Slabjacking

The first challenge you face is getting an experienced slabjacker. An experienced slabjacker can usually determine why a slab settled. He/she can also tell you if the settling is complete. Remember, some settling continues for years!

Make sure that you ask what is going to be pumped under your slab. Avoid slabjackers who simply use topsoil or drilling mud. These materials just aren't the best products. Professional slabjackers use different mixtures and combinations of materials depending upon the job. BUT, these mixtures always contain Portland cement. The cement gives the grout strength after it gets hard and prevents erosion of the grout.

Ask the slabjackers if they will collect and save the dust from the drill holes. Request that this dust be mixed with the material used to plug the drill holes at the end of the lift. By doing this, there is a good chance that the color of the holes will closely match that of the slab. Failure to do this will result in a polka dot slab.

As usual, ask for copies of Worker's Compensation and liability insurance certificates when you receive your bid or quotation. I know, I know, it says right on their contract that they have this coverage. Well, do they? A professional will not hesitate to give you copies of these certificates.

Why not call the Better Business Bureau? Ask if there are any unresolved complaints. If so, consider finding another slabjacker. You may pay slightly more, but it will be well worth it in the long run.

Reinforcing Steel

Steel adds enormous strength to concrete. Concrete is strong in compression (squeezing) but weak in tension (pulling apart). You can pull concrete apart quite easily. For example, let's pour a slab on fill dirt. The fill settles and a hollow spot develops under the slab. Now let's drive my truck across the slab. The concrete stretches (pulls apart) to fill this hollow spot.

Put steel into the slab and it may take a tank to create the same effect. The reason is simple. The typical steel you buy at the supply house is almost always grade 40 steel. This means that it takes 40,000 pounds per square inch (PSI) of pulling pressure to tear the steel apart. Your slab, on the other hand, has only 1/10th the strength in tension as compression. Typical residential outdoor concrete is supposed to be 4,000 PSI in compression. This means it only takes 400 PSI to crack or pull it apart. Adding enough reinforcing steel can make the concrete 100 times stronger than without the steel!

I always had fantastic results by constructing a grid of steel in my slabs. By placing the steel bars two feet on center in both directions, I created a cage of steel. This steel must be surrounded by concrete. If you simply place it on the dirt, gravel or soil it will be worthless. The tension forces in a slab are concentrated in the lower third of the slab, so you should place the steel at the top of this boundary.

If you want to get fancy, you can purchase little supports that suspend the steel above your fill material. I usually used small broken pieces of brick or concrete block to support the steel. If your slab is larger than the length of the steel bars, be sure to overlap the steel at least two feet and tie the steel together with thin wire.

Lifting Concrete

The technology to lift concrete slabs has been around for many years. Highway slabs, airport runways, factory floors, etc. have been successfully raised for the past 40 years. However, until recently, the companies that did this work seemed to completely ignore the residential market. Now, in most cities, you can locate an individual who can magically raise a sunken or tilted concrete slab, floor or set of steps.

How is it Done?

The technology to lift concrete is centuries old. It is the same technology that is used to raise your car on a hydraulic lift at the car repair garage. Holes are drilled through the tilted concrete, usually two inches in diameter. A mixture of cement, sand, fly ash and water is then pumped into these holes under pressure.

This mixture has the consistency of a thick mortar. As it begins to flow beneath the slab, it exerts an equal pressure on every square inch of the concrete. Thus, if the pump produces just 50 to 100 pounds per square inch pressure (which isn't much) it can easily raise the slab.

You see, a concrete slab that is four inches thick only weighs 1/3 pound per square inch! Now do you see why it is so easy to raise a sunken or tilted slab?

Why did the Concrete Sink?

Good question!! There are all kinds of reasons. Usually, concrete slabs around your house tilt or sink because they were placed on fill dirt that was not compacted. This can happen just about anywhere.

For example, what about a sidewalk that is next to your foundation? How about a garage slab? What about a portion of a driveway or sidewalk that crosses a utility trench (one that contains a water, sewer, electric or phone line?) These situations almost always involve an excavation where dirt may have been simply dumped in after the work was complete.

