We receive a lot of questions about garage floor concrete repair, so we have prepared this section of articles to give you the best possible answers as to how to execute the necessary repairs, depending upon the condition of your garage floor.
A lot of property owners contact us with questions concerning placing a new concrete slab over the top of an existing failed garage floor. Generally, this is not a good practice if the original floor has cracked, with sections of it sinking below its original elevation. This is known as differential settlement and is indicative of poor sub-grade preparation beneath the original concrete slab as shown in the diagram above.
What this means is that the original garage floor is a slab-on-grade (non-structural) and the sub-grade material supporting it has settled leaving a void beneath the bottom of the floor that is now lacking of support. The floor's own weight, and that of autos on it, has broken a portion of the slab away from the remainder and it has settled below the desired elevation. Sometimes, this occurs in numerous locations across a garage floor or driveway leading to it.
If you place a new concrete slab over the top of this original floor, it will suffer from what is called reflective cracking with cracks appearing in the new surface that are over the general location of the cracks in the original floor. This approach generally has proved to constitute economic waste of new concrete and does not constitute an effective concrete repair. One approach that can assist in making this procedure successful is mud jacking, and we have devoted a separate page on this process.
Concrete Crack Repairs
If you have hairline cracking in your garage floor you can seal them with epoxy compounds even if they have slightly separated horizontally. Before you do this you may want to consider if your problem is related to the problem discussed above. If it is, crack repairs will not be effective. If your cracks are caused by excessive and rapid hydration of the original concrete mix (shrinkage cracks) then you can successfully repair them and we will discuss how to do that on a separate page devoted to that subject.
Concrete Restoration—Surface Repairs
Another major problem is surface spalling where portions of the top of the garage floor turn to a crumbly dust-like substance forming a dip (bird-bath) in the floor that usually grows over time. This is caused by excessive hydration of the original concrete mix (allowing it to dry-out too quickly) which leads to a lack of bond between the portland mix and the aggregate. Eventually, the surface turns to dust and leaves the depression called a bird-bath. These can be repaired if you reach a good substrate that is solid. We will deal with this on a separate page that covers floor surface degradation and concrete restoration.
Concrete Resurfacing And Toppings
Occasionally we get a question concerning a garage floor that has no cracking or settlement problems, but that does not drain properly due to how it was placed originally. Since the basic floor is sound, we usually recommend a high strength topping that can be sloped to the proper elevations to allow for drainage. Today, with some of the high-strength mixed material products available this can be done successfully with applications ranging from 1" thick to 2.5 inches thick. This makes for an excellent concrete repair solution.
Concrete Garage Floor Replacement
Sometimes, concrete repairs to garage floors can only be accomplished by removing the old floor and improper sub-grade supporting materials, then starting anew with the proper supporting sub-grade and new concrete slab. Most often, this drastic and the most expensive repair, is caused simply by poor supporting material below a non-structural concrete slab. We will cover this procedure and how to make sure it doesn't happen again with your new concrete garage floor.
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