EdSt

Nick from Wales. Thank you for that. I had been weighing up what the 160mm PIR would span if I put two brick under it and then stood on it on a 18mm board (simulating dissipated loading of the screed) sure it would stand a span of 600mm.I’m so paranoid about getting this wrong and the potential backtracking needed… that’s the problem with DIY, you’ve no experience to know where the performance gaps are acceptable or just too anal, and so have to resort to text book (or sleeping pill! 😂) need to find a tiler. But I just wanted to hear people’s thoughts on decoupler. I understand it deals with movements but just wondered if it would deal with such a stark difference in insualted&heat vs cold slab&screed. huge thanks for sharing your thoughts - have you any recommendations on good decoupling adhesive and decoupling membrane? Thanks

Thanks Nod. Somehow got the B&B slurry stage wrong. Don’t think I wet it down enough and have ended up with a thin uneven layer of cement&sand on top of blocks meaning an uneven finish. When I put straight edge down can see it’s not bang flush contact throughout. Would hate for any problem so was thinking self level just to be belt and braces, somebody suggested sand blind but was thinking a thin layer might be difficult (and faffy) to achieve, again hence self level. 8mm tile adhesive - thanks will check with tiler what he wants.👍

Hi, built a 6x3M block and beam (B&B) single story extension (new dining room) on to existing extension (old kitchen&dining room being turned in to kitchen and utility) which backs on to original stone house. B&B level 26Omm below existing Finish Floor Level (FFL). Make up will be: SBR prime&self level B&B 3mm, DPM, 160mm PIR slab with 25mm insulation around perimeter, VCL/UFH Mat/grid, UFH pipes tacked down and encased in 65mm semi dry sand&cement with fibre, self level 2/3mm?, 5mm adhesive?, decoupling mat, 8mm adhesive then 15mm tumbled limestone tiles. I have 3M two pane sliding doors to go in and plan (fingers crossed) is flush threshold. I also want the UFH to extend in to Exisiting part of the house. So will be hiring diamond floor saw with 18” disc to achieve 175mm cuts. Current make up of that floor is top>down is: 12mm quarry tile,60mm S&C screed, 100mm conc slab, dpm, 300+mm builders waste infil/MOT. Plan is to get down in to the infil re tamp/whack any disturbed ground, and build up with 100mm conc slab to match B&B floor height and then same build up from there. Due to position of new kitchen units -a 6M ‘L’ shape run along back and side of old extension, some of the old floor might as well stay insitu with a clean cut say 650mm out from walls so around worktop kickboard depth. *Question* is how do I deal with the boundary of insulated &UFH built up section with old floor slab? and taking in to account the tumbled limestone tiles will span across this boundary? I was thinking 25mm perimeter PIR cut flush with FFL (?) - but will decoupling adhesive bond to PIR and/or be ok across this 25mm gap? Will the decoupling mat cope with movement between heated and none heated floor slabs? I will have quite a bit of this interfacing old&new to deal with as also UFH will head through a trench in other part of Exisiting house which will become utility. As this small space houses the oil boiler and UFH manifold it will be plenty warm enough so hence just a 2.5M long trench for flow&return UFH pipes (make up 100mm new con slab,160PIR,65screed, 25 Matt/adhesive/tiles) across the old slab Any observations on the plan much appreciated! Sorry it’s long winded but thought I’d tag and explain what I’m up to for benefit of anybody else on this route. Thanks!

Yeah, thanks I knew that already but you‘ve conveyed it well, it’s a mentality shift. 👍.

Cool. Thanks for that.

Doing a kitchen extension and due to our lifestyle (both out at work all day and require warm house quickly of an evening) I’d ruled out UFH at planning stage. Partly also because the existing house space which we’ll break through to wouldn’t match as just has radiators. (current heating system is oil boiler which I’ve confirmed can run UFH as well as rest of house heating system) Was talking to bricky the other day and he got me thinking about it on basis that it’s relatively cheap to put in, gives a nice heat and wouldn’t matter about existing areas as air temp would balance and be nicer ambient temp. Different levels out the back of the house mean the extension is in block and beam (B&B) construction and block work shell is now up… I.e my levels are set. Current drawings/plan is sand blind on B&B, 125mm PIR, 100mm Concrete slab, 5-8mm self level, 8mm tile on 8mm bed. Question. Could I do sand blind, 150mm Kooltherm/PIR then 75mm Screed (instead of conc) as a structural floor finish before self level and tiles? Thanks in advance !

Thanks Dave. I’m not sure. There were plenty around covering block stacks which were lower priority.

Thanks Russell 👍

..just to add, I messaged him with some pictures to say a lot of mortar had washed out and he said he’d come repoint when he comes back to finish it.

