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General: Floor repair, screed drying time

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    • CommentAuthorRex
    • CommentTimeJan 23rd 2018
     
    What ho one and all,

    I seem to be the local 'expert' because I built a house!

    An elderly lady a few doors away is having a ground floor problem that is being handled by her insurance company. Basically, I don't know how the house is constructed (built around 40 years ago) but I don't think there is an air gap under the ground floor, not that that should make nay difference to the issue.

    Around three years ago, she had a bad gutter leak that resulted in water dripping through the lounge ceiling and onto the oak flooring. The ceiling did not collapse. The leak was cured, the ceiling plasterboard replaced and floor was allowed to dry out and new oak tiles stuck down with bitumen.

    All good until six months ago, when the oak tiles started to lift in a number of places on this newly laid floor. The original flooring has absolutely no problems. After a lot of umming and arring, the insurance company have finally taken a second repair on board. They have decided to remove the previously 'wet' section screed, and have cut it all out, down to the DPC level. I guess they will be replacing it with a sand / cement mix before replacing the floor tiles.

    I am sure they will want to get on the job ASAP, but since they will need to replace around 60 mm + of screed, I am guessing they will just allow the calculated dry time, lay the lies and get her to sign a disclaimer of some kind.

    So my question is, how much longer should 60mm (that is a guess) take to dry to a point where wooden tiles can be laid without future issues? Does leaving longer than the recommend time reduce the moisture level? She does not have UFH, so there is no way to improve the curing time.

    Toodle pip and thanks

    Rex
    • CommentAuthortony
    • CommentTimeJan 23rd 2018
     
    Resin screed will be a good idea, we used to say a millimetre a day with heating and ventilation so 60mm = two months

    They should measure the dryness before laying.

    I wouldn’t let my neighbour lay new wood floor for 18 months after their garage conversion with new concrete and screed floor.
    • CommentAuthorRex
    • CommentTimeJan 23rd 2018
     
    I was visiting her this morning when the builders turned up.

    They have put a bitumen layer over the base, then a thick DPC followed by 25mm of insulation. They will apparently put another plastic sheet then around 30mm of Mapei fast setting screed. At a guess, it is TopCem which as a drying time of 4 days according to the tech-spec pdf blurb.

    I don't think she would get anyone to sign some kind of disclaimer, but 4 days seems pretty damned quick to me.

    Rex
    • CommentAuthortony
    • CommentTimeJan 23rd 2018
     
    Keep heating on in the roof after first few days, with window open a crack then wait til at least after Easter to do floor finish.

    Screed sounds awfully thin to me.
    • CommentAuthorRex
    • CommentTimeJan 27th 2018
     
    Agreed. But it is an insurance job. The first time around, the floor tiles lifted after one year because the builders had not removed all the damp screed.

    The insurance company caused quite a stink about doing it all again, but they finally agreed. Unfortunately, I think the builder has already put the tiles in place. He told me that the screed is an expensive Mapei, fast dry screed and there will be no problem. I Googled and found one Mapei product called TopCem, dries to less than 2% moisture content after four days.

    I would not be happy, and have advised the neighbour to write to the insurance company telling them that she has concerns regarding the moisture content after four days and if the tiles fail again, they will accept full responsibility. Doubt that it will produce anything, but at least they will know should the floor fail again.
    • CommentAuthorcc64
    • CommentTimeMar 16th 2023
     
    Heading into the unknown here I'd appreciate some suggestions for how to repair a localised screed failure.

    This was over the cavity crossing just inside the entrance door threshold. The screed broke for want of decent support over the cavity. The fragmented screed I've removed, also removed from the cavity the varied rubble not providing support, and filled the cavity with graphite EPS sheet with flanking thermal upstands from the same against the blockwork of the reveals and the threshold. (There were no thermal upstands originally installed). Next I need to renew a section of insulation and get the screed back in place. This is new territory and I'm slightly at a loss on how best to proceed on 3 aspects

    1. The broken edges of screed are coarse/rough. For getting a good bond between original screed and new is this rough surface good or bad? Should it be straighted off with an angle grinder to offer a better face for some bonding slurry

    2. Thickness of insulation and screed. These total 65mm, with what was probably 25mm EPS (before it compacted) under 40mm screed. Given the way in which the EPS compacted, which undermined the support to the screed, probably leading to its failure, I'm inclined to use some XPS since it has better compressive strength. Is 300 adequate? Or would more compressive strength be worthwhile? 40mm is not much of a depth for the screed, and any improved support it can get from the underlying insulation seems more likely to protect it from flex and breakage again.

    3. Materials. Research came up with Mapei EPORIP as bonding agent (fresh mortar to old) and their 3240 repair premix (fibre reinforced, self leveling, superplasticizers, rapid setting ... it's got all the buzzwords). I've about 0.4mm of screed to replace, so a single 25kg bag should be enough The specs say drytime 4-6 hours for 3mm thickness but also that it can be applied as thick as 40mm. Is there any reason not to apply it at that thickness in one go?

