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Old 06-18-2010, 11:00 AM   #1
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Concrete Patio drainage issues

I have a new raised patio that appears to be causing water to be forced against my basement and water is coming into the basement via cracks in the foundation wall.

The retaining wall built was filled with AB3 and fabric to keep the AB3 inside the wall. It is sloped away from the house (3" drop), except in the one section I note. The blocks used in the retaining wall were glued together. It's not water tight, but water does appear to have a difficult time "weeping" through it.

I had two engineers look at my patio to give me ideas on what issues might be causing the problems. Here is generally what they said.
(1) not pouring the concrete patio over the retaining wall as opposed to butting up to it which leaves a seem so water can get into the retaining wall.
(2) not using a better draining filler such as "clean gravel" as opposed to all AB3 which will retain water.
(3) not adequatly slopping in spots
(4) under ground conduits that might be directing water back to the house, because of the AB3 or concrete?
(5) not water proofing the foundation or draining the filler properly by the foundation.
generally, their concerns were with drainage both on the patio and in the AB3, and use of only AB3..
I've prepared a diagram of the (4) trouble areas and labeled them as Sec1 thru Sec4 with some pictures to help describe what is happening (patio_diag). The blue dotted lines is the general water flow that the engineers looked at with a house to see the direction water travels on the patio.

I also have more detail and pictures but I'm having trouble uploading them at the moment.

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Concrete Patio drainage issues-patio_diag.jpg  
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Old 06-19-2010, 06:02 AM   #2
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Is there a question? Not sure how anyone can really tell what the problem really is as the engineers' thoughts all are possible. I guess you could try the cheapest and easiest solution first and see what happens.
Does this patio have a roof? Have you addressed water drainage from gutter downspouts? How about yard slope away from the patio?
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Old 06-19-2010, 06:57 AM   #3
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whoever installed the patio shouldda made certain to slope it AWAY from the house,,, forget the engineers - find a retired guy who knows why water runs downhill & how to properly waterproof conc block,,, otoh, if you've already pd TWO engineers, hire a pro waterproofer

doesn't matter what base was used,,, btw, foundation walls are NOT supposed to have cracks
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Old 06-20-2010, 09:49 AM   #4
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So long as water on the patio slab flows towards the house, you must provide a way (possibly a pit with sump pump) to quickly drain practically all the water that ponds up against the house and get that water away from the house. Or roof the patio so rain doesn't get on it.

If you correcct the patio slope by putting a skim coat of concrete on it, water must not be permitted to pond elsewhere on the patio. Otherwise the water will seep between the skim coat and original slab and make its way to the foundation anyway.
Stick to your lawn watering schedule until it really pours. Otherwise the storm might miss and the part that gets watered last (3 days away?) will dry up.

Last edited by AllanJ; 06-20-2010 at 09:56 AM.
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