The three essentials of a lasting tile assembly
What follows is informed by trade association and manufacturer literature. Subject to the misinformation and errors an individual is likely to impart on it.
Still there are two thousand year old Roman floors and what works isn't particularly hard to understand.
Whether or not these methods are used, tile assemblies often look the same, but without them investments in projects aren't likely to last.
I've installed Error method tile in properties valued in the tens of millions. Cost simply wasn't the reason those methods were used, rather a collective ignorance of the trade.
Informed consent being a worthwhile endeavor, the hope is that the reader will be left effectively informed regarding their purchasing decision.
Credit my wife's photography on a trip to Pompeii.
The essentials
Substrate prep
Clean, Sound, stable, and flat
Clean
The removal of bond breakers. Anything that prevents cement or adhesives from bonding with a substrate.
Dust on its own is a bond breaker, others include sealers and curing compounds on concrete. Cement is not an adhesive, meaning it needs easy access to a porous surfaces to grab hold. Adhesives have been added to modern mortars, but their function is complementary.
Sound
Sturdy with integrity, obviously tile likes to be well supported.
Concrete shrinkage cracks need to be addressed with an isolation or uncoupling membrane.
Wood floor diaphragms need to meet deflection ratings, L/360 for ceramics, and L/720 for natural stone. The APA (American Plywood Association) defines the span ratings and installation of subfloors.
Wallboard should have seams taped for a monolithic surfaces. A plaster finish of level 2, defined in GA214, is the method employed for tile.
Stable
We mean dimensionally stable. Concrete expands and contracts about twice the rate of ceramic, plywood about ten times the rate. We can bond to both well.
Dimensional lumber like 2x4s are a good example of dimensionally unstable material that a lasting bond simply can't be maintained on.
Flat is required, but here's how to cheat
Large format tile (LFT, with an edge 15" or greater) wont bend with it's substrate. Resulting in air pockets under tile or hideous "lippage" between them.
The guideline for LFT is to be in plane of 1/8" over 10', and 1/16" over 2'.
All flattening is done prior to setting tile. For walls this can be fairly straight forward, either shimming the framing flat or rendering the wallboard into plane. Floors are where this requirement can be problematic. Concrete is so notoriously out of plane that the industry calls for self leveling underlayment in all cases. While even the best framers can have a change in plane run across their floor like a crease.
Remember the spirit of this rule is for tile to be fully supported with little lippage. Smaller tile like 8"x8" can cope fairly well, and penny rounds don't care at all. LFT can have a grout joint land on a high joist if possible, this case dictates the layout of the tile.
The point is that in plane tolerances needs to be addressed. LFT often incurs an additional cost, and a tile setter not crawling across a floor with a straight edge is a red flag.
Clean
Can't fault the plaster man for doing his job, it's the tile setter's to clean up.
Tile setting
ANSI A108.5
"Keying in"
Also called buttering. Once water is added to cement in a mortar mix, the molecules combine to form a gel, curing is that gel crystalizing. Cement is not an adhesive, it must crystalize around the texture of a surfaces to grab hold. Adhesives have been added to modern mortars, they too benefit from keying in.
"Keying in" should be performed on the substrate and tile. Though the monotony of buttering a few thousand 2"x2" often has smaller tile left out in this process. As the alternate name implies, we simply butter mortar over the substrate and tile.
Tile being varying levels of vitreous (like glass), there are few pores. Keying in helps the mortar grab, and is attributed with 30% of the bond strength.
Troweling
Trowels are simply gages for spreading equal quantities of mortar over an already flat substrate.
Mortar must be troweled in a linier direction for air to escape, and tile must be set while the mortar is "open" (prior to it skimming over).
Setting a tile
With a tile buttered and troweled mortar open, we place the tile and shake the air out.
Here is an overview of the standards, form the TCNA & TTMAC(Tile Council North America & Tile Terrazzo Marble Association of Canada), by which workmanship is jugged.
typically tile lippage should not exceed 1/32". Walls are judged from 3' back in designed lighting conditions. Floors are judged from standing in designed lighting.
From there grout lines should appear consistent and straight, and cut tile shouldn't have visible chipping.
Without these standards fickle tile setters wouldn't get any work done. We're human beings working with imperfect materials in an imperfect environment.
Inspect my portfolio here should these standards be of concern.
Tile setting
With a former employer, using error methods I could slap up several hundred feet of tile in a day .
Proper setting is methodical and time consuming. Tethering an individual installer to under a hundred.
Movement joints
Expansion, perimeter, corners, and carried through.
Expansion joints
Used to prevent tiles from "tenting". A Joint clear of cement that is often filled with a flexible sealant.
All products that have a kiln involved in their manufacturing process will expand as they take on moister, so with their use employing expansion joints is best practice. As well, in extreme cases thermal expansion on it's own can have tiles loudly pop off floors in the absence of expansion joints.
Depending on your reference material, these joints are used every 25' interior and 12' exterior. Thresholds are the usual location for them.
As well, joints need not be linear and can weave through a pattern along a grout joint.
Perimeter joints
Another kind of expansion joint. Their names says it all, an open perimeter that allows the tile to move freely. for most residential floors this is the only joint needed.
Corners
A home will in fact move to some extent, so regardless of the size of an assembly we leave about an 1/8" gap in corners to fill with a flexible sealant. Inside corners only for interior, and all corners exterior.
Carried through
Movement joints are used throughout construction, when installing over a substrate with existing joints we know there will be movement there, so it must be carried through our tile.
To preserve patterns in a floor, a crack isolation or uncoupling membrane can be used for a tile to bridge the joint and have it's own joint installed at the next available grout joint.
Expansion joint
An joint placed at a threshold.
Staining
Cleaning, and sealers.
Staining
Staining is a result of foreign matter penetration the pores of grout or tile, if there's no pores there's no staining.
Porcelain tile, being similar to glass, is quite stain resistant. As well, epoxy and acrylic grout perform well not being porous.
Cementitious grout and natural stone tile are of primary concern here.
Cleaning
Ceramics are based on silica and are non reactive with harsh cleaners, meaning they can be aggressively cleaned to a like new state. Diluted muriatic acid (pool cleaner) is commonly used on tile.
Cement has calcium in it, so the act of cleaning grout is actually burning off the stained layer to start fresh
Natural stone having varying amounts of calcium among other reactive metals will also be "etched" by acids, resulting in a honed finish. Refer to countertop specialists for more info on cleaning them.
Sealers
Sealers are a straight forward idea. Don't want the pores of a material to be stained? Lets just plug them with a polymer. The polymers are suspended in a liquid, the porous material soaks it up, and the liquid evaporates leaving them to cure.
When needed sealers should be applied every few years for effective maintenance. There's a wide product range with a high or low shine, removers etc...
Sealers are critical for natural stone tile. Which should be applied prior to it's installation and prior to grouting. Otherwise expect the grouting process to stain the stone.
If stain resistance is preferred, all cementitious grout would need sealing, regardless if sealers are included in the grout mix.
Staining natural stone
There is often some level of staining from grouting natural stone(including the image on the right). I use the one on the left to remind myself how bad it can get.