As concrete contractors who work with concrete equipment day in and day out know, a crack or hole in a single section of precast wall can be repaired good as new. You might find this kind of crack in the basement or garage of a home on ground that’s settled, for example.

The procedure below describes the concrete repair, including tools to do a more professional job and signs that it’s time to call in a professional to evaluate structural impact and concerns.

Measure 1: Clean and Prep the Area 

Clean the area around hairline cracks or any hole in the precast concrete that needs to be repaired by sanding with coarse sand paper; 50-80 should do the job nicely. Remove all dust, dirt and any white mineral buildup from humidity leaching from the concrete. 

Soak the region around the crack or hole with a fabric and keep it wet for a couple of hours. This will help with adhesion of the Portland cement grout whenever you apply it. 

Measure 2: Apply Portland Cement Grout 

Mix Portland cement and water to form a thick, smooth paste the consistency of peanut butter. Stir continuously with a shovel or mixing attachment on your drill to prevent lumping. If you’re looking to upgrade your drill – and particularly if you drill a few 1-inch deep holes at the ends of a long crack as stop-points – check out the Metabo SDS Hammer Drill. [LINK TO:   http://www.acecutting.com/brands/metabo/khe-3250-metabo-sds-plus-hammer-drill.html  ] With its Variospeed (V) Full-wave Electronic Speed Control and its comparatively light weight, just depress the trigger partially for reduced hammer effect and a steady, pulsing mixing effect when used with a mixer attachment.

Next, fill the crack with the Portland cement grout using your trowel. Pack the cement grout completely into any openings. Press it into the crack and above the edges of the crack. Gently coax the grout down the crack with the horizontal side of your trowel, allowing about 1/8” -1/4” thick film of the grout to escape the back of your trowel. You can increase pressure as you move away from the crack, which will allow less cement to escape the back of the trowel and feather the texture to smooth with the existing wall.

Step 3: Begin the Curing Procedure 

Allow the cement grout patch to dry 2 to 3 hours. Cover the fixed spot with a huge plastic sheet, and tape it down with duct tape. Once a day for five days, soften the repaired spot with a little water and cover it over again. Apply a silane-based sealant to the fixed spot and a couple of inches beyond it all around, with a synthetic bristle paint brush. 

Measure 4: To Repair Larger Holes in Precast Concrete 

Enlarge the crack or hole beneath the surface with a cold chisel and hammer, or hammer drill such as the Metabo SDS Hammer Drill. This can assist the adhesion of the fresh concrete mixture. Mix enough ready-mix concrete with water to fill the hole or crack and apply it rapidly. Press the concrete mixture into holes and cracks with the handle of your trowel and smooth it on the surface evenly. Cure the fixed spot as explained in Step 3, including sealing it with a silane-based water-repelling sealer. 

Measure 5: Repair Unstable Precast Concrete Walls 

If you need to fix more than a few large holes or redo several hairline crack repairs, these can be signs of structural issues like bowing or shifting. Staples made from carbon fiber and Kevlar might be applied to re-stabilize and strengthen the walls. These staples transfer wall load away from the damaged region. The staples will then be coated with cementitious adhesive, a fresh layer of concrete, and coated with silane sealant. If you’re a handyman or do-it-yourself, contact a company which specializes in structural repairs with this technology to get this work done or consult your local concrete contractor to have the section professionally replaced. Don’t gamble on structural support.