Herein lies the problem. Buildings are built on dirt all the time. If done correctly, a house built on dirt will not settle or develop structural problems. The trick is to build the house on undisturbed dirt or soil that has good strength, or build it on compacted dirt that will support the structure.

Compaction

How many times have you dug a hole and tried to put the same dirt back in? Have you ever been able to do it without much work? I didn't think so. When you dig dirt, you fluff it. That is the technical term. In other words, you introduce much more air space around each clump or dirt particle than it had in the ground.

So, if you or your builder simply dumps dirt into a hole, trench or alongside a foundation, it will always have too much air in it.

The process of compacting dirt simply removes this excess air. Many years ago, shepherds noted that the paths that sheep walked on were very firm. They figured out that the shape of the sheep's hooves did an excellent job of compacting the soil on the path. That is why that big round roller that you see behind a bulldozer is called a sheep's foot roller!

Mother Nature will compact dirt. But, she often takes a while to do it. The sewer trench in my front yard continues to settle even after 10 years. Gravity and rainwater continue to force out the air I dumped into the trench.

This type of settlement not only causes concrete to tilt inwards towards the foundation, but it also causes a majority of basement leak problems. People generally don't recognize the the slow process of compaction as performed by Mother Nature.

Expensive Stuff

Concrete is made from basic, inexpensive raw materials. However, transportation and placement of these materials is costly and labor intensive. Because of its high cost and durability, people expect concrete to last for a long time. This is not an unreasonable expectation, as I have seen concrete 50 plus years old that is in very good shape.

But sometimes things go wrong. Your concrete drive, sidewalk or patio may experience a popout (depression caused by a piece of stone that explodes for numerous reasons). Those living in cold climates may experience spalling, a condition where the top surface of the concrete peels off. A corner of a concrete step may crack and fall off due to a handrail post expanding (rust and/or freezing expansion). In any event, a patch can be employed rather than replacing an entire segment of the concrete.

Challenging Task

I have seen numerous attempts at patching concrete. The majority of them have failed miserably. There are many reasons for patch failure. I'll try to cover some of the most persistent causes.

Concrete, in its original form (when first mixed) sticks together because of the cement. When the cement is mixed with water, a chemical reaction begins that is really pretty neat. Very small crystals begin to grow. These crystals interlock with one another and lock onto the pieces of clean sand and gravel. Also, when concrete is mixed, there is usually lots of extra water around to help keep the crystals growing. And grow they do, as the crystal growth slows down but can continue for years.

However, when patching, these two conditions are not always present. The area to be patched may be dirty and bone dry! If this is the case, there is a great chance that the patch will fail.

Water, water everywhere...

Remember when I spoke above of the growing crystals? The same thing happens, to a large degree, with many concrete patching compounds. They also need water for their crystals to grow.

Many people forget that concrete can and does absorb water. You can demonstrate this easily by getting on your hands and knees. Do this and place a drop of water on a piece of concrete. Observe what happens. The water, in almost all cases, readily soaks into the concrete surface.

When you place water based patching compounds on dry concrete, the concrete robs the water from the patching compound. No water, no crystals. No crystals, no bond. It is that simple.

Dirt also gets in the way as well. If dirt blocks the crystals from bonding to the concrete to be patched, all that happens is that the crystals bond to the dirt, not the old concrete.

Additives / Bonding Agents

To improve the chances of a patch sticking to old concrete, there are two categories of materials that you should consider. One category is additives and the other is bonding agents. They work towards the same goal, but they do it very differently.

Additives are chemicals or compounds such as rubber, vinyls, acrylics and different polymers that are sometimes added to portland cement mixtures. All they do is simply make the concrete mixture stickier. These compounds can be in a dry form premixed with a patching compound, or a wet milky liquid that you add to your patching compound. In either case, they work quite well when applied to a clean surface.

