How Do You Repair Hairline Cracks In Concrete?

Outside of hairline cracks, larger stress cracks occur when a house settles or the ground beneath it shifts. These types of cracks don't usually pose a threat to the structural integrity of a house, but they do allow for a potential opening for groundwater, insects and radon gas.

We'll show you a simple and effective way to patch cracks with the best concrete crack filler.

Fix Concrete Cracks in 8 Steps

Step 1: Repair a Foundation Crack With an Epoxy Sealer

Man Using Wire Brush to Clean Crack in Concrete

We repaired a foundation wall, which had an 8-ft.-long crack that leaked water into the basement during periods of heavy rainfall. To permanently patch the crack we used an epoxy-injection system from Polygem, called the Liquid Concrete Repair Kit (about $60).

Each kit contains a two-part epoxy crack sealer, two 10-oz. tubes of Liquid Concrete Repair (LCR), a viscous epoxy that comes in a caulk-type cartridge, and seven plastic injection ports that deliver the LCR deep into the crack. There's enough material in each kit to repair a 1/16-in.-wide x 8-in.-deep x 8-ft.-long crack.

Before you start, check to make sure the crack is dry. If the crack is slightly damp, dry it with a blow-dryer, then wait 15 minutes. If it remains dry, proceed with the repair. However, if the dampness returns, water is still seeping into the crack and you'll have to wait for it to dry out on its own.

First, scrub the crack clean of any loose concrete, paint or old crack filler using a wire brush. Remove all dust and debris with a shop vacuum.

Step 2: Block Out the Injection Ports

Hammering Nail In Crack For Injection Ports

Tap 3-in. (10d) finishing nails partway into the crack, spaced 12 in. apart. You'll use them to align the injection ports with the crack.

Step 3: Mix the Epoxy Sealer

Open up the two containers of epoxy crack sealer and scoop out equal amounts of Part A and Part B; use two separate sticks to avoid contamination. Mix the two parts on a scrap board using a clean putty knife; blend until you achieve a uniform gray color.

Step 4: Attach the Injection Port

Attaching Injection Port in Cracked Concrete

Spread some sealer onto the base of one of the plastic injection ports, being careful not to plug up its hole. Slide the port over one of the nails sticking out of the crack and press it to the wall. Install the remaining ports in a similar manner.

Step 5: Spread Sealer Along the Crack

Applying Epoxy Sealer on Crack on Concrete Wall

Next, mix up a slightly larger batch of epoxy sealer and apply it to the entire crack using a 1 ½-in.-wide putty knife or margin trowel. Spread the sealer about 1/8 in. thick and 1 in. on either side of the crack. Also, cover the entire flange of each injection port with crack sealer, leaving only the extended neck portion showing. Smooth out the sealer and feather its edges with a paintbrush dipped in mineral spirits.

Step 6: Inject the Epoxy into the Crack

If the other side of the wall is accessible, see if the crack goes clean through. If it does, seal it up with crack sealer, too. Allow the sealer to cure for 6 to 10 hours before injecting the epoxy. Thoroughly mix the LCR epoxy using the plunger rod that comes with the kit. Place the LCR cartridge into a caulk gun. Starting at the lowest injection port, dispense the epoxy into the crack. Continue squeezing the trigger until epoxy begins to ooze out of the port directly above.

Step 7: Seal Up the Injection Ports

Remove the gun and plug up the port you just filled. Now insert the cartridge tip into the port that's oozing and squeeze the trigger to dispense the epoxy. Repeat this procedure for the remaining ports; plug up each one before moving on to the next.

Step 8: Cut Away the Injection Ports

Allow the LCR to cure for five days, then cut off the necks of the ports with a hacksaw. If desired, you can patch the severed ports with a little crack sealer.

Resource:

Polygem
Box 609
Dept. TH700
W. Chicago, IL 60186
Polygem
630/231-5600