Issues bedding shower tray - advice needed

[JamieG1985]

Afternoon all,

 

I'm currently in the middle of refurbishing our ensuite and having some issues bedding a stone resin shower tray on a 5:1 sand cement mix with a bit of plasticiser which is specified in the tray fitting instructions. It is being set on 18mm wbp plywood screwed to a fixed frame with plenty of support which is solid with no movement and is screwed into adjacent stud walls. There is access in the frame to fit the trap but a length of cls will be fixed in the void for full support. I primed the ply with 1:3 sbr/water mix before applying mortar mix.

I'm not sure what I am doing wrong but the mortar seems to crack after a few days drying out and leaves a slight movement in the shower tray. This is now my second attempt and the same thing has happened again but not as bad this time, although there is a very slight movement on the corner where the waste is if i push it down. I've not yet sealed around the tray and I'm now convincing myself to rip it out again and just use a flexible tile adhesive which the manufacturer has agreed in an email that I can use as an alternative without voiding warranty.

 

I've enquired about adhesive today and the guy in the shop recommended to use s2 flexible adhesive as opposed to s1 due to it having fibres and can flex more so the adhesive will never crack. I have since read online that s2 does not provide as much support as s1 so I'm just wondering if there is a prefered type to use in my situation. They quoted £30 for a bag of ultra tile s2 which I thought was steep but is available cheaper online.

 

I've read a bit on the forum and I'd just like to check my methods before taking the plunge with tile adhesive...

 

1. Sbr the tray 1 part sbr 3 part water as per priming instructions on bottle (everbuild sbr bond). Not sure if I need to do the same to the tray, it's a hudson reed pearlstone tray and has a rough finish - photo attached. Also not sure if I should leave sbr to fully dry or apply adhesive when it is still wet.

 

2. The base is level front to back but there is a run of 5mm across the 1m wide tray. I could have packed frame but I thought it would be better to fix the frame solid against the floor and level out with the original mortar mix instead. With this in mind I was thinking to use a 12mm notch trowel to lay a 12mm bed of adhesive on the ply and also back butter the tray. Would this be a sufficient bed thickness to allow for the 5mm run when levelling out?

 

3. Fit and level tray. After adhesive has dried out, seal around edges and fit trap and remainder of pipework.

 

Any advice or answers to my queries above are appreciated.

 

 

 

[nod]

Mortar is no good As you are finding out 

Use a flexible tile adhesive 

[Marvin]

1 hour ago, nod said:

Mortar is no good As you are finding out 

Use a flexible tile adhesive 

+1 

To be honest I never use the flexible tile adhesive but I do always use the tile adhesive for shower areas.

 

I run the waste pipe and trap to the correct level for the trap base to be level with the underside of the tray before starting.

 

I always seal the floor area before using adhesive on it. (PVA or wood glue watered down or Acrylic primer). This helps to stop the adhesive from drying out too quickly.

 

I use a big notched trowel and trowel the mix on the floor 1 way, trowel on the underside of the tray the other. Lay the tray gently down and lift it up again to see if there's any places where the crossing adhesive doesn't touch. Adjust the adhesive as required to make the bond uniform. 

 

The final push is when I check the tray is level, silicone both sides of the rubber ring between the trap base and insert, silicone the underside of the part of the trap to be screwed in from above, and fit all these together and tighten, and clean off all the mess I have created. Checking the tray stays level I usually place some tubs in the tray or a couple of boxes of tiles

 

Once set - usually one to two days I silicone between the edges of the shower tray and the walls squeezing the silicone so it is not proud of the top of the tray before tiling.

 

(If installing a quadrant shower tray the same as above.)

 

Once the adhesive has gone off, with the silicone, in your case, to 3 walls/sides. It isn't going anywhere. Especially after being tiled in and sealed again with the shower door in as well. 

 

Good luck 

 

M

 

 

Edited April 13 by Marvin
clarification

[Marvin]

Further...

 

Leave the the SBR to dry out. No need to do the underside of the tray with sealant. Its all about stopping the moisture from being sucked into the timber causing the adhesive to shrink...

 

I use spacers in the corners on a dry run and work out how deep I need to be where to make the tray level. Then after sealing but before coating the floor I re fit the spacers. Then when coating the floor I use timbers or straight edges to scrape the coat of adhesive on the floor to the required level before removing the spacers. then notch the adhesive to the underside of the shower tray.

 

If the spacers are where I can remove them later, I leave them in to help. I still sit the tray down and lift it up again to ensure an even bonding. Sometimes the trays are not flat and as long as there is a fall to the drain hole I ensure the shower tray edge that the shower enclosure sits on is always level  which sometimes mean the wall sides are not so level.

