Concrete in Anchorage fails from below. Water in the ground freezes, the ground lifts, and the slab goes with it. Nearly every question on this page is about keeping water away from the soil under a slab.
Do I need to worry about drainage when I pour concrete?
Yes. Drainage is the first thing to plan here. A slab sheds all the water that lands on it, plus the snow piled along its edges when that melts. If that water soaks into the ground next to the slab, it freezes there the next winter and lifts the edge. Every slab needs a slope and a place for the water to go.
My patio or driveway slopes toward the house. Can it be fixed?
A slab that slopes toward the house should be fixed, because breakup sends weeks of meltwater to the foundation. Sometimes a channel drain cut in near the house, with a pipe to daylight, is enough. If the fall is strong, the panels nearest the house are replaced with the slope reversed. Lifting the house side with foam can work on a slab that has simply settled.
What causes glaciation on a driveway?
Glaciation is ice that builds up in layers where water keeps seeping onto a cold surface, from a hillside spring, a sump outlet or a roof drain. It is common on Hillside lots. The answer is to catch the water before it reaches the slab, with a ditch, a buried drain below frost or a rerouted outlet.
Can tree roots crack or lift concrete?
Yes, tree roots can lift concrete. Birch, cottonwood and spruce in Anchorage root shallowly, because the soil below is cold. Those roots thicken under a slab and raise it, and cottonwood is the worst for this. Roots also draw a path for water. A lifted panel beside a big tree is usually the tree and frost working together.
Can I fix the concrete and keep the tree?
Often you can keep the tree. We can curve the walk away from the trunk, bridge over a root with a thicker reinforced panel, or use separate pads that can be reset. Cutting large roots close to the trunk can weaken the tree against wind, so we avoid it. For a valued tree, an arborist should say which roots can go.
My neighbor's new concrete sends runoff onto my property. What can I do?
Start with a calm talk and photos taken during melt or rain. As a general rule, a property owner should not change grading so that runoff is concentrated onto the lot next door. If talking fails, ask the municipality whether a drainage or grading rule was broken, and consider legal advice. On your side, a swale or drain along the line can carry the water to the street.
Does clay or soft soil change the job?
Yes, a great deal. Parts of west Anchorage sit over the soft Bootlegger Cove clay. Low areas across the bowl hold peat, and silt is common everywhere. All of them hold water. Peat also compresses under load. For flat work the usual answer is to dig the soft soil out to firm ground and replace it with compacted gravel. For buildings on deep peat or soft clay, an engineer should be involved.
My gravel driveway turns to mud at breakup. Will concrete solve it?
A gravel driveway turns to mud because the fines in it hold meltwater while the ground below is still frozen. Concrete will solve the mud, but only if the muddy layer is removed first and clean gravel goes in. Pouring on top of the old muddy gravel just moves the problem under the slab, where it will heave.
My patio was poured over an old trench and it settled. Why?
The fill in the trench was never compacted. Water, sewer and gas trenches are often backfilled loosely, and the soil settles for years, faster after an earthquake. The patio above bends and cracks along the line of the trench. The fix is to remove that strip, compact the fill in layers and pour it again, or lift it with foam if the slab is unbroken.
My lot floods or ponds in spring. Should I raise the slab?
Raising the slab on a thicker gravel pad helps on a lot that ponds, and it keeps the base drier. It does not replace giving the water an outlet. Lots near Campbell Creek, Chester Creek and other streams may be in a mapped flood hazard area, where the municipality has rules on fill and building. We check that before raising anything.
Do earthquakes damage driveways and patios?
They can. Strong shaking, like the magnitude 7.1 earthquake in November 2018, cracks slabs and settles loose fill, which then shows up as sunken panels. Flat work is not designed like a building, but good practice helps: a compacted base, steel in the slab and isolation joints so the slab can move apart from the house.
The only real price is one written after we have seen the site. Call (907) 331-4363 or text us a photo of the area to set up a free on-site estimate.