Installation: Unsuitable/Questionable Substrates for Installing Tile

By Steve Rausch

Installation: Unsuitable/Questionable Substrates for Installing Tile
Photo Credit: National Tile Contractors Association

Many installers seem to feel free to do anything, install anything, on any surface without considering the potential failures that more experienced installers are aware of, and have either avoided or charged more money for the required specific treatments to make the job work properly. It is imperative that a properly prepared substrate be used for a successful tile installation, or else the installer will be responsible for the cost of the replacement installation when the job fails.


Today’s newer technology and larger format tiles have put more pressure on proper installation methods, especially as an increased amount of tile and stone is being installed on a variety of floor and wall substrates.


The main and most important source for proper installation is the Reference Manual from National Tile Contractors Association (NTCA). This single document not only references all the industry accepted/required standards, but it also gives you the hands on, nationwide, fact-based experience and information on what to do and how to do it.


NTCA has created several documents in their Reference Manual that address these issues. The articles/chapters including “Tile over Tile,” “Tile Over Gypsum,” and “Wood Subfloors,” along with “Questionable/Unsuitable Substrates” pages are a great example. While it is true you can install over plywood, you need to know the appropriate conditions, and what thickness, etc. OSB board and different types of backer boards and/or the use of certain membranes are also discussed in this manual. In my discussions with installers all over the country, I have found most, if not all, cite access to this Reference Manual access is worth their entire membership fee.


There are a great many substrates and applications that require specific consideration from both the design/structural engineering aspect, as well as the installation methods chosen. Some of these considerations are design related and therefore require a design professional to determine the proper specifications for the tile or stone installation. As a tile installer, do not allow yourself to be drawn into making those decisions because we (installers) haven’t been paid to do that, nor do most of us have the knowledge to make those calculations properly.

Installation: Unsuitable/Questionable Substrates for Installing Tile
Photo Credit: National Tile Contractors Association

For example, framing deflection criteria, including metal gauge, lateral bracing, fastener types and pattern, and type of steel, frame spacing and depth, as well as Wind loads, Air Barrier requirements/locations — all fall under requirements from other contractors rather than tile installers. Another consideration on flooring applications is the subsurface tolerances of allowable variation (for both concrete and wood substrates), as well as the disparity between concrete flatness based on the F-Numbers (used by concrete contractors) and the 10’ straightedge method used by tile installers.


Consider the appropriate use of cement type versus other types of backer boards. There are limitations associated with all backer board products so choose carefully for your situation and needs. Remember that no backer board (or membrane) is structural, therefore, the substrate must be correctly rated for both the deflection that every floor or wall endures, as well as the overall loading weight for the entire system including the substrate, underlayment, setting materials, and tile or stone weight.


Currently within our industry, it seems some membrane systems manufacturers are making performance claims about their products as a cure all for all installation situations. When considering a membrane system for waterproofing, crack isolation, vapor retarder or low perm retarding, sound reduction, or uncoupling, take the time prior to using those products and call the manufacturer’s technical services department. Sometimes you’ll just confirm what you know, but occasionally, you’ll discover a huge money-saving bit of knowledge that can mean the difference between a successful installation or a failure you’ll be fighting in court.


Let’s begin with definitions of both unsuitable and questionable substrates:


Unsuitable substrates are substrate types that are not suitable to receive direct bond applications of ceramic tile and stone products, under any circumstances. Several examples (this is not a complete list) include: Masonite, lauan plywood (all grades and types), polystyrene foam insulation boards (those not designed for tile installation), particle board, wall paneling, stripwood/hardwood floors, contaminated concrete (including curing compound treated), most vinyl flooring, and chemically treated concrete or plywood.


Even more importantly are the questionable substrates, which unlike those listed above, are sometimes acceptable to installation. However, they require specific and unique treatments to make them work.


Questionable substrates are substrate types that when properly designed and prepared can receive direct bond applications of ceramic tile and stone. Some questionable substrates conform to specific industry installation methodology when applicable requirements are added and followed. This means using installation materials specifically designed for the unique application. It’s important to consult the selected installation material manufacturers for their specific installation recommendations. The following are examples of some (not all) questionable substrate types: Installations over old cutback or other bond breaker type adhesives, painted floors or walls, metal, plastic laminates, most epoxy coatings, some direct bond vinyl floors, chemically treated or hardened concrete, pre-cast and/or post-tensioned concrete, dirt, oil (especially kerosene) or grease-contaminated concrete or wood flooring, some gypsum concrete or self-leveling gypsum concrete, and access tile floors.


Many questionable substrates can successfully receive ceramic tile and stone installation when specific, industry accepted treatments and products are used during installation. This may include a non-bonded thick bed mortar assembly, or a cleavage membrane unit. Again, it’s imperative that you contact the manufacturers of these products for their specific recommendations.


Knowledge is power and without learning about these unsuitable and questionable substrates, you may find yourself spending your hard-earned money replacing someone’s tile job. Following the Reference Manual can eliminate jobsite failures, save money and keep your reputation spotless.


As always, feel free to email me at: or call me at (404) 281-2218 to discuss your situation directly.

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