Hi folks I am hoping to get some expert advice here on how to ensure my floor is properly prepped for the soon to be installed Impey Aqua Dec. Here's a spec I've drawn up from instructions / videos / this forum Sorry its so long but I'd very much appreciate any pointers people have on this as I'd like to make sure its done as well as possible. I have no DIY expertise as will be obvious reading this lol! I'm just paying for it!

1. Remove existing floorboards

2. Reinforce existing joists – how do I determine if this needs done at all, and if it does, what exactly to do? Joiner will err on the side of ‘it’ll be fine’ so I’ll need to know!

3. Use noggins where needed – does this only apply if joists spaced > 600mm? Floor hasn’t been lifted yet so I don’t know what the set up is at the moment.

4. Use Celotex FF3000 insulation board between joists

5. Install trap part of the floor gully & connect to waste

6. Lay new WBP ply floor – 22 mm screwed at 300mm centres – does this have to be coated in something above / below?!

7. Cut out a section of this ply for the 1m x 1m Impey aqua dec

8. Attach battens to existing joists & use 18mm ply to create platform for dec

9. Add noggins to support all 4 sides of dec

10. Install dec – screw to joists

11. Create groove for UFH sensor in floor – cut channel in ply for this near the timer control

12. Apply single-part flexible cement based adhesive to dry clean floor.

13. Tank floor (& up walls 75mm) with TileSafe

14. Use Dural WP or other tanking system on 2 shower walls

15. Install DEVI mat directly onto TileSafe membrane

15. Apply SLC then tile

There will be a new stud wall built which the shower head will be on. Should I use Wedi board to construct the new stud wall & to box in the bath, or PB and a tanking membrane? The stud wall will incorporate 3 recesses, 1 of which is in the shower area – might be difficult to tank a recess with membrane? Would Bal WP1 be better to use in this case?

Thanks in advance for your time

the joists are braced to stop movement by adding noggins, one row is usually enough plus supprting noggins at the end of each board, lay the boards offset or brickbond pattern

prime the underside of the boards before laying

amcm2 -Just to add my thoughts on your project.
Why do you wish to remove the existing floorboards - except where the shower deck is being fitted.If the floor is in good condition and NO deflection overboard using a suitable thickness tile backer board/ wbp plywood.
How big is the floor area to be tiled and are you using the Tilesafe/Impey membrane over the whole floor.
The groove for the sensor should be placed between the UFH wires - so your final position should be chosen for maximum efficiency of the heating mat. I understand that Devi recommend a 100watt mat for use on top of Impey tanking.
No.12 - at what stage is the adhesive being used?
Tile safe is self adhesive!
No. 14 - you can use Tile Safe on the walls as well.
No.15 - Ensure you use a SLC suitable for underfloor heating - Mapei Fibreplan.
I'd use a waterproof board for the walls!

Hi Mike

Thanks for the structural advice on the floor - I'd never heard the word noggin before this site!
What would you use to prime the underside of the boards - Bal Bond SBR?

Hi John

Unfortunately, the existing floorboards aren't in good condition, so hopefully laying a new ply floor will work out ok & give more stability.
The floor area to be tiled will be 3m x 2.2m.
Yes I was planning to use the TS over the whole floor as per Impey's recommendation - is that what you guys normally do?
Thanks for the detail on the UFH sensor - that helps confirm where we will put it. I am using the Devi 100w mat.
Re TS being self-adhesive - whoops! Thanks for pointing that out - I think I must've been thinking of the primer? I shall update my list accordingly
Thanks v much for the SLC recommendation - I will certainly put this on my shopping list.
We gutted the bathroom yesterday and as feared the walls are in a very rough state. I can post pics later today.
I certainly think we might as well use the waterproof board to construct the stud wall if there's a choice cos it kills 2 birds w/ 1 stone and also better for tiling onto?
The external window wall is gonna have to be stripped back to the brick. I assumed it would have to be completely plastered and this would mean major delay from a tiling perspective but my tiler said I could always just plasterboard the wall. What do you guys think about the 2 options - is just putting PB or of course the waterproof board such as wedi a good option here or is it just quicker? I'll be delighted if its a good solution & not just a quick fix that could cause problems further down the line.
If that is the way to go, and I also use the wedi board for the stud, should I also put this board over the 1 wall which is ok lol?!
Because that is the other shower wall - therefore no need to tank any of the walls with membrane?
Thanks so much for responding - it is extremely helpful to a non-expert like myself to get this kind of feedback.