The Right Way

• In the perfect scenario, a concrete patio is poured so that it slopes gently away from your home. This naturally directs water both away from the house and off the patio. In areas of high rainfall it may be necessary to install a drain at the lowest edge of the patio so that water drains off and away from the patio. In cases where the grade doesn't allow for the proper sloping of concrete a drain may be installed in the middle of the patio to catch and redirect any standing water.
  
  

The Problems

• Problems such as improper slope or no slope at all can begin with the pouring of the concrete. But the problems may not end there. It is not uncommon to see improper or inadequate drainage, such as drain pipes that are too small for the amount of water they must move, drain pipes that flow uphill or do not have enough drop to move water fast enough. A patio may have no drains at all, or the drain may may be clogged with leaves, grass or other debris. Sometimes a drain line may be shared with a driveway drain, downspouts or another drainage source.
  
  

What Happens

• With any of these problems the first symptom is almost always standing water. In the mildest cases that's as far as it goes. It doesn't look the best, and it might attract bugs, but no long-term damage is done. In worst cases, the water may run against the house, causing mold or rot. It might even seep into the house. Drains can also back up, and when a drain pipe is shared with another runoff source, the backed-up water can be downright disgusting and unsanitary.
  
  Further, cement expands and contracts with temperature changes. If expansion joints are not installed to support the true amount of water that the patio will be exposed to, freezing and thawing could cause the patio to crack.
  
  

Repairs

• Some patio drainage problems, even serious ones, can be fixed in simple ways. Drains can be unplugged with long pipe snakes, and drain pipes that are undersized or overshared can be dug up, replaced and split into individual runs. The expensive and more involved repairs come when there is no drain at all, or the slope of the patio is very incorrect. This generally requires cutting a portion of the patio away with a concrete saw to install a drain or possibly removing the entire patio and repouring it.