Tanking

[Bitpipe]

We have three bathrooms in the new build, one with a bath, one with a shower tray and one with both a bath and a wetroom former tray (because we couldn't get a 900mm square tray to line up the waste with the joists).

These rooms have all been tacked with green board and plastered so we're now looking at tanking and installing the showers so we can get on with tiling.

So, given we have two different types of shower tray, what's the right order to tank?

Tiler says put the former in, tank both rooms and then put the tray in. Plumber says tank both afterwards.

Tiler has also offered to tank for a fee - but is this an easy DIY job?

Finally, Nick previously recommended this material http://www.bcprofiles.co.uk/aquaseal-wet-room-system-4-5m2-kit/?gclid=CPijq4SShswCFTUW0wod7GAL2g are the coverage rates for one coat or mulktiple?

Take it away Nick...

 

 

 

 

[Nickfromwales]

The wetroom formers have to be in first, so they both agree there.

A good tanking kit will have a rubberised strip ( like a 4" wide fabric plaster ) that joins the horizontal surface to the verticals, so water can't get past that ( after its run down the tanked wall ) as that's the bottom of the watertight seal formed BY tanking. That strip needs to be on top of the former and over coated with tanking solution to be a complete system.

Any water that gets to the tanked layer needs to drain freely so must be able to fall south until it can get to a drain / waste.

1) tanking has to be the FINAL waterproof layer. It has to be built up in layers, with subsequent drying times observed between coats, so you'd not want to be applying layers first then fitting the former and strips ( which have to be bedded into wet tanking solution btw ) and then having to repeat the whole process again.

2) tanking below former is just a waste of time as water should never get that far, ( unless your the cock that fitted the one I'm currently ripping out as part of a big insurance claim  ). 

Shower trays have a different discipline as you cannot use the strip. So given that I'd say your tiler is making the right sounds, and the plumber is,.........a plumber.

I'll chuck some pics on later when I get back on the iPad ( as kids have commandeered it again ) and show you a couple of examples. 

Fwiw, I'd pay the tiler to tank. It's not as straight-forward as your making it sound. The strips have to be bed in etc and if it's left too thick in places it really knackers the tiler up. That's one job to just stump up for and let the tiler do imho.

[Bitpipe]

Cheers Nick, always happy to hear that it's a job best paid for rather than have a go and stuff it up.

So former first, then tank both then shower tray. That said, if the tray goes in after tanking, how would the water get into the tray ?

Follow up question - plasterer has not gone tight to the floor in the bathrooms  - says he's happy to do so if the tiler wants - does it make the tanking job easier & better quality or no difference?

I have a related question on electric UFH but will start another thread.

 

 

[Nickfromwales]

A bit late to say don't bother skimming the plasterboards

[Bitpipe]

Ah well, the room is a mix of full and half height tiling so at least half would need skimming anyway, so should I hassle him to take it neat to the bottom?

Any issue if it all gets mist coated before the tiling/tanking or is that a no-no?

Also, still a bit confused about the tanking and tray (vs former) - if I tank behind the tray, won't any stray water want to go down the back? How do I ensure it runs into the tray itself - tray is 25mm deep so with adhesive / 6mm backer board / ufh mat / adhesive and tile, should be just about flush.

 

[Nickfromwales]

DO NOT PAINT WHERE YOU ARE TILING OR TANKING. !!!!

[Nickfromwales]

I'll update later. Got a conservatory to grout now. 

Yay, I love grouting. 

[Bitpipe]

17 hours ago, Nickfromwales said:

DO NOT PAINT WHERE YOU ARE TILING OR TANKING. !!!!

Ok, I think I heard that!

Will await the post grout update.

[Nickfromwales]

Crazy busy at the mo !

I'll update ASAP. 

[Nickfromwales]

This is a former I'd just laid. The corners made up in sand and cement where an old pipe went through. The light grey stuff is the tanking primer which I cut in prior to fixing the tray into position. That just gave me a nice clean surface to bond the tray to.

This shot shows the stud wall in place, blame the bathroom showroom for not having the tray the full width, and with the first coat of tanking applied. After the first coat was tacky, I then applied the 4" strip ( as seen with Roman written on it ) into a layer of wet tanking. That then gets brushed quite firmly to remove excess tanking from behind the strip to ensure it's as flush and flat as possible so as not to hinder tiling. The strips run between the former and the insulation backer boards on the floor ( insulation boards as this had undertile heating on a ground floor ( concrete )), in all the internal angles both horizontal and vertical, and around the turn of the boxing in eg the external also.  

