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.


38 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?

  12. Sudershan says:

    Hi there,
    Had built the house on Chesapeake bay and have a large outside balcony facing the water. During construction we missed waterproofing step outside under the tiles and now have been trying to figure ways to stop the leak but unable to so far.

    The house is ICF construction and the balcony is made of galvanized steel posts and base with 4″ concrete on it that was sloped properly and above the concrete we have travertine tiles that were sealed and grouted. The undersurface or ceiling below is hanging green boards attached to steel frame and stucco applied. There is no gap for water or drain as was supposed to be a water sealed structure but found that’s not true anymore.

    Now the problem is effervescence on the undersurface as well as water leakage .

    Have struggled to find a product to waterproof with clear as the tiles have color. I used Remedial membranes from Australia, and followed to the “T” but now that is flaking away. Also looked and considered Diasen ORA antirain but have not applied that.

    Whats your insight into this situation. Trying to rip everything apart would be a mess. I can send or post pictures or you can reach me back. Thanks for your suggestions.

    • Donato Pompo says:

      Trying to seal or coat the travertine stone itself will not make it waterproof and won’t last.

      There isn’t any type of sealer that you can apply over the grout and stone to seal . The travertine should be very dense and impervious, so water can’t migrate through it other than through any unfilled portions of it. You could remove all of the grout and then install in the joints 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.

  13. Dianne McDermott says:

    I bought a house in a forest and the deck is slate. Below the deck is a large storage room that I think the previous owner was going to use as a media room. The room is completely sheet rocked but I noticed the ceiling in that room was wet and spongy and started to develop what I think is black mold. I called a plumber because I thought there might be a leak in a pipe. When the plumber came, he pulled out some of the sheet rock and there are no pipes and the deck it’s the deck that is leaking. It looks like the previous owner replaced some of the sheet rock before so I am suspicious that this problem existed before I bought the house. The home is only 4 years old. Do you think I am going to have to rip out that entire deck and I am not sure if it had any waterproof material below the slate. I have a construction guy coming to take a look but I would like to find out what expenses I may incur. I bought this house because it was fairly new and I was retiring (I did) so I wouldn’t have to sink money into it. Help!!!!!!!!!!!

    • Donato Pompo says:

      If it has been verified that there are no plumbing pipes that could have caused the leak, then it is likely that the exterior deck is leaking.

      If the deck had been installed correctly then it should not leak. Exterior decks over occupied space do require a roofing membrane to be applied first over the deck structure. It has to be applied to a slope surface that will allow moisture to evacuate from the deck. Waterproof flashing should have been applied at the deck to wall transitions. So there are a lot of things they could have done wrong. If it had leaked in the past or was leaking then that should have been disclosed during the escrow.

      To determine what is wrong and how to fix it requires an intrusive forensic inspection to determine the cause and to then determine how to remediate.

  14. Dianne McDermott says:

    Well, you were right. The slate deck is leaking and is causing black mold to grow. The construction guy he couldn’t tell if a waterproof membrane was used, or if one was it was faulty. To remediate, he would have to do intrusive inspection and remove and rebuild the desk. Total cost for repair of both the deck and the sheetrock removal an estimated cost of $25,000. If the builder did use a waterproof membrane, he would have needed to property install it and file the product guidelines, if not, voids any warranty. Needless to say, I am heartbroken. Pieces of the slate are coming off in pieces and I am not sure what is causing that. Thank you for your reply.

  15. Mike M says:

    hi Donato – i recently bought a home with a travertine tile patio balcony off the kitchen and directly above the poured-concrete garage foundation.

    The patio lost its pitch either from house settling (we are on a hill) or because it is structurally sagging from rotted support beams. Water now pools at the low point of the patio (where it meets the house), and occasionally finds its way into the garage underneath.

    What are the proper steps to address? I am considering ripping up, repitch and relay the patio to ensure no new water enters the house, but others have suggested that we start by first opening up the sheetrock underneath to assess the structure, support beams. Their point being that if support beams have rotted and are indeed sagging, you we will want to address that first, before the “superficial” fix of the tiles above.

    Appreciate your expertise. Thank you!

    • Donato Pompo says:

      You want to make sure that you aren’t just treating the symptom of the problem rather than the cause of the problem.

