Things You'll Need
Grinder (if needed)
Drill with paddle bit
Concrete mix (no aggregate)
Triangular hand trowel
Metal hand concrete float
Sponge hand concrete float
Vertical concrete surfaces, whether they be interior or exterior walls, columns or in any other form, need to be resurfaced periodically to maintain their structural integrity. The surface of the concrete is what prevents the elements from penetrating and destroying the interior. Resurfacing vertical concrete surfaces is a surprisingly easy thing to do; however, it takes some practice and concentration to create a new surface that looks good and provides adequate and long-lasting protection.
Fill one bucket with water and wipe the wall down with a sponge to clean off any dirt or dust.
Using a wire brush, clean out any cracks and crevices. If necessary, use a grinder to remove any bits of old finish or concrete as well as you can. Wipe the wall down again.
Mix a batch of concrete in your other bucket using a drill with a paddle bit. You do not want any aggregate stone in your mix, as might be used in other concrete applications. Keep the consistency of the concrete to that of pancake batter.
Wipe an area of the wall where you will begin working with a damp sponge. Scoop out half a hand trowel of your concrete mix and place it on the flat side of the concrete float (holding it upside down like a tray). Quickly bring the flat of the float onto the surface of the wall so it is holding the concrete to the vertical concrete surface. Holding the float at a 45-degree angle, smooth the concrete onto the surface in an arc. You will want the coating of new concrete to be about an 1/8" thick. Repeat this step until you have covered the entire area that you wiped with the sponge.
Watch for the new concrete to begin to become evenly lighter in color. When it is no longer a dark grey but a pale grey, dip your sponge float in the water bucket and very gently touch it to the surface and begin rubbing the flat of the sponge in circles. You will begin to see a textured finish appear on the concrete. Continue doing this until the entire area is evenly textured. Then go back to Step 4 and resurface a new area of the vertical concrete surface.
Make sure that you are neither applying the new concrete finish in direct sunlight (for example, at high noon) nor in too much shade; either condition will make it difficult to tell when your concrete is ready to be sponge finished.
Do not apply the new concrete onto the old concrete without first wetting the surface. Without that small amount of moisture, your finish will not adhere properly and will crack and fall off.