Drainage pooling: repair options

Water pooling on a paver patio is a path problem. The water is arriving faster than it can leave, or it has no outlet at all. The repair is to give it one: regrade to a 2 percent slope, cut in a channel drain at the low edge, or install a French drain where the subgrade holds water.

Why pooling happens

There are four common causes, and they are often present together. A patio can have a wrong slope, a blocked outlet and a soft subgrade at once, which is why a single fix sometimes does not solve the puddle.

The first is a slope that runs toward the house or toward a wall, so the water has nowhere to go. The second is a blocked or missing outlet at the low edge.

The third is a settled low spot, where the base has consolidated and created a bowl. The fourth is a subgrade that does not drain, such as clay, which holds water under the base until it rises.

Each has a different repair, so the diagnosis comes before the quote.

Repair options

The cheapest fixes are often the last two, which is why it is worth checking the outlet and the downspouts before pricing a regrade.

Regrading the surface

A regrade means lifting the pavers in the affected area, correcting the bedding depth, and relaying so the surface falls away from the house.

The target is 2 percent, or a quarter inch per foot. On a 10 foot run that is 2.5 inches of fall. Less than that and water sheets slowly and finds the low spots. More than about 4 percent and the pavers can slide on the bedding, so the slope has a practical upper limit.

A regrade is a partial rebuild. If the base is sound, it is a bedding correction; if the base is soft, it becomes base repair at $4 to $8 per square foot. On a 200 square foot patio at $6, the base portion alone is 200 × $6 = $1,200.

Channel drains

A linear channel drain at the low edge catches water before it pools. It is set in a concrete surround, connected to an outlet, and covered with a grate.

It is the right answer where the patio meets a wall or a door and the water has nowhere else to go. A channel across the garage door apron is the same principle.

The drain has to discharge somewhere. A channel that ends in soil is a channel that fills with silt.

French drains and gravel trenches

Where the subgrade holds water, a French drain intercepts it before it reaches the patio. A perforated pipe in a gravel trench, wrapped in geotextile, carries water to a lower outlet.

A simpler version is a gravel-filled trench at the patio edge, which gives surface water somewhere to disappear. It works on free-draining soil and fails on clay. The test is simple: dig a 12 inch hole beside the patio, fill it with water, and see whether it drains within a few hours.

Both are quoted per linear foot and depend on the depth and the outlet.

Repairing a settled low spot

If the water pools in a bowl rather than along an edge, the base under that area has consolidated. Lifting and re-bedding without correcting the base produces the same bowl in a season.

The repair is to lift the pavers, remove the bedding, recompact or rebuild the base, and relay to the correct slope. That is the $4 to $8 per square foot base repair.

On a 200 square foot patio at $6, that is 200 × $6 = $1,200. Sealing afterward at $2 per square foot adds 200 × $2 = $400.

What not to do

Do not drill holes in the pavers to let water through. It creates a point inlet that erodes the bedding and does nothing for the volume of water.

Do not add sand to the low spot. It washes out and takes the joint fill with it.

Do not slope the patio toward the house to avoid a drain. Water against the foundation is a much larger repair than a channel drain.

Do not seal a patio that pools. The sealer slows absorption, which sounds helpful, but it also slows drying, and the water sits on the surface longer. Fix the drainage first, then seal.

How to diagnose the cause

1. Watch the patio during rain and note where the water first stands.
2. Check the slope with a level in two directions.
3. Look for an outlet at the low edge and confirm it is clear.
4. Check the downspouts and confirm they discharge past the patio.
5. Lift one paver in the low area and inspect the bedding.
6. Test whether water drains from a hole dug beside the patio.

For the cost detail, read drainage pooling cost. For prevention, see drainage pooling prevention, and for the early signs, check drainage pooling warning signs.