    This is a new (and unexpected) area of endeavour so the thoughts hints and tips of those that know better are welcome
    •  
      CommentAuthordjh
    • CommentTimeMar 16th 2023
     
    I'm no expert so hopefully you'll get some better answers from people who know more than me, but ...

    Posted By: cc64The broken edges of screed are coarse/rough. For getting a good bond between original screed and new is this rough surface good or bad? Should it be straighted off with an angle grinder to offer a better face for some bonding slurry
    Rough surfaces are generally good to improve bonding, so I'd suggest a wire brush to make sure there's no loose bits and then work some bonding agent into the rough surface.
    Thickness of insulation and screed. These total 65mm, with what was probably 25mm EPS (before it compacted) under 40mm screed. Given the way in which the EPS compacted, which undermined the support to the screed, probably leading to its failure, I'm inclined to use some XPS since it has better compressive strength. Is 300 adequate? Or would more compressive strength be worthwhile? 40mm is not much of a depth for the screed, and any improved support it can get from the underlying insulation seems more likely to protect it from flex and breakage again.
    I wouldn't have thought a door threshold was a particularly heavily loaded area unless you're regularly going over it in a wheelchair or with washing machines on sack barrows or suchlike. So I'm surprised the previous insulation failed, unless it was very lightweight stuff. But EPS250 or EPS 300 should be plenty strong enough (it's what our house sits on). As you say 40 mm doesn't seem very deep for the screed and if that could be increased it would probably help. Also be sure to put some reinforcement in it, to give it some tensile strength - either fibres or some mesh.
    Posted By: cc64Materials. Research came up with Mapei EPORIP as bonding agent (fresh mortar to old) and their 3240 repair premix (fibre reinforced, self leveling, superplasticizers, rapid setting ... it's got all the buzzwords). I've about 0.4mm of screed to replace, so a single 25kg bag should be enough The specs say drytime 4-6 hours for 3mm thickness but also that it can be applied as thick as 40mm. Is there any reason not to apply it at that thickness in one go?
    I don't know anything about materials but I believe you do want to do it all in one pour, otherwise it's liable to fail at the interface. From the Mapei site, the 3240 looks like a product used on top of an existing supporting substrate. I would ask Mapei or a supplier what the right product is.
    • CommentAuthorGreenPaddy
    • CommentTimeMar 17th 2023
     
    The area around door thresholds are often an issue, as there is repeated, concentrated traffic, thermal expansion being adjacent to the perimeter wall, at the edge of the slab so not as well supported as the rest of the floor, stress raisers at the two external corners of the reveal, etc.

    what's the finished floor covering? Tiles, carpet, timber, polished concrete?? If the screed will be covered, then any hairline cracking won't be an issue. Make sure the insulation (high compressive strength as you suggested) is firmly held in place, ie squashed between the door threshold side and the room edge of the original. If the substrate is firm, and cannot "rock" or move, then the screed on top will have no reason to move. Is the cavity filler also a high compressive strength insulation (graphite EPS but what comp strength). If that is not robust, then same issue may arise. Personally, I'd cut the old screed to a straight line, ensuring any weak edges are removed. I wouldn't bother with the surface bonding agent, but will do no harm. The key thing is the substrate.

    Mapei 3240 looks fine. 3 to 40mm thickness. If you get some slump after drying, could top it off with a thin skim over to make flush.
    • CommentAuthorcc64
    • CommentTimeMar 18th 2023
     
    Thanks both for your helpful comments. I got mapei technical support input (from Andy, whose hand you can see in utube video for HB R3) who said the renovation 3240 was more of a levelling cmpd than a screed, and recommended HB R3 instead. No bonding agent required to original edges, either, just wet them down.
    • CommentAuthorcc64
    • CommentTimeMar 18th 2023
     
    Addendum
    I don't really know about reinforcement to give screed more strength. The existing screed had what looks like standard chicken wire frankly (twisted, not welded, from 1mm diameter wire with peripheral wire of 2mm. It's positioned between the underlying EPS and the screed, not where I understand it ought to be i.e. within the screed itself).

    Happy to hear suggestions from those with more experience, particularly on how to support said reinforcement in midscreed depth position? I suppose a 20mm first pass thickness could be followed by putting down some reinforcement and followed by another 20mm layer - all within the screed open time of course. Sounds like something that could make an amusing utube video. Not the kind of amusement I'm looking to provide. Suggestions welcome
    •  
      CommentAuthordjh
    • CommentTimeMar 18th 2023
     
    Sounds like the existing was somewhat of a bodge. I'd suggest mixing some PP fibres into the mix rather than calculating what size of mesh is needed and then anchoring it. But check with Mapei to make sure that's OK. I'm glad they suggested a more appropriate product.

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