Repair a crack in a home concrete foundation. Welcome to Find N Choose, your free information site.
Concrete Foundation Cracks
Crack in house foundation grooved out and repair
Repair Cracks in a Concrete Foundation
Dig the soil down below insect level. Wash the crack out with a garden hose and paint the crack with a water glue mixture, of bond glue at six parts of water to one part glue (weldbond or equivalent). The glue helps the cement patch to bond with the foundation.
Use a premixed, ready to use cement to repair the crack.
Start with a slightly watery mix of cement and coat the crack, and allow the watery mix to seep down into the crack, then coat both sides of the crack with a paintbrush. Add more premixed dry-mix cement to your wet mixture, to obtain a coarse cement, fill the crack completely and trowel flat.
Concrete Foundation Cracks
Concrete home foundations will eventually develop cracks in one area or another. The soil settles differently in different locations under the footing, this causes tremendous pressures which causing cracks in the foundation. Clay type soils along the foundation develop tremendous pressures when they freeze, they cause expanded soil pressures against a foundation. Concrete steps attached to a house foundation, without proper footing depth, below the soil, can be raised by frost, lifting the steps that can cause a concrete foundation to crack. Any outside structure above ground should not be attached to a house foundation.
Cracks in foundations allow water and insects to enter into a basement.
Over watering near a house, downspouts to close to the house, or just the lay of the land, allow water to flow towards the house, and collect at the house foundation wall.
If cracks in the house foundation are not repaired, they can lead to bigger problems, such as more cracks developing, which can cause chunks of concrete to fall out of the wall.
City work on the road can amplify cracks developing in house foundations, the excess vibration of their tamping machines puts added distress onto the foundation Their machines can do as much damage at one time, as ten years or more over normal wear and tear.
It is not viable to replace a house foundation, so the next best thing is to repair the existing cracks in the foundation before it becomes a real problem.
Repaired foundations will never be like new again, but it is to your advantage to repair the cracks.
It is important to clean the concrete thoroughly before applying a patch.
A chemical reaction between the Portland cement and water forms concrete. This hydration creates tiny crystals that interlock the patch and foundation together.
If there is any dirt or grime, on the concrete, the crystals will bond to the dirt, instead of the old concrete, resulting in a poor bond.
Prepare Cracks in Concrete for Repair
Use goggles or safety glasses. Take a hammer, metal chisel or old screwdriver and tap out a V groove about 3/4 inch across and about 1/2 inch deep. Do this for the entire length of the crack. Clean out all chips and dust.
Drive in a few galvanized gyprock nails into the crack, spacing them three or four inches apart, the entire length of the crack. Drive the head of the nails a little lower than the surface of the wall. These nails will help hold the cement from falling out and help make a good bond between the new patch cement and existing wall.
If the crack is very wide, use longer nails, one inch nails works for most jobs.
Mix up a mixture of white glue and water, such as weldbond glue, recommended for cement work. Mix the solution at a ratio of 6 parts of water to 1 part of glue. Mix it thoroughly and paint it into and around the crack to help the cement bond.
To mix cement from scratch, use Portland cement, a mixing bucket, water, cement finishing trowel or putty knife, sand and some sort of screen to filter out the larger pebbles out of the sand.
Strive for a fine smooth mixture. Mix the water, sand and cement with a ratio of three to one, one part cement and 3 parts sand (mix the dry sand with the dry cement thoroughly, before adding water and the glue mixture). Add some of the water-glue mixture to the cement mixture, and mix it together. Repaint the crack again with the glue-water mix, just before applying the patch.
If you buy premixed dry cement patching compound that contains latex, epoxy, or other polymers, just add water and mix. Mix thoroughly and let stand for about ten minutes before applying.
When the mix is right you should be able to form a raised portion in the center of your mixing bucket and it should remain standing, if it flattens, the mix is too watery, add a little more sand and cement until you get it right. It is a good idea to try to match the hardness of the existing cement. If the house is very old you might want to go with a 4 to one mix which makes a softer cement.
Clean out all loose pieces of concrete and concrete dust in the crack, wet down the concrete with a spray of water, this helps make a good bond between the existing cement and the patch cement.
Trowel the cement into the V groove, then with a back and forth motion, force the cement as deep as possible into the crack, and scrape off the excess.
Allow the patch material to set up, spray with water a couple of times throughout the day, this helps temper the cement and prevents it from drying too fast, which can produce hairline cracks within the patch cement.
If the crack is on the outside of the building, and patched on a sunny hot day, provide a cover from the sun. Use cardboard or plywood over the patch area, this will also help slow down the drying time.
If the crack is very large, fill the area in steps, allowing each layer to dry before Appling the next layer. This helps prevent hairline cracks from developing.
These same techniques can also be used to repair cracks in sidewalks and other concrete crack problems.
A cement patch usually dries to a different shade than the original wall, when cured. To obtain consistent a shade, mix up a mixture of cement and water to form a paint like mixture. Paint the entire area, when it dries the complete area will be one shade.
Synthetic Repair Compounds
There are synthetic patching compounds available such as concrete-repair caulks and vinyl-repair materials, which are malleable and just about as strong as cement when hardened.
The plus side of cartridge repair, is the repair material under pressure, penetrate deeper into tight cracks.
Stonemason concrete repair caulk comes in a cartridge that fits into caulking gun, delivering a bead under pressure to the exact area of the crack.
Estimating Concrete Quantity on Large Jobs
Measure the area to be cemented, and draw the plan onto graph paper with a scale of one square equaling 1 sq. foot. Count all the filled squares and those that are one-third or more filled.
Convert the slab thickness from inches to feet. ( example 4 inches becomes 1/3 Ft.) Then multiply the total area by the thickness in Sq. Ft.
Divide this figure by 27 and you have the amount of concrete needed in cubic yards. Add 10 percent to this and you should have enough concrete to do the job. Build a few square sidewalk forms, to make sidewalk slabs, with any leftover concrete.
Avoid over-working any poured concrete, as this will weaken the concrete.
Concrete must be used within 2 hours of mixing.
Best time to work concrete is early morning or late afternoon, but be aware there is a waiting time for surface water to evaporate, if you wait too long in the afternoon to do the job, it could end up late in the evening, when you will be toweling the concrete.
It takes about 7 days for concrete to fully cure. Concrete that cures too fast will crack, scale, and flake, and lack strength and durability. If the weather is windy or very hot, cover the concrete to prevent the quick evaporation.
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