YorkieSelfBuild Posted February 22 Posted February 22 Hi, I'm building a new house and trying to find out what prep is needed for the subfloor before I glue down LVT. Ground floor is 150mm concrete slab > 50mm EPS > DPM > 175mm PUR insulation > vapour control > anhydrite screed minimum 45mm over wet UFH. Upstairs is 22mm moisture resistant chipboard integral to timber frame. Originally fit out was floating LVT downstairs, carpet upstairs and on stairs but I'm going for glue down LVT all over with no transitions (stairs will be painted). Building contract doesn't mention any underlayment at all, just LVT and carpet. From online research here and elsewhere, here's my current ideas. 1. Downstairs, 22mm P5 chipboard over screed, bonded with PU glue at the joist top and a minimum of 5 screws per joist. 2. Glue and screw 6mm flooring grade plywood to chipboard, with PVA glue and feather on top. Is FG1 ply better than SP101? Is gluing needed? Screws or crown staples instead? Do I need waterproofing of any kind in the bathrooms, WBP or marine plywood, Ditra or something else? How about the kitchen area if washing machine leaks? A big question is do I need SLC over the plywood, even if builder says it'll be flat enough? Sorry for the long post. All comments, criticisms and ideas are welcome!
Russell griffiths Posted February 22 Posted February 22 Don’t do a bloody thing until you have a LVT contractor, then let him do everything, as soon as you touch it they won’t warrant any of the work they do.
Gone West Posted February 22 Posted February 22 3 hours ago, YorkieSelfBuild said: before I glue down LVT 3 hours ago, YorkieSelfBuild said: even if builder says it'll be flat enough We had glue down LVT laid in our bathrooms. I fitted 10mm ply to the 22mm subfloor, filled all the screw holes, sanded then sanded and sanded again. When the chap turned up he looked at it and said I'll just prep the floor. By the time he was finished it was as smooth as a mirror. Our tiles were 2.5mm thick Amtico and the installer said that any tiny imperfection on the floor will show through the tiles. He did an amazing job.
Nickfromwales Posted February 22 Posted February 22 Why aren’t you just going straight into the screed? Anhydrite screed has a ‘scum’ that needs to be ground off mechanically, have you or the screed company done this? If not, sweet FA will stick to it. You just use a feathering compound, a SLC that can be laid very thin and gets blocked down to leave absolutely zero imperfections, then your glue + LVT goes straight down onto this. Who has suggested chipboard plus plywood over the screed? Will make the UFH performance a bit worse too, longer heat up tines etc. Not the end of the world but if you can’t screw the chipboard down because of the UFH then you’d be no better off? 5 hours ago, YorkieSelfBuild said: From online research here and elsewhere, here's my current ideas. 1. Downstairs, 22mm P5 chipboard over screed, bonded with PU glue at the joist top and a minimum of 5 screws per joist. ? Downstairs joist tops? Eh?
YorkieSelfBuild Posted February 22 Author Posted February 22 (edited) 3 hours ago, Nickfromwales said: Why aren’t you just going straight into the screed? Who has suggested chipboard plus plywood over the screed? My mistake, ignore that chipboard over screed bit. I was reading a thread in Underfloor Heating which was taking about a suspended timber floor. Edited February 22 by YorkieSelfBuild
YorkieSelfBuild Posted February 22 Author Posted February 22 Maybe it's just a bad idea to DIY any of it but I've been made redundant so was hoping I could save a bit in the flooring.
Russell griffiths Posted February 22 Posted February 22 6 minutes ago, YorkieSelfBuild said: Maybe it's just a bad idea to DIY any of it but I've been made redundant so was hoping I could save a bit in the flooring. You could, but get the flooring guy in to give you a spec and see if there happy, it’s the fussiest trade I’ve come across.
YorkieSelfBuild Posted February 22 Author Posted February 22 31 minutes ago, Russell griffiths said: You could, but get the flooring guy in to give you a spec and see if there happy, it’s the fussiest trade I’ve come across. Will do, thanks. I've contacted a local (is 20ml local?) stockist about Kahrs Dry Back LVT, £30m² exc VAT. Need to find out how much installation would cost vs DIY
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