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whpacejr@yahoo.com
07-19-2019, 12:28 PM
I’m making plans to tile my outdoor concrete patio and seeking advice and tips. The work will be done on our house here in San Antonio, TX where the weather is mostly hot and dry with an occasional freeze in the winter. The soil is mostly clay. I’ve done some tiling work in the past, but it was all indoors. I apologize for the length of this post but want to be as thorough as possible to avoid playing “20 questions” back and forth. I’ll save my questions for the end.

The patio slab is 10’x20’ and was made with 1/2-inch rebar and a concrete rating of 3000 PSI. A tampered down sub-base made of crushed granite was used before the concrete was poured. The patio butts up against the home’s foundation with a 3/4" expansion joint between the patio and the foundation. The patio is five years old and was laid by a well known general contractor whose engineers did soil tests, drew up plans and had them approved by the city of San Antonio. It was part of a project where we also had an aluminum patio cover system added to our home. The patio cover is tied into the eaves of the house and the patio slab is tied into the foundation. So, the patio and cover, I believe, are constructed well, and conform to all building codes for such a structure and water drains off very well. That said, there are numerous hairline cracks on the surface and by my estimate, only .5mm wide (if that). From what I’ve researched and what I’ve been told, these are simply due to “crazing” or settling and are not a structural concern. I’ve checked the level of the concrete on each side of each crack and there is no height difference on either side of any crack.

So now we would like to tile and screen in the patio/cover which has been the long-range plan all along. The tiles I’ve chosen are porcelain, rated at 4 PEI, and recommended for outdoor use. The dimensions are 17”x26” and 1/4” thick. The tiles have a faux flagstone appearance with a wavy shape to them (not rectified, straight square/rectangle edges). My goal is to lay the tiles so that the grout lines are as near seamless as possible. While each tile has the same exact shape, there are two different “stone” patterns. The uniform shape allows the stones to fit together regardless of how they are placed (e.g., alternated between patterns “A” and “B”, turned 180 degrees, or staggered between the grout lines). Placing the tiles in various positions avoids repeating the same pattern and also breaks up the grout lines so that they do not run the length of the patio and are less noticeable. I’ve already “dry laid” a dozen tiles out to see how they look and to ensure they fit together in various configurations. Simply alternating and turning the tiles looks OK, but better when they are also staggered between the grout lines.

The faux grout lines between the “stone” pattern on the tiles are approximately 1/8th of an inch wide and that is the width I’d like to use for the real grout lines.

I plan to edge the perimeter of the patio tiles with a metal tile frame around the outside edge of the patio.

Before I lay down the tiles, I plan on applying two coats of RedGard liquid waterproofing and crack prevention membrane.

The only expansion joint on the whole patio is a 3/4” wide joint between the foundation and the patio. The joint is currently filled with a fiber expansion board and does not have anything, such as expansion joint caulk on top of it. For whatever reason, the fiber board sticks up approximately 3/16th” higher than the top of the patio. It appears the fiber board is inserted all the way into the joint, so it’s not like it’s coming out. The very top of the fiber board does appear somewhat frayed (probably from power washing the patio or perhaps weather) but I don’t believe it is deteriorating below that. The exterior of my home is brick. Between the top of the patio and where the first row of bricks begin is approximately 6” of the exposed foundation. I plan to lay the row of tiles that will be closest to the foundation along the expansion joint (not over it) to honor it. The tiles in this row will be cut straight along that edge. This will still leave a 3/4” gap between the tiles and the foundation where the expansion joint is that I’ll need to address somehow.

QUESTIONS:
1. Should I be concerned about the “surface cracks” in my concrete patio?
2. Do you think it is worth the effort, time and resources to stagger the tiles? As mentioned, the tiles look OK when simply alternated and turned 180 degrees, but are there any concerns with staggering them between the grout lines as well? I know it may require more cuts and more resources, but I do want the patio to look as seamless as possible.
3. Is 1/8th of an inch wide grout line suitable for non-rectified shape tiles that will be installed outdoors?
4. Given my location, San Antonio, TX, do you think using RedGard is a good idea or is it overkill? I want to do everything possible I can to waterproof the concrete and to prevent any transmission cracking of the tiles, so I’m leaning towards using it. If you believe it is overkill, OK, I’m good with overkill. But, if there are valid reasons why I should not use it, please state the reason.
5. For the tiles themselves, do I need to do anything else to account for expansion or can I just lay them as I intend with just the Redgard? If so, how?
6. Should I be concerned about the fiber board in the expansion joint and should I replace it now?
7. Any recommendations for filling in the 3/4" gap between the tiles and the foundation where the expansion joint is? As mentioned, I plan to honor the expansion joint; however, it still needs addressed. Otherwise, given the 1/4" thickness of the tile, water is bound to collect in that gap. I’ve thought about using a self-leveling joint filler, but believe that would look sloppy and unfinished regardless of how well it is applied. Besides, I don’t know if you can apply something like Sika in a joint that already has a fiber board filler and expect it to stick to it as well as the tile and the foundation to seal it. I've looked everywhere but can't find any kind of trim/profile that I would work either.

Attached Photos: 1) Patio and cover, 2) Cracks, 3) Tiles “A” and “B”, 4) Tiles NOT staggered-floor display, 5) Tiles staggered-brochure, 6) Expansion joint

Appreciate and look forward to your inputs.

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cx
07-19-2019, 01:57 PM
Welcome, Vasilis. :)

First, if you don't add that geographic location to your User Profile it'll be lost before we leave this page.

Second, is that new concrete slab sloped a minimum of 1/4" per foot away from the house?

1. There's always a concern with cracks in the substrate, 'specially on exterior applications. Whether they will be of much consequence over time is an unknown and may be addressed by your use of a crack isolation membrane if you also provide the requisite movement accommodation joints.

2. You'll need to dry lay a whole gaggle of those tiles to determine if the dimensions and shape are sufficiently consistent to allow what you have in mind. I would want to do that if possible.

3. See #2. The tile industry standards call for the grout joint width to be determined by the difference in size among the tiles. The recommendation is that the joint be equal to three times the difference in size between the largest and smallest tiles in your layout. If your tiles are very accurately manufactured, you may get by with that 1/8th" joint. What does the tile manufacturer recommend?

4. Definitely not overkill.

5. You must provide, as an absolute minimum, movement joints around the entire perimeter, which you've already addressed, and one near the center of that layout dividing the 20' dimension in half. The industry requires a movement accommodation joint every 8 to 12 feet for exterior tile installations. And you should already have a similar "control" joint in that location in the concrete anyway. If you don't, that could also be part of the reason for the cracking in the concrete surface you see.

6. I would at least want to cut it flush with the concrete surface or below. I'm afraid I can't see what you've got in your photos.

7. What you really wanted there was to have your waterproofing membrane (the RedGard) flashed properly to the house walls and under the entry door. Some sort of metal flashing would be best, tying into the RedGard membrane with a reinforcing fabric.

Been a good while since you've had a really hard freeze down there, but it does happen and it only takes one good one to do some serious damage if conditions are just wrong.

My opinion; worth price charged.