Tiling over 22mm Chipboard (MR) ?

[SproutsDad]

Your help please, I can almost answer my own question on tiling over chipboard (!!) - start again!
But because I have already come so far, I would appreciate your advice before making any more false starts and wasted material purchases.

I am raising the floor of a tiny downstairs cloakroom 110cm x 100cm that stepped down 120mm from the hallway. It will be tiled with 30cm sq granite tiles on flexible adhesive. The underfloor is concrete, rock solid. I wish I had just filled it in with concrete and screed but, on 'good' advice from a builder friend I have built a very robust exterior grade wooden 'eggbox' understructure with maxm 220mm between any joists or cross pieces. I was going to cover it with 18mm exterior ply, but was told that moisture resistant 22mm chipboard screwed and glued very close together, with all edges PVA'd would be solid enough for this small toilet area, and that using flexible tile adhesive there would be no movement. It does feel incredibly solid even before screwing it down. I have bought, cut and am ready to fix the chipboard down.

However ....... I have just read on this site and elsewhere that plywood is the only way. The MR chipboard was new to me and I believed what I had been told. However, if this could all lead to problems in the future, then now is the time to change approach. But if I use 18mm plywood I will have to pack it up by 4mm as I have already made the underframe to line up with the hall floor based on 22mm chipboard. The next size up plywood is 25mm which is too thick. And all this expense when concrete would have been more robust and a fraction of the cost.

From what I have described is there any way I can continue and use the chipboard - screwed & glued close and tight with sealed edges?
Many thanks

 

[iwaters]

You can get 22mm Plywood, its just not stocked by the usual sheds. This place here for one has it:

http://www.james-chambers.co.uk/she...w-b-p-plywood/w-b-p-eterior-plywood-1231.html

You may get away with the chipboard but it is generally considered to be a useless base for tiles. I would go with WPB ply.

 

[SproutsDad]

Thanks very much for your prompt reply. I now realise the folly of just trusting somebody 'in the trade', believing that a 'moisture resistant' chipboard would be just that, and their reassurances that it would be fine and plywood wasn't necessary were as unstable as chipboard itself.

>> A warning to others that this moisture resistant chipboard is at best only that, and only on the surfaces. All cut edges have to be sealed up. I wrongly assumed the board was fully impregnated and would be almost waterproof !!

Thanks for the link, 22mm ply is £54 per sheet from them plus delivery if they will do a single sheet - and I need just half a sheet.

I may step up to 25mm plywood, which is more readily available (I think?) and try to juggle the extra 3mm height with a threshold strip to the new carpet and underlay. Or would 18mm be Ok supported at 20cm, 8" intervals? This is a tiny cloakroom!!

After all the work I have put in to this and committed to a 22mm board, naturally I keep trying to find a way around this; whereas a couple of barrows load of concrete would have made up the levels admirably.

Any other suggestions to salvage this would be welcomed. I am sure the chipboard is robust enough when glued and screwed down, but would it remain stable, not take in moisture and swell? Or would I see tile movement/ cracking in a year or so, who knows? It's not a risk I really want to take but then again granite tiles are very thick, and on flexible adhesive !!!! Or is the risk still the same. Thanks.

 

[iwaters]

You maybe able to get 22mm from other places. That was just the first one I came across. It is not as common at the 25mm which you can get in any timber yard and DIY shed. The usually also do half sheets as well.

Using the chipboard is a risk. It maybe fine, it quite probably wont be. Probably sized and fixed plywood will never fail which is why pro tilers will always recommend using this (some use No More Ply or Hardibacker boards also).

Don't forget you still need to seal the underside and edges of ply when laying down so it doesn't absorb water. Don't use PVA though, use something like BAL SBR.

 

[tpt]

beware MR chipboard, most flexi adhesives wont stick to the wax coating its given. you'll need to sand\abrade it which removes the protection anyway!

