How should I build my floor to accomodate future tiles?

[Rob1980]

Hi all, I know questions regarding wooden type floors has been asked many times on many forums, as Ive been reading.

However, I feel I need to ask the question specific to my own project to feel confident I'm doing the right thing.

I'll try to keep it short and to the point but hopefully provide enough info.

I'm building an extension on my 1950s bungalow, the new flooring is a concrete finish, with a height lower than that of the existing floor allowing for 100mm joists and 18mm floorboards.

So my basic question is how to build the floor in the bathroom..

The joists are long enough so that there will be no joins, noggins will be in place, they are c16 treated 4x2, (100x50) sat directly on the concrete, or at the most, raised slightly in places but remaining supported if the concrete floor is slightly out in that room anywhere (the other rooms have been pretty good so far).

I think you use the term deflection, am I right in thinking this would be close to, if not zero, as in no movement?

joists will be 400mm centres.

Should I put a single 18mm board onto the joists or use two layers to build up to 18mm?

What material should I use, please bare in mind, the cheaper the better, but of course I'm here asking to get a product that will suit tiles, so I understand its going to cost more than chipboard.


I think that covers it.


Thanks

Rob

 

[Time's Ran Out]

Although its a bathroom you haven't mentioned if you intend to tile this floor!
I personally don't think that 18mm is substantial enough for flooring and whatever board you use (plywood would be my choice) you need to add a further covering of a tile backer board if you are going that route.

 

[DHTiling]

Are you tiling just this bathroom floor. ?

 

[Protilers]

Cut the joists back if they are sitting on concrete........fill the bathroom floor with modified sand and cement (fibre reinforced) and tile on that.........just a thought....if I understood correctly?

 

[widler]

Why not just concrete it?

 

[Rob1980]

Yes, I plan to have the room floor tiled, that's why I'm here asking

(The clue is in the thread title lol)

18mm is more than adequate for flooring with 400mm centre joists surely? it complies with building regs, and my whole house has 18mm boards and is still standing 60 years on.

The joists are not in place, but I will not be screeding the floor, the joists are paid for, here, and something I can do myself to keep my costs down, I'm useless at any wet trades, and trying to save labour costs where I can.

I will be having this bathroom, another bathroom, and a kitchen tiled, but this question only applies to this room which is part of the extension, and the room with no floor at all yet (other than concrete which is not the finished floor as its roughly 120mm too low)

Many floors are tiled on wooden floors with joists, I have the luxury of ensuring this is flat, level and solid, I just need to know how to finish it to ensure tiling will be easier later on.

Thanks

 

[Rob1980]

Why not just concrete it?

I assume you mean screed, costs of materials, cost of labour, and the fact that I have the joists ready.

I wouldn't need to ask the question if it was a solid floor

 

[Rob1980]

Easiest way to think of this.

Forget it's downstairs, forget the concrete.

Imagine it's upstairs, I've ripped the floorboards up, and have the chance to support the joists making them solid, I want to tile the room, how should I cover the joists.

Thanks

 

[Wood's better]

Ok. You want to save money by not screeding.
The joists should be treated c16. If tiling on, it would be more solid to put them in at 300mm centres, but 400mm is ok.
18mm ply is, as you say, compliant with building regs at 400mm joist centres. However, this is minimum requirement and really only for carpet.
We have always used 22mm minimum. 25mm is better. My builders merchants stocks 22mm tongue and groove flooring plywood, which is good for a sub layer for tiling. 6mm Hardibacker glued and screwed over the top. It sounds like you are going to put the joists in more like battens. They must be packed and fixed down at close centres. 47x100mm timber can only span around 2 metres. All edges of plywood need to have noggins. I always glue the ply to the joists as well as the tongue and groove. I prefer the Spax flooring screw to fix, at 200mm centres, 60mm long. (Screwfix)

 

[DHTiling]

The clue might be in the title doh!!! ... but you didn't explain very well... IMO anyway..

 

[Rob1980]

Thanks, 300mm centres I can do, I've not put the joists in yet.

I can garantee there is no movement in the joists, they are c16 treated regulated.

The joists will all be fixed with angle brackets - solid.

Not sure what you mean
About spanning 2 meters, these will be sat directly with no spanning and laid in the normal fashion as if they were spanning gaps.

My concern in terms of the thickness of the boards is the fact that the room joining it will be floorboards with no carpet, and I want to avoid a big step if possible.

So if by reducing the gap in the joists to 300 will be ok, would I then need marine ply or normal ply?

