willbish Posted October 4, 2020 Share Posted October 4, 2020 On top of my insulated raft slab I had intended to lay flagstones reclaimed from the old property and have left 60mm for these. Not having enough intact flags and tired of reclamation yard Del boy's I've decided to do the whole lot with concrete imitation flagstones. These are 20mm thick and I was thinking to lay them on a stone dust mortar 40mm thick to bring it up to the required height. With the backs coated in an SBR slurry Now with low temp, wet UFH in the slab is this going to be an issue? Link to comment Share on other sites More sharing options...
PeterW Posted October 4, 2020 Share Posted October 4, 2020 40mm is quite thick - you may be better adding a 30mm screed on the current slab and then setting them on a 10mm mortar mix. If you make the screed more of a cement mixer (4:1) or even a concrete mix with a 10mm ballast it will be easier to level between a couple of rails. Link to comment Share on other sites More sharing options...
willbish Posted October 4, 2020 Author Share Posted October 4, 2020 A screed to bring the level up has been considered but I thought it would be a bit thin and risk of cracking plus it adds another layer of work/labour @PeterW You haven't suggested flexible adhesive on top of the screed, so it's not really necessary in this case? Link to comment Share on other sites More sharing options...
PeterW Posted October 4, 2020 Share Posted October 4, 2020 20 minutes ago, willbish said: A screed to bring the level up has been considered but I thought it would be a bit thin and risk of cracking plus it adds another layer of work/labour @PeterW You haven't suggested flexible adhesive on top of the screed, so it's not really necessary in this case? Why would you..? Concrete slab - Concrete screed - Concrete slabs There is nothing with an adverse expansion coefficient so why start introducing a flexible adhesive ..? I expect the slabs are recommended with a thin mortar bed too. 1 Link to comment Share on other sites More sharing options...
willbish Posted October 4, 2020 Author Share Posted October 4, 2020 32 minutes ago, PeterW said: Why would you..? Concrete slab - Concrete screed - Concrete slabs There is nothing with an adverse expansion coefficient so why start introducing a flexible adhesive ..? True that. Adding UFH to the mix though and I begin to doubt myself 33 minutes ago, PeterW said: I expect the slabs are recommended with a thin mortar bed too. Nope, trying to sell me flexible adhesive. Link to comment Share on other sites More sharing options...
Nickfromwales Posted October 4, 2020 Share Posted October 4, 2020 26 minutes ago, PeterW said: Why would you..? Concrete slab - Concrete screed - Concrete slabs There is nothing with an adverse expansion coefficient so why start introducing a flexible adhesive ..? I expect the slabs are recommended with a thin mortar bed too. +1. The low temp passive raft won't see any adverse temps or swings so pointless going to the expense of flexible adhesive. It would cost a fortune by comparison. 50 minutes ago, willbish said: A screed to bring the level up has been considered but I thought it would be a bit thin and risk of cracking plus it adds another layer of work/labour Errrrrrr......you have 40mm missing, so labour and cost is already a known in order to make that up somehow. SBR the slab and get it soaking wet prior to dropping a 10mm concrete slurry down, around 30mm thick ( so as to allow you to not have to employ laser precision when doing so ) and then make the difference up with the regular tile adhesive. TBH I would employ a screeder to get this to 40mm dead for you as this is going to be a labour intensive PITA to DIY over the whole area. Get the mix delivered and a guy to drop it for you, and then 10mm + finish product will be a breeze. 10mm is a very heavy bed though tbh, so if you get someone to drop this for you you could even get as close as 35mm and make the laying of the flag's less of a ball-ache. But then......a look-see on their website says; Larsen Professional Flexible Rapid Set+ Adhesive We recommend using Larsen Professional Flexible Rapid Set+ Adhesive with our flagstones. Professional Flexible Rapid Set+ is a specially formulated, fully flexible, S1 rated, fast setting, cement based adhesive. It is suitable for beds of 3-20mm, interior, exterior and wall applications. Professional Flexible Rapid Set+ is suitable for fixing most types of tiles and is recommended for fixing glass mosaic, porcelain, natural stone and large format tiles. It is recommended for use on more demanding substrates including heated screeds, over-boarded timber and swimming pools. Deformable Grout after 3 hours BS EN 12004 Type C2FS1 Grey and White Downloads Larsen Rapid Set Adhesive Datasheet So that's out of the window then. Flexible is the way forward from these chaps information? Link to comment Share on other sites More sharing options...