When using concrete patching compounds that contain additives, be sure to follow the instructions carefully. Some of these compounds must be applied to dry concrete surfaces, while others instruct you to wet the area to be patched. You must pay attention!

Bonding agents are glues that are applied to the old or damaged concrete surface that is going to receive the patch. These are almost always liquid compounds that you simply brush onto the clean, dust free area to be patched.

Once again, you must follow directions to the letter to achieve the best results. It is possible to use both compounds to maximize your chances of success. In other words, you can purchase a patching compound that contains additives - these are usually labeled as containing vinyl or acrylic,etc. - and use it in conjunction with a bonding agent. Always check the labeling to make sure the materials are compatible.

Epoxies

If you really want to go all out on your patching project, consider epoxies. These are no different than regular epoxy. You simply mix equal parts of a resin and a hardener together, often with a sand aggregate. You apply it and BINGO, super patch! The problem with some epoxies however, is coloration. You may not be really excited about the finished color. Some are white, beige, and very light grey. In contrast, regular Portland cement patching compounds dry to a medium grey.

The Old Stand By

Guess what? You can use just plain cement, sand and sometimes pea gravel to patch that hole. If done properly (50 percent cement - 50 percent sand and/or gravel), your patch will perform just fine.

Manufacturers of Concrete Patch Products

Some of the manufacturers, besides making great products, also have very informative product literature. For example, the Quikrete Company has a book that may interest you. It is called Build and Repair with Concrete. The Portland Cement Association (www.cement.org) also has a huge amount of excellent literature on concrete. Go to the bookstore on their web site. Many of the publications are available for free download.

At the same time, consider ordering a book called The Homeowner's Guide to Building with Concrete, Brick & Stone. This is a great book that covers building new masonry projects as well as maintenance and repair. No homeowner should be without this book!

• Abatron, Inc.
  • Abocrete - concrete repair product
    Aboweld - epoxy repair compound
    Abocoat - concrete coating product
• Quikrete Companies
  • Vinyl patching compounds, bonding adhesives, concrete acrylic fortifiers, concrete cleaners (acid free), quick setting cement & more.
• Bonsal Sakrete Concrete
  • Complete line of concrete patching compounds and repair/ maintenance products.
• Tamms Industries Company
  • Concrete repair admixtures, bonding agents, and sealers.

Other companies who make concrete repair products:

• • Ardex Engineered Cement
    

• • AVM Industries
    

• • DAP
    

• • Kryton Intl.
    

• • Maxxon Corp.
    

• • Quality Systems Inc. (QSI)
    

• • Sinak Corp.
    

• • Sto Corp.
    

• • United Gilsonite Laboratories
    

• • White Lightning Products Inc.
    

• • W R Meadows
    

• • Xypex Chemical Corp.

Concrete Crack Repair | Here's a normal concrete shrinkage crack in a basement slab. One year after the slab is poured you can start to think about repairing it. You have several options. See below. Copyright 2019 Tim Carter

Concrete Crack Repair Tips - It's Detail Work

What Concrete Crack Repair Options Are Available?

You have several options to repair concrete cracks:

• inject the crack with epoxy
• fill it with gray ceramic tile grout
• patch with expanding hydraulic cement

What is the Best Epoxy To Use?

The best epoxy for concrete crack repair, in my opinion, is made by PC Products.

This is the magic epoxy that fits into a regular caulk gun. I've used it with great success. CLICK on THE PHOTO NOW TO HAVE IT DELIVERED TO YOUR HOME.

As you might imagine, the prep work before installing your patching material is the most important part of the job. This is really true of most building and remodeling jobs.

Why is Prep Important?

The concrete surfaces need to be clean and free of all dust and anything else that will interfere with the bonding of the repair material to the sides of the crack.

Is Epoxy the Best Material for Concrete Crack Repair?

Epoxy is a fantastic repair material. Most are quite thick so the crack needs to be about 1/4-inch wide for you to be able to inject the epoxy with ease.

You can buy a durable epoxy that has a special mixing nozzle. I demonstrate it in this video:

What is the Caulk Gun in the Video?

