Levelling a slighty undulating wooden floor for tiling

Joined
22 Jun 2009
Messages
54
Reaction score
0
Country
United Kingdom
I would like to lay ceramic tiles in an area of about 2mx2m of my bathroom. The bathroom is on the first floor as usual and has floorboards, some of which creak slightly. The floor is currently covered in horrible cork tiling and undulates by about 5mm from the measurements I have made with a 1m spirit level. The floor does seem to be essentially level, but I suppose I should check this further.

I would rather not rip up the floorboards so presumably the job list would look something like

1) Rip up cork tiles and try and scrape as much of the old adhesive off the floorboards as possible.
2) Screw in floorboards with some 20mm screws or some such to firm them up.
3) Now at this point would it be worth trying to sand down the undulations in the floor boards to remove the 5mm undulations and if so how would be the best way to do it? Presumably one shouldn't screw in the 12mm ply recommended in the sticky thread onto an undulating floor? I would rather not use a levelling compound as I really don't want the bathroom floor any higher than is absolutely necessary. Should I aim to get 2mm or some other value of undulation before fixing ply?
4) If necessary apply some levelling compound
5) Firmly fix 12mm ply into floorboards with counter sunk screws (20mm?) ( and through boards into joists where possible?) every 150mm
6) Lay Carra Satin Marble ceramic tiles from Homebase of 10mm thickness, these are rectangular, do I have to lay these in a brick layer pattern? I know I should use an expensive flexible adhesive such as UltraProRapid PB, which a local tile shop gave me for another tile job I am doing in my kitchen where there is a concrete floor. Tile link
7) Apply a flexible top notch grout, can I use white grout to go with the tiles? Or will that discolour with age?
8 ) Attempt to make step from landing floor carpet to new bathroom floor as inconspicuous as possible with wedge shaped wood or some other fitting.
 
Sponsored Links
In the excellent sticky thread at the top of the forum gcol doesn't say what a "very flat floor" is. Is that 2, 3 or 5mm undulations of a distance of a metre? He describes not having "large gaps" between floor and a 1.5m straight piece of timber placed on the floor. What is a large gap? To me that could be anywhere from 3mm to 15mm.
 
lift f/boards lay either with 18wbp prime wbp before fitting, overboard withs 6mm backerboards glued and screwed.
or 12wbp "primed" and o/board with 12mm b/boards.
or as some will say just lay 25mm wbp...i prefer to o/board.

if not lifting f/boards screw to joist every 150mm "no deflection"at all.
sand down high spots,prime wbp underside and edges if using wbp or glue and screw either 6mm or 12mm backerboards.

using a good flex addy and grout never used that one you mention.
 
As tictic except I always prefer to replace the floor & tile on one lump ;) It also answers one of your questions in that it avoids excessive difference in threshold heights but (with exceptions) I'm not really convinced that tiling onto several layers is better than tiling onto one.

I’ve never used Ultra Pro Rapid PB either so can’t comment. It’s important to remember that with this stuff you generally get what you pay for BUT it can work out a lot more expensive if it fails & you have to rip the whole lot up & start again. For that reason alone, I only have only ever used BAL for around 5 years but that's not to say there are other products, some of which I've also used, that are equally as good.

There are some gaps in the gcol sticky but its a very good, basic guide & there is a lot more from him in the forum archive. The Tiling forum has a lot to thank him for but for “reasons” he hasn’t posted since Oct 2009, or so he says; & even his best mate jeffoss seems to have deserted us. ;)

Re gaps, just think about it :!: 15mm undulation over a span of 3m wall to wall is excessive, can probably be tolerated but will be visible; a 3mm difference you won’t even notice. A 15mm undulation over ½ metre would be a total disaster & will have far more serious implications than getting level tiles on the floor; but 3mm can easily be accommodated with tile adhesive as long as the floor isn’t rippled (between the joists); it’s an intelligence call & I don’t mean that as a criticism. IMO, replacing the floor will almost certainly take care of the problems you currently have even if you have to pack the joists level under the ply; unless you’re into the 15mm over a ½ metre territory :eek:

For the reason you posted, never, ever use white grout on floor tiles even in a bathroom. :LOL:
 
Sponsored Links
There are some gaps in the gcol sticky but its a very good, basic guide & there is a lot more from him in the forum archive. The Tiling forum has a lot to thank him for but for “reasons” he hasn’t posted since Oct 2009, or so he says; & even his best mate jeffoss seems to have deserted us. ;)

Have you noticed Richard that since Gcol and Jeff haven't been posting another "regular" has stopped posting too,one who was constantly getting up peoples noses!Makes me think he really was just doing it to annoy.
 
Thanks very much for all the comments and suggestions.

I am still thinking I will avoid ripping up the floorboards despite appreciating that is the best solution.

There are a few outstanding questions.

