Oh dear, oh dear, oh dear...

[Alex Carr]

Here's a mess I need advice on: wet ufh pipes running through 5 rooms & a hallway; engineered wood floor in two of the rooms & the hallway; the other 3 rooms tiled. Dry biscuit screed (8:1 w. sharp sand & battens laid @ 400mm centres to support the engineered wood floor) in the 2 rooms and the hallway; semi-dry screed (4:1 w. sharp sand) laid in the 3 rooms to be tiled.

 

The semi-dry screed was about to be put down in the 3 rooms to be tiled: my contractor, usually so reliable, said he would lay down some battens (45 x 45mm) as levelling guides for the fellow doing the screeding. And then we'd lay a decoupling mat (current choice: Schluter Ditra Matting) over the screed when it had dried out (at the breakneck speed of 1mm per day) and then pull in the tiler. However, this is where the ordure hit the fan: I assumed the battens were temporary & were only to be used for levelling purposes and would be removed as the work progressed – very wrong.

 

I went home because I was unwell and have been laid low with a virus for the past 10 days; my wife went to the job site (our home to be) after the screed had been laid and took some photos of the finished work, which is when I saw battens where they shouldn't have been. They had been heavily screwed into the sub-floor of the 3 to-be-tiled rooms. I called the contractor and said the battens would have to be removed as we couldn't have strips of softwood supporting a tiled floor as stresses could be created with wood shrinking and ridges forming between the battens and the screed, and so on, and so on. He said he would have a look at the situation Monday morning. I dragged myself out of my sickbed today, Sunday, and went along to have a look for myself.

 

On the basis that I wouldn't ask the contractor to do what I wouldn't be prepared do myself (even at the age of 75) I tried to get one of the battens up, but that turned into a mess, with the still damp screed crumbling at the edges because it was adhesively clinging to the sides of the battens, and the ufh pipe getting partly exposed, and deep screw holes filled with screed muck that was impossible to remove. Needless to say the air turned blue

 

Net result: it looks like the battens will have to stay: The $64,000 question: will the Schluter Ditra matting (3.5mm thick) provide a sufficiently permeable barrier to block the influence of potentially misbehaving softwood battens? I do realise that when the ufh is going, in the fullness of time the battens will dry out, but until then I don't know what to expect.

 

Please, compassionate responses only as it was someone else who dropped me in this sh*t. Constructive opinion would be very much appreciated

[Mr Punter]

I understand that the Ditra stuff is fine over most stable surfaces.  You can see that removing the battens will make a mess, so just let it all dry thoroughly, Ditra and tile away.

[Adsibob]

I don’t think this is terrible. Mistakes happen. There are much worse than this.

i think there are two options, but whichever you do i would wait 70 days or so first for the screed to properly cure.

Then, you could either cut the battens out (or most of them) and fill gaps with screed OR lay 1mm thick steel plates over the battens overlapping the adjacent screed.

 

 Before doing the second option, consult an experienced tiler, such as @nod

Edited May 5 by Adsibob

[nod]

As long as everything is dry You should be ok 

Once the screed has dried out the batons will have shrunk 

I’ve laid Ditra on top of old floorboards and they have been fine 

[Alex Carr]

5 hours ago, Adsibob said:

I don’t think this is terrible. Mistakes happen. There are much worse than this.

i think there are two options, but whichever you do i would wait 70 days or so first for the screed to properly cure.

Then, you could either cut the battens out (or most of them) and fill gaps with screed OR lay 1mm thick steel plates over the battens overlapping the adjacent screed.

 

 Before doing the second option, consult an experienced tiler, such as @nod

1mm thick steel plates? What is the function of the plates?

4 hours ago, nod said:

As long as everything is dry You should be ok 

Once the screed has dried out the batons will have shrunk 

I’ve laid Ditra on top of old floorboards and they have been fine 

And then tiled over that?

[Alex Carr]

2 hours ago, Mr Punter said:

I understand that the Ditra stuff is fine over most stable surfaces.  You can see that removing the battens will make a mess, so just let it all dry thoroughly, Ditra and tile away.

Thanks for that. I suspect that is what I'll do.

[nod]

2 hours ago, Alex Carr said:

1mm thick steel plates? What is the function of the plates?

And then tiled over that?

Yes

[Nickfromwales]

5 hours ago, Adsibob said:

OR lay 1mm thick steel plates over the battens overlapping the adjacent screed.

