Finally got a plumber to give a decent quote; so going to treat myself to having bathroom plumbed in.

Thing is, he’s moving faster than I expected, which is no bad thing, but the floor is just exposed floorboard and he wants to know how much to allow for the base panel & tiles.

AARGH?!

I charged down to the local tile place, who just baffled me with non committal randomness, but kindly offered to allay the confusion they had instilled in me, by offering to sell me some newfangled wonderful stuff that’s only 6mm, strong as titanium etc (maybe it is), but to be fair, it was approaching closing time, so I left.

Two questions in my little noggin:

1) Is it very sensible to get the board down first and then fit pan/basin onto it and tile around these things later or may I as well just cut the base board around these fittings, as well as the tiles?

2) What depth ply do I really need? One plumber said 9mm, tile man today said 15m 😯 and the confirmed plumber was just talking something about 3/8th of a iinsh?

(and a cheeky 3rd, anyone used this ‘cement’ base board stuff?

15m

ok if you have a very tall room.

I used 15mm recently, gives a solid floor but you end up with a bit of a step up. If you’re havign ceramic tiles thicker the better I think

I’d go with under the toilet pan but I’m not a pro.

At least 15mm ply but better still use 6mm Hardiebacker boards, use a flexible adhesive underneath these, keraflex is good and screw down. For me definitely first fit get the pipework in, tile everything then second fit get the basin, bath and bog in, much neater.

Thanks. That’s the 6mm stuff this chap was talking about.

The order you say sounds sensible, I’m just a bit up against it with timings. Wanted to tile myself.

Also, aren’t you mean to install bath and tile down to it? I may be wrong.

I tile up from the bath, so the whole tile is by the bath and the cut tile is next to the ceiling where you won’t notice it.

Fill it up first & tile up then?

At least 15mm ply but better still use 6mm Hardiebacker boards, use a flexible adhesive underneath these, keraflex is good and screw down. For me definitely first fit get the pipework in, tile everything then second fit get the basin, bath and bog in, much neater.

Have you used these 6mm Hardiebacker boards, I have on the advice of a useless plumber, I will be pulling these up quite soon and replacing with 15mm ply that I wanted to use in the first place. The backer boards are flexing like crazy.

I presume you mean putting the tile backer board onto a structural board, not sure 6mm alone will span between joists – but happily proven wrong. No more ply – is also meant to be an alternative to……well ply.

Also at work we tend to specify an anti-fracture membrane that goes into the tile adhesive, something like ditra mat or norcos. Probably belt and braces but when your specifying stuff i always err on the side of caution.

Edit: righog seems to be indicating my concerns over 6mm of anything really.

Fill it up first & tile up then?

Nope, if it does sag a mm that’s what the mastic is for, to take the slack. If you tiled to a rigid full bath then emptied it, you risk shattering the tiles as the bath puts them under compression when it rises unloaded.

NB Being paranoid about water getting under the tiles and under the bath, I used expanding foam to seal the bath to the wall on three sides, then tiled, then added mastic as a cosmetic layer. Any water has got to get through 1″ of foam before it can get under the bath.

Oh and i personally wouldn’t want to go any thinner than 15mm ply – i certainly wouldn’t specify less than that.

Edit: ignore the majority of what i’ve put, if you haven’t already, just seen you have existing floor boards! That teach me to read 😳

Oh, I’m rethinking everything now. There are floorboard down already, but they’re 90 years old and a bit shitty in parts. Would it be sensible to actually remove them all and put a new sheet of ply (say 20mm) onto the joists?

The backer boards are flexing like crazy.

That’s interesting. If anything goes wrong with this bathroom once it’s finished, there will be murders.

I had crappy chipboard in my bathroom and replaced the whole thing with ply. On top of that I used Ditra Matting and its been rock solid ever since. No movement at all.

Personally i would say yes – depending on joist centres i would say minimum 18mm for 400mm-ish centres and 22mm for 600mm centres, sure someone will come along to confirm.

Order is really up to you and if the plumber doesn’t mind doing multiple hits, if he can then do what I said, tile so much and tile down to the bath. I’ve always filled the bath, mark the wall level and fixed a batten to the wall, loads of silicone then drop the bath onto it, it won’t really bare any weight but it will as much as possible stop the bath moving up and down when full/empty.

Have you used these 6mm Hardiebacker boards, I have on the advice of a useless plumber, I will be pulling these up quite soon and replacing with 15mm ply that I wanted to use in the first place. The backer boards are flexing like crazy.

I presume you mean putting the tile backer board onto a structural board, not sure 6mm alone will span between joists – but happily proven wrong. No more ply – is also meant to be an alternative to……well ply.

When glued and screwed to solid floorboards it’s perfectly rigid in my experience.

Top tip; shut off valves on everything watery, and a flexy waste pipe on the toilet.

Shit does happen, be prepared…

By putting a thicker floor on the existing boards youre raising the floor and reducing the height of whatever door door youre going to be fiting, lots of internal doors are hollow core, or chip board core and you dont want moisture getting into them.

I would secure all floorboards down with screws then 12 mm WBP ply on top, screwed to floorboards.

Also as its a bathroom fit an extractor fan and wiring before tiling starts, either through external wall or through ceiling and out through soffit, much esier to do when there is no bath in there .

