There are endless posts on this forum from people who have come across problems with tiling onto ply. Some have had pro tilers tile the floors in there homes and the tile installation has failed later down the line, others are doing there own tiling and have installed plywood onto a floor ready for tiling as they think that it is a good substrate to tile onto. This isnt the case, plywood really isnt a good substrate to tile onto at all.

Years ago plywood was used as a substrate for tiling because there was little else on the market. Builders would over board floor boards with plywood to give the tiler a flat and even surface to tile onto and in time this has become the norm to a lot of builders, even more DIYers and even some tilers. The problem is that you can tile straight onto plywood with no problems as long as the right ply is used and it is installed correctly, this rarely happens as nine times out of ten the ply that is used to over board a floor before tiling is left over from another job to save money. I have been on many jobs over the years where builders/plumbers/tilers have over boarded with ply as a solve-all because it is quick,easy and relatively cheap.

Some of the problems with tiling directly onto plywood are:

• Ply wood swells and contracts with moisture and humidity, as the plywood swells and contracts the bond between the adhesive and the plywood boards can be broken
• A lot of plywood on the market now a days is treated with chemicals to make the boards fire resistant, these chemicals make it very hard to bond to
• Plywood rots very easily when it comes into contact with water, most areas that are tiled are areas that are likely to become wet
• Plywood can absorb moisture out of the adhesive that is being used for tiling and begin to rot

I very rarely tile directly onto plywood and if I do I make sure that the ply is suitable and is installed correctly.

There are products on the market now that mean that there is rarely a need to tile straight onto plywood. Cement backer boards are a great way of over boarding floors. There are several different brands on the market and can give you the best possible substrate to tile onto if they are installed properly.

Some benefits to over boarding with a cement backer board rather than ply are:

• Cement backer boards are completely impervious to water, they do not swell or rot
• They offer a superb surface to bond to
• Floors can be over boarded with boards 6mm thick rather than 18mm with ply
• They can be installed to make the substrate waterproof, ideal for wet areas and wet rooms

For more info on Hardiebacker, click on the Link below

• HardieBacker...
  
  
  
  

If ply wood must be used, it must be installed correctly to minimize the chances of a failed tile installation.

• BS state that the ply used for over boarding floors must be a min of 15mm thick (I recommend 18mm min)
• The ply must be boil and water proof marine grade
• The ply must not be damp/wet or show any signs of rot or damp
• The underneath of the boards should be sealed to reduce the risk of the ply absorbing moisture from underneath
• BS state that the boards must be mechanically fixed down at a min of 300mm centers (I recommend 150mm to be safe and to use either ceramic coated screws as the screws can rust and discolor grout)
• The boards shouldn't be butted up together, a gap of around 2mm should be left around each board to allow for expansion
• The joints in the boards should be staggered
• Before the ply is put down, some people recommend that the ply is left in the room it is to be used in over night so that it will do any expansion/contraction before it is fixed down
• The tile adhesive manufacturers instructions should be followed to the letter and the correct adhesive must be used (I will only use a 2 part adhesive to tile onto ply)
• I would also recommend tanking any ply that is going to be tiled onto with a tanking kit like Mapei's Mapegum

It is easy to see how any of the above can be missed or over looked. Any tiler has seem countless tile installations that have failed due to the wrong plywood being used or the plywood not being fitted properly. If the wrong ply has been used or the ply has not been fixed down properly the tile installation will most likely fail, this can happen in a matter of days after the job is completed or months or even years. I get many calls from people that are concerned about a small crack in the grout on one of there floors. This is usually only the beginning and the first sign that the floor will fail. Usually the signs of a wrongly installed tile on ply floor come as follows:

• Small hair line cracks begin to appear in the grout joints between the grout and the edge of the tile
• These hair line cracks spread over time and sections of grout will start to come away leaving gaps between tiles
• One or two of the floor tiles will show small hair line cracks running from one edge to another
• these cracks will spread and get worse and the cracked tiles will become loose

Unfortunately the only answer at any stage of this, is to rip out, sort out the substrate out and re tile.

Note: Not all cracked or loose tiles are due to a problem with a ply substrate, this is just a common problem that I come across a lot.

Nice one Rich

Another good post Rich.

A top thread from" A tilers forums trusted Advisor ".. nice one..

Nice one Rich

The text below is taken from a book written by the tile master Michael Byrne

"Before the introduction of cement backer boards in the late 1970s, installers had few choices but to install most floor tiles directly on to plywood. Millions of square feet of ceramic and stone tiles have been installed on plywood setting beds with no apparent problems. Mortar manufacturers continue to produce and research thinbed adhesives that bond extremely well to plywood, and one manufacturer even offers a lifetime limited warranty on its plywood installation systems. As a consultant, however, I have inspected hundreds of failed plywood installations and consider them to be problematic.
Plywood installed as a setting bed in dry, moderate climates should remain relatively stable, but in damp or wet areas, and in locations subject to seasonal changes, plywood is a less than ideal choice for tile. Unless it has been protected with a waterproofing membrane made specifically for use with ceramic tile, plywood should never be used as a setting bed in a wet or damp installation. Wet or dry, your installation will be more durable if you select a backer board made especially for tile."

Hay Dave, wheres me thanks?

Originally Posted by Rich

Hay Dave, wheres me thanks?

You got a 'like', don't be greedy

Originally Posted by Bri

You got a 'like', don't be greedy

If anybody wants to add anything to this post, feel free

I'm using Tapatalk, so my kind words will have to be enough.........

Originally Posted by Stewart

I'm using Tapatalk, so my kind words will have to be enough.........

What is that?

Originally Posted by Rich

What is that?

