Fixing sunken or cracked concrete in Boise

Not every cracked or sunken slab needs to be torn out. Sometimes lifting it or sealing the cracks buys years for much less.

Why slabs sink and crack

• Washed-out base. Downspouts or sprinklers wash soil from under the slab.
• Freeze and thaw. Treasure Valley winters freeze water in cracks, which pushes them wider.
• Tree roots. Roots lift one side.
• Poor fill. Loose fill near a new house settles over the first years.

Lifting a slab

Two common ways:

• Mudjacking. A cement slurry is pumped under the slab through holes. Heavier, larger holes.
• Foam lifting. Light foam is injected through small holes. Sets fast.

Lifting works best on slabs that are sunken but mostly in one piece.

When to replace instead

• Many broken pieces
• Crumbling or flaking surface across large areas
• Heaving from roots that will keep growing
• A slab that slopes toward the house and cannot be lifted enough

Small cracks

Hairline cracks are normal. Cleaning and sealing them with a flexible filler keeps water out. Seal joints before winter.

Fix the water

Lifting or patching will not last if water keeps washing out the base. Extend downspouts away from the slab and aim sprinklers off the concrete.

Trip hazards

A raised edge on a sidewalk can trip someone. Repairs to a public sidewalk can fall on the owner next to it. Ask the city about rules and permits before work on one.

On the quote

• Method and number of holes
• How holes are patched
• Joint sealing included or not
• What happens if it settles again

Timing

Lifting and crack sealing need dry weather above freezing. Plan for spring through fall in the Treasure Valley.