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.


21 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

  8. Rachel says:

    Hi. I have recently bought a first floor flat with a slate tiled patio. The lady who rents the flat downstairs is complaining of damp coming through. There are cracks in the grout above the area she says is damp. Is there something effective I can seal the grout with in the short term? I do not have funds to rip up the patio and start again, and need to explore my liability given I have just bought the property from her landlord. Etc. Thanks.

    • Donato Pompo says:

      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 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.

  9. sbansal says:

    We have an office building with mid terrace at lvl 13 (approx. area 1800 sq.m.).
    The terrace is allowed for tenants access.
    The terrace slab is metal deck slab (steel framing topped with deck sheet topped with concrete & screed). The slab is waterproofed with AFM waterproofing membrane & finish with porcelain tiles thinset & grouted joints.
    issue faced is that there is sagging in deck slab & surface draining is not working properly.
    Water is leaking down below at many places.
    Kindly suggest an economical solution

    • Donato Pompo says:

      If the concrete slab on the exterior terrace deck then that suggests it is not structural stable. The floor joists and deck sheet are not providing adequate support for the concrete topping. To fix that you need to access the floor joists add bracing between the joists.

      The sheeting that was used might not be able to handle the loads it is subjected to so you need to evaluate it for the intended use.

      The screed mortar bed that the waterproof membrane was applied to should have been sloped to a drain before the waterproofing was applied. There should be provisions for water to be able to drain away. If the sagging deck has interfered with the slope of the deck then there is no way to fix that symptom of the problem without first fixing the problem of the sagging deck.

  10. Sara Hirsch says:

    Second floor ceramic tile deck over garage. No leaking evidence on garage ceiling. Much efflorescence in grout. In summer heat, the grout pops out. All grout was removed last year and replaced with Mapei waterproof grout but the problem is even worse this year. Reading the above problems, I was thinking of removing the grout again, waterproofing tile and area to be regrouted. I was thinking of using Tec 850 sanded siliconized acrylic lates caulk to fill the grout lines, since it comes in colors and the GE silicone grout does not. Your opinion please.

    • Donato Pompo says:

      You can’t have efflorescence if there is no water migration coming from below the tile. Sounds like there is an inadequate slope under the tile and it lacks a mechanism to allow the water to evacuate.

      In theory if you remove the grout and let the underlying conditions fully dry out, and if there are no breaches that would allow water to enter elsewhere, then you could use an appropriate sealant caulking for the grout.

      A sanded siliconized acrylic caulking is not suitable. It doesn’t meet the industry standard of ASTM C920 and it will not perform as well or last as well as an ASTM C920 sealant such as a 100% traffic grade silicone or a traffic grade polyurethane sealant caulk.

      It is important that after removing the existing grout that you clean the edge of the tiles and that it is dry before applying the sealant. Some sealants require a primer to be applied to the edges of the tile first.

      You should have a foam bond breaker backer material or a tape if there isn’t room so the sealant doesn’t bond to the substrate and only to the edges of the tile.

      During the application of the sealant make sure it is tooled to a slight concave surface. You don’t want foot traffic to make direct contact to the sealant or it will tend to get dirty and will be difficult to maintain.

  11. Cooper says:

    Hi there! I may have a similar issue to these other scenarios but hoping you can shed light on what you think my specific problem is. I have a third floor balcony on a townhome that was rebuilt 4 years ago. It has slate tile for its flooring. I believe it has a waterproof barrier underneath. Whenever there has been moderate to heavy rain consistently raining for 2-3 days, a very local part of the ceiling develops a slow leak. Over the 4 years, this has happened twice and in different local spots on the ceiling. The ceilings paint layer bubbles as it fills with water and I end up having to do a repair and refinish job. I have not done any kind of sealing maintenance for the balcony but wondering if applying sealant to the tile, grout and tile/wall edges may solve this issue.

    • Donato Pompo says:

      Obviously the balcony wasn’t properly waterproofed. The challenge is to determine where the water is breaching the waterproofing or if the water is intruding from an adjacent area.

      Balcony’s should be waterproofed like we do for shower floors. The tile floor has to be designed so water has a path to drain away either into a floor drain or off the edge of the balcony into a drain gutter or with some sort of drip edge flashing so the water doesn’t drain over the surface of the exterior wall below it.

      The waterproofing should have transitioned up the sides of the building at least 3″ so water can’t migrate through those transitions. The slope of the waterproof membrane and the slope of the deck should be 1/4″ per foot towards the drain.

      The floor drain should be a two part drain so water that gets under the tile will travel to the waterproof membrane surface . The drain weep holes should be protected so water at that level can flow into the drain. In addition to that we will add a secondary waterproof membrane over the mortar bed if there is one so water can’t be retained in the mortar and so it will provide additional protection. All perimeters should be caulked with an ASTM C920 sealant as well as around the drain.

      So you challenge is to determine is the breach under the tile where you can remove the grout and fill with the ASTM C920 sealant, or is it coming from a transition area that you can seal with the caulking?

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