Here's the fantastic caulk gun I used in the video. It's designed to give you lots of control when you squeeze the handle.

My caulk gun is just like this one. Once you use a gun like this, you'll throw away the one you have that has the click notches. They're pieces of crap. CLICK on THE IMAGE NOW TO ORDER THIS GUN.

How Do You Repair Cracks and Holes on Flat Concrete?

You can use sanded ceramic tile grout or Portland cement mixed with fine or medium sand to repair large cracks and holes in concrete.

Most repairs on flat surfaces, such as a driveway, patio or sidewalk, consist of filling a depression or hole. The hole usually has tapered sides.

These tapered edges can cause real problems for the long term durability of the patch. The patching compounds thin out at these spots and can easily peel or fail. The result is an unsightly second area to patch the following month or year.

How Do You Prevent the Failure of the Patching Compound?

I have had the best success patching when I alter the sides of these holes. This can be done with either a chisel and a hammer or a saw equipped with a masonry blade.

NOTE: Always wear eye protection and/or ear protection when doing this type of work. Small pieces of concrete, dust, metal or masonry blades can cause severe eye injury. Hearing loss is a real threat as well.

The challenge is to remove the taper from the edges of the hole. If you are successful, the finished edges will be 1/8 inch thick or so instead of tapering to a feather edge.

SECRET TIP: Mix pure Portland cement with water to the consistency of latex paint. Brush this into the crack or the hole immediately before filling with the patching material. Do NOT allow the cement paint to dry. Work FAST.

How Do You Mix the Patching Materials?

Always follow directions. Most compounds should achieve the consistency of cake icing or a very thick gravy (don't eat these compounds!) Only mix enough compound that you can apply in 15 to 20 minutes.

How Do You Apply the Patching Material?

When using water-based repair compounds, wet the surface to be patched, if you are not using a bonding agent. If using a bonding agent follow directions carefully.

For deep repairs, consider installing hardened nails in the depression. For extra deep repairs, drill a 1/2 inch diameter hole and pound a 1/2 inch piece of reinforcing steel into the hole. These items will help hold the patch in place. Be sure that these pieces of steel are at least 1/2 inch below the top of the patch.

Use a finishing tool (magnesium or wood float, steel trowel, etc.) to finish your patched area. Finishing is an art and takes practice. You may have to wait a few minutes until the patching compound begins to stiffen to achieve the desired results. Practice in some out of the way spot, if in doubt.

When you are satisfied with the patch, cover it with a piece of plastic. Weight the edges of the plastic so it will not blow away and so air cannot blow underneath the plastic. This is very important!! Keep the plastic in place for three to four days.

What are the Best Weather Conditions to do Concrete Crack Repair?

Sunny, hot, breezy weather is the worst time to do this type of work! Many people think it is the best time. These conditions cause the patching compound to dry out too fast. Fifty-five degree F weather, overcast and damp is a great time to do this work. If you insist on doing it in warm weather, do it in the early morning. Then, shade the repairs so the sun can't hit them.

Don't attempt to repair concrete in freezing weather. The patches will readily freeze and fail. Use common sense.

Time to Work

Let's get to work! Now that the concrete surface is clean and all loose material is gone (you did do that didn't you?), we just need to provide the forms to create crisp lines on the sides of the slab.

You can do this with 3/4 inch thick pieces of 1x4, or 1/2 inch pieces of plywood which have been ripped cleanly and evenly with a table saw. Hold the edging up to the desired thickness of your overlay. A gauge block works great for this! What's that? Well, let's say you are doing a 1/2 inch overlay.

CLICK this image and listen to the first call on the podcast. I talk to Vic about how he can do a concrete overlay and save THOUSANDS of $$$. Copyright 2018 Tim Carter

Cut a 4 inch by 4 inch piece of plywood and set it on the old surface at the edge. Hold your form board flush with this little block, nail the form board to a stake to secure the established height and you are ready to rock and roll.

