Why Drainage Is the Most Important Part of Any Concrete or Hardscape Project

If we could get homeowners to care about one invisible thing, it would be this.

The Puget Sound region gets somewhere around three feet of rain a year, most of it between October and April, much of it as steady soaking rain rather than downpours. A lot of our soil is glacial till and clay, dense material that drains slowly and holds water.

Rain that can't drain goes somewhere. Usually it goes under whatever you just paid to have built.

What water actually does

Under a slab, moving water carries away the fine material in the base. That leaves voids. Concrete is strong in compression but weak in bending, so a slab spanning a void cracks. Then water enters the crack, and in a freeze-thaw cycle it expands and widens it. That's how a five-year-old driveway starts looking like a twenty-year-old one.

Behind a retaining wall, saturated soil is dramatically heavier than dry soil and exerts hydrostatic pressure against the back of the wall. Retaining walls almost never fail because the blocks were weak. They fail because water built up behind them and pushed. A wall without drainage behind it is a wall on a countdown.

Against a foundation, water that pools next to the house finds its way in, and you're into a much more expensive category of problem.

Under pavers, washed-out bedding sand produces the sunken, uneven patio that people assume was just “settling.”

What proper drainage looks like

It isn't complicated, but it takes time and material that don't show up in the finished photo:

• Slope, deliberately. Hard surfaces should shed water away from structures, generally around a quarter-inch of fall per foot. This is decided before anything is poured.
• A free-draining base. Compacted crushed rock that lets water move through rather than sit.
• Drainage behind walls. Clean gravel backfill and perforated pipe, so water is collected and carried off rather than pushing.
• Somewhere for it to go. A French drain or pipe run that actually daylights somewhere sensible. Drainage that dead-ends just moves the problem.
• Geotextile fabric where needed, to keep soil from migrating into the drainage rock and clogging it.

How to tell if you have a problem now

• Puddles that sit on your patio or driveway for hours after rain stops
• Moss or algae on one area of hardscape but not others
• A retaining wall that leans, bulges, or shows cracked or separating blocks
• Soil or mulch washing across a walkway after storms
• Efflorescence, that white powdery residue on concrete or block, which means water is moving through the material
• A section of yard that stays soft well after the rest has dried

Any of these is worth looking at before it becomes structural.

Why this is the part to ask about

Drainage is the easiest thing for a contractor to skip. It's buried, the customer can't see it, and cutting it makes a bid look sharper. The consequences show up in year three or four, long after the job is closed out.

When you're comparing bids and one is noticeably cheaper, this is often where the difference lives. It's a fair question to ask directly: what are you doing about drainage, and what does the base look like?

Dealing with a drainage problem, or planning a project you want done right the first time? We build for this specific climate. Call (253) 258-9141 or request a free estimate.