underfloor heating - insulation boards and tiling

arroli

We are thinking of installing underfloor electric heating in our bathroom, but as we have a concrete floor, and dont wish to loose too much heat into the concrete, intend to lay the recommended insulation boards onto the concrete, then lay wiring cables, then ceramic floor tiles

Our worry is that over time, the tiles and grout may work loose
Any one had experience of laying these insulation boards under tiles?

sillygoose

Do you mean the loose heating wiring cable or mats? most people use mats with the heating wire fixed into it. When using electric underfloor heating you MUST use a flexible tile adhesive and a flexible grout - due to the large temperature swing with the system anyway.

The mat is a mesh and you need to use quite a thick bed of tiling cement to cover the heating wire and trowel it down firmly it passes through the mesh onto the cement surface of the insulation board so everything is bonded fine. Must use plastic tools to avoid any damage to the cable insulation.

I highly recommend this adhesive from Wickes, not cheap but very rapid so you making up small batches you can do an area and soon be able to step on it to reach the rest.

For grout this one from Homebase (available in different colours) is excellent and again rapid setting and flexible.

redlee

I'm a tiler by trade and have put down a few heated floors, they aren't rocket science but we've had a few call outs to redo bodged floors this last 12 months. If your'e getting someone in to do it ask for evidence that they've done it before and make sure the electricianis registered. There are a lot of systems now available try and get one with a lifetime guarantee. If the job is done properly there will be no movement - especially as its a solid sub floor.
The insulation board (10mm thick minimum and cement faced) needs to be laid on a bed of flexible tile adhesive, then left to dry.
Heating mat or loose wire (depends which suits the room the best) laid along with the probe.
You then have the option of covering the heating with self leveling compound (costs more but best practice) allow to dry.
Fix tiles on to a solid bed (air pockets can cause uneven heat up and blown tiles)
The cockups i've seen in the last 12 months include insulation board put down with too thin a bed of adhesive on a floor that wasn't primed - the self levelling showed the floor move before the final covering. Job done by a general builder.
Thermostat probe left half way up the garage wall instead of in the floor. Done by a registered electrician.
Tiles laid on insulation boards that weren't stuck down. Supposedly done by a tiler and electrician.
The most common mistake by far is a mat or cable that is too big/small for the area this applies to pros and diyers alike.
I hope none of the above has diswayed you as done correctly a heated floor is well worth the initial outlay and ours is in use for the 9 or so months of winter here.
Forgot to say i've never used plastic tools and a tiler should be able to get you discounts on the type of adhesive shown in the above links (although if the tiler wants to use stuff from a diy shed i'd be dubious about him).
You can get an alarm to connect to the heating whilst working on it to let you know if it gets damaged.

sillygoose

I would be more worried about a tiler that unnecessarily used sharp edged metal tools over my heating cable than where he got his grout from.. shows he can't read the number one rule on the instructions, or thinks he knows better.

It's only a bathroom so probably a small room, the cost of the adhesive and grout are not so major I would rather have good brand DIY stuff than some cheapo plumb merchant stuff.

I watched a how to video from a company that are a specialist for these systems, you can clearly see they have placed the wires closer than allowed. Initially I got quotes from tiling companies, the prices were ridiculous, including doubling the material costs as a nice little mark up.
Just be careful!

You do need to prime the concrete for the insulation layer, easy enough. Also need to prime the upper surface of the insulation board before sticking down the matting. My supplier puts the primer and a roller in the kit.

Matting is best for a fairly straight forward area. If its an odd room with lots of obstacles the loose heating cable is better.

redlee

sillygoose wrote: »

I would be more worried about a tiler that unnecessarily used sharp edged metal tools over my heating cable than where he got his grout from.. shows he can't read the number one rule on the instructions, or thinks he knows better.

It's only a bathroom so probably a small room, the cost of the adhesive and grout are not so major I would rather have good brand DIY stuff than some cheapo plumb merchant stuff.

I watched a how to video from a company that are a specialist for these systems, you can clearly see they have placed the wires closer than allowed. Initially I got quotes from tiling companies, the prices were ridiculous, including doubling the material costs as a nice little mark up.
Just be careful!

You do need to prime the concrete for the insulation layer, easy enough. Also need to prime the upper surface of the insulation board before sticking down the matting. My supplier puts the primer and a roller in the kit.

Matting is best for a fairly straight forward area. If its an odd room with lots of obstacles the loose heating cable is better.

Apologies if my post upset you it wasn't meant in that way i was offering advice from my personal opinion as a professional tiler who has laid a fair amount of these systems over the last 7 years from devi, warmup, heatpads, uheat, radiant floors and a few others whose name i forget mat and loose cable.
The plastic trowel being the number one rule i do know better. I've never used anything other than metal trowels 10mm crescent, 20mm crescent, 10mm square etc etc you'd have to try quite hard to damage the cable. Careful on priming the board some manufacturers tell you not too. Good brand and DIY own brand are two different things and i'm sorry if the people you got in to quote doubled the price - i pass my adhesive and grout on at cost and i know who manufactured it, i also offer my customers a fair saving on the heating in most cases but i am aware that there maybe some poor tradesmen out there.
Cheers
Lee.

arroli

Thanks for all advice,

The insulation board (10mm thick minimum and cement faced) needs to be laid on a bed of flexible tile adhesive, then left to dry.

This is a very good tip, didnt realise from fitting instructions and youtube videos we have seen that its wise to do this, but makes more sense so that insulation boards do not flex

We would intend to fit cable type as opposed to mats, as for use in bathroom around bath, loo fittings etc.