Pre-existing Cracks

Undoubtedly, your concrete surface may have some original control joints or other cracks. These must be marked on the sides of the forms. Why? Because these cracks WILL telegraph through the new overlay. You need to install your own new control joints with a standard jointing tool to make a nice new line!

You can also take care of this condition by pouring the overlay in sections. Simply do one block at a time. Install a form board the same height or depth of the overlay in between the two side form boards. This will produce a nice crisp line for you as well.

The Materials

Your material requirements are simple and inexpensive. You need Portland cement, fine and coarse sand, and possibly some pea gravel. You will need pea gravel if you intend to do an overlay thicker than one inch.

The cement and fine sand are used as your glue. The cement, coarse sand, and possibly pea gravel are used for the overlay material.

If you are doing a thin overlay, less than one inch, moisture loss from the thin overlay is critical. If water leaves the mixture too quickly, the overlay can be subject to plastic shrinkage cracks and 'curling'. The overlay can actually delaminate from rapid moisture loss.

One of the ways the material looses water is by suction from the old concrete. In other words, the concrete sucks the water from the fresh overlay. To avoid this, the old slab should be wetted and kept wet for 12 hours before you start. You can do this by wetting the slab and covering it with a plastic sheet. Be sure to remove standing puddles before starting to work.

The Mixtures

You don't need fancy admixtures or bonding agents to get great results. Good old cement will do just fine. The mixture for your overlay consists of coarse sand, cement and possibly gravel. You want a minimum of seven bags of cement for each cubic yard of overlay you apply. For purposes of volume measurement, this equates to three parts sand to one part cement. Of course, if you add more cement, say 2.5 parts sand to one part cement, your chances of success will do nothing but increase.

If you are doing an overlay that contains gravel, you would mix two parts gravel, one part sand and one part cement.

The cement paint is easy. It is a one to one mixture of fine sand and cement. Of course you can also go a little heavy on the cement to get a greater bond. You mix these two ingredients dry and then add water to make a slurry just like a rich paint. Only mix what you can use in one hour or less. Remember, it is easy to mix up a quick batch!

Consistency

Remember earlier when I said that water is the primary cause of concrete failure? Well, don't goof up! I would like to see you mix up your overlay material so that it resembles a somewhat stiff mortar. If you can readily pour it from your wheelbarrow and it flows like a bowl of clam chowder soup, too much water!!

I would like to see the consistency of thick oatmeal. Remember it can't be so stiff that you can't easily spread it.

Ten Feet at a Time

Let's work in sections. Don't try to tackle the entire driveway at one time, especially if you have not finished concrete before. Let's just do 10 feet or so at a time, or work block to block on top of the existing surface. We already talked about recreating lines and how to form at a line.

Remember that as you mix each batch, that batch has a separate setting time than the one before. It is kind of like putting rolls in an oven at different times. They will all brown at different times! You don't want to get caught trying to mix or install a new batch while the other one is ready to finish!

Blending Your Overlay

Earlier we talked about different levels where the bad surface meets a good one. If you have to taper your overlay to meet a surface that is flush, it is not a problem. The overlay material without pea gravel can be applied successfully in a layer as thin as 1/8 inch! Just make sure that it has a good amount of cement in it. If you dilute this thin layer with water, it will surely fail.

If you are doing an overlay that contains pea gravel, you will need to mix a batch of overlay that just contains sand. This overlay will be blended into the gravel batches as you get close to the surface you are working towards. In other words, you may wish to start to taper your overlay four feet away from the flush surface. The last four feet of overlay will then contain lesser and lesser amounts of gravel. The final foot may be just the pure sand mix.

The Paint

OK, the stuff is mixed and we are ready to go. Well, did you have your helper mix up a batch of cement paint? Great! Is the surface damp? Wonderful! The helper should start to paint the old surface just ahead of the individual who is applying the overlay. Don't put paint down that can't be covered with overlay concrete within five minutes!