 

If your not going to put the trap in  until later make sure the area is free of adhesive ( most of my shower trays are fitted on to the floor, not raised so has to be done at the same time.

 

Here's a shower room I did last month.

 

 

Hope this helps

 

M

 

Edited April 13 by Marvin
further thoughts

[JamieG1985]

On 13/04/2024 at 20:15, Marvin said:

+1 

To be honest I never use the flexible tile adhesive but I do always use the tile adhesive for shower areas.

 

I run the waste pipe and trap to the correct level for the trap base to be level with the underside of the tray before starting.

 

I always seal the floor area before using adhesive on it. (PVA or wood glue watered down or Acrylic primer). This helps to stop the adhesive from drying out too quickly.

 

I use a big notched trowel and trowel the mix on the floor 1 way, trowel on the underside of the tray the other. Lay the tray gently down and lift it up again to see if there's any places where the crossing adhesive doesn't touch. Adjust the adhesive as required to make the bond uniform. 

 

The final push is when I check the tray is level, silicone both sides of the rubber ring between the trap base and insert, silicone the underside of the part of the trap to be screwed in from above, and fit all these together and tighten, and clean off all the mess I have created. Checking the tray stays level I usually place some tubs in the tray or a couple of boxes of tiles

 

Once set - usually one to two days I silicone between the edges of the shower tray and the walls squeezing the silicone so it is not proud of the top of the tray before tiling.

 

(If installing a quadrant shower tray the same as above.)

 

Once the adhesive has gone off, with the silicone, in your case, to 3 walls/sides. It isn't going anywhere. Especially after being tiled in and sealed again with the shower door in as well. 

 

Good luck 

 

M

 

 

Thanks for the detailed reply. What adhesive do you use out of interest?

[Nickfromwales]

Ultra / Mapei / Bal etc are all fine and usually on the shelf in most decent outlets. Been installing bathrooms for over 30 years with all of them, never missed a beat .

My 2 cents, do not use silicone for fundamental sealing, just use it as a cosmetic seal; I don't EVER use silicone to seal trays before tiling, instead use CT1 as it is a completely different product without the short service life that silicone(s) tend to have.

[JamieG1985]

17 hours ago, Nickfromwales said:

Ultra / Mapei / Bal etc are all fine and usually on the shelf in most decent outlets. Been installing bathrooms for over 30 years with all of them, never missed a beat .

My 2 cents, do not use silicone for fundamental sealing, just use it as a cosmetic seal; I don't EVER use silicone to seal trays before tiling, instead use CT1 as it is a completely different product without the short service life that silicone(s) tend to have.

Thanks for the reply Nick. I was going to use Ultra S1 flexi standard set to give myself a bit of time to set the tray or should I go for S2 rapid set as suggested by my local tile centre? Not sure if either type is more suited to my situation. The house is a timber frame if that would make much difference with movement?

 

So with the advice Marvin has already given...

 

1. Sbr the plywood again with 3 parts water to 1 part sbr and give it an hour or 2 to dry out.

2. Apply a bed of adhesive to the plywood using a 10mm notched trowel in one direction and apply another bed of adhesive to the back of the tray with a 10mm trowel in the other direction. I presume a 20mm bed would be enough to account for the 5mm run out I have side to side by the time it's pressed down and levelled out?

As Marvin suggested after the adhesive is spread on the plywood, I could use a straight edge batten with a 5mm packer screwed on one side and 10mm packer on the other and scrape across the adhesive front to back to level it out. I have already used this method with the mortar mix and it worked well but not sure if it's necessary if applying adhesive to both plywood and underside of the tray? Any ideas how much I can expect the tray to drop from the original 20mm when squashed down? Obviously there's going to be 5mm difference from 1 side to the other.

As an alternative, would a 12mm notched bed on the plywood and back buttering the tray be sufficient to keep the adhesive height to a minimum taking into account the 5mm run?

3. Set and level tray and leave adhesive to set for a day or 2. I was going to leave the tray set without any weight as it's a fair weight anyway. I didn't want to introduce any stresses by applying additional weight.

4. Check levels after adhesive is dry and providing its OK, then use ct1 to flood and seal the 3 edges of the tray. I will then tank the area prior to tiling.

 

Anything I've missed or any other suggestions?

 

Sorry for being so thorough. I'm a bit of a perfectionist and want to get it right this time so I can get cracking on the rest of it. There's so much contradicting information on the net I've been going around in circles 🤣.

