Properly Installing Tile Assemblies – What You Need To Know

You know, nothing beats tile when it comes to beauty and durablility.  That’s why you want tile in your home.  You are doing your due diligence and getting multiple bids for your project.  How do you decide which contractor to hire from here?  One thing you’re certain to find is that the costs are all over the place.  It’s not uncommon for some estimates to be different by 40-50%.  In some instances that’s thousands of dollars different.  Let me encourage you to read this article completely.  It will help you  determine who is qualified to do your project, and who isn’t.

American National Standards Institute (ANSI)

ANSI A108, ANSI A118, ANSI A136 handbookTo ensure that tile assemblies last a long time, and that they are predictable, ANSI testing is done.  ANSI tests everything and labels the approved method accordingly.  Tile methods are contained in ANSI A108, ANSI A118, and ANSI A136.  I will be making references to those standards throughout this article.  Don’t hesitate to ask any questions you may have at the bottom of this article.

Workmanship standards (ANSI A108.02)

There are standards for acceptable workmanship.  No job is going to be perfect, but they shouldn’t be sloppy either.  For the most part people can determine for themselves what’s appropriate and what isn’t.  In the unlikely case of litigation, these are the standards that would apply.  This standard covers allowable lippage, grout spacing, grout sizing and other visual aesthetics.

Grout spacing

Many homeowners want the grout lines as tight as possible.  I use the smallest joint I can given the tile I have to work with.  Most porcelain tile can accommodate a 3/16” grout joint.  To get a smaller joint, you will need a rectified porcelain tile.  There are size differences between each tile.  The grout joint is determined by finding what that difference is (usually 1/16”) and multiplying it by 3.  That’s why a 3/16” joint is typically the smallest we can do.  No grout joint for porcelain tile should be smaller than 1/16”.

Substrate Preparation (ANSI A108.01)

Before we begin to think about setting any tile, we need to know if the substrate is ready.  We need to know if the substrate is strong enough to support the tile we want to use.  It’s also necessary to know if the substrate is flat enough for the tile we want to use.  The type of tile will have an effect on both questions.  A natural stone installation, for instance, requires a wood subfloor to be twice as rigid than a porcelain tile requires.

The substrate must be flat

How flat it has to be is determined by the tile itself.  Standard tile, with no edge 15” or longer, requires a deviation of no more than 1/4” in ten feet.  Tile with an edge 15” or longer requires no more than 1/8” in ten feet.  The larger the tile, the flatter the substrate must be.  This is true for both walls and floors.  Most concrete surfaces do not meet either requirement, making the use of self leveling cements more likely.

A wood subfloor must be rigid

For standard tile installations, the subfloor must meet L/360 deflection requirements.  L/360 is a load calculation based on the span of the floor joists and the floor joist material.  Floor joist span isn’t based on the size of the room, but the distance between the supports of the joists themselves.  Natural stone tile requires a load of L/720 and double layer plywood before tile installation can begin.   The installation of a second layer of plywood must conform to APA (American Plywood Association) standards.

Tile Underlayment Considerations

There are many things that should be considered when choosing a tile underlayment.  Let’s look at what it takes to properly install tile underlayments here.

Concrete board installation

Concrete board can only be installed over wood substrates, it shouldn’t be used over concrete slabs.  All concrete boards require thinset mortar under them for support.  The thinset is not to bond the concrete board to the plywood.  Concrete boards need to be spaced 1/8” apart from each other and the sheets must be staggered.  Alkali resistant tape must be used on the seams of concrete board as well.  The alkali tape makes the concrete boards behave as one, expanding and contracting.  Skipping the alkali tape increases the chances of reflective cracking appearing around the sheets.

Uncoupling membranes

DItra XL in BathroomWe prefer to use uncoupling membranes as much as possible.  The only time we cannot use an uncoupling mat is if the tile is less than 2” on each side.  This is due to point loading concerns.  Schluter Ditra is our mat of choice.  Ditra allows the substrate and tile to expand and contract separately from one another.  This means that reflective cracking is not a concern for me with Ditra.  Schluter Ditra can be used over concrete or plywood substrates.

Other uncoupling mat benefits

Ditra is waterproof.  Many times when a basement is to be tiled moisture migration is an issue.  The end result of moisture migration is typically efflorescence.  Efflorescence is salt deposits left behind, usually in grout joints.  Ditra practically eliminates efflorescence because of the air cavities integrated into the system.  The concrete subfloor is still able to breathe, the moisture is just re-directed to the perimeter of the room.

Waterproofing Considerations

There are two ways to correctly waterproof a shower.  Both systems are independent of each other, and should not be mixed together.  In other words, use all of one or the other, not parts of both.  The first method we will look at is called water in, water out.  This method consists of cleavage membranes and pan liners, water is managed through primary and secondary drains.  The next method is called sealed systems.  In a sealed shower the waterproofing material is located immediately behind the tile layer.  This allows the shower to dry faster and there is only one drain.

