DerbyLad Posted January 25, 2021 Share Posted January 25, 2021 Hi All, My new build will have a beam and block floor. My architect has shown 65mm sand and cement screed. The 1st screed installer I contacted has said I would need 75mm flowing concrete with steel fibres or the floor will bounce. The 2nd installer said not and that I would be best with 50mm standard liquid screed. Any thoughts? Cheers Link to comment Share on other sites More sharing options...
Mr Punter Posted January 25, 2021 Share Posted January 25, 2021 The bounce is down to the beam and bearing spacings more than the screed. Where is the insulation going? Link to comment Share on other sites More sharing options...
Russell griffiths Posted January 25, 2021 Share Posted January 25, 2021 My beam floor is the biggest item in mine I dislike. I over specified everything apart from the beams and just went with the design given to me, I wish I had of spent a bit more and got bigger beams and reduced the bounce. Probably another £1000-£1500 would have been money well spent. I have gone with 80mm traditional screed, I have a dislike of the flowing screeds and having seen two local to me I’m glad I stuck with what I know. Link to comment Share on other sites More sharing options...
nod Posted January 25, 2021 Share Posted January 25, 2021 We have a BB floor I laid the screed myself (20ton) definitely no bounce Flow screed is fine at 50 mil Link to comment Share on other sites More sharing options...
DerbyLad Posted January 26, 2021 Author Share Posted January 26, 2021 21 hours ago, Mr Punter said: The bounce is down to the beam and bearing spacings more than the screed. Where is the insulation going? The insulation is going on top of the beams. We will have underfloor heating laid on top of the insulation Link to comment Share on other sites More sharing options...
DerbyLad Posted January 26, 2021 Author Share Posted January 26, 2021 21 hours ago, Russell griffiths said: My beam floor is the biggest item in mine I dislike. I over specified everything apart from the beams and just went with the design given to me, I wish I had of spent a bit more and got bigger beams and reduced the bounce. Probably another £1000-£1500 would have been money well spent. I have gone with 80mm traditional screed, I have a dislike of the flowing screeds and having seen two local to me I’m glad I stuck with what I know. Did you have long spans on your beams? I have looked on my building reg drawings and sizes aren't indicated. My longest span is just over 5 meters What is it that you dislike about flowing screeds and what have you seen from the ones local to you? Link to comment Share on other sites More sharing options...
Mr Punter Posted January 26, 2021 Share Posted January 26, 2021 If you are tiling and using a flow screed you may be better using a cement based one as it does not require scraping and priming. Regarding deflection, this table gives maximum spans for different beam / block combinations: https://www.forterra.co.uk/bison-precast-concrete/beam-and-block-floors/load-span-tables-1 Once you are near to the maximum span you are likely to experience more deflection. 5 metres is really pushing it for a standard beam. The fatter beams are a struggle to move around. Link to comment Share on other sites More sharing options...
Temp Posted January 26, 2021 Share Posted January 26, 2021 If this is a ground floor I would recommend a supporting wall mid span. If its a first floor then.. We have a 6m room and our SE recommended two steel beams to reduce the span of the concrete beams. It was only two because of the location of a window. One mid span would have been fine. Are you having UFH? If so I recommend at least 100mm or PIR and ideally more like 120mm under the screed. Normally 65mm sand cement screed is fine. Could go thinner and add more insulation if FFL is an issue. Could add fibres to reinforce. What I would recommend is expansion gaps (aka deliberate cracks) at door ways where the screed in two rooms meet. Think figure 8. Our screed shrank towards the centres of each room and a crack appeared at a doorway where there is a narrow strip of screed. Needless to say the crack isn't straight but curves into one room. This propagated through the stone floor tiles. Be careful of the laitance issue with Anhydrite liquid screeds if tiling.. https://www.bal-adhesives.com/tiling-onto-calcium-sulfate-anhydrite-screeds/ Link to comment Share on other sites More sharing options...
dpmiller Posted January 26, 2021 Share Posted January 26, 2021 43 minutes ago, Mr Punter said: If you are tiling and using a flow screed you may be better using a cement based one as it does not require scraping and priming. this keeps being repeated, but is it actually true? Not in the case of the gypsum Hemihydrate product we used. Link to comment Share on other sites More sharing options...