I would secure all floorboards down with screws then 12 mm WBP ply on top, screwed to floorboards

do make sure that some previous well meaning individual didn’t run all the central heating pipes in grooves cut into the tops of the joists before you do this. I nearly didn’t check 😳

Surely , you mean white carpet! 😉

There are more top tips in http://singletrackworld.com/forum/topic/weird-shit-people-do-to-their-houses

By putting a thicker floor on the existing boards youre raising the floor and reducing the height of whatever door door youre going to be fiting

I agree, one reason my little brain is now ticking away with replacing the floorboards with ply; any opinions on merits/downfall of this would be gratefully received.

If you replace the floorboards with chipboard make sure its green coloured, that shows it water resistant.

Or use 22 mm WBP plywood,secure well to floor joists.

mrben100 – Member
Personally i would say yes – depending on joist centres i would say minimum 18mm for 400mm-ish centres and 22mm for 600mm centres, sure someone will come along to confirm.

Roger that, thanks. It’s a no-brainer then really, rip out floor boards, replace with that WPB ply stuff and just bang the suite onto that and tile around?

Floor down, wall tiles up, floor tiles down, sit bog, basin etc on tiles not in them.

Floor down, wall tiles up, floor tiles down, sit bog, basin etc on tiles not in them.

then if you decide you dont like anything you can just remove them and replant something on top without a nasty gap.

if you do not mind me asking what sort of price did your plumber give??? I need to do the same soon

Hmm, ok. So no-one has shouted up that replacing the floor is a bad idea.

Doing all the tiling as suggested, would still require bath installed & shower first fit to be done first though?

Why the **** is it so tricky to to just plan one room?!

EDIT:

if you do not mind me asking what sort of price did your plumber give?

Mine’s a bit special – involves connecting up new mains supply (already run), removing lead pipe, installing a new bog waste (bathroom didn’t have a toilet before) and running into soil stack at side of house, re-routing the rainwater pipes to allow new toilet waste pipe, new basin waste & reposition (external), new bath waste & reposition (external), replacing the cast iron external pipes/soilstack and then installing the bathroom. £1150, from a reputable local plumber. £800 cheaper than the most expensive quote I had. Nice chap too, albeit 100 years old. Couldn’t grumble at that price.

Right, I do this for a living. There’s some good advice about and some not so.

Personally, If there’s floorboards down already, they need fixing down properly then a 6mm Hardiebacker (no more ply) layer over the top secured with flexible cement based tile adhesive and a few screws. You can then tile over using flexible tile adhesive and grout.

If it’s chipboard, I tend to stick down Ditramat, instead of cement board, with a flexible tile adhesive then tile over with flexible adhesive and grout.

You can alternatively use a minimum of 15mm wpb ply screwed at 150mm centres then flexible adhesive and grout but this raises the floor thickness somewhat and is just as difficult to work with and not any cheaper really all things considered.

Do NOT use 6mm board instead of the floorboards or chip board, they are not strong enough.

Board and tile 1st then fit basin and toilet on top.

Fit the Bath/shower tray and then wall tile afterwards, as if you silicon the bath to wall gap then the tile to bath gap it gives double defence from leaks. Work out the biggest cut you can to the tray and the bath, this stops the bottom tile being pulled off the wall by flex in the tray/bath.

I also like to use a tanking membrane such as PCI Lastogum on the shower walls and bath wall to protect the plasterboard from potential water ingress. I will also ONLY use cement based adhesive and grout as these are waterproof, ready mix adhesive is not.

replacing the floor wholesale with ply is not a bad idea per se, but you might struggle to get enough support around the edges of the room without additional joists or nogs.

Oh, and I always tile the walls bar the bottom cut, then tile the floor the tile the last cut to the floor. this gives the best finish and stops the edges cracking away with any shrinkage.

Blazin-saddles – Member
replacing the floor wholesale with ply is not a bad idea per se, but you might struggle to get enough support around the edges of the room without additional joists or nogs.

POSTED 3 MINUTES AGO # REPORT-POST

And after all, in the original OP he did have concerns over his noggin…………………….i’ll get my coat.

Mr Blazin

In this sort of situation are you best to just take all the floorboards out? Then sort your pipe work out while you have access. Then fit waterproof / treated ply floor, with as little joins as possible to retain rigidity?

If so what thickness ply would you need then?

Then just lay the floor tiles as normal?

Thanks Blazin’, much appreciated you taking the time to post that. I’m off from Sat from 2 weeks, so I can let plumber crack on with the bath, whilst I then use that 6mm cement board and tile the floor? (saying like it won’t be a huge stress!).

He can the jog on with the outside plumbing in the meantime and then once floor is down & tiled, he can drop pan & basin down, and I can tile walls at leisure…think that’s the order you’re suggesting?

EDIT: Access is not a problem as there is no ceiling underneath!

You can take out the existing boards, sort plumbing then reboard with 18mm ply, it must be supported at all edges and joints and screwed down at tight centres. it’s pretty tricky to do right though and much easier to use the existing floorboards or chip, the overboard with cement board.

Bear – That’s what I’d do if using a different tiler to plumber, I do prefer to tile the wall then the floor however as it cuts down on the risk of damage by dropping things on the floor but time constraints often dictate the other way around.

Thanks Blazin’ (& others) – plenty for me to no ponder during another sleepless night! Useful stuff though, thank you.

Sorry to dig up an old thread but does anyone know the difference between WBP and structural board? or are they the same thing. Wickes dosnt seem to list WBP and they are the only place near me that delivers.

Ta.

Wbp is generally hardwood, better quality, heavier, stronger, has a more dense core with more layers, stronger water proof glue and minimal voids