Plywood floors...

[Rich]

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.

 

[Ian]

Nice one Rich

 

[White Room]

Another good post Rich.

 

[DHTiling]

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

 

[Stewart]

Nice one Rich

 

[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."

 

[Rich]

Hay Dave, wheres me thanks? :smilewinkgrin:

 

[Ian]

Hay Dave, wheres me thanks? :smilewinkgrin:

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

 

[Rich]

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

rrr:

 

[Rich]

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

 

[Stewart]

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

 

[Rich]

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

What is that?

 

[Stewart]

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.

 

[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

 

[White Room]

'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.