Cheers

Ok. You want to save money by not screeding.
The joists should be treated c16. If tiling on, it would be more solid to put them in at 300mm centres, but 400mm is ok.
18mm ply is, as you say, compliant with building regs at 400mm joist centres. However, this is minimum requirement and really only for carpet.
We have always used 22mm minimum. 25mm is better. My builders merchants stocks 22mm tongue and groove flooring plywood, which is good for a sub layer for tiling. 6mm Hardibacker glued and screwed over the top. It sounds like you are going to put the joists in more like battens. They must be packed and fixed down at close centres. 47x100mm timber can only span around 2 metres. All edges of plywood need to have noggins. I always glue the ply to the joists as well as the tongue and groove. I prefer the Spax flooring screw to fix, at 200mm centres, 60mm long. (Screwfix)

 

[widler]

I assume you mean screed, costs of materials, cost of labour, and the fact that I have the joists ready.

I wouldn't need to ask the question if it was a solid floor

No i was on a out concrete !
I was taking the mick outa tbe post of the other fellow on about 'screeding with sand cement polywhatever filled poo filled screedy thingiemijib' waste of time and money in this instance.
u wanna joist it and board it, if its solid after, hardi it and tile it, easy really

 

[Protilers]

hahhahahaha.........great stuff........

just for reference.....

sharp sand =£1.99 per 20kg
modified cement=£7.00 per 25kg
Fibre glass strands= 3.99 per bag.....(loads)........

hehheheheheheeee

modified cement cures in 24 hours.......how long before you can tile on new "concrete"?

all the best

Lee

 

[Rob1980]

No i was on a out concrete !
I was taking the mick outa tbe post of the other fellow on about 'screeding with sand cement polywhatever filled poo filled screedy thingiemijib' waste of time and money in this instance.
u wanna joist it and board it, if its solid after, hardi it and tile it, easy really

Lol, sorry, I missed your sarcasm... ;p



Yeah I think reading from some of the replies, and after speaking to a carpenter friend today, and also a tiler, I think the main thing is that I get the floor rock solid, no movement in the joists, no bounce between them, and the surface can be prepared for tiles.

I'll be using a plyboard, 300mm centres on the joists, screwed down no more than about 150mm between screws.

I just fixed the 18mm chipboard to the two bedrooms today on 400mm centres, and that is solid, so I'm more than confident in the 300 centres being overkill which is good in this case im sure.

Thanks for the help guys, Ill get the floor so its rock solid, level and flat, then leave it to the tiler to get the last of it ready so the he is confident his work will last.

 

[Wood's better]

There is always confusion with marine plywood and the generally available WBP (water & boil proof)
WBP is ok for your use.
Marine ply has better veneers with no voids in the veneer, the glue used is exactly the same in both cases.
I can't find in your posts the exact height difference you are making up. But as i said before, I would use 22 or 25 mm ply. This may mean adjusting the joist size. (By planing or rip sawing)
Or using smaller joist and packing up!!
As a note you cannot guarantee there will be no movement in any joist, you need to ensure they cannot twist in use by fixing noggins.
What I meant by the span of 2 metres is that a 47x100 joist will span 2 metres unsupported (as in the case of a normal joist) but this doesn't apply to you as you are fixing down to an assumed flat level surface. Fix your brackets at 600mm apart maximum!!
I would hardibacker over the top of ply, if you want to tile straight on ply I would use a spruce ply, not what is commonly called far eastern ply. I don't trust these plywoods, they de-laminate & may bleed out oils.

 

[Rob1980]

Thanks, thats really helpful, your right, I had assumed marine ply was the way to go, but very pricey!

I already have the joists, but not the tools to rip them down, so I think my best option, as I have a few extras, Is to close the gap on them as said to 300mm, to be fair, when we poured in the concrete, and tampered it down, it was that wet, it almost self level'd, the two rooms I completed today were very flat, I put a few angle brackets in for good measure, but in reality, they were not needed.

plenty of noggins will be thrown in as I would regardless of the floor finish, and ill be sure to put lots of angle brackets in fixing the joists to the concrete, I think I may have to suffer a slight step into the room in order to accomodate hardibacker.

The size being made up is 118mm, I'm pretty anal with a tape measure, thought I was being clever getting it spot on, turns out it wouldnt of hurt if id got it too low lol...

Thanks again for the help everyone!

 

[widler]

hahhahahaha.........great stuff........

just for reference.....

sharp sand =£1.99 per 20kg
modified cement=£7.00 per 25kg
Fibre glass strands= 3.99 per bag.....(loads)........

hehheheheheheeee

modified cement cures in 24 hours.......how long before you can tile on new "concrete"?

all the best

Lee

you a funny guy lee, a funny guy .
Im sure you could tile a few inch of concrete in the same time as 'cured, modified cement .
But you know best lee .
All the best x