 

[SproutsDad]

Thanks both for your replies.
The area to be boarded and tiled is tiny. It is 1m wide by 1.2m long but tapers off after just 700mm at a 45deg angle. So it is a very small space indeed.

That's why between £45 to £85 + VAT + carriage, if they will supply just a single sheet of 22mm ply at all, which is special order for most; is a hard one to swallow.

Travis Perkins boast supply of 22mm but then want a large order. The place in Halifax, James Chambers likewise won't deliver outside the local area for a small order. Just half a sheet would do me?!! But from where?

It does look as though the chipboard route is risky if I don't want to be re-doing it all in a year or so. Why does a builder of some repute and years experience give out such 'advice'?? "No, MR chipboard will be fine!!" - some hope!
My whole approach for the structure has been based on using 22mm of moisture resistant chipboard - doesn't seem to be such a thing in practice though.

Any more suggestions please chaps on the 22mm plywood??
Thanks

 

[iwaters]

http://oxfordtimber.co.uk/PlywoodFlooring.html

Give em a call and see what else they have in stock?

 

[SproutsDad]

iwaters and tpt !
24mm plywood - Ok?
After a pretty fruitless trawl for the elusive 22mm, unless I order a lorry load of it, and crazy prices; it turns out my local timber merchant will deliver a 24mm WBP plywood full sheet for £40+VAT = £48. A marine ply 25mm sheet would £85 but that feels OTT for a micro room toilet area.

Even though I only need a half sheet - 1200 x 1000, and it is 2mm thicker than the 22mm chipboard it is replacing, I think I should take them up on the 24mm at £48, a bargain in the circumstances - and keep the other half for another job.

Floor Levels
I will be aligning to a thick high quality carpet and underlay still to be purchased via a door threshold strip so I'm sure any few mm level differences will be absorbed - or your comments please?

Sealing & adhesive?
You mention a BAL SBR sealer. Like all BAL products, they are very expensive compared to others, but you will probably say they are the best and you get what you pay for?

> Sealer - a 1 litre of SBR from Topps is £14, will that do for my small room application, and should I use it on the ply surface to seal or bond to?

> Adhesive - I am fitting black granite tiles, I already have a ready mix Wickes flexible adhesive tub. Should I return that and get BAL or?

> Grout - which one, and would you use white or a grey/ off white on a floor?

Thanks both of you for your help.

 

[SproutsDad]

Thanks iw,
I called Oxford Timber and although it is on their website, they don't do/ can't get 22mm. Their 18mm or 25mm is expensive so I have found 24mm WBP plywood from a local timber merchant Powells down the road for £48 delivered tomorrow. I think I should get that as it is both a good deal and nearest to 22mm. See my earlier post.

Would also greatly appreciate your response on the other questions on sealer and adhesive.
Many thanks

 

[iwaters]

24mm ply will be fine.

BAL is more expensive than others but it is a trade quality product and recommend by most pros. Topps Tiles are very expensive for non-trade card members. If you are buying a few bits from them you can ask for a discount, some stores/managers will give it to you, others wont.

You can get BAL products much cheaper on line. You may have to buy you addy, grout, sealer all in one go to get a free delivery offer.

You only seal the edges and underside of the ply. This is to stop it absorbing moisture. Do not seal the face you will be applying the tiles to.

Ready mix adhesive is generally considered to be rubbish, especially own brand shed stuff. I wouldn't use it.

Grout - BAL flexible. White grout is hard to keep clean and I think will look odd with black granite. I would go with a silver/grey.

I don't think you will notice a few mm difference between floor heights at all

 

[SproutsDad]

Thanks, I will get the 24mm ply.

> Which BAL adhesive should I get, flexible I presume? Is it easy to mix/use? I presume I use a notched steel float-like spreader?

I will take the Wickes ready mixed flexible adhesive back for refund. It has terrible reviews which i have only just noticed. Most complain that it doesn't go off at all and can't be walked over for weeks.

> So do I not prime or seal the upper face of the plywood at all?