Hi, just jumping on this thread with my issue.. block layer was suppose to come yesterday but was a no show, arrived this morning unannounced and caught me unawares as I was off to work. He set his lads going on the 7M 215mm block flat wall they are building for my block and beam and himself left site. When I spoke to him mid morning to see how things were he still wasn’t at my house. Came home this evening to find standing 30mm of water in parts of the trench and a load of, what looks like run off mortar, in the trench (looks like a lot - might they have thrown some sand in to try and soak up the standing water - is that a trick if the trade?) Any way there were token tarps thrown here and there but only half covered and not tidy. Had a poke around with a wall tie about 6pm and found the bottom beds soft and exposed vertical ones soft and washed out not much better now at 1130pm. The trench had a load of fluffy bubbles on the sand/mortar spoil like which I guess is the plasticiser. I’m not happy, and don’t see why I should have to compromise on a weaker wall, he can’t be saying this is top notch work - for one he wasn’t around. However ,I read in a few of the forums that actually mortar isn’t too affected by wetness. Please can the experienced brick/block layers provide their thoughts? I’m not to worried about the cosmetics as the wall will get rendered. Is the structural strength compromised and does it all need taking down and starting again? It’s a outside wall to carry the end of 4m block and beam patio. Thanks in advance.

Thanks Connor. Committed to b&b now.

Thank you all for your comments. After stumbling across another thread on here I’ve decided to put in an intermediate wall and split the 5M in to 3M & 2M. Mixed myself with bell mixer and at just short of a cube it was a long day! I already had the materials on-site so apart from cement it wasn’t that expensive. The 3+2 spans are likely to mean I drop the double beams saving 14 lengths of 5M equating to about £500. More importantly though, any chance of bounce should now be gone. For any that follow behind me on the issue of bounce on 5M spans have a look for the thread titled ‘Spans - Precast Flooring or intermediate support’ started by moggaman

Looking for peoples experience and thoughts on block and beam (B&B) bounce please… I’m middle of Self building single storey K/D extension and due to ground levels using block and beam (B&B) for the extension itself and the patio which leads on to back garden. Extension floor slab B&B to be set off internal block skin and external patio and side walkway B&B to be build off external skin. Extension above ground cavity block work to then continue up off of these. The patio span is 5.2M (by 7M wide) and currently have extension subfloor walls built, and garden supporting patio B&B foundation poured. Plan back from B&B manufacture is attached (FYI price on beam only is £1.4kExVaT) Their response to my follow up enquiry asking about bounce the manuf. said: ‘The design currently has a natural frequency of 4.35 Hz. We could improve to 5.28 Hz by reducing all block spacing to 215, or 6.09 Hz by using 150 wide beams only & 215 spacing. The only way to improve on this would be to introduce a spine wall and use shorter beams.’ First off I’ve no concept of bounce from the plan or the improved levels from the proposed alternatives - do folks think the real life experience will be bad/annoying? (very subjective I know but don’t want to be stuck with this and it grate on me at family bbqs or when have friends over entertaining as I guess all will experience the bounce not just person moving. Secondly, do the reduced figures significantly improve things?! These would further increase cost and Seriously considering getting the plant back and digging and pouring another foundation to split the 5.2M span down in to a 3M&2M to reduce the bounce. Downside is this is costly as wet conc (and additional pallets of blocks for wall) has to be moved in telehandler bucket driven backwards down a 400m very narrow lane. (Ahh joys of rural living!) Lastly do people advise on screed topping to further bind the ‘slab’ beyond that of just grouting as a way to reduce bounce. From my reading it seems common occurrence but this does seem in an internal setting. (I’m using 100m concr finish for the internal floor slab but thinking/hoping don’t need to for patio outside. Thanks for any input. ed (note photo shows a partial foundation already but this was added just for a small upstand wall to retain the earth)

Can I ask how have others have achieved waterproofed block and beam (B&B) layouts? .. I’m doing a B&B patio to extend out from new single floor kitchen/dinner extension. Level of garden is approx 1.3 meters to top of foundation cover, so plan to use the undercroft below for storage of scaffold, mixer, wheely bins, kids plastic garden toys/tatt I.e generally inert outdoors stuff - so no Rembrants - but maybe some seasoning/seasoned logs/firewood. The patio span is 5M (by x7M wide) and I’m thinking of breaking down into 3M&2M with support wall, to remove any bounce. (Bounce question will probably be another forum post!) Current thinking on patio surfacing is 37mm 600x600 pavers set on wall barn pedestals and lay these on top of some kind of membrane (Edpm?). Looking to achieve 60mm total thickness by extension to sit level with 50mm Aco sat on 10mm bed to pick up the drainage on the bifold cill - aiming to achieve low threshold (again subject if another post most likely). I’ve read about people tanking B&B with cementious products but not really feeling like that would be robust given potential for cracking with heat expansion and bounce, all-be it greatly reduced. Concerns with edpm would be cost and also risk of puncture once loaded from concrete snot/grit from the beams or block concrete products. With project to date I’ve found the build hub forum supper helpful so hopeful for ideas and input on this one. Thanks in advance! Ed