      If the deck is sagging that suggests a structural issue. You definitely want to access the floor joist to evaluate their condition and fix whatever is deficient. I would add some bracing between the floor joists to make it stiffer and stronger.

      If water is leaking into the garage then you have a waterproof problem that needs fixing. You need to stop the leak so you don’t get collateral damages such as microbial growth.

      I would start over. I would pull down the ceiling below and make sure there isn’t any microbial growth or rotten wood. Fix any floor joists and add blocking between.

      Remove travertine floor above. fix the sagging floor. Put in new plywood subfloor where necessary and shim it up so you can get a 1/4″ per foot slope to the drains or to the outer edge of the deck for drainage. You put a gutter along the deck edge to direct the water to a drain and to prevent staining along the side.

      I would waterproof the prepared sloped deck and run it up the wall at the house at least 3 inches with a primary roofing membrane. I would then install either backer board or a mortar bed over the properly prepared substrate. I would apply a tile liquid applied waterproof membrane over the backer board or mortar bed and bond the new tile directly to it.

      Install movement joints every 8 to 12 feet in the tile assembly and at all perimeters and fill those movement joints with a backer rod and an appropriate ASTM C920 sealant.

      • Mike M says:

        very helpful Donato. I very much appreciate the thought and detail you have shared here. Will keep you posted!

      • Mike says:

        Donato – we are moving forward with the project this spring as you’ve suggested. Quick follow up q for you. We currently have a travertine tile deck floor. Is/are there better tile/stone/paver options you would recommend instead? Recall this deck sits atop the garage. Thank you!

        • Donato Pompo says:

          I love natural stone because it is millions of years old and is so earthy, but not all natural stones are equal. There will be more maintenance with natural stone generally speaking. Although the granites and quartzites are very dense and low absorbing and normally don’t require as much maintenance. Being a natural product the stone physical properties can vary significant from one source to another, so you need to vet the stone’s physical properties.

          On the other hand there are many great porcelain tiles that are very durable and have relatively much less maintenance than a natural stone. Although if a natural stone chips or wear you can restore it to be like new. The porcelain tile isn’t likely to wear or chip, but it can and you can’t restore it. You can get some nice porcelain tiles that look just like a natural stone and that are slip resistant. Typically the more slip resistant the tile is the more it will tend to pick up dirt and the more effort is needed in cleaning. Although there are some newer tiles on the market today that are promoted as slip resistant but easy to clean. You can now get the porcelain tiles in large sizes and as thick as 3/4″ that makes it very resistant to damage.

  16. MAHENDER K says:

    I live in seattle area and have a 500ft tile(10ft * 50ft) deck and the water has been leaking between facia and gutter and seeping through the facia to the bottom of soffit and to the underlying wood beams.

    The tiles grout joints were torn off at many place and it looks like the waterproof under tiles are working as expected but the joints where water needs to enter into gutter is leaking into facia.

    What should I do here in fixing this ?

    • Donato Pompo says:

      If the deck is leaking below then it isn’t properly waterproofed. To manage water drainage there are number of things that have to be done correctly.
      1. The underlying slope on the waterproof membrane has to be slopped at a 1/4″ per foot towards the drain.
      2. The waterproof membrane has to tie into an area drain or to the perimeter of the deck where there should be a gutter for the water to flow into and away from the building.
      3. The waterproof membrane should flash up the side of any perimeter walls at least 3 inches.
      3. The tile installation has to be sloped 1/4″ per foot to a drain or to the perimeter gutter.
      4. The slopes have to be consistent and can’t have low or high spots.

      In order to fix the problem, you first have to determine what was constructed wrong that is causing the leaking. You need to fix the problem and not the symptom of the problem or it will reoccur. Normally that requires having an expert intrusively remove some of the tiles to determine the problem.

  17. Tammie Houston says:

    I never knew that a waterproof membrane had to be installed onto new decks. My father and uncle were the ones that built the deck of my home for me and it seems they didn’t do that. I’ll have to look for a deck waterproofing service to do just that for me. Hopefully that resolves the leaking problem and can ensure it doesn’t happen again in the future.

  18. Sven says:

    I would like to install a drain into an existing tile deck that has a polyurea membrane. What can I use to seal the drain flang or flashing to the polyurea?