Screeding & Finishing Tips

Use a straight 2x4 or other board that will stretch beyond each form board by one foot. This is how you level off the overlay material. Start at one end. Using a back and forth motion like sawing a piece of wood, slide the board over the form boards while you advance it like a bulldozer. Fill in any low spots as you go.

Within a matter of minutes, maybe a half hour, the overlay mixture will get fairly stiff. You can imprint it with your thumb say 1/16th inch. It is time to finish. Use a wood or magnesium float or a broom to give the slab your finish. Brooms are easy. You just lightly drag it over the material. Floating requires some technique. Don't press too hard. Use a circular motion and lift the leading edge of the float so it doesn't dig in.

After you are finished, spray the surface with curing compound or cover it with plastic for four to five days. Rapid moisture loss will weaken the overlay! The following day, feel free to lift the plastic and mist the concrete. Keep the top surface damp and you will have an awesome surface!

Curing Surface Problems

Often, the concrete below the surface is in good shape. The surface peels away because the cement which holds the sand and gravel together was very likely diluted by the installer.

This happens when the finisher sprinkles water onto the concrete surface or floats the bleed water back into the concrete while working it. This extra water simply dilutes the cement in the upper surface.

CLICK this image and listen to the first call on the podcast. I talk to Vic about how he can use a concrete overlay to save THOUSANDS of $$$. Copyright 2018 Tim Carter

With less cement present, the concrete is very susceptible to damage by ice formation or pressures exerted by salt crystallization. With enough cement present in all parts of the concrete, it can withstand years and years of snow, ice, salt, etc. That is a proven fact.

The Fix

Do you drive the Interstate highway system? If so, you probably have seen bridge resurfacing/restoration projects happening.

Here in Cincinnati, workers have been applying a one to two 2 inch concrete overlay on top of the old concrete surface. No doubt they use specialized bonding agents and a special mix due to the abnormally high traffic loads and abuse the bridges receive.

You, however, can redo your driveway in a simple fashion that will last for many, many years.

Want perfect concrete work? Find a pro by using my Concrete Work (Sidewalks, Driveways, Patios & Steps) Checklist. I offer a 100% Money Back Guarantee.

Adhesion - The Key

The concrete overlay you are about to install will succeed if it adheres or sticks to the old surface. If it does not, it will simply peel like your existing surface. Regular Portland cement is an excellent glue or adhesive. Just think - had the original concrete mason/finisher done his/her job, the Portland cement in the original mix would be working just fine.

Adhesion of the new overlay to the old concrete has both a physical and chemical aspect. The Portland cement crystals grow into and chemically bond to the clean, old cement matrix. Mechanically, the greater the surface area of the bond the more crystals will grow and create greater adhesion. This simply means that the rougher the surface, the better the bond!

Thus, it is to your advantage to remove all loose concrete, dust, etc. from the surface. A pressure washing to blast away concrete that appears sound but actually isn't is not a bad idea!

Grease and oil stains will interfere with adhesion. You must remove them using soap, solvents or a combination of the two.

Once all of the loose material and contaminants have been removed, wash the surface to be repaired with soap, water and a stiff broom. We want it squeaky clean. Rinse to remove all soap, dirt, dust, etc.

The Overlay - How Thick?

The thickness of the overlay is critical. It is often dictated by conditions other than the slab you are going to repair. In other words, the slab may abut a garage slab or city sidewalk. The current levels of these two surfaces may be level! What do you do then? I'll tell you in a moment.

I have successfully installed overlays that are only 1/2 inch thick. These can easily be accomplished by a novice homeowner. The thin overlay allows a large area to be covered by a minimal amount of material. For example, if you install a 1/2 inch overlay on your driveway, and your driveway measures 648 square feet, you only need one cubic yard of overlay material! That is not much. Your original driveway probably required 10 times as much material.

Concrete Overlay Literature Sources

The following two organizations have the absolute best information on all aspects of concrete and concrete installation. Each has an online Bookstore listing all of their publications. Their literature is authoritative, easy to understand and user friendly. Check it out!

• American Concrete Institute (www.concrete.org)
• Portland Cement Association (www.cement.org)