Shower Tray in Finished Concrete Floor

[Visti]

We're stuck on how to incorporate a shower tray into the ground floor bathroom.

 

It'll be a 75mm deep concrete slab on top of EPS (300mm), but that is it. Powerfloated and done as a finished floor. Ideally all continuous throughout the entire ground floor.

 

 

How should we go about fitting the 1400x800mm tray? 

• Finish the floor, then cut out the concrete where the tray will go.
• Place in a box frame before the concrete pour to make space for it (not even considering the risk of locating it correctly)

 

Any bright alternatives?

 

 

 

[Oz07]

Have you been told 75mm conc ok? Thought 80 was min for structural floor or are you on top of b&b?

I've shuttered out before but not with a concfibished floor. I'd try to set a box up level with top ffl so they can polish over then set tray and thinner slab in afterwards if want flush. May need rods?

[Oz07]

You would never cut it out neat

[scottishjohn]

I would accept bathroom is different and not do that polished --but make it a wet room and tile floor 

you making a lot of possible boobytraps for yourself i think 

[ragg987]

We installed a Bette shower tray flush to the floor. The installation kit creates a box and the screed poured outside that. Works well.

 

 

You might need something solid over the polystyrene to support the frame.

[Nick1c]

We hope to achieve the same end result & it has been bothering me too. My assumption was that we would have to shutter the exact void we want (I will buy the shower trays so they are on site to make sure it all works) and get the siting of the drain pretty accurate. Hopefully @Nickfromwales will sort it all out!

A 75mm slab seems thin, our design arrived earlier & looks to have a minimum thickness of 150mm, with areas of reinforcement for areas under high load. 

[Onoff]

1400x1400 on plan, 100mm at the edges and about 80mm at the wall drain. Great fun too:

 

Wall drain in:

 

 

1mm angle iron formers

 

 

 

 

Exotic, very "resinous", SBR heavy mix with 10mm pea shingle as the aggregate:

 

 

Tamped with two fall lines from corners to drain:

 

 

You can see the slope here:

 

 

Mark up the tiles:

 

 

Dry fit:

 

 

Etc

[Visti]

On 18/04/2019 at 18:09, Oz07 said:

Have you been told 75mm conc ok? Thought 80 was min for structural floor or are you on top of b&b?

I've shuttered out before but not with a concfibished floor. I'd try to set a box up level with top ffl so they can polish over then set tray and thinner slab in afterwards if want flush. May need rods?

 

We've had engineering confirm that it is ok, particularly as it isn't the main structural component of the foundation. That is instead the underlying Beam and Block beneath the EPS and the external walls which most of the MBC frame rests on. Only a few internal walls are situated on top of this 75mm floor, and that is transferred directly into some dwarf walls which come through the EPS to ensure the weight is transferred direct to the B&B.

 

On 18/04/2019 at 19:21, Nick1c said:

We hope to achieve the same end result & it has been bothering me too. My assumption was that we would have to shutter the exact void we want (I will buy the shower trays so they are on site to make sure it all works) and get the siting of the drain pretty accurate. Hopefully @Nickfromwales will sort it all out!

A 75mm slab seems thin, our design arrived earlier & looks to have a minimum thickness of 150mm, with areas of reinforcement for areas under high load. 

 

I think you and @Oz07 are right as we'll have to box out that void and allow it to be polished over, extracting that bit afterwards. Nick is help us too, so hopefully the experience will translate across!

 

@Onoff Awesome example of doing it yourself. I'm almost tempted to take that approach rather than a tray... will allow us to be a bit more flexible if we don't get the void situated exactly!

[Onoff]

1 hour ago, Visti said:

@Onoff Awesome example of doing it yourself. I'm almost tempted to take that approach rather than a tray... will allow us to be a bit more flexible if we don't get the void situated exactly!

 

Ta. I would aim for a good 2% fall. For the Geberit wall drain they say 1 to 2% so in my case 13 - 26mm. Think it's ended up about 18/19mm so circa 1.5%. Not been tested in anger yet I hasten to add. Just got to do the tile sealer before that happens and run a temp waste pipe outside.

 

Forgot to say I added fibres to my exotic pea shingle mix.

Edited April 20, 2019 by Onoff

[Oz07]

75 is fine as you're on top of a suspended floor

[Mr Punter]

You can get a tray like that which is only 30mm deep and sit it on the concrete.  You just need to box out the bit for the waste.  You not notice the 30mm step. Get one that is slip resistant and easy clean.

[Nickfromwales]

On 20/04/2019 at 17:16, Visti said:

Nick is help us too, so hopefully the experience will translate across! 

How about buying a pre-formed concrete tray ( Link ) and set in situ prior to the pour ?

Then just let them polish to this and ask the polishers to blend it in as best as possible? I’d say go for a bigger area if no shower enclosure is to be used. 1500x1500mm. Getting closure to match may be controlled by asking what’s the sand comes from for the tray manufacture to forecast if there will be big differences between the two. 

Sounds a tall order unless you put a break at the door and address the room al-a- @Onoff‘s solution. 

[Visti]

I think there's a solution following some more thought and Nicks help!

 

Shutter 50mm all the way around from the tray edge and fill with up to 50mm concrete during the floor pout to accommodate the depth of the tray (30mm) so that it only sticks up by a few mm. The SVP / Waste value area is boxed off fully with no concrete poured in so that the pipework can fit.

 

The diamond cut the slab to the tray outline after the pour and polish to allow the whole tray to drop into the recess.

 

This way there's much more tolerance for inaccurate placement of the tray shutter prior to the pour, with accurate cutting out of the tray profile once the TF is up.

