What Is Wind Checking?

Wind checking is the most preventable concrete failure I see, and it’s also one of the most common — because most homeowners don’t know to watch for it and a lot of contractors don’t know how to prevent it.

Here’s what it is: the top of the slab dries and crusts over while the bottom is still wet and unset. From the outside, the surface looks finished. You float it, you trowel it, you walk away thinking the pour went well. But under that crust, the concrete hasn’t bonded right. The whole slab is weaker than it should be, and within a year or two the surface starts scaling, flaking, or spalling off.

Why “wind” checking?

Wind is the most common cause. When dry wind moves across a fresh pour, it pulls moisture out of the surface faster than the slab can pull moisture up from below. The top loses water and crusts. The bottom doesn’t get the moisture exchange it needs. That’s the “check” — a mismatch in cure rate between the top and the body of the slab.

Wind isn’t the only cause though. Hot sun does it. Low humidity does it. Pouring later in the day on a warm afternoon does it. Anything that pulls moisture out of the surface too fast.

How to spot it during the pour

When I’m finishing a slab and I get this funny look wondering what’s going on, that’s wind checking starting. The float doesn’t bring water up the way it should. The surface feels like it’s already set even though it’s been minutes since I screeded. That’s the moment a contractor with experience knows to slow down, wet down, or send the truck back if it’s really gone bad.

You as a homeowner aren’t going to spot this. By the time it’s visible at the surface, the pour is done. What you CAN do is ask your contractor before the pour what their plan is if it’s a dry, windy, or hot day. Real answers include:

• Pour early morning or late afternoon, not midday
• Pre-soak the subgrade so it doesn’t pull water out of the bottom of the slab
• Use evaporation retarder (it’s a sprayable product that slows surface drying)
• Have enough crew on site to finish faster than the surface dries
• If conditions are too bad, reschedule the pour. Real contractors do this and don’t apologize for it.

How to spot it after the fact

If your driveway, sidewalk, or patio is showing any of these after the first year — and the contractor swears the slab was fine — wind checking during the pour is one of the likely causes:

• Scaling: the top layer is flaking off in thin sheets, exposing the aggregate underneath
• Spalling: chunks the size of a quarter popping off the surface, especially after winter
• Surface dust:if you can rub the surface and powder comes off, the top didn’t cure properly
• Crazing: a network of fine hairline cracks that look like cracked porcelain

None of these are normal wear. They’re symptoms of a slab that wasn’t cured right at the surface. Sometimes it’s salvageable with a resurfacing product. Sometimes the slab needs to come out and be repoured. Hard to tell without looking at it.