It's an iPhone app for using forums, but I can't use "thanks" or "likes" on posts. So I have to catch up with them when I'm using my computer.

'Floors can be over boarded with boards 6mm thick rather than 18mm with ply'
i thought that 6mm boards will not add sufficient strength to a 'deflecting' floor, merely an ideal substrate to tile on? i use 18mm ply AND 6mm backerboards on a deflecting floor

Originally Posted by Mike

'Floors can be over boarded with boards 6mm thick rather than 18mm with ply'
i thought that 6mm boards will not add sufficient strength to a 'deflecting' floor, merely an ideal substrate to tile on? i use 18mm ply AND 6mm backerboards on a deflecting floor

Your right mike, it just makes a good surface to tile on but adds no strength.

that quote was taken from rich's post . did i misunderstand it?

as for tiling on timber , most timber that are used are crap , years ago i would tile to marine ply 3/4 seal with neoprime primer and then tile using s16 and ardion 90 admix great products and i have still got customers that have floors down for 20 years and never had a problem , but then it was fixed at 6inch centres and solid as a rock, neoprime primer was bad banned as it made you as high as a kite and very flammable but i loved it , the adrex s16 and adrion 90 you can still buy what a great product but its just so expensive shame

and yes the worst product to install on is chip-board the green aint no better and most of the timber thats used today has many different glues that just dont stand up to the job , its all about cost now and to flood market with it , and the amouunt of time i hear 6mm ply thats alright NO IT AINT it will delamate CRAP CRAP CRAP

Originally Posted by Stewart

It's an iPhone app for using forums, but I can't use "thanks" or "likes" on posts. So I have to catch up with them when I'm using my computer.

To follow brians post earlier i though you were jsut being rude

Originally Posted by marbleman

as for tiling on timber , most timber that are used are crap , years ago i would tile to marine ply 3/4 seal with neoprime primer and then tile using s16 and ardion 90 admix great products and i have still got customers that have floors down for 20 years and never had a problem , but then it was fixed at 6inch centres and solid as a rock, neoprime primer was bad banned as it made you as high as a kite and very flammable but i loved it , the adrex s16 and adrion 90 you can still buy what a great product but its just so expensive shame

Amen to that Bro. things don't always change for the best, Neoprene, S16, and Ardion 90 . Now we are talking good stuff, also the high from the Neoprene was OK.

Thanks for posting this thread Rich ,It really concerns me reading guidelines about tiling on wooden surfaces bottom line there is no guaranteed fixing method and even if you use backerboards you can still get failures unless you are sure on how the floor is constructed and what load the floor is to be put under then every tile installation on a wooden substrate must be very carefully considered and there is not a one method for all solution ,hardibacker is not impervious to water it is just stable and doesnt break down when wet and i would not use it in a wetroom floor unless it was tanked with sheet membrane ,

Good one, Rich.

Two-layer plywood floors are very, very common here. There some high-qualtiy thinsets on our market that have been designed especially for setting tile directly to plywood. I know some guys that do this all the time, and they do a good job and are good tile setters.

With that said, I think all the attention to detail that is needed to make a tile-over-ply installation work exceeds what would be needed to install a membrane over ply.

It's too much of a crap shoot for me, and I prefer to sell the job with a membrane or a mud bed. So far, and still crossing my fingers, I've been able to sell the jobs the proper way and avoid doing more than just a few tile on ply jobs in the past 21 years.

Originally Posted by whitebeam

Your right mike, it just makes a good surface to tile on but adds no strength.

makes you wonder why it has to be 6mm cement sheet and not 4mm

vote 1 for making this a sticky

Thank you everybody. I agree with you all.

Gary i agree totally, every installation needs to be looked at from every different angle and the right process chosen, there is no such thing as a fail proof method. Thanks for that, i understood that hardie and NMP are impervious to water, goes to show that there is always things to learn

Mike, if a floor has deflection, it is going to fail whatever you lay on top of it unless it is sorted. 6mm cement board is not suitable for laying onto joists, I meant that if you wanted to over board floorboards or chipboard, min 18mm ply and 6mm cement boards. Sorry, I am not very good at wording some of this If a floor has movement in it, I do the same, screw the ply down as much as possible to get rid of any deflection and then over board with cement boards, I think that this gives you about as good substrate to tile onto you could hope for.

Marbleman, Iv never used any of those products but Im willing to have a go
You are 100% right, chipboard is NOT a suitable substrate to tile on, green or otherwise IMO. Thats an entire post in itself.

very constructive and informative thread

rich -honestly neoprene was good gear, and marine ply them days was the gear expensive but it worked , most timber that are installed are cheap crap so builders can save a few quid and advice customers that it will be alright nah never is , cement boards are only any good if substrate is sound , and installed correctly,
As for S16 ardex and ardion 90 is expensive for a reason - its good but at trade its still £45.00 per unit bag and bottle + vat which puts it out of use for most . use it still on top end clients but like everybody contractors and builders will never pay for it,

Cost cost cost thats what its all about today --shame but its life

99% of the problems we come across is down to that IMO, cost. I personally dont tile straight on to ply of the reasons in the first post and also, as you say, nobody is willing to pay the price to have it done properly. The builders I work for (although I like to think that they work for me ) get the floors deflection free and sound so that I can come in and over board before tiling, this has taken years of holding up their projects refusing to tile onto a floor that Im not happy with. Iv lost count how many times Iv walked on to a job and found that the floor has been over boarded with left over ply from the rest of the build .

On a good note tho, now all my builders get the floor up together before I go in, like I said this has taken years of work on my part, thinking that they have decided that it is easier just to shut me up and let me do it how I want to but they all say the same thing now "I want it done properly". It prob helps that they have had no call backs regarding the tiling.