How To Repair Cracks In Concrete Foundations
The first three pictures are of a crack in the house foundation on the outside of the house. The crack was vee'd out with a hammer and chisel. All loose material was removed. Dig down in the soil as deep as needed; try and get below insect level. The crack was washed out with a hose and painted with a water and glue mixture of bond glue at ten parts of water to one part glue. Mix up a half bucket of glue mixture; wash the crack with this mixture and use the left over to make your cement. Start with a slightly watery mix of ready mix cement and coat both sides of the crack; add more ready mixed cement to your mix, for a coarse blended cement. Fill the crack completely and trowel flat.
This is a picture of a crack in the basement wall
How To Repair Cracks In Concrete Foundations
Cement foundations of homes 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.
These cracks will allow water to come into a basement if excessive water is allowed to gather on the outside of the house from over watering, downspout to close to house or just the lay of the land allowing water to collect at the house.
Small ants and insects can also pass through these cracks. If these cracks are not repaired they can lead to bigger problems, such as more cracks and chunks of cement following out of the wall.
City work on the road can amplify the problem with their vibration tamping machines. This machine can do as much damage at one time, as ten years of normal wear and tear.
It is not viable to replace the foundation, so the next best thing is to repair the existing cracks in the foundation. The foundation will never be like new again, but you can repair these cracks. It is important to clean the concrete thoroughly before applying a patch. Concrete is formed by a chemical reaction between the Portland-cement and water. This hydration creates tiny crystals that interlock everything together. If there is any dirt or grime on the cement the crystals will bond to the dirt, instead of the old concrete, resulting in a poor bond and flaking will be the result. The next step is to prepare the cracks for treatment. Using goggles or safety glasses take a hammer, metal chisel or an old screwdriver and tap out a Vee groove about 3/4 inch across and about 1/2 inch deep. Do this for the entire length of the crack. Then 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 make a good bond between the new patch cement and existing wall. If the crack is very wide you need to use longer nails, one inch nails works for most jobs.
Next mix up a mixture of white glue (Bond Weld) (this kind of glue is recommended for cement work) and water at a ratio of 10 parts of water to 1 part of glue. Mix it thoroughly and paint it into and around the crack; this will help the patch cement bond.
Then what you will need is some 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. You want a fine smooth mixture. Mix the water, sand and cement with a 2 1/2 or 3 ratios, one part cement and 2 1/2 parts sand ( mix the dry mix thoroughly before adding water and the glue mixture). Add some of the water/glue mixture to the
cement and mix it together. Also repaint the crack again just before applying the patch cement. If you buy premixed cement (patching compound that contains latex, epoxy, or other polymers); you 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, then the mix is too watery; just add a little more sand and cement until you get it right. It is a good idea to try and 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 for a little softer cement, a better match to the existing cement.
Clean out any loose pieces of cement and wet down the cement with a spray of water, this will help make a good bond between the existing cement and the patch cement. Trowel the cement into the vee groove, then with a back and forth motion, force the cement as deep as possible and scrape off the excess. Allow to set up, and 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 patched on the outside of the house, provide a cover from the sun, use cardboard or plywood, this will also help slow down the drying time. If the area to be filled 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.
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 these compounds, is they penetrate deeper into tight cracks, than a cement based repair compound. Stonemason concrete repair caulk comes in a cartridge that fits into caulking guns. A bead can be delivered under pressure to the exact
area of the crack.
Estimating Concrete Quantity
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.
Working 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, this 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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How to repair cracks in home foundations, tips for the average home owner