Littleton Concrete Pools

There's a valve in the floor of a properly built concrete pool that most owners never think about, right up to the afternoon it keeps their pool in the ground. It's a one-way relief valve, and its whole job is letting water that has collected under the shell come inside rather than pushing up on eleven tons of concrete from below.

That valve exists because a pool is a boat parked in dirt. Full of water it's heavy enough to stay put. Empty, in wet ground, it becomes something that wants to float. Everything we do below the finished surface, from where the excavation stops to how the backfill drains, is about the ground and water underneath. Littleton hands us two very different versions of that ground depending on which side of town you're on.

Water under a shell is the whole design problem

Concrete doesn't mind being wet. What it minds is being asked to hold back pressure it wasn't designed for. Groundwater collecting outside a shell pushes inward on the walls and upward on the floor, and if the pool is empty at the time, nothing is pushing back. That's how shells crack, and in bad cases how they lift.

So we build the escape routes. A gravel drainage layer under the floor, a relief valve set at the low point, and sometimes a perimeter drain running to daylight when the lot allows it. On a sloped Ken Caryl property, daylight is often available and we take it. On flatter ground around Columbine, a sump or a dry well may do the same job.

Which is also why we tell you never to drain your pool because it looks dirty. If it has to come down for repairs, that happens with a plan, with the valve pulled, and preferably in a dry stretch. A pool is safest full.

What the excavation turns up around Littleton

The nicest hole I ever dug was in rock. Took two days longer and cost more, and I'd take it every time over a soft one, because nothing under that shell is ever going to move.

What the crew sees on site

Getting concrete into the hole, and when to do it

Two ways to build the shell. Shotcrete is sprayed at high velocity onto the steel cage from inside the excavation, which means the earth itself acts as the outside form and the crew can shape a curved wall, a bench, or a sun ledge freehand. Cast-in-place means building forms on both faces and placing concrete between them, and it makes sense for straight walls, tanks, and elements we want formed to a hard line. Most residential pools around here are shot, because the shapes people want are not rectangles and because there's no practical way to form the back of a wall against a dirt bank.

Either way, curing is where the shell is won. We keep water on it, repeatedly, for a solid week. High-altitude air in June will pull moisture out of fresh concrete faster than the crew can hose it back in, and a shell that dries out early is a more porous shell for the rest of its life.

On timing, breaking ground in late summer or early fall is a good play if you want to swim the following season. The shell and the deck go in before the weather turns, the interior finish and startup wait for spring, and you're not standing in a construction site in June wondering why nothing's done.