 

 

FYI @Nick1c if you're considering the same.

[markharro]

This thread is of interest to me. We are using MBC and their insulated slab will be our finished floor surface on the ground floor. We have 2 ground floor shower rooms. I have still to decide on the trays to use but am thinking of something that stands on the slab rather than flush. This type of thing - https://www.my-bette.com/en/product/shower-trays-and-shower-areas/betteultra-700-900-mm?variant=DW_0095

 but my partner is also interested in designs with linear wastes. The issue is that I am struggling to understand how to allow for the waste provision. MBC will instal a 110mm waste I think and we can specify where but can I be confident for example that they can place it accurately if we want to use a vertical connection from the tray? 

[Onoff]

8 minutes ago, markharro said:

The issue is that I am struggling to understand how to allow for the waste provision. MBC will instal a 110mm waste I think and we can specify where but can I be confident for example that they can place it accurately if we want to use a vertical connection from the tray? 

 

You usually put in a chunk of EPS or pir in the slab and cast it in level. Then dig out and position the waste. 

[IanR]

24 minutes ago, markharro said:

... insulated slab will be our finished floor surface on the ground floor. We have 2 ground floor shower rooms. I have still to decide on the trays

...but my partner is also interested in designs with linear wastes. The issue is that I am struggling to understand how to allow for the waste provision. MBC will instal a 110mm waste I think and we can specify where but can I be confident for example that they can place it accurately if we want to use a vertical connection from the tray? 

 

You can avoid a tray and cut the slope into the slab, and then tank and tile.

 

The 110mm waste will give you a +/- 50mm tolerance as you can fit a 110/50 offset adapter that you can then rotate into any position to move the drain coupling left or right.

 

I used a linear drain like this, with an integral trap and a 50mm outlet. It's not rodable, but has a strainer at the top that doesn't let anything significant through. 

 

 

I've got 4 showers set up like this, and after 5 years is a really robust solution.

 

[markharro]

16 hours ago, IanR said:

You can avoid a tray and cut the slope into the slab, and then tank and tile.

Thats a really neat solution but we won't be screeding or tiling so it wouldn't work for us.

 

Good tip about the 110-50mm adaptor however - thanks for that

[IanR]

12 minutes ago, markharro said:

Thats a really neat solution but we won't be screeding or tiling so it wouldn't work for us.

 

Good tip about the 110-50mm adaptor however - thanks for that

 

There's no screed on mine either. It's a Insulated raft.

 

We were between tiles and a poured resin (which we have elsewhere) in the bathrooms. For poured resin we would have needed to skim coat (with an epoxy mortar) the slope that had been cut into the slab, to get it back to smooth, and to overlap the linear drain.

[markharro]

but I think you have tiled havent you? we dont want anything on top of the poured concrete.

[IanR]

Yes, we went with tiled, but could have done poured resin.

 

You've got a tricky interface between a tray and the slab if you're not putting any finish on the slab.

 

We initially wanted polished concrete in other areas, but the slab engineer wouldn't accept any curring product in the mix to help with cracking, so we decided on poured resin in the living areas. We would have had quite a few visible surface cracks if we'd gone polished concrete. 

[markharro]

Yes that's what put me off trying to rebate a tray in flush. So now planning standard stand on top tray but even with this struggling to understand what recesses in slab needed underneath it to accommodate drain etc and whether to aim for vertical connection to drain etc.

 

We are going for powerfloated concrete as the final finish and hoping to luck that no major cracks. 

[IanR]

10 minutes ago, markharro said:

We are going for powerfloated concrete as the final finish and hoping to luck that no major cracks. 

 

That will put holes in your socks...

 

Ours was power-floated to get it level and smooth, but it's only smooth compared to tamped concrete.

 

Cracks were less visible in the power-float finish, but got more visible as we lightly ground the surface in the prep for the poured resin. 

[Russell griffiths]

1 hour ago, markharro said:

Yes that's what put me off trying to rebate a tray in flush. So now planning standard stand on top tray but even with this struggling to understand what recesses in slab needed underneath it to accommodate drain etc and whether to aim for vertical connection to drain etc.

 

We are going for powerfloated concrete as the final finish and hoping to luck that no major cracks. 

I bet my left nut it will crack, how much is anybody’s guess, will it annoy you , well that’s up to you. 

Go for a walk around b and q or wickes and look at the floor slabs, polished concrete with a clear sealer normally. 

Look for the cracks, there will be plenty. 

The only way to do what you want is with a pre formed tray that is designed to take concrete or screed, this will be metal or fibreglass. 

It gets laid on top of the insulation and the concrete poured in it, then concrete is floated and a sealer put on. 

Waste is incorporated into the former. 

 

[markharro]

Ah sorry my last comment was about the whole ground floor concrete slab - not the shower - tray area. Yes accept there may be cracks but we have been to other houses with powerfloated slab finishes and they have been quite acceptable

[saveasteading]

The b and q example is good. I often suggested to clients that they looked at the floors to see what they would be getting. They had never looked closely, of course.

I am told that b and q and the supermarkets install extremely conservative construction ( overdesigned), but they still crack in shrinkage, and most then cover in resin or other finish.

 

All concrete cracks, but it can be controlled in location and width.

The b and q type floor has a cementy paste encouraged on  the surface, to get it ultra smooth, and this emphasises the cracks. If you were to grind off the surface and expose aggregate, then the cracks would be less visible. Presumably you would seal the surface.

 

Cracks can be microscopic, as in dams and reservoirs, but this is complex design.