If a precast concrete wall in your garage or basement has developed cracks, holes or has become delaminated, you can repair it so it will perform as well as when it was new. Follow the process outlined below to repair a precast concrete wall.
Step 1: Clean and Prep the Area
Clean the area around hairline cracks and small holes in precast concrete by sanding with coarse sandpaper. Use a grit of 50-80. Remove all dust, dirt and any white mineral buildup from moisture leaching out of the concrete.
Soak the area around the crack or hole with a damp cloth and keep it wet for a few hours. This will prevent the dry concrete from absorbing the water in the Portland cement grout when you apply it.
Step 2: Portland Cement Grout
In a metal bucket, mix Portland cement and water to form a thick, smooth grout. Stir continuously with the metal stir wand to prevent lumping.
Fill the fine crack with the Portland cement grout on your trowel. Use the trowel handle tip to pack the cement grout fully into any holes. Press the cement grout into the crack and over the edges of the crack. Smooth down the grout with the flat side of your trowel.
Step 3: Begin the Curing Process
Allow the cement grout patch to dry for 2 to 3 hours. Cover the repaired spot with a large plastic sheet, taped down with duct tape. Each day for 5 days, dampen the repaired spot with just a little water and cover it over again. Apply a silane-based sealant to the repaired spot and a few inches beyond it all around, with a synthetic bristle paint brush.
Step 4: Repair Larger Concrete Holes in Precast Concrete
Enlarge the crack or hole below the surface with a cold chisel and hammer. This will help concrete adhesive and new concrete mix penetrate and blend with the old concrete. Mix enough ready-mix concrete with water to fill the hole or crack and apply it quickly. Press the concrete mixture into holes and cracks with the handle of your trowel and smooth it over the surface evenly. Cure the repaired spot as explained in Step 5, and then seal with a silane-based water-repelling sealer.
Step 5: Repair Unstable Precast Concrete Walls
If you need to repair large holes or redo hairline crack repairs, these may be signs of structural problems such as bowing or shifting. Staples made of carbon fiber and Kevlar (TM) can be applied to restabilize and reinforce the wall. These unique staples transfer wall load away from the damaged area. The staples will then be coated with cementitious adhesive, a fresh layer of concrete, and sealed with silane sealant. Contact a company that specializes in structural repairs with this technology to have this work done.