Advice Please On Problems with Screed for UFH!

[ebaxter]

Hi, I am new on here so I hope I am posting in the correct place. We have had underfloor heating pipes for a wet system attached to 75mm of insultaion now for about 3 weeks.

Our builder very slowly, after trampelling all over it is starting to put the screed in. The first batch he got a a readymix delivered to go straight in. The delivery man told me they had two hours, this was for one man to lay about 100m.

At 2 in the afternoon, 5 hours after delivery they were still putting in it. Two of the rooms the guy had worked on and in three other rooms they had kind of barrowed it in and spread it around.

Half of the finished floor didn't go off so they have taken this up and finished it off with a site mixed screed. The other room they brushed up what had not gone off and again finished these off with a site mixed screed.

We know have a couple of spots on the original laid screed that basically is just powder, we can actually uncover the pipes. I am so concerned that perhaps alot of this floor below the tope layer which has set is like this.

From what I've read for the underflorr heating to work effectively it needs to have a good compacted layer of screed with a little air gaps/holes as possible and to have a good overall consistany.

I'm not only worried about this floor but also the ones where they had just barrowed this mixture in and have now covered it over with this mew site mixed screed.

PLease give me some advice, my builder is currently all over the place I don't think he's ever done a job of this size himself andf it's starting to show. Our windows and doors aren't in yet and aside from the potential damage to the UFH that has yet to be covered The screed that is in in places keeps getting wet when it rains!

Do I need to get him to replace all of the screed again or can he patch it up? He is now saying the floor is bound to get damaged and they put a self levelling mixture of the top!

 

[chappers]

if you have patches showing that are unsatisfactory then there is probably stuff underneath that hasn't been done properly but the only way to be sure is to take the lot up and see.
The screed should last a bit longer than 2 hours but 100m should have been delivered in two or three spaced loads and any decent screeder should have known that.
What does the floor look like generally (any pics.) With premix a decent screeder should get it as flat and smooth as a paving slab, then no need for it to get damaged , just cover it in hardboard.

 

[ebaxter]

Three of the rooms do have a very smooth finish and look fine it's the kitchen that looks pants, we can literally dig holes in it by twisting our boots in it.

I.ve written a list and I'm going to bite the bullett tomorrow and ask him to provide boards for all of the areas people are going to be working off. I am going to ask him to take up but the last laid part of the floor and redo it as it's simply not acceptable.l

My husband has easily made 10 holes in different parts of it tonight how on earth he thinks he can just put a self leveller on it. We are learning on the job but even we know it's not good enough!

 

[mointainwalker]

Not clear from your first post.

Was the delivered mix just a concrete mortar screed or was it a self-levelling screed specifically for UFH ?

I ask the question because it sounds as if it was the former but that makes absolutely no sense.

There is not much cost difference between the two and the self-levelling screed gives better thermal performance as it is denser than mortar, avoids air-voids ( difficult that ) and should give a very flat surface thus avoiding hours of work by the builder.

What is the total thickness of the screed and how was the pipe secured to the insulation ?

 

[ebaxter]

The first type of mixture you mentioned. We have pipes clipped to the insulation. We have a 75 mm screed.

 

[mointainwalker]

Well, on the basis of the information given, IMO the person who ordered ready-mixed screed is an idiot and has needlessly caused extra work and extra cost which has furthermore resulted in a sub-standard screed.

If your builder did this, then he has made so many basic errors ( including ordering too much screed in one delivery to be able to lay properly ) that I would have huge reluctance to allow him to carry on as he seems to have no idea.

Ask him outright ( if it was his decision ) why he ordered a screed mix rather than the specific self-levelling UFH mix.

 

[ebaxter]

Job is 3/4 of the way there and everything else has been carried out to our satifaction so I'd rather try and resolve this issue and move on.

I was goin to ask him to take up all of the screed in the kitchen that was originally put in and redo it using the site mixed method. They have enough of the material remaining and have two other floors to screed as well.

If this is done would this floor be adequate for the UFH system to work effectively? The guy who is actually laying the floor, I should point out has done a good job on the other rooms, he was just trying to do the best he could. As you point out too much material was ordered by the builder in one day.

My main concern is we've spent a fortune putting the UFH in for it to not work effectively, plus we've paid extra fdor the builder to put in the floors to be suitable for UFH. All of our pricing is set prices so it's up to him to make good, we don't have any more to pay being my point.

Only have a short window of time to sort this out and I am meeting the builder tomorrow with a list of jobs for next week (don't know whether he is losing his enthusiam as job gets towards the end or his forte was the early stuff. He is having to get trades in now as opposed to doing the work himself.

 

[mointainwalker]

Leaving aside the question of the surface being soft/breaking up, it is highly unlikely that your floor and UFH "won't work" , but what you won't know is if it could have worked better and therefore cost less to run.

