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Housing - Renovation: Mesh In Screed?

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  1.  
    How important is A142 mesh when screeding a hallway of just 75mm depth using traditional screed with fibres.

    16mm UFH pipe will be used

    And can it just sit on top of the PIR or does it have to be raised further?

    Also can each sheet be cable tied together or have I got to use wire ties? Or do they even need to be tied together?

    Many thanks
    • CommentAuthorrevor
    • CommentTimeApr 7th 2020
     
    Don't understand why you would need to put mesh in the screed. Screed with fibres is very strong provided the mix is correct. There are several types of "cement" that can be used. What is the base layer i.e. under the PIR.
    what is the floor covering going to be.
    • CommentAuthorjamesingram
    • CommentTimeApr 7th 2020 edited
     
    ive used the mesh to tie the ufh pipes to and raise them up off the insulation and get them surrounded in screed.
    for that i think it a useful better way of doing it, but not essential.
    i just cable tie them together and lay them on the screed with the uper mesh pointing the way it makes tying the pipes to easier
    • CommentAuthortony
    • CommentTimeApr 7th 2020
     
    👍. Will work ok no need to tie with wire
    •  
      CommentAuthorfostertom
    • CommentTimeApr 9th 2020
     
    How do you keep the pattern of pipes in place then?
    • CommentAuthorrevor
    • CommentTimeApr 9th 2020
     
    You can get clips that holds the pipes off the insulation if that is what you want to do. (Robbens do them) You say you are using traditional screed, it is necessary to pay a lot of attention to get the screed which is quite stiff to surround the pipe. You will need to walk it in by treading either side of the pipe. Tamping down and levelling a stiff screed is difficult enough without having mesh in the way. I think you will end up with lots of voids because you will not be able to get the screed to surround the pipe, the voids will affect the heat transfer properties of the floor in a negative way. I think you are making extra work for yourself by using mesh. It would be a different mater if it was liquid screed you were using.
  7.  
    We have used the A142 mesh for this purpose before now and it was fine. It was straight on to the slab though (limecrete) and the screed was a bit runny (lime screed made with recycled crushed glass sharp sand)
  8.  
    Finished surface was blue brick pavers in one room and thick sandstone slabs in the other
  9.  
    We even halved the spacing in some places (down to 100mm) to get a bit more heat in some areas. I found that it gave more flexibility/choice in pipe runs. I think it was cheaper than using the “egg crates” and didn’t use unnecessary plastic. Just a few cable ties. It was a bugger on the knees tying the pipes on though!
    Insulation was under the slab.
  10.  
    Also seemed a bit pointless covering the whole slab in a continuous plastic layer when it was supposed to be a breathing floor!
    • CommentAuthorjamesingram
    • CommentTimeApr 10th 2020 edited
     
    Posted By: fostertomHow do you keep the pattern of pipes in place then?

    cable ties
    • CommentAuthorMike1
    • CommentTimeApr 15th 2020
     
    FWIW D49 is normally used for screed reinforcement, rather than the thicker A142. No problem using cable ties, or clipping the pipe to the insulation instead.
  13.  
    Chicken wire any good?

    Found various links suggesting that too
    • CommentAuthorJonti
    • CommentTimeApr 18th 2020
     
    Posted By: VictorianecoChicken wire any good?

    Found various links suggesting that too


    Yes, chicken wire works well.
    • CommentAuthorMike1
    • CommentTimeApr 19th 2020 edited
     
    Posted By: VictorianecoChicken wire any good?

    BS 8204 requires the use of either:
    50mm square 16 gauge (1.2 mm) welded wire mesh,
    D49 (2.5mm bars, normally used), or
    A98 (5mm bars).

    Chicken wire can be as thin as 0.4mm, and isn't welded. It is sometimes used in DIY, but shouldn't be. It should provide some cracking resistance, but not much load distribution or curl resistance. However trying to keep it flat while attaching UFCH pipe to it might make an amusing YouTube video.
  16.  
    I actually used a142 mesh in the end. Finished all the UFH pipes literally 15mins ago, all set for the screed Tuesday
    • CommentAuthorJonti
    • CommentTimeApr 20th 2020
     
    Mike,

    I didn't use the chicken wire to strengthen the slab but to set the height of the UFH pipes by bending small pieces into arches to support the piping whilst the slab was poured.
  18.  
    Posted By: VictorianecoI actually used a142 mesh in the end. Finished all the UFH pipes literally 15mins ago, all set for the screed Tuesday


    Hope it goes well tomorrow with the screed. We still have to do that bit yet on this project.
    Currently scratching my head about MVHR install and ducting routes, having taken a delivery from BPC Ventilation today.
  19.  
    Screed delivered at 7.30am and all done.

    It's up to 100mm in places, how long till:

    1. We can walk on it?
    2. Till we can run the UFH?
    3. Till we can put finished floor down? (likely to be an LVT tile)
    • CommentAuthorbarney
    • CommentTimeApr 21st 2020
     
    1 day per mm

    Stay off it for at least a week

    What did the installers say when you asked them ?

    Regards

    Barney
  21.  
    He said to lay a 4" insulation board from the dining room to bottom of stairs and will be fine to walk across this evening to get upstairs.

    But advised to not walk on direct for 2 days
    • CommentAuthorMike1
    • CommentTimeApr 21st 2020
     
    1) I'd give it at least 48 hours, and a week before doing anything other than walking on it. It will take a month to achieve most of it's ultimate strength. Keep it moist for at least 1 week too, to aid curing - ideally cover it with plastic sheeting.

    2) As long as possible - the autumn would be good - and don't be tempted to use the UFCH to dry it out.

    3) That depends on the temperature and humidity; 1 day / mm is one rule of thumb, but basically leave it for as long as possible - it will continue to shrink slightly for some months.

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