1) Is a 5mm undulation in the floor boards too great to consider screwing a 12mm ply onto?
2) I presume screwing in the ply would not reduce the undulation as it is suppsoed to closely follow the contours of the underlying surface, so is a 5mm undulation something the adhesive can compensate for if laid sufficiently thickly?
3) Why is rippling between the joists more serious than other rippling ? Is it because the distance between ripples is so small? I have a suspicion my undulations may be joist related, but they are not quite frequent enough to be between every joist, I think.
3) Do I really have to lay rectangular tiles of 40x30cm in a brick layer pattern?

I can see from the comments I really should use the Bal flexible adhesive and I will definitely avoid white grout despite the tiles being white. I wonder if black grout would look good to contrast with the white tiles?
 
1) Is a 5mm undulation in the floor boards too great to consider screwing a 12mm ply onto?
5mm over what distance & over how large an area?

2) I presume screwing in the ply would not reduce the undulation as it is suppsoed to closely follow the contours of the underlying surface, so is a 5mm undulation something the adhesive can compensate for if laid sufficiently thickly?
The overlay must be screwed tightly down to the floor; any voids under there will allow flexing & cause tile failure.

3) Why is rippling between the joists more serious than other rippling? Is it because the distance between ripples is so small?
Yes.

I have a suspicion my undulations may be joist related, but they are not quite frequent enough to be between every joist, I think.
Give your earlier post regarding the cork tiles & the undulations, the overall condition of the floor doesn’t sound good to me, are they timber floor boards or is it chipboard? Is there any discernable flexing in the floor boards or joists underneath? I would certainly adsvise you check out the joists & why the floor is undulating; if the joists are OK, replace the warped floor boards with WBP ply to give you a nice flat base. If the existing floor is not flat, it will be very difficult to get the tiles flat & looking good & if it's not in good condition, you may well end up having to do it all over again in the not too distant future; not worth it given the cost of new ply over the total cost of your project.

3) Do I really have to lay rectangular tiles of 40x30cm in a brick layer pattern?
Your choice really, have a look at this it may help you decide.
http://www.floorstransformed.com/patterns.html

I wonder if black grout would look good to contrast with the white tiles?
I think black over white looks a bit garish but it’s down to personal taste really; grey would be my choice it works well with practically anything.
 
1) There seem to be two main high spots in the bathroom floor that are 5mm above the centre of the 2m*2m area I am trying to tile, this perhaps would be a more accurate description rather than undulating. The main high spot is near the bathroom wall where the bathroom floor goes over an area which is in line with the edge of the landing floor where it hangs over the stairs, presumably there is some huge joist at this point. The fall is greater than I thought, over a distance of about a 80cm from the wall next to the bath to the middle of the doorway is about 1cm.

2) I believe the floor underneath the tiles are floorboards, I can feel a slight movement of about a 6 width in the areas that creak slightly. Could I not remove the high area with sanding? Or levelling the bathroom floor? Or a mixture of both?

3) Presumably laying rectangular tiles as though there were square tiles and aligning the edges looks wrong? None of the patterns on the web page you mention has such an arrangement

Thank you very much Richard for taking the time to post answers with such clarity.
 
There seem to be two main high spots in the bathroom floor that are 5mm above the centre of the 2m*2m area I am trying to tile, this perhaps would be a more accurate description rather than undulating. The main high spot is near the bathroom wall where the bathroom floor goes over an area which is in line with the edge of the landing floor where it hangs over the stairs, presumably there is some huge joist at this point. The fall is greater than I thought, over a distance of about a 80cm from the wall next to the bath to the middle of the doorway is about 1cm.
You should be able to loose 5mm over 1m without too much difficulty, at least to the point where it would not normally be noticeable. A fall of 1cm over 80cm, however, is considerable & I would certainly want to investigate that with a view to leveling it off. That sort of fall would be visible in the finished tiled floor to most prople.
2) I believe the floor underneath the tiles are floorboards, I can feel a slight movement of about a 6 width in the areas that creak slightly. Could I not remove the high area with sanding? Or levelling the bathroom floor? Or a mixture of both?
Sanding would be time consuming & hit & miss & would certainly cause a lot of dust & is only really masking whatever problem is causing the high spots in the floor. Leveling with the boards down is an equally hit & miss way of doing it & would leave voids under the ply. If you can perceive any movement in the floor, it’s too much & your tiles will crack. You’re understandably reluctant to take the existing floor up but that is exactly what I would do. Floorboards are relatively easy to lift & then you can see what’s going on, take corrective action & provide a decent flat base to accept the new tiles.
3) Presumably laying rectangular tiles as though there were square tiles and aligning the edges looks wrong? None of the patterns on the web page you mention has such an arrangement
It’s only a small room & personally I would lay the oblong tiles brick weave; aligning the grout lines may look a little uniform & strange to me but what looks odd to one looks perfectly OK to another.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top