Hi

I've just looked at a new job. Currently the floors are carpeted in 2 bathrooms. However, the owner tells me that there is blockboard underneath. They want me to install u/f heating (I will probably use devimat) and then tile over it.

My previous experience has all been on solid floors, or wet rooms, where I've laid wedi-board over the floor.

So my question is - with blockboard as my base - should I lay something over this first - before laying the heating mat? Or can I lay the mat straight on top of it, then cover it in self levelling and tile as normal (flex addy etc. of course)?

I could possible use wedi board again - as it would also provide a bit of insulation underneath. Thin stuff should be sufficient? Thoughts?

Paul

What exactly do they mean by "Blockboard". I recall (in my youth!) that block board was a bit like ply execpt that it was just a 3 layer laminate with long "block" strips held between the 2 outer layers. if that is correct, I don't think it is suitable for tiling on to and would need to be replaced.

Other more experienced guys may know different though.

I think this must be plywood or chipboard. In which case use insulation boards with 2 part flexi, and the same for the tiles....Gaz

Originally Posted by grumpygrouter

What exactly do they mean by "Blockboard". I recall (in my youth!) that block board was a bit like ply execpt that it was just a 3 layer laminate with long "block" strips held between the 2 outer layers. if that is correct, I don't think it is suitable for tiling on to and would need to be replaced.

Hence my question

I've heard of block-board - and no doubt seen it in my youth. But when they said it to me I just said, is that plywood or chipboard? A quick google states that it is as you say, a 3 or 5 layer ply - with blocks forming the central part of the sandwich.

Paul

PS - what's a 2 part adhesive? (I'm still SO new to this game). Surely if its a fully flexible waterproof mix, as I always use, then that should suffice? Plus adding a layer of insulation, such as Wedi board, will stop a lot of the flex.

Originally Posted by pt44

Hence my question

I've heard of block-board - and no doubt seen it in my youth. But when they said it to me I just said, is that plywood or chipboard? A quick google states that it is as you say, a 3 or 5 layer ply - with blocks forming the central part of the sandwich.

Paul

PS - what's a 2 part adhesive? (I'm still SO new to this game). Surely if its a fully flexible waterproof mix, as I always use, then that should suffice? Plus adding a layer of insulation, such as Wedi board, will stop a lot of the flex.

Paul firstly, 2 part adhesive is powder mixed with a liquid polymer not water. The only flexible and true waterproof adhesive is epoxy resin again a 2 part or 3 part mix. True laying Wedi board will add strength, but you have to glue that down 1st, and if you are using as you say a "fully flexible waterproof mix, as I always use", then I presume it is a single part (slow set) or Rapid set flexible, which has the polymer already added so you just add water. If this is what you are using a minimum 10mm board should be fixed down first....Gaz

Thanks gaz

Yes, I often use Weber SPF - single part flex - so as you say, it has the polymer already in it. Good point about gluing the wedi board down.

I was just reading the installation instructions for devimat onto wooden floors. And it states that if its going over t&g, then you need to add a 15mm layer of ply under the mat, then cover and tile as normal. I probably need to phone them direct, to check if that would be the same for blockboard. As no doubt the t&g flexes far more.

Paul

Originally Posted by pt44

Thanks gaz

Yes, I often use Weber SPF - single part flex - so as you say, it has the polymer already in it. Good point about gluing the wedi board down.

I was just reading the installation instructions for devimat onto wooden floors. And it states that if its going over t&g, then you need to add a 15mm layer of ply under the mat, then cover and tile as normal. I probably need to phone them direct, to check if that would be the same for blockboard. As no doubt the t&g flexes far more.

Paul

Paul mate, always advisable to talk to the board makers and also consult such as ourselves on the adhesive grout & prep side....Gaz

I would use 10mm marmox board Cheaper than wedi and screw down with proper washes and screws (don't glue), then level over with weber niv dur levelling compound over the under floor heating mat (giving more strength) then use the sp rapid.

What size is the bathroom? I'm just asking coz you say you want to lay devimat. I'm just doing some work for a plumber and he's just used devimat in a small bathroom coz his customer wanted that make. He did struggle laying it down coz of constantly cutting the netting from the wire to avoid laying under toilet etc. I always use a loose wire system in small areas

Its 3 or 3.5 mt sq. I've used devimat about 5 times now and I'm very used to twisting it around to fit. Takes a little trial and error sometimes - as the self adhesive sticks a bit too well. However, I've never found it a problem to fit. Once you cut through the mat in the right places - it becomes a single cable, and so you can bend and twist it how you like. If it doesn't sit flat - then a quick shot with a hot melt glue gun usually works.

Paul

Originally Posted by aardvaarktiling

I would use 10mm marmox board Cheaper than wedi and screw down with proper washes and screws (don't glue), then level over with weber niv dur levelling compound over the under floor heating mat (giving more strength) then use the sp rapid.

Marmox is of the most expensive board, though wedi being more expensive it does have more uses.

Checkout Underfloor Heating | Electric | Floor Insulation | Uheat for a really decent UFH Insulation board.

Originally Posted by pt44

Its 3 or 3.5 mt sq. I've used devimat about 5 times now and I'm very used to twisting it around to fit. Takes a little trial and error sometimes - as the self adhesive sticks a bit too well. However, I've never found it a problem to fit. Once you cut through the mat in the right places - it becomes a single cable, and so you can bend and twist it how you like. If it doesn't sit flat - then a quick shot with a hot melt glue gun usually works.

Paul

On smaller or less square rooms I'd always opt for cable over mat. Though on large square rooms or L shapes and the likes (Certainly conservatories in most cases) the mats win over time:cost. The time to fit it can be halved, meaning your labour for the job is doubled for that little bit, in theory.

I'd always opt for twin-core cable over single-core too, which means you get one end connected to the stat making your life easier but nothing else. So the customer is often paying for that benefit to you, unless you're charging and making cash on the heating also.

I'm afraid that I've not seen a controller as good as the DeviMat 550, so devi is always the way to go for me. I wouldn't supply someone with something that I didn't personally like. Devi do a cable system, but I actually find the mats really easy to lay, even the small one's - so I don't see that as a problem.

As I charge per day - the time it takes me to lay is not an issue either.

Paul

i pay about £9 + vat for 10mm marmox board is this expensive? Also i prefer the mat system in small areas but i order in a special mat which is only 300mm wide instead of 500mm wide so its easy to work in small areas