Leftover strip used around the shower valve. Belt and braces, aka OCD. 

Finished article prior to grouting. Note the shower valve is dead centre of the border tile ribbon, and also there are two same size tiles either side equally intersecting the shower valve. That's gives the same size cut of tile around the entire valve plate. Aka OCD

All of the above can also be observed when fitting a shower tray, just the only difference being that you can't use the strip between the shower tray and the wall. As the tile will only cover 12-14mm of the edge of the tray, you can't have the strip showing so another change of discipline is needed. The next one is a one piece shower tray, so basically you just tank the walls prior to the tray being fitted, which gives an excellent surface for the adhesive ( mastic type ) to adhere to when bonding the tray into its final position. What the picture doesn't show is the masking tape that I put onto the tray to allow me to get a neat edge to the sealant where it sits on the tray edge. 

That junction is quite important as it's the last line of defence against any water getting behind the tiles. What I do I these circumstances is to pump a load of mastic ( sikaflex for these is best as it's non silicone based and also doubles up as a sealant as well as an adhesive ) between the tray and the wall and then push the tray against the walls thus displacing any excess above the tray edge. This is when you'll be glad you masked it up first . Get a plastic spatula and then spread the excess sealant, whilst still wet, against the vertical wall face. Do this so you get an up-stand of sealant forming a 'skirting board' which is continuous between the tray, the wall, and vertical face of the wall, preferably all in one application. I set the masking tape around 5-6mm in from the edge of the tray so I know I'll get a straight line, and also a bead of sealant that's has a decent purchase on the tray, which then transfers to the wall. The action of tooling the sealant with the spatula pushes it against the tray itself thus forming a good / strong bond to both. After the horizontal sealant has cured, next run a bead up the internal angle for at least 600-900mm up the corner. 

With the fundamental sealing done, in goes the 45'd shower valve & pipework frame sections which them get plasterboarded and sealed, plus tanked prior to tiling. 

Roberts your mothers brother

The end.

[Guest Alphonsox]

Thanks a lot Nick - Very useful, We will be at this stage in a month or so

[Bitpipe]

Perfect Nick! 

Now need to persuade my plumber's lads to play along - they will want to put in both showers (former and tray) plus wastes in one visit so I need to prep the shower tray area in advance by tanking the walls to create a good surface for the Sikaflex.

Then when both are in, get the tiler to tank the rest of the rooms as required prior to tiling.

We're having electric UFH for the floors - do I tank below this prior to laying the backer board?

 

 

[Nickfromwales]

The tanking can stop pretty much after the defined wet area. If water's going to get that far then you have issues elsewhere. 

where is the uth going? Both rooms? Expensive ornament alert!

[Bitpipe]

The electric UFH is going in each bathroom - per the other thread I have been issued a 'no cold feet' directive. Jack has also experienced cold tiles in his MBC house so better safe than sorry, even if it's only used for an hour at shower time.

So,  tank floor to ceiling in the showers and on the floor for the former and just beyond where the enclosures will be, basically anywhere that will get a good soaking from the shower.

We're using Hansgrohe kit (sourced from Megabad) and the iBoxes installed came with a fabric collar  - looks like this is used to in the tanking to form a nice seal around the box?

One other thought - the ensuite and second bathroom have pencil shower attachments for washing hair in the free standing baths, I expect that there will be occasional spray to the walls so we will be tiling fairly high around the baths also. Sounds like I should also tank those walls and the floor under the bath just to be bomb proof. As these are not wet rooms (the floor drains are only in the enclosed showers), any splashes will just puddle on the floor and will need dried up but this should be manageable.

 

[Nickfromwales]

Splash zones are best managed by good tiling and grouting tbh. Pointless tanking behind there IMO. Only worth tanking when a drip of water can follow the tanking / water tight layer and eventually get to a waste / drain. Other than that it'll just sit there and pool. In a TF house the one point that will let you down there will be the junction between the wall tiles and the floor tiles. That'll develop a hairline crack, which will open very slightly when the bath is full and you get in it, so make sure your tiler runs a bead of CLEAR CT 1 along that line after it's been grouted. Sealing the grout in that area will probably be beneficial too. 

