How do I stop our Exterior Tile Deck from leaking?


We have a 1600 sq. foot second floor exposed deck. Surface slope is 1/4" per foot. Wood frame, plywood subfloor, covered by 18" squares of porcelain tile. Grout has minimal cracking, but enough to cause water to enter and drip into the screen porch below the deck. porch ceiling is finished compounding the problem. Is there any sort of elastomeric sealer that we could apply over the grout joints that are cracked that is viscous enough that it would seal the cracks in the grout and keep the water out??


ANSWER - The leaking of deck causing damages in the ceiling below is the symptom of the cause of the problem.  Treating the symptom will not remediate the cause of the problem.

If the deck is leaking then it hasn't been properly waterproofed below the tile over the substrate.   If there wasn't a waterproof membrane installed when it was constructed, then that is the cause of the problem.  If there was a waterproof membrane installed when it was constructed, then it was installed incorrectly or something damaged it after it was installed.

If there is a waterproof membrane under the tile assembly then maybe you can try to find the leak and then make the appropriate repairs.

There isn't any type of sealer that you can apply over the grout to seal the grout joints.  If the tile is impervious, so water can't migrate through it, you could remove all of the grout and then install a sealant foam backer rod in the joints and install an ASTM C920 sealant over it filling the grout joints.  Also all transition joints from floor to walls or to other materials should be filled with the sealant too.  This type of sealant is generally a full strength silicone sealant or a urethane sealant.  Always follow the manufacturers' directions of the sealant for how to use and apply it.

This repair is not considered a legitimate way to waterproof a tile installation, but in theory it could work.


10 thoughts on “How do I stop our Exterior Tile Deck from leaking?

  1. Amy Winters says:

    I’m glad you pointed out that if your deck is leaking, you can fix it by having the deck properly waterproofed. My husband and I recently moved in to a home with a deck, but we’ve noticed a couple signs that it’s leaking. I’ll definitely take your advice and find a local deck waterproofing company!

  2. Frank says:

    I followed the advice given above and fixed my leaky balcony. Basically, I grind all the old grout out (it was actually thinset and not grout) then filled it with the recommended ASTM C920 sealant that I purchased from Amazon and made by GE. After few weeks of rain, my balcony has no sign of leakage at all. I was quoted $4,000 to replace everything. Many thanks for saving me the money. Merry Xmas!

  3. Elizabeth Gell says:

    I am really enjoying reading your well written article. It looks like you spend a lot of effort and time on your blog. I have bookmarked it and I am looking forward to reading new articles. Keep up the good work.

  4. ASTM D6747 says:

    That’s some really great discussion. Leakage can come from anywhere are it becomes quite necessary to deal with it properly. A lot of people are worried regarding their home leaks. Surely this discussion will be very helpful for everyone of them. Keep sharing!

  5. Mike Ragland says:

    I’m trying to figure out what would cause a calcification of sort hanging from my outside tile deck. I’m not sure if they used a membrane on the wood subfloor or not. Any suggestions?

    • Donato Pompo says:

      I assume you are saying that you have efflorescence that is dripping down the edge of the exterior tile deck. Efflorescence is a symptom of the tile assembly being subjected to excessive moisture or that the moisture isn’t being managed properly to ensure it reaches the drains.

      As water gets below the tile through the grout joints it needs to have a way to get out. There should be a waterproof membrane below the tile that has a slope of 1/4″ per foot towards the drain. So as water reaches the membrane it travels unrestricted to the drain. In this case perhaps the drain is over the edge of the perimeter of the tile. As the water travels through the mortars it picks up minerals that are a form of salt. Like a salt it dissolves in water. As the water evaporates it precipitates the minerals that becomes the efflorescence. So the slope on the membrane might not be adequate and the water is slowly draining off the side that cause the hanging efflorescence.

      Not much you can do about that now other than clean it off on a regular basis with a diluted acid and you can seal your tile grout joints to help limit how much water passes through.

  6. Matt says:

    I have the same problem as Frank, where our second floor exposed deck (wood frame, plywood subfloor), covered by porcelain tile is leaking. Both the grout and tiles have minimal cracking. The tiles cracked due to sinking of the balcony as a whole, I think, because the cracks are single lines and span the whole deck. I read what Frank did, but for my case, I don’t think it will help. I need a different solution, like some sort of waterproofing coating to apply on top of all the tiles. I read that some people use polyurethane waterproof coating, but I’m not sure which one is effective to use. Any thoughts?

    • Donato Pompo says:

      In your case it sounds like you have structural issues if the balcony has sunk. Waterproof membranes, even if they are also crack isolation membranes, are not recommended over structural deficient surfaces and will not mitigate structural cracks.

      The new waterproof and tile installation will only be as good as the substrate to which it is attached.

      Here again you are trying to treat the symptom of the problem rather than the problem. You need to first add some bracing to the floor joists to stabilize it and to raise it so you have the original within plane slopped surface. If in fact the existing tile is structurally sound you could scarify and skim coat the existing tile with a polymer modified mortar and then apply a liquid applied waterproof membrane over that and then install your tile per industry standards and the respective installation product manufacturer’s directions.

  7. steve williams says:

    I have a similar problem on a house in Mexico, about 1600 sq./ft travetine 16 x16 ” tiles, the grout line is 1/8″ and very weak, drainage is excellent no bird baths, also have 4″ same tile coving on perimeter. I did extensive water testing and have determind it is definitely the grout. Installation on the tile overall is good. No membrane was installed.

    The rip out and replace, with a proper membrane will be about 10k.

    Before i go there I was thinking of wet sawing ALL grout lines with a 1/4″ blade and re-grouting with epoxy grout, the structure has no movement.

    What are your thoughts on this approach ?

    Thank you in advance

    • Donato Pompo says:

      I wouldn’t use epoxy. I would remove the grout and clean the joints out thoroughly. Then use an ASTM C920 100% silicone traffic grade sealant caulking to fill the joints. It should be less expensive, easier to install and probably more effective.

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