Self levelling compound over heating mats

[jimmbo]

Hi

I could do with some advice about flooring, please. Mainly how to do the self levelling compound....

I'm hoping to get our kitchen/family room floor done this week.

It's a pretty big area, about 36m2 of exposed floor space including utility room.

My plan is to prime the concrete/screeded floor then put insulation boards down with tile adhesive.

When that's done I've got electric heating mats to lay out.

I'm pretty confident I know what I'm doing up to this point...

But before tiling, I was planning on encapsulated the heating mats with self levelling compound - which is the bit I'm unsure of....

1. What's best to use as barriers to stop the liquid running through doorways and under the kitchen units. (I am now kinda regretting not doing the floor before the units, but hey ho!)
I've seen a few videos of folk using foam edging strips, but that seems to be more of a US thing?
I can't seem to find anywhere that supplies anything like that over here?
I'm only after about a 5mm depth.
Any suggestions?

2. I've got 13 bags of 'Ultra Floor level it 2' SLC which is workable for 20-30mins and needs at least 2mins mixing per unit. If I try and do it all at once that's at least 26mins mixing!
Do I need to buy 13 buckets and try and mix them simultaneously as best I can then slap it all down together?
Or can I do it in sections somehow without leaving steps between adjacent areas??

Sorry about the ultra long post!!

Many thanks

 

[Doggit]

There are other threads on doing SLC, so have a look for them, but you'll find 36sqm difficult to do in this weather, as it'll go off too quickly.

But in essence, you need at least 2 buckets, 1 person to mix, whilst another person pours (dump it in the bucket, at it'll take 4-5 miniutes to mix) 1 to wash the buckets and fill with water, one person to carry and pour, and one to lay and level. And you need to make sure you have at least double the number of bags that you reckon you need.

But if you floors already flat, then there are other ways round the problem. You put the SLC over the heating mats so they don't get nicked whilst laying the tiles, but if you turn the heating mats over, then they are protected by the webbing. If you decide to go the SLC route, then you can use an adhesive foam gun to lay a thin bead to act as a barrier.

 

[Ian H]

Try a car body paint place for the foam strips.

 

[jimmbo]

Thanks for the replies guys.

Not really a one person job then!

I have been in two minds whether to forget about the SLC but I think it would be better with it. Some of the matting might still end up being mesh side down because of the layout. And obviously don't want to risk damaging the cable and need to make sure it's fully incased.

Does the expanding foam come off easily afterwards? I also want to stop it going under the walls at the edges. Should I also stop it going right up to the bifold doors? Or does that not matter? Does it need an expansion gap? Or is that irrelevant because it's a latex screed?

I've seen some adhesive rubber seal strips at screwfix that I thought I could use as a barrier then remove afterwards?
Thought that might be cheaper and easier than the expanding foam?

The guy I spoke to in the technical department where I got the stuff from said I would be better doing it in sections, but I don't really know how that would work without leaving steps between each section.

He said work out the area for the 5mm depth - but it's not going to be exact though because that's reliant on me getting the boards absolutely bang on to start with and also the volume that the heating mats take up!!

Going round in circles with this!

 

[Doggit]

Definitely not a one man job by any stretch of the imagination; three's the minimum I'd go for. 5mm is way too thin to aim for on top of foam, it'll just crack whilst you're trying to lay the tiles, unless you put down boards to walk on) but you might get away with 10. You should use adhesive foam rather than expanding foam if you'r going down that route, as it won't expand too much, but it'll scrape off the floor dead easy afterwards, but whilst it wouldn't be as cheap as the foam strips, it's quick and easy to use. You could try doing it in sections, but as SLC doesn't actually level itself, you might find you end up with stepped sections.

 

[jimmbo]

You mean 5mm is too thin on top of the insulation boards?

That's what they recommended at the underfloor heating store. I've got the Prowarm XPS boards.

If I did create a barrier over the matting with the adhesive foam to split it up, would it be easily scraped of the cables without damaging it?

Thanks again

 

[Doggit]

If you aim for 5mm, you can't guarantee that you'll get it all over, and you could have 3mm some places, and 10mm elsewhere, but it's up to you. All you've got to do is kneel on a weak spot, and it'll crack. But I suppose it may not be serious, so it's going to be your call at the end of the day. Asking if adhesive foam can be scraped off of the cables, suggests you're thinking of doing it in stages, but never having tried it on the cables, I couldn't say how easy/safe it would be.

