Slab foundation building in Tacoma WA - a level floor on firm, packed ground

Maybe you're putting up a house, an addition or a shop, and a slab came up because it's the simpler way to go. What moves the price is how much digging and packing it takes to get your ground level and firm, the size and thickness of the slab, and what goes under and around it. The schedule turns on the weather around pour day, any soils report you're still waiting on and the curing wait before framing can start. Your written estimate gives you the figure for your own lot. We're based in Tacoma and work in the cities around it in Pierce County and south King County, so if you're not sure we come out your way, just ask.

First I check whether the lot is level enough for a slab at all, and if you have a soils report, we build the plan around it instead of guessing. I also look at where water runs on the lot so it heads away from the slab and not under it. Then our crew digs the soft topsoil out down to firm ground and packs the base in layers, because a base that's only raked level settles with the dirt and takes the slab with it. We clear out rocks and debris, set the forms and tie in rebar, the steel inside the slab that holds the concrete together if it does crack. We plan the pour away from the hottest part of the day so the top doesn't end up weak and dusty, and we cut control joints, shallow grooves that give the slab a straight line to crack along, before it's had a chance to crack on its own. After that it cures, which is the slow hardening that sets how strong it gets. If a budget has to give somewhere, I'd rather trim the finish than the base, because nobody sees the base on day one but it decides how your slab holds up for years.

A slab is one of several ways to put a building on the ground, and when your lot or plans point another way, foundation installation covers foundations built on walls and footings. Property owners putting up a shop or rental on a slab often need room for vehicles too, and concrete parking lot building is flatwork, our word for concrete laid flat on the ground, that starts with the same kind of packed base.

Pierce County's design criteria set the frost depth at 12 inches below grade for all low-land areas, which is how deep the ground is counted on to freeze, and the slab design has to account for it. The same criteria assume a default soil bearing value, meaning how much weight the ground is counted on to carry, unless a licensed geotechnical engineer gives you a soils report. When you have one, that report takes the place of the county's default in the design, so we build the plan around it. If you don't have one, I'll tell you what the default means for your slab.

What we see most on jobs around here is ground that stays wet for months and lots that are rarely as flat as they look, so I check how much the lot falls before we talk about a slab. We run into the same thing on jobs in Lakewood and Parkland.