Q&A / 

Repairing a Cracked Concrete Slab


DEAR TIM: I have a cement slab for a front porch and it is badly cracked. I would like to replace it with a composite deck. The problem is when it rains the water will run through the joints to the ground below. Should I slope the ground away from the house and cover with plastic for drainage? As photo shows the porch is not very high. Any other ideas? George H., Junction City, OH

DEAR GEORGE: Ideas? You bet I've got some ideas. I can give you more options than you probably want, but the great news is you can fix this problem for much less money than you're currently thinking of spending, and you can do the job much faster.

While composite decking is a great material, it can be a little pricey. What's more, you'll have all sorts of issues where the decking touches up against the siding on the two sides of your porch. To do the job correctly, you'd have to install flashing up behind the siding, and solder it at the inside corner and any lap joints. This can be very challenging.

You don't need a new slab. It's easy to permanently repair the large crack that runs across this slab. Photo Credit: George Householder

You don't need a new slab. It's easy to permanently repair the large crack that runs across this slab. Photo Credit: George Householder

I think the better solution is to just patch the crack permanently. Other than the crack, the slab appears to be in great shape. The slab is not spalling, there are no other cracks I can see in the photo, and the slab appears to be in the same plane and sloped so water drains away from the house.

If all of the above is true, then all you need to do is clean out the crack and inject it with some epoxy that's formulated to adhere to concrete. These products have been around for many years and are used on large construction projects all the time. Some of the epoxies, once cured, are far stronger than the actual concrete.

These epoxies are available in all sorts of formulations. You can even get strong urethane adhesive products that have many of the characteristics of the epoxies. Most of the products come in special caulking tubes where the two-part epoxies or urethanes mix as you squirt them from the caulking gun. The tubes have unique nozzles that blend the two components together so they are properly mixed.

The key is to practice using the gun and the material so you can get the finished surface flush with the existing slab. I'd even experiment using some simple inexpensive concrete patio stones that you could place near one another to simulate the crack in your current slab. Practice applying the epoxy and getting it even. I'd even consider broadcasting coarse dry sand into the epoxy to give it the texture and color of your current concrete slab.

If after you repair the crack you don't like the look of it, as it will be tough to disguise it much like a scar on a person's face, you can cover the entire porch slab with a very thin concrete or stucco plaster overlay.

This coating would only need to be one-quarter inch thick, and it would make the slab look like it was just poured yesterday. This overlay is made using a mixture of coarse sand and Portland cement. I would mix three parts sand, one part Portland cement and just enough clear water to make the mixture the consistency of bricklayer's mortar or stiff apple sauce.

To ensure this mixture bonds well to the existing slab, you just need to clean the slab. Consider using a power washer to blast away any loose cement or sand particles, dirt, algae or mold.

It's vital that you apply a coat of cement paint to the slab just before you put down the stucco overlay mixture. Cement paint is a mixture of Portland cement and water. Mix it to the consistency of latex paint. Slightly dampen the clean slab, apply the cement paint and immediately cover the paint with the stucco mixture. Do not allow the cement paint to flash dry.

You finish the stucco mixture with a magnesium float, a wood float or you can apply a light broom finish. It's whatever you want it to look like. This cement stucco mixture will have no issues bonding to the epoxy that was used to fill the crack. Once the final finish is applied, be sure to keep the overlay mixture damp by misting it with water for about a day. You can also cover it with heavy plastic, but be sure you don't mess up the finish if you put down plastic.

But wait, it gets better! What if I told you that you could make your new porch just about any color you want? Have you seen the gorgeous stamped concrete drives, walkways and patios? They come in all sorts of earthy colors like black, browns, greens, reds, oranges, etc.

All you have to do is purchase the dry pigments the concrete installers use and mix them in with your stucco. It's vitally important that you mix the exact same amount of pigment in each batch so you have even coloration with your stucco mixture.

Your new porch will be the talk of the neighborhood. I estimate, in 2013 dollars, that you could do the entire job for less than $150, perhaps less! The best part is you can do the entire job in one day if you have some help. It should only take an hour or two to install the epoxy and the stucco overlay should take you no more than four hours.

Wait about two days before you walk on the porch. Wait at least a week before you put any furniture on the new stucco overlay.

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