What do you do if it rains while pouring a concrete floor?

Q. What about rain during a pour? Heavy/light, need to cover etc.?

A. If it rains while you are pouring a concrete floor it is very important to cover the fresh concrete as fast as you can with a tarp or some plastic.

If left uncovered the rain will begin to wash away the cement paste on the surface of the floor and eventually expose the aggregates just beneath the surface.

Even a quick five minute shower on the freshly poured concrete will increase the water cement ratio at the surface enough to weaken it causing craze cracking (cracks that look like a spider web), dusting, and eventually surface delamination.

If you do get caught in the rain. Cover the floor as fast as you can. Wait for it to stop raining, uncover the concrete and let the surface dry completely, don't work the surface water into the surface of the concrete. You may need to squeegee the water off to speed up the process.

If the concrete hasn't set up too much, you can power trowel the surface and begin to finish the concrete as you would before it rained.

If it rained too long and the concrete is too hard to power trowel, you will have to grind the surface and apply a concrete overlay to get a smooth finish.