Mr Punter Posted October 4, 2020 Share Posted October 4, 2020 I would go with what they spec. You don't fancy a polished concrete or terrazzo type thing? Link to comment Share on other sites More sharing options...
willbish Posted October 4, 2020 Author Share Posted October 4, 2020 Farmhouse flags have said no issues with a mortar bed, but then backtracked when UFH is mentioned As.. 9 minutes ago, Nickfromwales said: low temp passive raft won't see any adverse temps or swings and 47 minutes ago, PeterW said: nothing with an adverse expansion coefficient I think Im good to carry on with plan A Link to comment Share on other sites More sharing options...
Nickfromwales Posted October 4, 2020 Share Posted October 4, 2020 (edited) 1 minute ago, willbish said: Farmhouse flags have said no issues with a mortar bed, but then backtracked when UFH is mentioned As.. and I think Im good to carry on with plan A Hope your back is in good condition, as that's a lot of mixing, hand-balling and levelling. Pics too please!! Oh, and make sure the slab is soaking wet with the primer / water mix before laying. I use a janitors mop and just keep hitting it until it appears saturated. Edited October 4, 2020 by Nickfromwales Link to comment Share on other sites More sharing options...
willbish Posted October 4, 2020 Author Share Posted October 4, 2020 Majority of slabs 900x600 so should fly down.... ? only 86m2 to do. Will probably take me til Christmas Link to comment Share on other sites More sharing options...
Nickfromwales Posted October 4, 2020 Share Posted October 4, 2020 2 minutes ago, willbish said: so should fly down... ?. I'll drop in mid December for a brew and to see how far you've got lol. ? Link to comment Share on other sites More sharing options...
Mr Punter Posted October 4, 2020 Share Posted October 4, 2020 160 slabs at about 55kg each. Hopefully not too many cuts to do. Link to comment Share on other sites More sharing options...
willbish Posted December 29, 2020 Author Share Posted December 29, 2020 On 04/10/2020 at 21:00, Nickfromwales said: Hope your back is in good condition, as that's a lot of mixing, hand-balling and levelling. Pics too please!! Finished.... Didn't make the Christmas deadline or do it without some help so I can't take all the credit. On 04/10/2020 at 23:24, Mr Punter said: Hopefully not too many cuts to do. It wasn't the cuts that got me but the grouting. I nearly walked off my own site vowing never to return during that job! 3 1 Link to comment Share on other sites More sharing options...
Mr Punter Posted December 29, 2020 Share Posted December 29, 2020 Great job. If you were to price this to do for someone else, how much would you charge per metre? Link to comment Share on other sites More sharing options...
willbish Posted December 29, 2020 Author Share Posted December 29, 2020 11 minutes ago, Mr Punter said: Great job. If you were to price this to do for someone else, how much would you charge per metre? Good question Just did a rough calculation which came out at £25/m, labour only. Seems too cheap! Link to comment Share on other sites More sharing options...
Nickfromwales Posted December 29, 2020 Share Posted December 29, 2020 1 hour ago, willbish said: Good question Just did a rough calculation which came out at £25/m, labour only. Seems too cheap! To lay and grout that, including logistics, would be in triple digits for me. Cracking job on the grouting btw, and yup, a labour of love that is. 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted December 29, 2020 Share Posted December 29, 2020 Should add to the thermal ma........ 1 Link to comment Share on other sites More sharing options...
willbish Posted December 29, 2020 Author Share Posted December 29, 2020 13 minutes ago, Nickfromwales said: Should add to the thermal ma........ Yep that's now 360mm of thermal... inertia. When the time comes, heating it up is going to take an age, much like @Petes recent warm up. Link to comment Share on other sites More sharing options...
Nickfromwales Posted December 29, 2020 Share Posted December 29, 2020 5 hours ago, willbish said: Yep that's now 360mm of thermal... inertia. When the time comes, heating it up is going to take an age, much like @Petes recent warm up. Yup, but the thermal time constant will be conducive to heating once a day during Octopus Go’s 5p/kWh / 4hrs plus maybe one more midday nudge in the Baltic times. ? Tres bien, Rodney. Link to comment Share on other sites More sharing options...
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