Installing tile on an outdoor concrete patio may seem simple, but there are actually a lot of factors to consider if you want perfect results and no cracked tiles or crumbling grout in your future. Patio slabs are rarely level, and properly done patios larger than 6’x6′ or so are poured in multiple sections with expansion joints in between the individual slabs to account for expansion and contraction due to daily heating and cooling. If you don’t think carefully about thermal expansion or take the time to prep a level surface, then your tiled patio will be uneven with wavy grout lines and will also likely crack into pieces eventually.
Want to prevent these problems for YOUR patio makeover? Then read on to find out how!
The Challenge: Weather, Water, and Steps!
These clients had an outdoor patio space that was basic 1990s builder grade — just two slabs of bare concrete with a large expansion joint running roughly down the middle.
You can see what looks like a puddle in the middle of one slab. This was actually moisture left over from a typically Austin foggy fall morning, pooled in a depression. Concrete patio slabs are rarely level, and this was no exception. Also, concrete is great at absorbing and holding moisture both from the air above and the ground below. And finally, even covered concrete will expand and contract significantly from daily heating, nighttime cooling, and the occasional hard freeze.
All this makes a proper ceramic tile install challenging. Ceramic and porcelain tile aren’t completely waterproof, but close. So, just slapping tile down directly on concrete will trap moisture and cause cracking at every hard freeze. Ceramic and porcelain tiles also expand and contract at different rates than concrete when heated and cooled. So again, if you just slap tiles down directly on an outdoor concrete pad then you’ll get cracks with every big temperature swing.
And finally, these clients chose a very strongly patterned tile and also wanted to run the tile up and over the offset patio steps. It takes some careful planning to figure out a 3D layout that looks good on steps, is centered on the overall space, doesn’t cover the expansion joint, and that also minimizes tiny tile pieces around the patio perimeter.
The Steps: Clean, Isolate, Install, and Grout
An hour or so of playing around with layouts resulted in an option that would look good when combined with the stairs, wouldn’t cover the expansion joint, and wouldn’t result in tiny slivers of tile along the patio perimeter. DO NOT SKIP this, and DO EXPERIMENT with different layouts using the actual tile you’re wanting. There is no substitute for using the actual tile for layout planning. There are times when a certain tile simply won’t work well for a specific space. You’d be very unhappy to discover this after you’ve already started setting tile in stone.
ONE: Clean and then Clean Again
Bare concrete needs to be super duper clean for good thinset adhesion. Any dirt, oil, paint residue, bird crap, etc will cause problems. The best option for cleaning an outdoor patio slab is Trisodium Phosphate, commonly called TSP. It’s a powdered alkaline chemical that makes a very strong caustic cleaner when dissolved in water. It’s also very corrosive, so you’ll want to wear a good pair of rubber gloves and be mindful of where the runoff will go.
In this case, there weren’t any landscaping plants around the patio perimeter and the patio didn’t drain to a storm sewer. So it was a no-brainer to simply mop the patio with TSP, scrub with a stiff broom, and then rinse. This patio was pretty grungy so needed a few rounds of cleaning, but was nevertheless ready for thinset within an hour. You don’t need to wait for the concrete to dry before starting with thinset, since some added moisture actually helps make a tighter bond. The concrete pad simply needs to be really well rinsed and free of any dirt or oil.
TWO: Crack Isolation Membrane
There are a couple ways to help prevent tile from cracking on an outdoor patio slab. My preferred method is to use a crack isolation membrane to decouple the tile from the slab and also eliminate moisture problems. The gold standard for this is Schluter Ditra, a fantastically engineered product that prevents outdoor tile from cracking in literally any imaginable use case. It costs $1.50/ft2 but more than pays for itself with peace of mind. Seriously, it’s a great product and worth the investment for a guaranteed lifetime crack-free outdoor tile install project.
It’s also simple to install, so long as you follow the directions to USE UNMODIFIED THINSET and take care to get complete coverage for good adhesion. There’s no need to pay extra for ‘premium’ unmodified thinset. Just the least expensive will do, since it’s the membrane itself that provides the crack prevention performance.