[Bitpipe]

So we have our trays in - made the plumber follow your shower tray instructions to the letter and looks good. He was impressed at the method and use of Sikaflex vs standard silicone and the masking tape trick- says he'll do it this way from now on 

Impey wet-room former also in for the smaller shower, we removed the existing 22mm deck and laid a 12mm ply section  - this will ensure the former is flush with the floor once the backer board and UFH matt is laid.

The Impey installation instructions required the former to be screwed to the ply underneath - we did this and plugged each screw hole with Sikaflex before screwing in.

Now need to decide on what additional tanking products I need - Jeremy kindly donated a 7.5m2 tub (which I initially used to do the shower tray perimeter prior to Sikaflexing it in) so I obviously need to get some of the perimeter strip.

Impey assume that you use their wet-room membrane system to go on top of their former but I wasn't planning to do this as we're having a standard enclosure around it so should I paint the former with tanking compound (or around the screw heads at least)? They also advise that the top half of their two part sluice goes on top of the membrane when in-situ, but if we're not using the membrane, do we just assemble as normal?

 

[Nickfromwales]

On 7 June 2016 at 21:34, Bitpipe said:

So we have our trays in - made the plumber follow your shower tray instructions to the letter and looks good. He was impressed at the method and use of Sikaflex vs standard silicone and the masking tape trick- says he'll do it this way from now on 

Impey wet-room former also in for the smaller shower, we removed the existing 22mm deck and laid a 12mm ply section  - this will ensure the former is flush with the floor once the backer board and UFH matt is laid.

The Impey installation instructions required the former to be screwed to the ply underneath - we did this and plugged each screw hole with Sikaflex before screwing in.

Now need to decide on what additional tanking products I need - Jeremy kindly donated a 7.5m2 tub (which I initially used to do the shower tray perimeter prior to Sikaflexing it in) so I obviously need to get some of the perimeter strip.

Impey assume that you use their wet-room membrane system to go on top of their former but I wasn't planning to do this as we're having a standard enclosure around it so should I paint the former with tanking compound (or around the screw heads at least)? They also advise that the top half of their two part sluice goes on top of the membrane when in-situ, but if we're not using the membrane, do we just assemble as normal?

 

Happy days. 

Can I assume that the ply was bonded / glued and screwed down before fixing the tray down? 

If you're not using the Impey tanking membrane then you'll have no warranty based recourse   The one I pictured did use the specified Impey kit ( including the membrane ) so you're stepping into the unknown if you don't stick to their 'approved' method of fitting. The membrane covers you from the mouth of the waste opening, all the way to the tanked corner / wall junctions so is quite significant. The only reason I see that they pursue this particular discipline is that there is an obvious break after the waste where the off-settable disk sits in the former. The membrane ensures no water can get past that 'weak' point, but tbh you can cheat your way out of it with a good sealant.

The disc ( for the benefit of those reading this long after I'm immortalised ) has countersunk holes all the way round and you fix it down with self tappers, and iirc the Impey kit also comes with this absolutely horrible ( but good ) rubber solution in a mastic tube ( which you're supposed use to seal everything up from an Impey POV ). It's totally and utterly horrendous stuff to use and NEVER cures fully, and I MEAN never, which meant I had no choice other than to throw my mastic gun away after using it.......and my scraper.........and anything I touched whilst throwing my gun and scraper away. 

Dangerous territory I think as I can't say you will be watertight without the membrane, AND I can't say that anything will adhere to the former without the membrane. Have a think on how to progress and come back with your thoughts   

[Bitpipe]

I don't have an issue in using the membrane if it's the right way to go but I only really need to cover the tray and a small area outside it (around 1m2) as we'll be using a shower screen so a bit galling to spend £250 on the 5m2 kit (their smallest) and toss most of it away

Also we're using the AquaDec2 linear waste rather than the off-settable disk but I guess the principal is the same.

 

Edited June 7, 2016 by Bitpipe

[Bitpipe]

11 hours ago, Nickfromwales said:

Can I assume that the ply was bonded / glued and screwed down before fixing the tray down? 

Ply glued and screwed to the joists, tray just screwed down per installation instructions - it doesn't need Sikaflexed on to the ply, does it? 

[Nickfromwales]

I usually do tbh, and weight the tray down whilst it cures. That takes care of any final undulations ( 1,2 or 3mm max ) but if you're confident that the tray doesn't move one jot then I'd say you'd be ok. Is this one fitted now?

