it is only 10 days old and even at 40mm will take 40 days to dry.

so for putting it right you could overlay it with an additional 20mm of anhydrite but this is likely to be costly. alternatively you can use a levelling compound ... there are a few that can be laid quite deep. i dont know if Uzin still supply NC 113 which is a gypsum based compound to be laid between 3 and 50mm. Norcross and FBall and co also have similar compounds but i dont know the maximum depths for these so a call to the manufacturers is in order.

to apply the levelling compound you will need to allow the screed to dry, by forcing it if necesary using the underfloor heating which would need to be comissioned and run first anyway. sand off any laitance and then pr,e using an acrylic primer folowed by the levelling compound. unless you are a floor layer this is not a DIY job so costwise it may be just as costly as putting 20mm of TS20 over the existing and possibly more so.

i dont know how much you paid the screeders but it may be just as easy to take up what is there and start again with a screeder that knows what they are doing.

barrow job indeed.... truflow is designed to be pumped into place. it is NOT a barrow job material.

can you name the screeder...

 

[Chalker]

Best advice above.
You paid for a professional job 15mm out if level is way too much.
They should be ripping it up, fully at thier cost. Or if levelling, go with the advice above. Again at thier cost.
There seems to be lots of plasterers going into the pump screed game, as they can do the pumped rendering too.the hood ones go round with a laser and tripods.

 

[One Day]

Hi Fluff, sorry to hear your tale. I recently had a similar floor nr. Chorley - perhaps it was the same jokers?
If you want to go down the Anhylevel (self-leveling) route, I don't mind a trip out to take a look for you and offer some advice. Just PM me if you want to.