Ditra membrane comes rolled in 3-ft wide sheets. Just precut to fit, use a 1/8-in or smaller V-notch trowel to evenly spread pretty thinly mixed thinset over a not-too-big area, and then lay the sheet in place and stomp all over each square inch to lock it in place. Using gray thinset will help since it’ll show through the Ditra membrane. If there are any light spots, then stomp on ’em until you can see the grey shade showing through! It’s a good cardio dance workout.
In this case I actually used a 1/4-in square notch trowel because the concrete slabs had a pretty wavy surface. And, instead of stomping on the Ditra directly I instead used some pieces of scrap drywall to distribute the stomping pressure a bit.
This resulted in a much more level final surface for the tile install.
THREE: Install the Tile
The trick for straight tile lines on a relatively large surface is, once again, careful preplanning. In this case the main priority was not to cover the expansion joint running down the middle of the patio. Also, since each concrete slab sloped away from the expansion joint, I needed to carefully ensure that the centerline tile would still meet perfectly evenly at the centerline. Finally, the expansion joint wasn’t actually straight nor were the slab dimensions square.
Using a simple laser straightline makes it possible to balance all of these irregularities and still achieve a perfect result. Once the main centerlines are set and marked (I like using a big chunky magic marker), installing the rest of the field tile is relatively easy.
For this install of 6″x6″ tile with 1/8-in grout joints, I used a 3/8-in square notched trowel for plenty of room to float each tile flat to its neighbors. This resulted in two flat tile planes each sloping slightly away from the expansion joint centerline. The patio would now shed water evenly and effectively, eliminating the shallow puddles that used to collect on the concrete pad surface.
The patio was curved so installing the perimeter tile took some careful cutting. Also, wrapping the tile pattern over the patio stairs required some finagling since concrete steps are rarely level or square. Again, extra thinset is your friend for leveling tile on irregular surfaces.
You can also use thinset as a cheap stucco for dressing up otherwise bare concrete with a nice even scratchcoat finish.
The strong pattern also required some foresight for preventing trip injuries. While it’s nice to have a continuous tile pattern wrapping over stairsteps, you DO NOT want patterned tile to hide the fact that THERE ARE STAIRS! So, here’s a trick — make the pattern seem continuous from just one vantage point.
See the trick? When you’re viewing the stairs from a distance, it looks like one continuous pattern. But when looking down at the steps from a close angle, you can see the pattern breaks. This is a stylish way to help prevent folks from tripping on the steps. Seriously, think about the home insurance liability ramifications of wrapping your steps in patterned tile.
FOUR: Install the Grout
There are many different grout types to choose from. For outdoor patio tile, the main considerations are: color fade resistance, stain resistance, water resistance, and ease of install. Even covered patios will see significant sunlight and you don’t want your patio grout to sunbleach over time like a cheap rug. You also don’t want the grout to be a nightmare to keep clean-looking year after year.
The clients chose a very dark grey color to complement the tile, so this greatly simplified the grout choice. This color wears great outdoors and doesn’t show dirt or stains. Normally I would use epoxy grout for an outdoor patio, but in this case the tile had a matte no-slip surface finish that would have made epoxy haze very difficult to remove. Epoxy grout is also quite expensive and would have popped the client’s budget. So, I instead used Mapei Ultracolor Plus for all the advantages of regular sanded grout (relatively inexpensive, forgiving workability, easy release from tile surfaces) with added water resistance and color consistency.
No matter what grout you use for a patio, be sure to plan your install carefully. DO NOT install outside grout in direct sunlight (it will dry way too quick) or over multiple days (which can result in shade variations). Instead, grout all the tile in one day working in shade the entire time. In this case, I started on one shaded side of the patio in the morning and then did the other side once the shade flipped in the afternoon.
And finally, DO NOT fill expansion joints with grout! The whole point of an expansion joint is to provide a stress-relief seam for expanding and contracting concrete and tile. Filling these seams with solid grout defeats the purpose, and will result in crumbling grout and maybe cracked tile.
There are two choices for properly filling outside patio tile expansion joint grout lines. You can use fancy PVC or metal joint profiles, which look spiffy but can be pretty pricy. Or, you can simply fill expansion joint lines with color-matched siliconized grout caulk for the same result at a much lower cost. These folks chose the caulk option.
The Result? Judge for Yourself!
The clients were very happy with the final finish, and a year later it’s still crack free and looking good.