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Bathroom questions

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Bathroom questions

Postby RogerS » 04 May 2017, 19:28

SWMBO would like to have some gentle background underfloor heating in the bathroom. Current flooring is chipboard. I see some people recommend something like this Budget Backer Board

http://www.theunderfloorheatingstore.co ... ker-boards

to improve warm-up times and reduce heat loss through the floor.

What do you guys think?

Also what thickness tile-backer boards for the shower walls would you recommend? I've seen thicknesses ranging from 6mm (way too thin IMO) to 20mm..which is overkill ?

Researching this suggests that I should rip-up the chipboard and replace with plywood as I will be tiling the floor. ?? Overkill ?

And lastly, if I'm going for one of those overhead drenching type shower heads, is 15mm pipe OK or should I go up to 22mm? The manufacturers website is a bit sparse in detail.

TIA
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Re: Bathroom questions

Postby Doug » 04 May 2017, 20:18

Are you going for electrical underfloor heating Rog, if so they used to recommend 3/4" ply for fixing the element to then tiling on.

For your walls 12mm backer board is fine.

Your drenching head feed depends on the pressure, though it's a while since I've seen one that was 3/4" most heads are 1/2" BSP, that's not to say you couldn't run 22mm pipe to the head
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Re: Bathroom questions

Postby Robert » 04 May 2017, 22:08

We have a pump for the hot water from the cylinder which increases flow to the whole house. It also pumps cold from the storage tank to the shower and bath. It is rated at 1.5 bar. The rain head delivers plenty of water. SWMBO has it on full flow whereas I turn the flow down a bit. The pipes to the mixer and from the mixer to the heads (we have a hand held on a riser rail too) are all 15mm.

Down in the kitchen hot comes out the tap at a very similar flow to the mains cold and we have good mains pressure.
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Re: Bathroom questions

Postby MJ80 » 04 May 2017, 22:53

Cement backed foam core 12mm tile backer board, lay the ufh mat on top and pour some self leveller over. That is the standard way of doing it. Ply works as well, but the backerboards are better with the wet room tray and they are more thermally efficient.
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Re: Bathroom questions

Postby RogerS » 05 May 2017, 22:25

Thanks chaps for the input. Think I'll stick with the existing chipboard but go as MJ80 suggests.
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Re: Bathroom questions

Postby RogerS » 07 May 2017, 07:32

Doing a bit more Googling, there seems to be several opinions regarding the width between the studding (assume a recessed shower). Do you make the width exactly the outside dimension of the tray, slide the tray in and then apply your substrate (backer board etc) onto the studs and down onto the top of the tray, silicone seal the join then tile.

Or make the width wide enough to allow the substrate to be fitted to the studs all the way down to the floor so that the finished width is that of the shower tray which is then slid in etc.

Further complicated, I think, if the tray has an upstand ...
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Re: Bathroom questions

Postby Doug » 07 May 2017, 07:57

Personally i make the opening including the backer board just slightly larger than the tray, just enough to install the tray. I then seal the tray to the backer board, tile spacing the tile a couple of mm off the tray & then silicon seal.
The gap under the tiles allows the silicon to get right under the tile & I completely seal all round the tray prior to fitting the door/enclosure, this means any water that gets into the profiles of the enclosure can't escape down the sides of the tray, also only seal the door/enclosures horizontal profiles on the outside of the shower, never inside.
Many years ago I used to remedial work for a company, one of the common problems I had to rectify was with upstand trays, the bottom course of tiles cracking for this & other reasons I've never fitted upstand trays, that & the fact that in 30+ years I've never had a problem with standard trays.

PS sealing to the backer board is a bit belt & braces but I once went to a job were water was escaping from the shower on the corner of the tray between the seal & the tray. The installer had sealed to the backer board which had worked well but the internal seal had broken down.
Normally this would have lead to a leak through the ceiling but the seal between the board & tray was so good the only course for the water was to run out on the front corner of the tray, after seeing this I always seal trays as I'be stated.

PPS going back to your UFH I always used Warm-up (not done one for years) they supplied complete installation instructions, my advise would be to follow these to the letter if possible. As with most companies these days if you have a problem even if it is a fault with their product if you've not followed their suggested installation they will wriggle out of any liability.
Last edited by Doug on 07 May 2017, 08:05, edited 1 time in total.
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Re: Bathroom questions

Postby Mike G » 07 May 2017, 08:02

The latter, Roger.

The very best solution is to fit the shower tray then build the wall up against it., but that is seldom practical. Let me just add that you almost certainly have to put the shower tray into position twice, as you sort the drain out. My plumber told me that he now beds his shower trays on a full bed of tile adhesive, which gives you just enough "play" in setting the thing level. So this is what I did with mine, and it worked a treat.
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Re: Bathroom questions

Postby Doug » 07 May 2017, 08:19

Mike G wrote:My plumber told me that he now beds his shower trays on a full bed of tile adhesive, which gives you just enough "play" in setting the thing level. So this is what I did with mine, and it worked a treat.


Id be very surprised if this complied with the installation instructions, a weak bed of sand & cement is the standard instruction for bedding down trays & whilst you're free to bed it down on whatever you like if a fault develops & you've not followed the instructions the company will deny liability.