> What size spacers do I use between 30cm granite tiles? Normal floor spacers?

Thanks again for all your helpful tips.

 

[iwaters]

Yes use a notched trowel. Your tiles are quite large so you need a larger notched trowel, 10mm square should be ok. You should also back butter the tile before laying. Read upon on tile laying technique.

Yes you need to use flexible addy and grout. Unless you are confident in your ability to lay tile quickly I wouldn't use rapidset as you only get about 30 mins use before you have to bin it. You will either waste a load or spend all your time mixing tiny batches. Make sure you use a bagged cement based addy, not ready mixed.

Mixing is easy enough. You can get a mixing attachment for an electric drill for less than a tenner which makes mixing real easy.

4mm spacing will be fine. Don't rely solely on floor spacers. Pros don't use them because tiles are not always square and the same size but they are useful for consistency if you are a beginner. Make sure you use them properly. Many people lay them flat at the corner of each tile and leave them in place. This can mean they are still visible when grouted and it looks rubbish. They should be used so they stick out between the joints and a removed when the addy has set.

No you don't do anything to face of the plywood. If the plywood has a rough side and smooth side make sure the rough side is facing up as this will grab the addy better

 

[SproutsDad]

notched trowel.

>>> There are notched 20mm x 10mm trowels, is that Ok?

iwaters said
"Yes you need to use flexible addy and grout. Unless you are confident in your ability to lay tile quickly I wouldn't use rapidset as you only get about 30 mins use before you have to bin it. You will either waste a load or spend all your time mixing tiny batches. Make sure you use a bagged cement based addy, not ready mixed."

>>> Which BAL adhesive would that be please?

Thanks again for your detailed responses.

 

[tictic]

IMO
18mm wbp ply would be ok for flooring...primed underside and edges with sbr,then screwed every 150mm

Granite tiles ...what colour are they??..

Use a rapidset flexy addy for granite..

Weber/ardex/bal/mapei mfr will be best to use....

Grout will be flexy also....grey usually for floors

Look into sealing the tiles also....ltp/fila/lithofin ect..

 

[SproutsDad]

tictic
Many thanks for your input and everyone is at least agreed on plywood.
You say 18mm should be good enough and iwaters says 25mm....... and I know a raft of building tradesmen who think 22mm MR chipboard is fine with PVA as a sealer !! I know !!

I am very grateful for all your input but what I am trying to illustrate here is how individual, subjective and sometimes just plain conflicting the advice can be for the relative novice.

Even I, as a keen and capable DIY'er (an ex of 20yrs ago fine woodworker), know that PVA isn't waterproof and that chipboard will swell significantly under moisture or worse, water from a leak. So it was for that reason that I raised this thread in the first place, because I was getting so-called 'good advice' from 'professionals' but my instinct doubted it and there is an overwhelming opinion, plus common sense, that says "don't use chpboard".

You will see that I started off with 22mm MR chipboard (not fixed down) and tried to then get 22mm plywood but will now have to settle for 24mm.
I have taken back for refunf, the Wickes flexible floor adhesive which the 2* very poor review ratings said is "awful and takes forever" to cure, now I will be buying BAL sealer + adhesive.

So this little 'correction' in the world's smallest c;oakroom will cost me an extra £100, whereas my local 'experts' think this is OTT, but I bow to experience and trust that if you guys make the much appreciated effort to share your experience then you must know what you are talking about.

But the point I am trying to make is that for us the amateurs, it can be quite difficult when the individual posts are different but none of them are necessarily wrong - some are perhaps just more right than the others, or just different opinions or ways of achieving the same good job!

I am still slightly confused but willing to follow the most cautious approach for a belt and braces job.

Along that theme, today I will be swapping out my plumbing compression joints for copper end feed soldered ones because some of them wil be quite inaccessible and boxed in. Better safe than sorry !!
Thanks for all your help.

(Sprout is the 3-legged cat)