Installing tile outdoors - input appreciated!

Good afternoon,

I am planning on installing 12x12 tiles over existing concrete slabs/walkways. In the front of the house, it will be Blue Montauk Slate tile. In the back of the house it will be a textured porcelain tile. The idea is to cover the exposed concrete and give more of a finished patio/walkway look.

The cement surfaces are perfect - no cracks or evidence of heaving at all! However, the concrete is probably 30-50 years old and just looks old. Stable but old. I have a couple questions that I would appreciate input on:

1. The concrete DOES have small expansion joints - I was told by a professional to install a membrance to help prevent cracks and movement. At the Home Depot today I saw an 1/8" thick orange membrane (3'x 16' for $87) that seems to be for this exact purpose called an "uncoupling membrane". I also saw a liquid waterproofing and crack prevention membrane that comes out of about a 3 gallon bucket and you spread with a roller for about $124.00. Does anyone have any experience with either of these and should I go with the orange uncoupling membrane in order to ensure no cracking in the future?

2. What mortar should I use? There is basic thinset mixed with water, basic thinset with the latex additive instead of water, and I see there is something called "Flexbond mortar" which is twice as expensive and claims to allow for 1/16" of movement in the tile without cracking. Plus, this professional said I should look into a mortar called Keralastic made by Mapei. What mortar would you use? Would you use the additive instead of water?

3. Grout recommendations other than the basic stuff available at Home Depot?

Thanks!

Where are you geographically?

Chicago. Plan for freeze/thaw as well as shoveling/occasional salt

1. You should honor the expansion joints through to the tile surface. That will eliminate the need for a membrane. The membrane you are talking about is Schluter Ditra and is a fine product but probably not at all necessary with pristine fifty year old concrete.

The liquid product you refer to is Custom Building products "Redgard". Redgard will serve no purpose what-so-ever in this case. Nothing will bridge the expansion joints and guarantee tiles won't crack.

2. Your best bet for tile adhesive is to use an unmodified thinset and mix it with an additive NOT WATER. The mention of Mapei's Kerabond is the way I would go mixing it with Mapei's Keralastic additive.

3. Use a modified grout suitable for exterior use.

I should also say that porcelain tile is your best bet for exterior freeze/thaw installations and that slate wouldn't be the best thing to use but I have done it with good success.

Thanks! This is extremely helpful information. Do my local Home Depots, Lowes, or Menards carry a modified grout for exterior use or do I have to go through a tile supplier for that item?

Unfortunately, I don't think I can honor the existing expansion joints because of where they are - they will interrupt the field of the tile and negatively impact the overall look of the installation. Any ideas? Maybe I should revisit the Schluter Ditra membrane to help bridge them? I will say that this concrete is so stable that the expansion joints don't even seem to develop a hairline fracture in them at all - I think there is very low risk of breaking tile.

Also, for cost savings (I don't want to go through the trouble and expense of sourcing the Kerabond and the Keralastic) I think I will use the Custom brand FlexBond mortar with the additive. This should perhaps allow for a little bit of movement. Sound good?

Thanks again for the advice - I appreciate it very much.

Hi Steve,

NO, that doesn't sound good! Flexbond is a modified thin set and so is mixed with water only, just like is says on the bag.

The reluctance of homeowners willing to accept expansion joints where they should be is a major reason for failed tile installations. Do you want an additional joint to protect the tile work, or an unsightly irregular crack and loose tiles?

Jaz

One thought is the salt. If it's 30 to 50 yrs old it has probably seen it's share of salt. I once did some blue stone on an old salt water pool we had problems getting anything to stick. I finally called Laticrete who recommended one of their specialty additives.

Unfortunately, I don't think I can honor the existing expansion joints because of where they are.

they will interrupt the field of the tile and negatively impact the overall look

concrete is so stable that the expansion joints don't even seem to develop a hairline fracture

Also, for cost savings (I don't want to go through the trouble and expense of sourcing the Kerabond and the Keralastic)

I think I will use the Custom brand FlexBond

This should perhaps allow for a little bit of movement. Sound good?

OK now I have a question: Why are you here if you are going to poo-pooh everything that is recommended to you from professionals that know the answers?

Good Luck!

Dear newbie,
Mr. Cline has offered you the best advice of any poster here. Ditra is a fine exterior underlayment. It is a top quality crack isolation membrane and with the correct morter " kerabond / keralastic" you can have a install that will need little care and last a long time. It is true that using a natural product such as slate tiles will require care for every year you have it laid. Focus on a thru body porcelain or any commercial rated porcelain. They offer great psi ratings and if installed correctly you can be sure your install will last the test of time

Well I guess I didn't understand the difference between modified and unmodified mortar. I have done my fair share of interior tile work simply buying bags of thin-set from Home Depot, mixing with waer, and never knew the difference. Now that I am entering a new realm of outdoor tile work, I want to make sure that I do it properly.

I do not know how to find Kerabond/Keralastic and unfortunately it may be cost prohibitive for my budget. I assumed that Custom FlexBond was a mortar that would allow more flexibility and could be mixed with the additive per your recommendations. Now I know this is apparently not the case. So, I will go with the unmodified thin-set mixed with the additive.

I can honor all expansion joints except for one because it is totally off center and will significantly affect the look of the work no matter how I creatively try to hide it. So, shall I use the uncoupling membrance or not to help reduce the possibility of problems in the future?

Also, I wasn't sure if anyone mentioned if I can find "modified grout for exterior use" at a home center or do I need to go to a specialty tile store?

The thinset modified or non modified weather being a custom product, mapei, or my perfered tec. You should be more concerned with all the above comments. Slate has fractures as common makeup and will usually pop apart in time. Freeze areas of country and real slate maybe will last but not without above mentioned care. The recomendations to not tile over expantion joints is correct. In your case with the one in question I would keep enough spair tiles to repair if needed. I would still use good thinsets with movement properties for all of job front and back. Grouts like tec xt having crack resistant properties also like tec isolight 1/8 crack isolation properties in the thinset. Remember weather is also going to be your friend or enemy. Trying to go after cheep things will usually always bite you. The concrete age is excelent the fit of tile is good except one area. The coverage on each tile is up to you. With the right product and trowel and thinset and coverage. No membrain is needed. I also Know of A great lookalike slate through body porceline 12x or 18x just incase you want to check on.