A liquid concrete overlay is made to cover the surface of old concrete and fill in cracks or chips. It is also thin enough to level itself out without you having to smooth it over with a trowel. Also referred to as a self-levelling compound, a liquid overlay takes away the work of levelling the surface, but it does require you to work at a quicker pace to keep the surface from drying out before you finish.
Dig a trench around the concrete surface if it's outside. Go down to the bottom edge of the concrete. Level out the trench. Place a level in the trench to check your progress.
Measure the width and length of the concrete as well as the thickness. Use boards that are at least 1/4 inch wider than the thickness.
Measure the boards and mark them with the length and width dimensions. Cut the boards with a circular saw.
Put the boards together at right angles to build a frame. Use screws to hold the ends together and then set the frame around the concrete surface. If your concrete surface is inside with walls around it, you do not need to build a frame; however if the 1/4-inch addition to the floor will cause it to spill out the door, you need to anchor a thin metal strip across the doorway to hold the overlay.
Mix up six buckets of liquid overlay according to manufacturer's instructions. It dries quickly, especially along the edges of the pour, so you must have helpers constantly pouring until you are done.
Get two helpers to start pouring while you mix up more for when they bring back empty buckets. The helpers should alternate pouring so that someone is still pouring when the other brings back an empty bucket. Have exact measuring scoops on hand so you do not have to think about the process.
Wait to mix new buckets until they are on their fourth pour, so you can see if you really need to make more. If they have filled over half the surface, then mix one more and wait a little longer.
After about 12 hours, spray the concrete overlay with a sprinkling of water and lay plastic sheets over it. Repeat each day for a week. Do not walk on it for two days.