Paver Patio Drainage Problem - Annapolis

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  • slowpoke

    Ultimate Member
    Feb 2, 2011
    1,114
    Annapolis
    I've got a large paver patio behind the house under a second story deck. It's about 7 years old.

    The patio stays wet days after rain, and I've got a bumper crop of moss growing on it. It has become progressively worse the past couple of years.

    I suspect the installer somehow screwed up the foundation drainage.

    What I think needs to happen is taking it apart, and either finding what's blocking the drains or worst case a whole-scale rebuild.

    It's a more complex project than just a redoing the paver patio. Any recommendations for someone to give me an assessment?

    Thanks
     

    E.Shell

    Ultimate Member
    Feb 5, 2007
    10,242
    Mid-Merlind
    Are there actual drains?

    We have a lot of brick pavers done and they are all "sand set" with no real provision for drainage other than a planned minimum slope to drain off surface water. Sand set pavers are placed on a bed of leveled, compacted sand, then sand is brushed between the stones to fill the gaps. Makes a pretty decent surface, but it is not going to pass water in any substantial amounts.

    Some pavers are set with mortar on a concrete slab, which definitely doesn't drain through and would also rely on a correct slope for positive drainage.
     

    Archeryrob

    Undecided on a great many things
    Mar 7, 2013
    3,064
    Washington Co. - Fairplay
    I would check it with a level, or maybe a string level, and see if you have low spots. Its quite possible something undermined the pavers and made it sink in the middle.

    Once you get it graded make sure it is set with polymetric sand and watered to set. Once graded to run off water the polymetric sand will be water tight and run the water away from the house. I did this and it locks the pavers water tight and water runs away with proper grading.

    Spray the pavers now with simple straight white vinegar and it will kill the moss. It will turn brown in a couple days and you can brush it out.
     

    slowpoke

    Ultimate Member
    Feb 2, 2011
    1,114
    Annapolis
    No drains in the patio, I'm referring to the drainage pipes that run below the pavers that eventually daylight down the hill at the the back of the yard.

    No slab under the pavers.
     

    Boxcab

    MSI EM
    MDS Supporter
    Feb 22, 2007
    7,865
    AA County
    Keep an eye on the corrugated pipe that most use for drainage. The safest place for it is under the pavers, where load is distributed... as long as the tamping of the crusher stone and the worker's foot traffic did not compromise it. Once the corrugated stuff gets out into the open... without a ridged cover, all bets are off. It will eventually collapse, if it has not already. If they used the perforated stuff, did they put a sediment sock on it to keep dirt and other fines out? How deep did they put it? How close are your trees... they are always looking for a sub-surface water source? I'm a firm believer in the non-flex PVC pipe. Glue the joints to keep roots out and bury it about 24 inches down. Dirt can not find its way in along the run, and if you ever want to clean it out, the smooth surface facilitates that.

    I am no expert, but I have been chasing down spout and other drainage problems for awhile. I'm currently digging up old corrugated pipe (some only 4 inches below surface, collapsed, root infested and silted full of krap) and replacing with 4" PVC.




    .
     

    E.Shell

    Ultimate Member
    Feb 5, 2007
    10,242
    Mid-Merlind
    No drains in the patio, I'm referring to the drainage pipes that run below the pavers that eventually daylight down the hill at the the back of the yard.

    No slab under the pavers.
    The exterior drain tiles that surround your footing and lead to daylight are not specifically designed to remove water from your patio area. The foundation drains are in place to prevent hydrostatic pressure against the foundation of the house. Nothing more, nothing less.

    The patio surface should drain on its own with a certain minimum amount of fall (1/8" per foot) out away from the house.

    Sounds like the surface under the pavers may not have been fully compacted prior to placing the pavers and settlement over time has cause a negative fall condition, causing the trapped water. If the exterior drains were not properly bedded in gravel and wrapped in filter cloth, they may have become prematurely inundated with soil and thus unable to drain. This soil could have come from under the patio and cause it to sag back toward the house as well.

    As Boxcab posts above, there is also the possibility that the exterior draintile piping has collapsed.

    Even so, this hypothetical "failed draintile" situation would not cause the patio to hold water. Even if there were no foundations drains at all, a correctly installed patio should successfully "gravity drain" away from the house.
     