Bum steer, sorry. Do NOT fit steel plates, you just prime the battens and fill up with tile adhesive for the Ditra to bed into.

 

I'd recommend something like (a little more expensive but very good) Bal Flex One tile adhesive, LINK, as this offers even further decoupling by itself.

[Nickfromwales]

9 hours ago, Alex Carr said:

Net result: it looks like the battens will have to stay: The $64,000 question: will the Schluter Ditra matting (3.5mm thick) provide a sufficiently permeable barrier to block the influence of potentially misbehaving softwood battens? I do realise that when the ufh is going, in the fullness of time the battens will dry out, but until then I don't know what to expect.

You may be 'over-worrying' here tbh. Permeability isn't the issue here, it is movement. If you allow 2mm per day you'll be A OK, and if this is primed properly and a good, conscientious tiler employed vs 'the builders mate', then you have no reason why this shouldn't be a successful undertaking. Excellent prep work can be wasted on a shite tiler  and I've seen them all. FYI, I've been tiling high-end projects for 25+ years.

 

FWIW, I would have given you a bollocking for removing the battens, as that will likely do more harm than good. The battens will offer some fixed mechanical bonding, to both the screed and the Ditra + adhesive, and will likely be the backbone so they defo need to stay.

[saveasteading]

Why can't they remove the battens and then fill the gaps with more of the same mix?

A  bit of crumbling won't matter, as it will fill too.

That way there is nothing to concern you in the long term. 

Differential movement/shrinkage. rusting of screws, rot, distortion. all gone.

 

The screed is  semi-dry you say, so most or all of the water is converted chemically and isn't dampness any longer. The rest will dry in days.

[Alex Carr]

5 hours ago, Nickfromwales said:

You may be 'over-worrying' here tbh. Permeability isn't the issue here, it is movement. If you allow 2mm per day you'll be A OK, and if this is primed properly and a good, conscientious tiler employed vs 'the builders mate', then you have no reason why this shouldn't be a successful undertaking. Excellent prep work can be wasted on a shite tiler  and I've seen them all. FYI, I've been tiling high-end projects for 25+ years.

 

FWIW, I would have given you a bollocking for removing the battens, as that will likely do more harm than good. The battens will offer some fixed mechanical bonding, to both the screed and the Ditra + adhesive, and will likely be the backbone so they defo need to stay.

Thank you for that Nick. I confess I am a worrier and a believer in Murphy's Law, that anything that can go wrong will go wrong. Everything I've read says 1mm per day drying time, though 2mm sounds appealing.

[Adsibob]

My concern about leaving the battens in is that they will not conduct the heat from the UFH as well as the screed. So you'll get cold (or colder) spots, or rather lengths.

So my preference would be to remove them but only after the screed is fully dry.

 

If you can't take out the battens, I had suggested metal plates (could also be aluminium) to provide better support, just in case in 3 years' time after the house has gone through a couple of hundred heating cycles the battens have shrunk. But i accept that's unlikely. I guess it depends on the dimensions and type of battens, whether they are treated with the anti-rot stuff or whether they are just fresh pine.

 

Obviously I'm just a punter, so defer to more the much experienced minds on this thread. 

[Alan Ambrose]

Some careful use of a circ saw and an old chisel would probably sort that out easily enough.

[saveasteading]

5 hours ago, Alex Carr said:

Everything I've read says 1mm per day drying time, 

Everything is therefore wrong. I've heard it said but it is nonsense /  ultra cautious. 

150mm slab would dry in 5 months?. No

2mm is cautious too. 

A 150mm puddle would dry more quickly than that. A screed will only be 5% free water or so.

[Adsibob]

3 minutes ago, saveasteading said:

Everything is therefore wrong. I've heard it said but it is nonsense /  ultra cautious. 

150mm slab would dry in 5 months?. No

2mm is cautious too. 

A 150mm puddle would dry more quickly than that. A screed will only be 5% free water or so.

depends on:

• how you define "drying",
• how humid the building site is already (for example if airtight and MVHR is already commissioned (which is unlikely) you could whack that on max and this would likely speed up drying time); and
• how bothered you are about having a degree of moisture there trapped after you have sealed it - If it is sealed properly, it's probably not too much an issue, but I think allow at least 1.5mm a day drying time.

[Alex Carr]

48 minutes ago, Alan Ambrose said:

Some careful use of a circ saw and an old chisel would probably sort that out easily enough.