 

[Nick Laslett]

I have loads of tubes of CT1/OB1, could I use that for fixing down my wet room shower tray instead of tile adhesive?
 

 

 

 

 

@Nickfromwales  I think I saw a plumberparts YouTube video where he used just CT1.  

 

I don’t have any tiling tools, or tile adhesive. But I do think using a tube product will be more expensive. 
 

 

[Nickfromwales]

5 hours ago, Nick Laslett said:

I have loads of tubes of CT1/OB1, could I use that for fixing down my wet room shower tray instead of tile adhesive?
 

 

 

 

 

@Nickfromwales  I think I saw a plumberparts YouTube video where he used just CT1.  

 

I don’t have any tiling tools, or tile adhesive. But I do think using a tube product will be more expensive. 
 

 

What size gap do you think you'll need to fill? If the substrate is very robust and flat / level then a tube adhesive will suffice, prob cost sub £40 in CT1 to do this if it's a 900x900mm tray with a 6mm gap (undulation) to bridge. Is it a GRP or stone resin tray, or one made from the Wedi-like insulation material? 

[Nick Laslett]

17 minutes ago, Nickfromwales said:

What size gap do you think you'll need to fill? If the substrate is very robust and flat / level then a tube adhesive will suffice, prob cost sub £40 in CT1 to do this if it's a 900x900mm tray with a 6mm gap (undulation) to bridge. Is it a GRP or stone resin tray, or one made from the Wedi-like insulation material? 

Thank you for the feedback. It is a wedi style shower tray, to be fixed onto a power floated concrete floor. 

Edited April 16 by Nick Laslett

[Nickfromwales]

2 minutes ago, Nick Laslett said:

Thank you for the feedback. It is a wedi style shower tray, to be fixed onto a power floated concrete floor. 

1,000,000%, defo use tile adhesive.

[Marvin]

On 15/04/2024 at 22:24, Nickfromwales said:

My 2 cents, do not use silicone for fundamental sealing, just use it as a cosmetic seal; I don't EVER use silicone to seal trays before tiling, instead use CT1 as it is a completely different product without the short service life that silicone(s) tend to have.

Hi @Nickfromwales

 

Interesting...  I have replaced my work 12 years later for 2 clients. One was where I had sealed a bath to the wall before tiling down to the edge of the bath and then sealing the tile to the bath, and the other the same but on a shower tray. Neither would come off without a LOT of effort, however I use Dow 785. Having removed 20 or 30 shower trays over the years I found that when they were stuck to the wall, it was the wall that fails first (usually unsealed plasterboard or unsealed plaster). Secondly some trays on timber floors settle so I like to make a good depth of seal.

 

I will have to look up CT1 !

 

M 

 

 

[Barnboy]

I'm going to screed where my shower tray is going tomorrow. I'll eventually fit the tray with tile adhesive as mentioned, it's a stone resin tray. A 10mm notched trowel was mentioned earlier, is this the recommended notch depth ? If not what do people recommend? Also if I notch to both the floor and tray with a 10mm, what depth would I expect the bed to settle to once the tray is down ? I'm asking so that I know what level to finish my screed at to get the tray at the correct height when installed. 

Thanks

[Redbeard]

I use a 10mm notched trowel when I want a 6mm-ish bed, as the angle of the trowel 'closes it down'. A 6mm trowel 'closes down' to about 3mm depending on the angle.

[Barnboy]

52 minutes ago, Redbeard said:

I use a 10mm notched trowel when I want a 6mm-ish bed, as the angle of the trowel 'closes it down'. A 6mm trowel 'closes down' to about 3mm depending on the angle.

But is this the same if you notch both the floor and the bottom of the tray in opposite dirwctions as mentioned ? 

I thought your bed was ½ of your notch if you only put adhesive on one of the components. 

[Redbeard]

I had not noticed the ref to opposite directions - in fact I still cannot find it. Sorry if I missed one.

All I saw was this:

1 hour ago, Barnboy said:

Also if I notch to both the floor and tray with a 10mm, what depth would I expect the bed to settle to once the tray is down ? I'm asking so that I know what level to finish my screed at to get the tray at the correct height when installed. 

...so in my mind there was as much a chance of 'hills' and 'valleys' lining up (leading to effectively no increase in depth) as there was of 'hills' and 'hills' coinciding (10mm either way and you get a different result).

 

If you do it each at 90 degrees then maybe you could let one coat stiffen up a bit first? (Still not certain what depth you'll end up at when it 'sits down')