Water in, water out

This is an old method of building showers, and one that works well if executed properly.  This method takes the most skill and has  the most steps involved, making a failure more likely.  Looking at the picture, you can see several of the steps involved.  There is a three piece clamping drain that has its base located at the base of the shower receptor.  This is the secondary drain.  Water will migrate through the mud bed layer into this secondary drain, so protecting the weep holes is very important.  It’s also important that the fastener schedule be followed as well.  No penetrations through the curb (inside or top) and no fasteners located below 3” above finished height of the curb either.  This is where most of these showers fail, is not following the fastener schedule.

Sealed showers

Schulter systems waterproofingAs I mentioned earlier, the waterproofing is located immediately behind the tile.  In other words, the tile is bonded directly to the waterproofing material.  This means that the water won’t travel through a mud bed to a secondary drain.  A bonding flange drain is what makes this system possible.  The waterproofing material should be installed at least as high as the shower head all the way to the drain.  Every square inch of the shower must be waterproofed, not just the seams and corners.


Flood testing

Every tiled shower must be able to pass a flood test.  Both water in, water out systems and sealed showers require flood testing.  A flood test means that once the waterproofing is installed, the shower pan is filled with water for 24 hours.  We are looking for any shower pan leaks.  Many water in, water out systems will pass this test as it’s done before the wall board goes up.  I am a proponent of testing the shower pan when the installer is ready to set tile, not before.   Even a finished tile shower should still pass a flood test.  Simply remove the drain cover and fill the pan with water.  If your shower has a three piece drain, make sure the plug is located at the base of the drain.  Water can go around the upper section of the drain and give you a false sense of failure.

Vapor drive

Vapor drive is when one surface is wet, and immediately behind it is dry.  We know that moisture will migrate from the wet side to the dry side.  That is vapor drive.  As buildings become tighter and tighter, I recommend not using water in water out showers.  They don’t manage the moisture in the system as well as the sealed shower does.  The vapor drive of the water in water out system is more likely to get trapped in stud cavities and cause mold growth.  If you know your home is pretty air tight, use only a sealed shower system.

Approved substrates for walls

Concrete board and other similar boards should only be used for shower construction.  Do not use Sheetrock, no matter what color the paper is.  There is not a single Sheetrock manufacturer that will have instructions for installing their product in a shower.  Concrete board is not waterproof.  Install  6 mil plastic behind the concrete board or surface applied on top.  Always use plastic or a surface applied membrane, never both.  Using both plastic and a membrane can trap moisture in a moisture sandwich.  A moisture sandwich is typically a breeding ground for mold growth.

Drywall is ok for dry areas only

If you’re tiling a backsplash or accent wall that is not in a wet location, drywall is fine.  Drywall is a good substrate for bonding tile, as all types of mortar stick well to it.  If you are going to tile over drywall, don’t use joint compound.  Drywall mud and tape are bond breakers for tile.  If you use joint compound be sure to paint over it prior to setting your tile.

Mortar Types – What You Need To Know

There are primarily 4 different types of dry set mortar (thinset) as well as organic adhesives (mastic).  Knowing when and where to use these mortars will have a drastic impact on the performance of your project.  Each type of mortar and mastic is identified by it’s ANSI rating (A118.1, A118.4, A118.11, A118.15 and TYPE I, or TYPE II for mastic).  I will give a brief description of each below.


Both mastic types can be used almost interchangeably, TYPE 1 mastic has a higher shear strength requirement.  Mastic has mold inhibitors as part of its mix.  Mastic can only be used on walls of a shower or tub surround, never the floor.

Non-modified thinset mortar (A118.1)

Schluter set mortar, Columbia MO, certified tile installerNon-modified thinset mortar can be used to install concrete backer board. This mortar can also be used directly over concrete or drywall as well when installing ceramic tile.  It is typically not recommended for use to install porcelain tile.  However, when A118.1 mortar is used over an impervious material (such as Ditra or Kerdi) the installation of porcelain tiles is fine.

Modified dry-set mortar (A118.4)

Mortar meeting A118.4 requirements can be used over nearly any substrate except plywood.  The modifiers in A118.4 mortar make it stick better to both the substrate and the tile.

EGP Mortar (A118.11)

Exterior Glue Plywood mortar is used for bonding tile directly to plywood substrates.  This mortar is also required for bonding uncoupling mats to EGP as well.  Never bond tile directly to the subfloor.  If you are using EGP as a plywood underlayment, it must be a double layer installation.

Improved modified dry-set mortar (A118.15)

Many improved mortars are also fast set mortars.  Mortars that fall under this category have more modifiers built in and are far stickier than the ones listed above.  As you can imagine, the further down this list you go (with the exception of mastics) the more expensive the mortars get.  Mastics are always more expensive than mortar (including the 118.15 mortar).