I think not as there's no way of knowing how close the battens have been fitted to the ufh pipes; it would only need one slip with the saw to cause irreversable damage.

[Alex Carr]

38 minutes ago, saveasteading said:

Everything is therefore wrong. I've heard it said but it is nonsense /  ultra cautious. 

150mm slab would dry in 5 months?. No

2mm is cautious too. 

A 150mm puddle would dry more quickly than that. A screed will only be 5% free water or so.

I'm calculating 1mm per day. Also usue of a dehumidifier to reduce the rel. humidity. Anything that wil help.

[Alex Carr]

35 minutes ago, Adsibob said:

depends on:

• how you define "drying",
• how humid the building site is already (for example if airtight and MVHR is already commissioned (which is unlikely) you could whack that on max and this would likely speed up drying time); and
• how bothered you are about having a degree of moisture there trapped after you have sealed it - If it is sealed properly, it's probably not too much an issue, but I think allow at least 1.5mm a day drying time.

I think patience is the thing. 1mm per day drying time + dehumidifier left on overnight when the contractor & his crew are not there. Dry out the battens & screed, lower the rel. humidity levels... and anything else I can think of. Correct: no MVHR. The property is the bottom two floors of a 200-year old, 4-storey Edinburgh Grade II listed building. A f*cking nightmare to renovate but my wife insisted she wanted to buy the place because it is spacious like no other place we saw and it has a 30m long, 8.5m wide garden.

[saveasteading]

I've had to cover a concrete floor just 21 days after pouring 150 thick, pumped concrete.

Normally I allowed twice that to be sure.

It seemed to be taking too long to dry but suddenly  it made it (in normal damp weather).

Opening all doors and windows daily was more effective than dehumidifiers.

I've done this many tens of times, but maybe others have been less lucky. 

I think ,  cynically perhaps,  that the main driver of this concern is that flooring contractors want an extra for sealing the surface. They made me sign a firm that said I had declined the sealant: another sales ploy.

On the other hand, I controlled the concrete mix and forbade extra water.

But a dry screed should dry very quickly. If there are windows in yet, the presence or absence of condensation is a good guide.

[saveasteading]

10 minutes ago, Alex Carr said:

dehumidifier left on overnight

Can you warm the space? Not with gas though as it creates humidity.

[Alex Carr]

On 06/05/2024 at 12:59, saveasteading said:

Can you warm the space? Not with gas though as it creates humidity.

Yes, that's my plan. Dehumidifier left on and check the RH every few days.

[Alex Carr]

On 06/05/2024 at 12:55, saveasteading said:

I've had to cover a concrete floor just 21 days after pouring 150 thick, pumped concrete.

Normally I allowed twice that to be sure.

It seemed to be taking too long to dry but suddenly  it made it (in normal damp weather).

Opening all doors and windows daily was more effective than dehumidifiers.

I've done this many tens of times, but maybe others have been less lucky. 

I think ,  cynically perhaps,  that the main driver of this concern is that flooring contractors want an extra for sealing the surface. They made me sign a firm that said I had declined the sealant: another sales ploy.

On the other hand, I controlled the concrete mix and forbade extra water.

But a dry screed should dry very quickly. If there are windows in yet, the presence or absence of condensation is a good guide.

Having laid the screed the flooring contractor is now out of the picture. It was my contractor who screwed down the battens, much to my surprise. He's sensible most of the time, but he did mess this up; still, sins are there to be forgiven. He has a lot of work to do still on various other things and he will open all doors and windows during the day, shut them when it's time to go home and will leave the dehumidifier on overnight. As I said in my original post, there are five rooms and a hallway which have been screeded. I will wait 50 days for a 45mm thick dry screed to lose it's moisture and will periodically check the RH with a meter. Before laying decoupling mats in the 3 tiles rooms, I will seal the screed - any tips or advise on that?

[saveasteading]

1 hour ago, Alex Carr said:

I will seal the screed - any tips or advise on that?

Just that it shouldn't need it for moisture purposes, and I have only used it for binding the surface of  a loose old screed.

[Alex Carr]

1 hour ago, saveasteading said:

Just that it shouldn't need it for moisture purposes, and I have only used it for binding the surface of  a loose old screed.

I'll have to read up a bit on that to help me decide whether or not to do it. Also I'll see what the tiler says.