[Nickfromwales]

Also, I've just got off the phone to an Impey uk tech guy. The membrane ( as I thought ) is a must. It provides a bond to the GRP, acts as a decoupling barrier AND provides a critical key for the tile adhesive. The guy said to primer around 1000mm in each direction on the floor and lay more of the membrane down as belt n braces. ( And as a typical manufacturers arse cover ) they even went on to say to apply membrane to the entire floor area. He agreed that a over shoot of 1m should suffice but only as you're fitting glass. 

[Bitpipe]

Thanks Nick

2 hours ago, Nickfromwales said:

I usually do tbh, and weight the tray down whilst it cures. That takes care of any final undulations ( 1,2 or 3mm max ) but if your confident that the tray doesn't move one jot then I'd say you'd be ok. Is this one fitted now?

Yes but I can take the former out and seal under it  - not a big deal as it's only screwed onto the ply at present.

2 hours ago, Nickfromwales said:

Also, I've just got off the phone to an Impey uk tech guy. The membrane ( as I thought ) is a must. It provides a bond to the GRP, acts as a decoupling barrier AND provides a critical key for the tile adhesive. The guy said to primer around 1000mm in each direction on the floor and lay more of the membrane down as belt n braces. ( And as a typical manufacturers arse cover ) they even went on to say to apply membrane to the entire floor area. He agreed that a over shoot of 1m should suffice but only as your fitting glass. 

That makes sense, if I'm buying 5m² I may as well use it all as belt & braces.

Now, given I'm having 6mm backer boards with a UFH mat on the top, how does that particular sandwich work? The UFH mat will be to the front of the shower (where the door is) but not to the side as there's a bath there. Guessing that it's floor / adhesive / boards / primer / membrane and then mat or are the mat and membrane incompatible?

[Nickfromwales]

I assume it'll be100watt per m2 so it'll be fine to tank over. I'd probably recommend laying the mat and then flooding the area flush to the wire ( literally just covering it ) with a flexible self leveller. That would give you a flat clean surface which would get primed ( 2 coats, 1 watered down 75% water, and one neat ) with the Impey primer, and then the membrane. The idea being that no water could get to the Uth mat. 

Flooding the area will then make up the defect either side of the shower so the membrane has an even flush surface to continue onto. You'll use the same volume of tile adhesive to make up this deficit so it's 6 and two 3's cost wise but a much better job imo. 

[Jeremy Harris]

100 W/m² seems exceptionally high to me.  I'd have thought that for comfort floor warming you'd be looking at no more than about 20 W/m².   I appreciate that the floor sensor will kick in and cut the power to the floor pretty quickly, but IIRC the electric UFH we have in our current house (with minimal insulation between it and the slab and tiles on top)  is around 50 W/m² and even that is throttled back by the controller and floor sensor pretty quickly.  We've found that having the bathroom tiles at around 24 deg C is fine for just making them feel comfortable to walk on when you step out of the shower.

[Bitpipe]

2 hours ago, JSHarris said:

100 W/m² seems exceptionally high to me.  I'd have thought that for comfort floor warming you'd be looking at no more than about 20 W/m².   I appreciate that the floor sensor will kick in and cut the power to the floor pretty quickly, but IIRC the electric UFH we have in our current house (with minimal insulation between it and the slab and tiles on top)  is around 50 W/m² and even that is throttled back by the controller and floor sensor pretty quickly.  We've found that having the bathroom tiles at around 24 deg C is fine for just making them feel comfortable to walk on when you step out of the shower.

100 Wm2 seems to be the minimum rating for electric UFH mats that I can find (although I've not looked that far aside from the UFH store). I'm relying on the thermostat to keep it low temp.

 

6 hours ago, Nickfromwales said:

I assume it'll be100watt per m2 so it'll be fine to tank over. Id probably recommend laying the mat and then flooding the area flush to the wire ( literally just covering it ) with a flexible self leveller. That would give you a flat clean surface which would get primed ( 2 coats, 1 watered down 75% water, and one neat ) with the Impey primer, and then the membrane. The idea being that no water could get to the Uth mat. 

Flooding the area will then make up the defect either side of the shower so the membrane has an even flush surface to continue onto. You'll use the same volume of tile adhesive to make up this deficit so it's 6 and two 3's cost wise but a much better job imo. 

The Impey installation guide suggests the inverse, tanking first and then UFH mat - although this is in reference to their own AquaMat system.