    BrewDoc_MD

    Piss off, ghost!
    Apr 25, 2012
    633
    Myersville, MD
    I'm having similar issues with a large stone patio in out back yard. it goes from a large retaining wall all the way to the house. storms of any size generate a lot of water that flows through/around the retaining wall, over the stones, and ultimately towards my basement. my sump pump runs for 12-24 hrs after storms just pumping out that extra water. not sure how old that patio is (bought the house last year), but definitely has low spots and the way it was sloped , it goes right towards the house. terrible.

    I'm planning to dig up part of that patio patio myself and install a french drain system to redirect the surface water around our house towards the front yard. Miss Utility came out last week and gave me the green light to dig. My Dad recommends a dry well or similar outdoor sump pump....less digging. But i think the French Drain is a more permanent fix.
     

    Aventus

    Banned
    BANNED!!!
    Sep 5, 2016
    778
    No drains in the patio, I'm referring to the drainage pipes that run below the pavers that eventually daylight down the hill at the the back of the yard.

    No slab under the pavers.

    If properly installed, the drain tile would be running parallel and at the same elevation as the footers. For Maryland, the frost line is 30" so the footers must also be below the frost line. I seriously doubt the paver installation would have affected the drain tile 30" below grade.

    Under a deck, little sun, massive amount of rain this year, is the perfect environment for moss. If the pavers were installed relatively flat (even with a proper slope away from the house) will keep an area sufficiently wet for some time.

    I have to clean moss and mold off my home every year. It's a b!t@# but there's not much I can do to prevent it. The photo is an area on my house which gets little sun and was cleaned this spring. This spot is 6 feet above grade where a brick ledge meets the EFIS. I'm so tired of having it cleaned that I'm thinking of leaving it and calling it an architectural charm.

    ZDa1KOC.jpg
     

    Shamr0ck

    Ultimate Member
    Aug 6, 2011
    2,505
    Frederick
    WHBoyer did a fantastic job for me last summer with a drainage and hardscape project. Paver patio beneath a 15x30 deck and includes separate sitting area/wall, large bluestone steps and a dry stream bed/ground inlets and piping to control the run off entering the property from above.

    Fair price, great service after the project and they will do more work for me as we renovate my mothers house for sale.

    PM me if you’d like the designers reach information.


    Sent from my iPad using Tapatalk
     

    Archeryrob

    Undecided on a great many things
    Mar 7, 2013
    3,064
    Washington Co. - Fairplay
    When we bought our house it had wet basement walls, It is built into a hill and they had it graded, hard surface toward the house. Plus over flowing gutters causing an undermined hole under the deck. I tore it all out and regarded and concrete patio graded away from the house. Went to emptying a dehumidifier every day to it not even running ever.

    Just spray that moss with 5% white Vinegar heavily. It will die on its own and brown up. Let it sit for a while and should come right off. I get algea on my concrete where the sun never hits it and vinegar kills it easily, no scrubbing.
     

    jrumann59

    DILLIGAF
    MDS Supporter
    Feb 17, 2011
    14,024
    I doubt your patio is holding water I think that the fact it is under the Deck and does not get a lot of sun is the reason the moss is so prominent. With the polymeric sand if you had standing water you would know it.
     

    slowpoke

    Ultimate Member
    Feb 2, 2011
    1,114
    Annapolis
    Appreciate everyone's comments. I'm apparently not alone.

    My patio is 90% covered by the deck, plus north facing, so it's shade city.

    I am not getting standing water - and no water at all in the walkout basement - just the damp pavers.

    So while I need to check the grade, I am probably going to suit up to kill mold with bleach and/or vinegar and pressure washing every year.
     

    Archeryrob

    Undecided on a great many things
    Mar 7, 2013
    3,064
    Washington Co. - Fairplay
    Take it easy with the pressure washer!!!!!!!!!!!!! Even polymetric sand can be forced loose. Regular sand will wash right out under that pressure. I have seen many paver patios ruined with power washers undermining the sand. Saw a mexican guy do it on a commercial building and it looked bad!!

    Spray with Vinegar or diluted bleach and let it die. The use a stuff broom and maybe a regular hose only. The wet pavers is normal in "The year it never stops raining" ;) I killed algea once already this year on the north side of my patio in the shade and it needs it again as it doesn't dry out enough. Vinegar and bleach are cheap, just don't spray in your eyes.
     

    antco

    Ultimate Member
    Apr 28, 2010
    7,044
    Calvert, MD
    Up here in the land of constant wet (Seattle), there are moss killing and moss preventing products at every hardware store. You can likely find something on Amazon. Most of the liquid products contain a lot of iron. It’s great for greening your grass, but can potentially stain any hard surface. Read the labels.
     

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