If you have a concrete garage floor, driveway, sidewalk, or patio that is starting to show its age, you are left with two options: You can demolish and remove the old surface, prepare the base, and pour a new slab; or you can use a resurfacing process to restore the slab to its youthful appearance.
Sometimes a concrete slab is just too unstable or too badly damaged to make resurfacing possible. But when the problem is just superficial cracking, discoloring, or minor chipping or spalling, resurfacing is a very good option. It's a project that just about anyone can tackle, and it's a lot more affordable than replacing the concrete slab.
What Is Concrete Resurfacer?
There are lots of concrete mix products on the market—including mortars, repair patchers, fast-setting concrete mixes—and it can be hard to choose among them. Concrete resurfacer is a special cementitious product that blends ordinary Portland cement, fine sands, polymer modifiers, and other additives aimed at providing adhesion. Unlike other cement products, it is designed to be applied in very thin coats (no more than 1/2 inch thick), and its additives provide good adhesion to an existing slab.
Concrete resurfacer is a very strong product, rated for a compressive strength of about 4,500 psi. This is actually stronger than the slab itself, so properly applied, resurfacing layers can be very durable.
Evaluating a Concrete Slab
Product instructions generally advise that resurfacing is a viable option if the slab has not cracked all the way through and when damage is limited to cosmetic issues. This can be hard to determine, but if the height of the slab is offset on adjoining sides of cracks, it is an indication that major heaving is occurring. Such a slab is probably not a good candidate for resurfacing. But a slab with small cracks, chips, and spalls where pieces of aggregate have come loose is an ideal candidate for resurfacing.
Buying Concrete Resurfacer
There are some types of concrete resurfacers designed for use only on concrete substrates, while others can be used both on concrete or as a leveling compound when preparing plywood subfloors for flooring materials. If you are fully resurfacing a concrete slab, make sure to use a resurfacer designed for the purpose, such as Flo-Coat Concrete Resurfacer from Sakrete, Concrete Resurfacer from Quickrete, or Re-Cap Resurfacer, also from Quickrete. This type of product will be clearly labeled as "concrete resurfacer" rather than "floor leveler." You may also find both consumer-grade and commercial-grade products available; the commerical grades are designed to be more durable than the consumer grades.
Concrete resurfacer comes as a dry mix in 40-pound bags or 50-pound pails. A 40-pound bag typically covers 15 to 90 square feet, and you usually apply two or sometimes three coats. Expect to buy quite a number of bags if you are resurfacing a large slab. At $25 to $55 per 40-pound bag, or up to $70 for a 50-pound pail, resurfacing is not a cheap project, but it is less expensive (and much quicker) than tearing up an old slab and pouring a new one.
Don't Resurface With Ordinary Mortar
Because resurfacer is an expensive product, some homeowners try to do the job with ordinary mortar mix, which has a similar consistency to resurfacer and is much cheaper. This does not work for very long, since mortar lacks the additives and bonding agents that allow resurfacer to adhere to the slab. Always invest in a true concrete resurfacer when renewing a concrete slab.
Thorough preparation is the key to long-lasting results when resurfacing concrete. This preparation involves pressure-washing the slab, repairing significant damage using a quality concrete patch product, and removing any stains from oil, paint, or tree sap. Stains may seep through the resurfacing material unless they are removed prior to application.
The application of concrete resurfacer is quite an easy process. The dry powder is mixed with water to form a slurry, which is then spread over the concrete slab using a long-handled squeegee. Resurfacers are self-leveling, meaning that they don't need to be worked extensively to create a level surface. They pour and spread easily, and your only real job is just to ensure that the resurfacer has been spread around the entire surface. You don't have to worry about trowelling to a level surface, as you do when pouring a slab with new concrete.
If you are resurfacing a slab with expansion joints, don't cover over the joints with resurfacer. Instead, cover the joints with duct tape to prevent the resurfacer from sticking to them.
Concrete resurfacer should not be applied in cold weather. Make sure that the current temperature is at least 50 degrees Fahrenheit, and that the temperature will stay above 40 degrees for at least the next 24 hours. Also, work when the area is most shaded, or at least when the sun's glare is at a minimum. Finally, make sure there is no rain in the forecast for at least 8 hours after application.
Concrete resurfacers are only available in one color—ordinary gray. But they can be tinted with colorants made specifically for concrete products. If you plan to resurface only part of a larger slab, be aware that it is hard to match colors. New concrete looks new, and old concrete looks old. If you really want to make the surface look new again, it's best to plan on resurfacing all of it.
Most jobs require a second, and sometimes a third coat of resurfacer. The finish will be quite smooth, so you can add texture to the final coat by brushing it with a broom while it is still slightly wet.