Other Mortar Considerations

All mortars are available in both white and gray, typically.  Many manufactuers also offer the mortars in thixotropic options as well.  Thixotropic mortar (formerly called medium bed mortar) will hold its shape until moved.  Ketchup, is thixotropic.

Not leveling agents

Thinset mortars are not designed to correct substrate flatness, no matter what type of mortar it is.  If the substrate needs correcting a proper material should be used (self leveling cement over concrete, for example).  Mortars are designed for the installation of tile only.  It is recommended to stick to manufacturer requirements always.  This brings me to my next point on proper mixing of mortars.

Always Follow Manufacturer Mixing Instructions

All cementious products have a high chemistry formula behind them.  It’s important to follow each manufactuer’s written instructions on how to properly use their products.  Every manufacturer will put the proper mixing instructions on each individual bag of material you use.  Mixing mortar is not a guessing game, nor is it appropriate to mix it to the consistency you prefer.  We use measuring buckets for water and dry material and a stop watch for mixing.  It is especially important that self levelers are mixed exactly as well.   THERE IS ABSOLUTELY NO WIGGLE ROOM ON SELF LEVELING CEMENTS.

Grout Types

As with all other products, there are good, better and best grouts as well.  Sanded and non-sanded grouts will be the introductory products (A118.6).  High performance cement grouts are A118.7 and epoxy/urethane grouts are A118.8.  With each class upgrade a more stain resistant grout is achieved.

Sanded/unsanded grout (A118.6)

Sanded grouts are used for joints 1/8” and larger while unsanded is used for joints 1/8” and smaller.  These grouts are more susceptible to pigment washout, so installer care is a must.  If this type of grout is to be used on your project, I highly recommend sealing it as well.  This grout class has the least resistance to staining.

High performance cement grout (A118.7)

Most grouts in this category can be used from 1/6”-1/2” using the same mix.  These grouts typically have reduced silica in them allowing them to be used in smaller joints.  The stain resistance properties of this grout is also much better than with A118.6 grouts, though these grouts can be sealed if desired as well.  Color consitancy of this grout class is also superior.  It’s much more difficult to wash out the pigment when grouting. This is the minimum grout I recommend for all our projects.

Epoxy and urethane grouts (A118.8)

Epoxy and urethane grouts will have the most resistance to staining and be the most color consistant.  Some epoxy grouts are actually labeled as stain proof in residential settings.  If you want a one time application and no further worries, epoxy grout is a great addition to any project.  There are also added effects that epoxy grouts can do as well.  Glow in the dark and glitter are just a couple of additive types you can use with epoxy.


I only recommend the use of color matched silicone with the grout of your choice.  Siliconized latex or acrylic caulks will shrink and crack in a short amount of time.  100% silicone is also the only type of sealant that should be used in wet locations as well.  All change of planes (floor/walls and wall corners) should have a sealant instead of hard grout.

Movement Joints (EJ 171)

Physics says that all objects change size with load, temperature and humidity.  Tile is no different.  Every job requires the use of movement joints.  We always leave the perimeter of the room open for movement (1/4” minimum).  Additional movement joints may be required in the floor itself as well.  No tile installation should be larger than 24’ in any direction without additional movement accommodations.  Rooms that have a lot of windows or tile located outside should have movement joints no more than 8’-12’ apart.  Tile will tent and fail without the proper use of movement joints.


This article is just the tip of the iceberg on the knowledge it takes to properly install a tile assembly.  The information listed here is definitely not complete, and should not be used as the only source of education.  My intent for writing this post is to illustrate that most installers have no idea what it takes to properly build an assembly.  If you are an installer and this information is new to you, let me encourage you to seek further education opportunities.  The NTCA and CTEF have training events all over the country encouraging installers to do better.  I have attended many of these educational seminars and plan to attend many more.


If you are a homeowner looking to hire a tile installer for your project, please ask them questions.  Your job should not be a training ground for an unqualified tile setter.  I am all for educating installers, and that typically comes from working for a qualified installer first.  Don’t assume that because they have been in business for “x” number of years without a failure (that they know about) means they know what they’re doing.  Unfortunately many installers never educate themselves more after they install their first tile.  Your shower will see more water per year than your roof ever will.  A small leak will cause thousands of dollars in damage to your home.  Please find out all you can about your potential contractor before the work begins.

Thank you very much for reading this article, I hope you found the information valuable.

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About the Author

Eric Blumer is a Certified Tile Installer servicing all of Mid-Missouri. Properly installed tile will last a lifetime, it's Eric's desire to show that qualified labor is out there. Following industry standards helps to ensure that your project won't fail.

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Benjamin Marcos Santos - January 24, 2020 Reply

This is by far the best book for a “basics of tile” over view. Should be handed out to all builders and remodelers. Wish you could buy it on Amazon.

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