Can I make my entire patio into a drain?
June 9, 2010 7:34 PM Subscribe
Insane in the membrane? Can I turn my entire concrete patio into a drain?
posted by Izzy to home & garden (13 answers total) 1 user marked this as a favorite
When we purchased our house last year, the previous owner mentioned that during prolonged periods of rain the below-grade slab beneath the house (garage, basement) becomes “damp.” We had just such a period this spring, and damp = about three inches of water.
Our house is surrounded on three sides by typical California concrete hardscaped patio, backed by concrete block retaining walls (house is set into a small hill). I believe rain water is entering through two locations: (1) at the concrete block foundation-concrete patio interface, and (2) through several hairline cracks in the patio slab. I do not believe that there is a significant amount of water coming into through the foundation from the hill at the back of the house, as there’s hardpan clay after a foot or so of friable soil: I am not a hydrologist, so I may be completely misguided about this.
When the house was built, the concrete patio was engineered so that water flows away from the house, with a half-step down between the back of the house and each side. Water is meant to run off the back of the patio to the sides, emptying off the side of the patio to the street, but after almost six decades of seismic activity some of the slab has receded an inch or so here and there, and now about an inch of water collects near the foundation when it rains, rather than pouring off the front of the patio (most water does pour of the front).
I want to keep the water out of our basement, but do not want to resort to water proofing the entire foundation (expensive), or sawing concrete and installing drains (less expensive). I want to know if the following idea makes sense as less expensive solution that leaves the existing concrete intact.
1. Pour a thin layer of pebble gravel on the patio and grade so that it slopes away from the house, using a level. This will repair the minor grading problem.
2. Lay a flexible, waterproof fabric over the gravel, coving the fabric up the side of the concrete block of the foundation.
3. Paint the fabric with impermeable membrane coating. At this point, the patio should be waterproof, and the foundation-patio interface protected.
4. For aesthetics, pour another thin layer of gravel over the membrane, and then add a low lying deck to protect and cover the gravel (we wanted to hide the concrete anyway).
I picture this as turning the entire patio into a drain, with the fabric/membrane coved up the sides of the concrete block on three sides, like a bath tub or shallow swimming pool. The gravel-covered concrete would angle toward the street, and will no longer leak.