At the risk of sounding melodramatic, I'm losing the will to live because of the hassle I'm having with my bathroom so I could really use some hard and fast advice.

My bathroom was ripped apart, right back to bare joists and stud walls. I replaced the 18mm chipboard flooring with more of the same (at that point we were laying vinyl), and used the green moisture resistant plasterboard on the walls around the bath (we will have an overbath shower). I have a tanking kit for the walls but haven't yet used it.

We bought porcelain tiles 30mm x 60mm at the weekend and OH has now decided he wants them on the floor too. I first looked into overboarding with ply or a board such as Hardibacker but decided that as the chipboard had started creaking annoyingly, I would be as well biting the bullet and ripping it all up again.

I read online that 22mm or 25mm ply should be used but I can't get 22mm ply anywhere here (I live in the Highlands of Scotland). So my choice is 18mm or 25mm. I'm very much a 'belt and braces' type of person so my first instinct was to go with the 25mm but I'm concerned about the extra weight on the joists. As I was thinking of putting 6 mm Hardibacker or similar over the ply, the height increase would be fairly big.

So to cut a long story short....I have no idea what kind of floor I should be putting down in order to get a good base for the 30 x 60 porcelain tiles. Everyone seems to have a different opinion about this and I really dont know what to do.

Please can someone advise me?

I'm no expert, and someone may well be along soon to correct me, but my understanding is, if it is going straight onto the joists, you need 18mm ply screwed down at 300mm centres. You can tile directly onto that with no need for any hardibacker.

If you are going to lay it onto your current chipboard floor, then 12mm ply should suffice.

Apologies if this is duff advice.....

Hi Tired Gill.
Firstly well done, you seem to be attempting to everything correctly which is a good start.
Definitely use the tanking kit around the plasterboard and that should be fine. Im assuming the plasterboard isnt plasterered? If not then the plasterboard will hold the weight of the tiles and you are fine to proceed with flexible powdered adhesive. Tubbed dispersion adhesive will not do.

As for the floor, when it was lifted did you strengthen the joists at all with noggings or cross members. This really tightens up a floor and reduces movement.
You could ply ontop of the chipboard or use cement board. The advantages of the cement board as you know is that it wont rise the floor as much for the same addeded strength.

If it was me I would screw down the chipboard every 200 along the joists, then cement board on top, again screwed every 200.
Then use a 2 part flexi adhesive for the floor.
Im sure you will get some other good advice soon, Grumpy isnt too far from you and might advise of local stockists.

Good luck

you say the floor creaking was it screwed down or nailed,needs to b screwed, and is there any movement (might need extra noggings), with new ply i would go 25 if thats what u can get hold of, good luck with it sure some more advice will b along soon

Originally Posted by davy_G

Im assuming the plasterboard isnt plasterered?

As for the floor, when it was lifted did you strengthen the joists at all with noggings or cross members. This really tightens up a floor and reduces movement.

If it was me I would screw down the chipboard every 200 along the joists, then cement board on top, again screwed every 200.
Then use a 2 part flexi adhesive for the floor.
Im sure you will get some other good advice soon, Grumpy isnt too far from you and might advise of local stockists.

Good luck

Thanks for the replies guys, much appreciated.

Nope, plasterboard isn't plastered.

When the floor was up, I took out some of the noggins because the joiner we had in at one point told us the squeaking floor could have been caused by a noggin that wasn't exactly flush with the joist and unless there was a cut join in that area, they weren't needed. So when I found one or two in the area that was squeaking, I thought that was the cause, took them out and put down new chipboard. The noise went from that area but we have creaks but in other areas now. I can't live with the noises so the floor will have to come up again. It's glued and screwed to within an inch of it's life but still manages to squeak so it can't stay down. I suspect the 18mm chipboard has a tendency to sag ever so slightly between the joists tbh and the creaking we hear is the board itself rather than it rubbing on something. We noticed a difference in quality between this stuff and the stuff that was used for another room previously so I'm wondering if it's just not all that sturdy even although it's supposed to be 'standard'.

The local builder's merchant told me I should have glued along the top of the joists as well as the t & g's of the chipboard. Just as well I didn't now if it's coming up. They can get me 25mm WBP ply as an order in, or they carry 18mm as standard. Ply is stronger than chipboard so it shouldn't have the same creaking issues anyway?

It deffo needs the joists checking for squeeky noggins and then screw them rather than nail..it's the nails that squeek against the wood, screws won't.

But IMHO , you need to remove the chipboard and use 25mm ply and tile to this with an S1 adhesive and flexible grout.

But Also add the noggins at 300mm intervals like mentioned above...Prime the back and edges of the ply with either an SBR or similar to prevent moisture.

Leave a small expansion gap around the perimeter and between boards if more than one piece going down to allow for thermal movement.

Everything is screwed, no nails to be seen anywhere.