In literature it is always pointed out that it is important to make the screed as solid as possible and that it should be encouraged to flow around and coat the pipes completely. This is to effect the most efficient heat--transfer.

When using a mortar-screed it is strongly recommended to put an additive in the mix which is supposed to encourage the mix to flow more easily around the pipes. I don't know what effect this has - if any - which is the same as you will never know how much more efficient your floor could have been.

In any case it is important to remember that you are not actually losing any heat here. these inefficiencies mean that less heat is transferred to the floor, but stays in the water. The loss you have is that your pump may be working more than necessary to get the heat into the floor.

In respect of that, who actually designed your floor with the heat-loss calculations, pipe-spacings etc ? I ask because that would normally be based on a certain type of floor material and the builder should not be changing that as he feels like.

 

[ebaxter]

Thanks for your comments it's much appreciated. We gave the plumber our plans and he has forwarded them to his UFH company of choice Oponor?

The screed mix was actually specified on the plan by the architect as a sand/cement mix 75mm deep althought the actual make up of this is omitted - is there a standard mix for a screed?

I think the stuff the builder got premixed was this with the fibres added, it was a very dry mix. The stuff on site is wetter and the guy who lays it says it's better? Easier to lay and goes off better?

 

[mointainwalker]

I am rather surprised that the screed mix had fibres mixed in: I didn't believe that was very usual.

A screed mix is fairly dry - also called a biscuit-mix - so does not flow and needs more work to push it down and compress it around the pipes and this will have been made more difficult because of the fibres.

In your position i would approach the architect and ask him to justify the advice he gave to use the sand/cement screed. IMO he has failed to give you the best advice you are entitled to receive ( as far as circumstances disclosed ) thereby causing you extra expense ( labour) to have what is a less efficient product . This would be true even if the screed had been laid perfectly.

Unless there is a reason such as existing door heights etc, a specialist liquid UFH screed could also have been laid with a minimum depth of 50 mm which would have been an extra cost-saving and more height if that was important to you.

 

[RoyMacDonald]

It's difficult to say if the screed needs to come up without seeing it, but it takes a few days for screed to reach it's full strength. When it's laid the screed should be covered with polythene or similar to slow down the drying time and allow it to cure properly. The sand should be sharp sand for screeds.

Hard to understand why it has gone powdery. I does take a while to lay screed so I guess it must be something with the excessive length of time it was left uncompacted. Sounds like it's the builders resposibility. Your architect can condem the work ( I'm assuming you used a minor building works contract)and it is then the builders resposibility to correct it to the architects satisfaction.

 

[mac391]

Hi ebaxter,
I've read all previous comments regarding your flooring nightmare and have to agree from what i understand of it, that it's completely wrong !!! I understand you have a time scale but by moving on now i'm sure you will have problems later. You need to resolve it now even if it means delays.
The screed you need for underfloor heating is actually called "anhydrite" it should have been specified by your architect and i agree with mountain that he may have made a mistake. Your first point of call is with your architect ..
Anhydrite screeds are pumped on to underfloor heating and are very watery (unlike your dry readymix) to avoid air gaps around the pipework which can cause problems and make your heating system work too hard to get average results.
Also, anhydrite screeds need to be prepaired with the correct primers etc prior to any final floor covering, this is most important.
I'm still unsure what screed (with fibres) has been used and exact detail of this would help you move on . Your builder or architect should be able to specify this in an instant and it realy is the most important info you need before any more work is carried out.

 

[RoyMacDonald]

There's nothing wrong with the architects specification. It's the workmanship that's at fault hence it's down to the builder to meet his contractual liabilites and lay a screed that is fit for purpose at his own cost.

 

[mointainwalker]

@RMc

If a better product could have been specified at a lower cost and the architect hasn't done so, then I regard that as a a professional error and would seek compensation for it.

A sand/cement screed is not as efficient as an anhydride screed and costs more when labour is taken into account.

 

[RoyMacDonald]

I had costs for both types when I did my kitchen and the finished cost was £400 for a properly laid flooring screed and £2000 for an anhydride screed. I think for commercial projects with big floor areas it could be cost effective but not on small jobs.

As for the courts upholding a claim because someone had a personal preference for a particular screed when all the UHF manufacturers give range of acceptable screed materials, well you would just be wasting your money bringing it to court unless the client specifically requested a particular screed.

If my own kitchen is anything to go by the architect made the right decision in my book.

http://www.uponorhousingsolutions.c...hnical/09 - PEX20 Screed & Concrete Floor.pdf

P.S. A biscuit-mix screed is not for laying over a concrete slab but for filling between joists when the UHF is laid on a suspended wooden joist floor.