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HomeTechnicalAsk the ExpertsAsk the Experts - August 2018 - The Green Issue

Ask the Experts – August 2018 – The Green Issue

Many people reading the Ask the Experts on page 22 in our June issue (and the TileLetter
Weekly Tuesday Tech Tip on July 3rd) were puzzled by an answer that appeared to a question about T&G boards. The problem was the answer addressed issues with porcelain planks and expansion joints, and it left a lot of people scratching their heads. 

We admit it, we had a bit of an email mix up and so the answer to a different question that originally appeared in the same thread was posted. This is the T&G board question paired with the correct answer:


I’ve got a new question for you all. What about homes with subfloors consisting of T&G boards, not plywood? They run diagonally. In this one specific case, there is actually 3/4” solid wood installed over the top of it. My thought is that it would require double 3/4” plywood, and I can’t find a single method in the book that identifies such a subfloor.


We get this question quite often. The movement between the planks can be too much for a tile installation. Most manufacturers require 3/4” OSB or plywood to install concrete board and uncoupling membranes for ceramic and porcelain tile installations. Installations involving stone require additional layers of plywood . 

You really have two options here: you can remove the existing layer of plank subfloor and replace with plywood, or add additional layers of plywood to the existing plank. Check with your manufacturer, but most will warranty the installation by adding an additional layer of 1/2” plywood before installing their product. Fasten down any loose planks, and sand or chisel down any high planks before installing your plywood.  Use the correct amount and type of mortar between the plywood and concrete board or uncoupling membrane. With concrete board installation use the right type and number of fasteners, stagger sheets from each other running them perpendicular to the plywood you have just installed. Depending on the thickness of the tile and underlayment there could be height differences between adjoining floor surfaces. These are somewhat common in older homes and can be handled with wood, stone, or even metal transitions. I hope this helps. 

Robb Roderick, NTCA Technical Trainer/Presenter

And here’s an excerpt from the question that prompted the answer about plank porcelain tile and expansion joints (correct answer follows):



Wow. Just wow. There’s no way to make an expansion joint [with a long plank] look right. Zero chance. And I guarantee you 99% of every run over 25’ has no expansion joint filled with flexible sealant. I would love to see some installs from certified contractors who utilize them, if for no other reason than to generate ideas for placement and to show a customer what it will be like…Fortunately, most homes do not have that expanse because they’re doing single rooms or less than the whole house. It’s really only whole homes that are probably affected, so it’s a smaller subset.

But manufacturers keep making [planks] longer and longer, and they know the requirements. Without regard to installation requirements, they pump these things out at a cyclic rate, and customers have no idea. The average tile mechanic doesn’t either. And 9 times out of 10, incorrect installations rarely get held accountable, so when customers don’t want to listen to the right way and go get it done the wrong way, the competitor makes money, you don’t gain sales, and the customer is never the wiser. 


Attached are pictures of different installed tile work incorporating movement accommodation joints. The first is a residential installation with porcelain plank tile where a change of pattern is in a doorway to allow for a nearly unnoticeable movement accommodation joint. The other two are from commercial jobs where large areas of tile happen quite frequently.

In the TCNA Handbook from page 430 to 437 is section EJ171. It states under location and frequency of joints:

  • Interior – maximum of 25’ each direction Exterior- 8’ to 12’ in each direction
  • Interior tile work exposed to direct sunlight (heat) or moisture – maximum of 12’ each direction
  • Above ground concrete slabs – maximum of 12’ each direction
  • Perimeter joints – movement joints are required where tilework abuts restraining surfaces such as perimeter walls.
  • Change of plane, exterior – movement joints are required in all inside and outside corners.
  • Change of plane interior – movement joint required at all inside corners

Others and I believe it is the least used, most often misunderstood, and most important listing in our Handbook. Lack of correctly-installed expansion joints is thought to be – by many – the leading cause of failures in tile industry.

With plank installations, special considerations to layout should be considered. Installing expansion joints on the long side is easier, and less noticeable.

For example, if you have an installation that is 20’ x 80’ you would need a minimum of at least three joints perpendicular to the long wall creating four separate sections. Running the long edge of the plank perpendicular to the long wall would help hide these expansion joints, and would appear similar to a grout joint. Borders and change of pattern can also help you succeed in installing less-noticeable expansion joints.

Whether they are noticeable or not, they are required by our standards. If you look closely, you can find expansion joints in almost every airport, shopping mall, car lot, etc. There are great installers implementing the standards found in EJ 171 all across the country.

The TCNA Handbook says “The design professional or engineer shall show the specific location and details of movement joints.” If they don’t, reach out to them for information. If it’s just you and a homeowner, show them what the industry says in our standard and create a plan for a successful installation. 

Robb Roderick, NTCA Technical Trainer/Presenter

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