Forgive the simple question...but what is an SBR? I suspect it's obvious but my brain hurts right now.

SBR Bonding/Admix agent - (Everbuild)


(Do not be tempted to use cheaper PVA which moisture breaks down)

SBR Bond is a latex based - Highly suited for priming areas before tiling

Water resistant bonding/priming agent and admixture for use in areas subject to humidity, dampness and continuous water contact

Improves water resistance of cement mixtures by forming a reinforcing polymer that increases long term durability and flexibility of the mix on renderings and floor screeds adhesive etc.

Can be diluted up to 3:1 with water - follow instuction on bottle


Size: 5 litre


Price: £13.99 £16.09 Including VAT at 15%

Tradetiler Tilers Silicone and tools

The plumber who is putting in the bathroom has just phoned to say he will be able to do the tiling as well (he didn't think he was going to have time originally but we're going to move out for a couple of weeks so he can come and go as he pleases in between other jobs if need be).

He takes care with his plumbing so I'm hoping he'll be the same with his tiling. Thing is though, if I order in the 25mm ply, it'll hold things up so would 18mm ply plus 6mm cement backer board of some sort be ok or should I accept that in order to do things right I need to just wait a bit longer for delivery of the 25mm ply and tell him he can't start yet? I'd rather 'right' than 'quick' if it is going to make a difference.

Originally Posted by TiredGill

The plumber who is putting in the bathroom has just phoned to say he will be able to do the tiling as well (he didn't think he was going to have time originally but we're going to move out for a couple of weeks so he can come and go as he pleases in between other jobs if need be).

He takes care with his plumbing so I'm hoping he'll be the same with his tiling. Thing is though, if I order in the 25mm ply, it'll hold things up so would 18mm ply plus 6mm cement backer board of some sort be ok or should I accept that in order to do things right I need to just wait a bit longer for delivery of the 25mm ply and tell him he can't start yet? I'd rather 'right' than 'quick' if it is going to make a difference.

hi there, firstly i would like to say that i wish my customers had the forethought and appreciation that to get the best results you need the best preperation....so having said that i would definately wait for the 25mm ply and replace the missing noggins ensuring that they are perfectly level with the joists and as dave says use a good quality s1 adhesive and flexi grout.
chris

Ok, will get the order in for the 25mm ply first thing tomorrow.

Thanks very much all of you.

Sorry for bumping but I've just thought of another couple of questions....I know the cut ends need supported by noggins but should the ply sheet run the same way as the joists so the long side rests on the joist or should it go across the joists with the long end being supported down it's length by noggins?

Also OH wants under tile heating now and wants to put in a tile backer board to a) help insulate and b) just because he thinks they're a good idea. If we get them, do we only cover the area of floor that will be getting tiled (I assume you don't tile under the bath?)....or do we cover the whole floor an the bath just sits on the board itself?

The ply can lay either way as long as it's supported and no need for insulation boards as ply is quite insulating as it is.

and put the under floor heating (UFH) under the tiled area, also don't lay the ufh under toilet pans, shower trays etc

Is this the same kind of stuff as the everbuild sbr above?

Evo-Bond PVA 5Ltr - Screwfix.com, Where the Trade Buys

I forgot to order it online and I can't find anywhere to buy it across the counter. I need to deal with the floor this weekend and need something soonish.

Is the screwfix stuff the same thing? Or can anyone suggest where I might get the everbuild stuff in person?

Hi gill,

thats not the stuff you need, you want an acrylic bond, any tile shop should stock it.

Thanks dt...on the phone right now to check the tile places.

Does 'Primer G' sound okay?

Edit: Is that just for walls? Pdf doesn't mention plywood, but store told me it's ok on ply.

I'm way out of my depth when it comes to tiling/primers/adhesives etc, it's one area where I haven't got a clue. *insert thicko smilie here*

I am sure thats a mapei product, you will be fine with that gill

Yep just checked online for you and thats fine, how much are they charging you? I found it for £6.16 a litre

Yes it is, I phoned the TileGiant place where I bought the tiles and Mapei adhesive and grout and asked for 'SBR bond or an other 'acrylic bond' and Primer G was suggested.

Thanks v. much for the help.

Edit: Sorry cross posted. I have no idea, lol. I've bought all my stuff from the same place and been given good prices so I just asked her to put one aside for pickup tomorrow. Btw, any idea how much I might need for 4 8 x 4 sheets of ply?

Just checking......I only paint this stuff on the underside and edges....and not the upper side that the tiles go on? Is that right?

its goes on the face for the tiles gill as well, its to stop the ply sucking the moisture out of your adhesive and enable them to stick properly, there is a technical post on here somewhere explaining all the whys and wherefors, mix it at a ratio of 3/1, 3 being the water, and give a couple of coats, a litre will do your sheets.

Thank you!