Mr Punter Posted January 26, 2021 Share Posted January 26, 2021 29 minutes ago, dpmiller said: this keeps being repeated, but is it actually true? Not in the case of the gypsum Hemihydrate product we used. Sensible question. We had some floors done with a few years back with anhydrate screed and there did not seem to be any laitance so we did nothing. We tiled and had no issues. If I was doing it again I would use the concrete based one because I am liable for 2 years after the property is sold. Removing laitance is not something the tilers or screeders would take on so it would be left to muggins and I don't fancy it. Link to comment Share on other sites More sharing options...
Russell griffiths Posted January 26, 2021 Share Posted January 26, 2021 3 hours ago, DerbyLad said: Did you have long spans on your beams? I have looked on my building reg drawings and sizes aren't indicated. My longest span is just over 5 meters What is it that you dislike about flowing screeds and what have you seen from the ones local to you? Longest spans 5m your floor supplier will specify the beams needed, it won’t be on a drawing that’s for the floor supplier to spec then you include that paperwork in with the rest of the junk you give the council. My 5 m span used a wider beam, in the design they space the beams either a full block apart or a block sideways which doubles the amount of beams per room. I wish I had asked for a higher spec by including more beams. There is is nothing wrong with it it feels very solid, however somebody said stand a glass of water at one end of the room and bounce up and down at the other and see if you can see the water move. You definitely can, but it’s not silly like a timber floor it’s just not as good as I would like it. Flowing screed, I have seen 3 local to me, one is bouncy, the other didn’t flow into the corners correctly, that could be down to operator error and not the screeds fault, and the third had cracks in it in various locations, far to-big for me to be happy with it. Link to comment Share on other sites More sharing options...
DerbyLad Posted January 27, 2021 Author Share Posted January 27, 2021 Wow, thank you for all your replies. More to this than I realised. I will need to discuss with my builder to see what the floor supplier has specced. The company that suggested 50mm screed also suggested that I had the floor sanded. I didn't understand why but now I do, so thank you guys. The screed that they would use is an anhydrite liquid screed. My drawings specify 150mm insulation and yes, I'm having UF heating. Link to comment Share on other sites More sharing options...
Russell griffiths Posted January 27, 2021 Share Posted January 27, 2021 I would avoid that anhydride screed like the plague Link to comment Share on other sites More sharing options...
DerbyLad Posted January 27, 2021 Author Share Posted January 27, 2021 They also offered a Cemfloor fast drying screed that didn't need sanding. Perhaps this would be better? Link to comment Share on other sites More sharing options...
Russell griffiths Posted January 27, 2021 Share Posted January 27, 2021 Just now, DerbyLad said: They also offered a Cemfloor fast drying screed that didn't need sanding. Perhaps this would be better? Entirely up to you have you got a breakdown on prices, any liquid pumped screed added £1500 to the price of mine, so I went traditional as it was the cheapest but also the product I liked the most. Link to comment Share on other sites More sharing options...
DerbyLad Posted January 27, 2021 Author Share Posted January 27, 2021 I've been quoted £1800 for 100m2 for anhydride with £350 to sand. I was told that the Cemfloor would be around £2150 with no need to sand Link to comment Share on other sites More sharing options...
Mr Punter Posted January 27, 2021 Share Posted January 27, 2021 I prefer traditional screed. They do it readymix with fibres and drop it to site. It goes in a bit thicker. If the screeders are good it is a superb finish. I suspect it has better adhesion for tiles as it is not so smooth as the liquids. Link to comment Share on other sites More sharing options...
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