    • Donato Pompo says:

      Depending on what type of polyurea waterproof membrane you are using it may allow for bonding over the existing membrane, so you can install the drain and flash over the flange and existing membrane. It will also be necessary for it to bond to the drain flange.

      Not sure how you are going to make that work. The waterproof membrane should be pre-sloped to the drain. If you put the drain in the middle of the existing deck it is unlikely you will have the membrane sloped in all directions to the drain. Unless you have a trench drain at the perimeter of the deck and if the membrane is already sloped 1/4″ per foot to that drain.

      Then the question is what type of drain are you installing. Normally for tile installations we install two part drains so we can clamp the waterproof membrane into place and have weep holes to allow water at the membrane to evacuate. If you don’t have the existing depth to do that, then maybe you are using what we call an Integrated Bonding Flange drain. You still need the membrane to be sloped in all directions to the drain, but it is installed at the same plane as the waterproof membrane with the waterproof membrane flashing over its flange.

      Note that the critical surface to be properly slopped is the surface of the waterproof membrane. You still want the tile surface to reflect that same slope as the membrane. If the membrane isn’t sloped to a drain to evacuate water then the water just stays under the tile, which can lead to various types of water damages.

  19. Steve says:

    We have a tiled deck over the living room done about 25 years ago. Started to leak in the living room last week but very slowly. Maybe a drop every 5 to 10 secs. Deck has a 3″ to 4″ concrete base. I removed part of the ceiling gyprock to see where the leak was coming from. Have covered part of the tile with a tarp and up around the edges yesterday and the leak is much less. Edges of the deck has narrow cedar vertical siding right down to the tile so some are rotting away. No flashing was installed on all 4 walls to the tile. Had a sundeck and roofing company look at it and both suggested removing the concrete and start from there with a cost of about $10,000 to redo it with a Duradek or roofing tar type finish. Can any waterproofing material or method be done without removing the concrete? Eg. on top of the existing concrete? Not sure if the water is coming from grout and concrete or the edges where the tile meets the walls or elsewhere.

    • Donato Pompo says:

      The best approach is always to fix the problem and not just the symptom of the problem or it is only a temporary repair that will likely reoccur.

      If water is getting into the gyprock ceiling then you are likely to develop microbial growth (mold) and you might have some structural damages to the wood framing if it has persisted too long. If you stop the leak soon enough then you should be able to remediate the water damages.

      The proper way to waterproof and tile an exterior deck over an occupied space is to first install a primary roofing waterproof membrane over a pre-slopped surface, slopped to a drain for any water to evacuate, which could be gutters at the outer perimeter of the deck or two part area drains or to a trench drain system. The clean and porous concrete deck can be pre-slopped with a bonded polymer modified mortar. The waterproof membrane should transition up the side of the building at least 3″ above the intended tile finish surface.

      A wire reinforced mortar bed can be installed over it to the intended height maintaining the slope. You can install a bonded mortar bed on some primary waterproof membranes if recommended. A secondary tile waterproof membrane should be applied over the mortar bed and tied into or transitioned up the building wall perimeters. The tile is then bonded directly to the secondary waterproof membrane with caulked movement joints and perimeter joints using an ASTM C920 sealant e.g. silicone or polyurethane.

      If the deck is structurally sound and the tile is well bonded to its substrate and you do have an existing slope on the tile surface so it can adequately drain, then there is a possible repair that can work in some cases. There is no industry standard for it and it is not a normal recommended repair process, but we have done this type of repair on projects successfully; if it is done correctly….which is a big if….

      You can cut out all of the grout out of the grout joints that need to be at least 1/8″ wide or wider. Clean the joints out and let them dry. Fill the joints with an ASTM C920 traffic grade sealant; normally polyurethane. Tool the joint so there is a slight recess so footwear does not come into contact with it. Make sure all perimeters are waterproofed and caulked so no water can get into the tile deck assembly. This is assuming that your tile is impervious and doesn’t absorb water. This should be considered experimental. In theory, if the tile is impervious, and the sealant is installed correctly to be a water tight joint, and all transitions and perimeters are water tight so no water can get into the tile deck assembly then you have a water tight deck. Plus every grout joint becomes a movement joint to mitigate potential movement stresses.

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