 

[jimmbo]

Well yes, that was the thinking. I'm just trying to weigh up all the options.

The guy in Topps Tiles said it's not a good idea to put the SLC anyway because it creates another barrier for the heat to pass through.

So I'm wondering if it is worth all the extra effort, especially for it to be less efficient as well!

 

[Doggit]

As the heating mat will be embedded in the SLC, what tops has said isn't exactly correct. There is no right and wrong over this, and it'll mostly depend on the tiler. If he's good, he can handle the mat, and it'll just take more adhesive, but if the tiler is just average, then you want a good level floor to start with. Large tiles are a lot more difficult to lay that say 12x12s, but have you considered a floating engineered floor.

 

[jimmbo]

I'm doing the tiling myself. 600mm x 300mm porcelain. I've done a fair bit of wall tiling but not done floor tiles before!

That was another reason why I thought the SLC was best -

1. Coz it'll take up any errors levelling issues.

2. I can take my time with the tiling n not worry about matting being exposed.

3. If I do make any cock ups with the tiles, it will be easier to lift them n not damage the cables! Hopefully not need to though!

I think I will use the SLC anyway, seing as I've already spent £200 on 13 bags of it!!!

 

[Doggit]

Tiliing floors is completely different to tiling walls, as you can see the shadows and levels so well. You need as flat a floor as possible, but SLC doesn't actually level itself. The trick I was taught, was to find you're highest point using a 6ft spirit level, and then to set screws and rawlplugs into the floor in a metre sqaure pattern to give you points to level to. You need a slightly weter mix than recommended (although the manufacturers won't recommend that at all) so that it flows, so maybe half a litre extra per bag, but no more. You need to move the SLC around, and the screw heads will give you a level to work towards. You'd normally use a spiked roller to get the air bubbles out, but I'm not sure if that's a good idea with the heating mat, but any holes in the mix won't be an issue.

If you can do it on a cool day, or very very early in the morning, you'll more working time out of the mix, but you'll still need 2 people to do it. One to mix, and one spread, and both to help each other. Make a mark in the buckets at the level you need to fill to, and have a hose to fill with. You need to clean each bucket out between mixes, otherwise the old stuff will go solid and you'll get lumps in the next batch, so you need another bucket or two to empty the waste into to. But do get more bags than you think you'll need, as it never goes as far as you expect, and you don't want to have to start again, and feather edges never work out great.

Are you using the heating mat to take the cold off of the tiles, or to heat the room. Because having tried to tile a north facing kitchen that was damned cold, I eventually took the tiles back (they were sized badly) and went for an engineered wood floor with 5mm fibreboard underlay, and it's been great without the need for the heating.

 

[chappers]

no reason not to SLC in sections, but it is easier if you always have a wet edge to go to. It's just a matter of making sure you trowel it flush with the already set areas 1-2mm lips and ridges shouldn't be an issue, as for your format tiles I would use a 10mm notched trowel and give the backs a light butter.
Just take note as others have mentioned self levelling doesn't literally mean that you will still need to spread it down to level, use long sweeps of the trowel to keep spreading it and make sure you trowel the whole of the surface as this will release trapped air. normally you would use a spiked roller, but I'm not sure how sensible that would be over you heating mat.
You are doing the right thing as continuously walking over the bare mat could cause damage, lay it and keep off it as much as possible

 

[jimmbo]

Hi guys.

Thanks for the advice. Really appreciate it.

I've laid the boards and got the mats down.

Just about ready to do the SLC!

I'm just a little concerned that I didn't put enough primer down on the boards!

The tape on the matting is coming up a little in some areas and duct tape doesn't seem to hold it either! I did cover the whole area the Prowarm ultraprime - just worried I spread it too thinly!

The boards are Prowarm XPS (foam insulation boards) which are quite porous so I'm wondering if

1) the levelling compound will adhere properly

2) suck straight into the boards!

Not sure what to do now.

Many thanks again.

 

[jimmbo]

It's probably me just being a bit paranoid n over cautious but I've given it another coat of primer anyway!

 

[jimmbo]

The boards aren't actually as porous as I thought. I poured some water on a scrap piece (unprimed) and it sat there for ages so probably would've been ok!