HOME IMPROVEMENT : Patching Up Concrete Problems
It’s a good idea to repair damaged concrete as soon as possible. When ignored, small cracks and other damage will soon grow into projects that require much more time and work.
Materials
Patching compounds may be epoxy, latex or mortar. Epoxy or latex patching compounds cost more than patching mortars, but they form a stronger bond, do not require a bonding agent and are self-curing.
For larger jobs, however, epoxy and latex patching compounds tend to be too expensive and dry too fast. Instead, use a standard commercial patching mortar; follow directions on the package.
You can also make your own patching mortar by mixing one part portland cement with three parts sand, then stirring in enough water to form a stiff paste.
Cracks
* Fix hairline and narrow cracks with masonry crack filler, sold in home supply centers. This filler comes in cartridges that you insert in a caulking gun and apply like caulk.
* To fill a wider crack, chip away loose concrete with a hammer and a cold chisel. Holding the chisel at an angle, undercut the crack so that it’s wider at the base than at the surface.
Clear the rubble and chips with a steel brush, shop vacuum, air compressor or hand bellows. Then wash out the crack. The surface to be patched should be damp--not wet--so sponge out any water that remains.
Wear gloves and safety goggles when chiseling, drilling or sledge hammering concrete.
* To improve the bond of the patch, coat the damaged area with a commercial bonding agent or a one-to-one ratio cement-sand grout mixed with water to the consistency of thick paint. Apply the patch while the bonding agent or grout is still wet.
* With a trowel, pack the patch material into the crack and smooth it lightly. When the patch begins to stiffen, finish with a wood float or steel trowel, or brush it to match the adjacent surface. Cure the patch by covering it with wet burlap and keeping it damp for up to seven days. Keep traffic off it during that time.
Broken Concrete
* Break up a badly damaged slab with a sledgehammer. Remove the loosened concrete and clean the exposed surfaces.
* Set up forms made of two-by-four green lumber set on edge and braced with 18-inch stakes driven firmly into the ground. Oil the forms to prevent sticking and dampen the base of the opening.
* Tamp the patching mix in firmly, overfilling slightly to allow for shrinkage. Jab a trowel into the concrete several times to eliminate air pockets.
* Place a board on edge across one end of the form, then work it toward the other with a zigzag sawing motion.
* Fill in low spots and then repeat the sawing motion until the concrete is level with the top of the form. Finish with a wood float or a trowel.
* Cover the slab with wet burlap and keep it damp for at least a week. Keep traffic off the slab.
Step Edges
* If a step edge is broken off, chip away the loose concrete from the crumbling edge with a hammer and a cold chisel. Holding the chisel at an angle, undercut a V-shaped groove in the step edge. Clean and moisten the repair area.
* Make a form board the height of the step and prop it against the step with concrete block.
* Coat the area to be repaired with a bonding agent. Using a trowel, apply patching mortar or an epoxy or latex patching compound.
* Prod the patch with the trowel tip several times to remove air bubbles.
* Use the same trowel to smooth the patch flush with the rest of the step. Run an edger tool between the step and the board to compact the patch.
* Allow about one hour for the patch to set. Then carefully remove the form board and touch up the repair with a trowel.
* Cure the patch by covering it with wet burlap and keeping it damp for up to seven days. Keep traffic off the new edge for a week after curing.
Step Corners
* To rebuild a step corner, chisel away loose concrete and brush off dust and debris from the damaged area.
* Coat the corner with a bonding agent.
* With a trowel, build up the patch material in the shape of the original corner.
* Use the trowel to smooth the patch flush with the rest of the step.
* Tape scrap lumber around the corner.
* When the patch has set, remove the boards and smooth the repaired area. Cover with wet burlap and keep it damp for up to seven days. Then keep traffic off the corner for three weeks.