When I did trouble shooting work I came across this regularly. Best advise is to decide what product you want & then see what the manufacturer recommends for that product.
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Re: Bathroom questions

Postby Mike G » 07 May 2017, 09:02

That's one hundred percent correct of course. However, the issue with sand/ cement is that as you lower the tray down from the only accessible side, you compress the front edge of the bed of sand/ cement, which means it isn't in contact with the shower tray once the try is horizontal.........and this is the very place where all the traffic is.......climbing in and out of the door. Because sand-cement isn't sticky, it doesn't self-correct for this issue, and it is virtually incompressible, so you can't pound the tray down into it to make up the gap. None of that applies with the flex tile adhesive (I'm talking the thick bed adhesive which you buy in big bags, dry). So this is a case where the manufacturer's instructions aren't as good as the alternative (in my view, of course).
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Re: Bathroom questions

Postby Doug » 07 May 2017, 09:37

The trick I've found on trays over a meter square that are too heavy to lift on my own is to lower the tray with it pivoting on its back edge. The front edge is going to take the weight of the door/enclosure so it is imperative that a good bed is maintained there. Also lowering the tray with the front edge in contact with the floor means your hand is against the back wall & you could overstretch etc.

Adding a little more mortar along the the back edge of the bed when lowering from the back ensures that's any initial mortar that is compressed is trapped against the back wall & so is worked back under the tray as it is wiggled & pressure applied in getting the tray level.

Whilst I agree any "sticky" adhesive will by its nature stick to both sides when compressed, that bond will be stretched when the compression is removed & I wouldn't be happy installing a heavy glass door or enclosure on it.

As I say folks are free to bed their trays any way they want & ive seen plenty including what must have been half a dozen tubes of silicon, but done with a little thought mortar works very well & I see no fault with it.
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Re: Bathroom questions

Postby RogerS » 07 May 2017, 11:01

Thanks guys.
The shower tray is coming with the screen and not sure if it is an upstand or not. Their website has 'Page not found'. Taking Doug's advice will call them Mondy.
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Re: Bathroom questions

Postby RogerS » 08 May 2017, 07:40

Mike G wrote:The latter, Roger.

The very best solution is to fit the shower tray then build the wall up against it., but that is seldom practical. ....


That's a great idea as I am in the lucky position of being able to do this.

On UKW, someone recommended Marmox board which looks to be easier to work with then boards like Hardibacker.

Has anyone come across these?
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Re: Bathroom questions

Postby Doug » 08 May 2017, 08:52

A couple of years ago I used this boarding though it was about 1/2 that price


https://www.travisperkins.co.uk/Knauf-T ... m/p/633021

It was a lot easier to work than standard cement based backer board, also lighter & can be dot& dabbed
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Re: Bathroom questions

Postby RogerS » 08 May 2017, 18:58

Thanks Doug..I'll check it out.
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Re: Bathroom questions

Postby RogerS » 14 May 2017, 11:47

Doug wrote:A couple of years ago I used this boarding though it was about 1/2 that price


https://www.travisperkins.co.uk/Knauf-T ... m/p/633021

It was a lot easier to work than standard cement based backer board, also lighter & can be dot& dabbed


Doug, what stud spacings would you use with this board ? Seems to me that it might flex more than others?

TIA
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Re: Bathroom questions

Postby Doug » 14 May 2017, 15:04

RogerS wrote:
Doug wrote:A couple of years ago I used this boarding though it was about 1/2 that price


https://www.travisperkins.co.uk/Knauf-T ... m/p/633021

It was a lot easier to work than standard cement based backer board, also lighter & can be dot& dabbed


Doug, what stud spacings would you use with this board ? Seems to me that it might flex more than others?

TIA


As the boards are 900mm wide 450mm would seem most suitable, I'd used them in an old house where the studding would have been 16" on centres & had no problems
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Re: Bathroom questions

Postby RogerS » 14 May 2017, 15:44

Ta muchly, Doug. Having seen the current situation more closely, I think there's going to be all manner of stud distances as one of the existing walls is all over the place and I'm having to pack out and faff around getting a flat, perpendicular surface. Maybe I'm being too much of a perfectionist but I think that getting the two reference walls bang on for the shower will pay dividends. We're talking an inch out of vertical and not the odd mm.
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Re: Bathroom questions

Postby Doug » 14 May 2017, 17:22

Definitely will Rog, as with most jobs initial preparation is the key to a good job & will usually save time in the long run.
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Re: Bathroom questions

Postby RogerS » 22 Oct 2017, 17:16

What is a 'weak sand and cement' mix? 10:1 ? 5:1 ?

How thick a bed should I make ?

TIA
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Re: Bathroom questions

Postby Mike G » 22 Oct 2017, 17:23

5:1 would be strongish. 10:1 is very weak. I'd say you might go for 8:1, and If you go any less than say 20mm thick there would be a danger of it powdering in due course. As I'm sure I've said, I think a flexible tile adhesive is a better solution, but it isn't what the manufacturer's recommend.
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Re: Bathroom questions

Postby Doug » 22 Oct 2017, 17:43

I usually do 6:1 Rog I also mx a little pva in the water before pouring into the mix I usually end up with around a 3/4” bed
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Re: Bathroom questions

Postby RogerS » 22 Oct 2017, 21:14

Thanks guys.

One thought....if you have a flat piece of WBP ply then why not just a bit of silicon ? Unless the base is hollow or uneven, of course.

Ummmm...maybe that's why. :eusa-think:
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Re: Bathroom questions

Postby RogerS » 23 Oct 2017, 16:01

I ran a straight edge over the underside of the shower tray. There are four ribs that are coplanar with the edge surround but what necessitates the need for a good bed of sand/cement is the fact that the boss where the drain hole is is several mm deeper than the the rest.
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