Preplanning Your Concrete Repair
If you are considering branching into this type of construction, look at the Concrete Surface Repair Technician—Grade 1 certification program from the International Concrete Repair Institute (ICRI). Design by contractors, for contractors, the 10-hour course is for individuals who want to become a qualified inspector for concrete repair.
The course qualifies individuals to perform pre-placement and post-placement inspections and testing. The coursework brings you up to date with the current industry standards. ICRI - CE Catalog (ce21.com). Many White Cap product experts have participated in the development of this course.
All experts will tell you to start your concrete repair efforts on small common repair projects that will more easily result in client satisfaction, good practical experience, and increased profits.
What are the types of projects that you should consider?
- Patching popouts
- Repairing Small Static Cracks
- Small Concrete Surface Repairs using overlays
- Repairing control joints
These types of projects often don’t require a huge investment in specialized equipment. Your team probably has all the tools on the truck to do the work. And by matching the right type of repair material to the task, everything will go smoothly.
How to identify these projectsWhen walking on to the site of a prospective small repair project, there are some simple guidelines that help you ensure that the project is manageable:
- Check that the cracks or popouts are static and generally less than ¼” wide. These defects generally don’t pose a structural threat and can be filled using simple techniques.
- Look for signs of rust on the concrete’s surface near the crack or popout. Rust can be a sign that the reinforcement (either rebar or mesh) is corroding. The rust also might indicate that the reinforcement is too close to the concrete surface. Either situation may cause you additional steps to bring the concrete back to good quality.
- Use the “hammer test” to check for concrete integrity. You simply strike the concrete with a heavy object like hammer or even a piece of lumber. You should hear a solid “thud”. That means the concrete is sound. If you hear a hollow drum-like sound, this is cause for concern. The drum like sound could be the result of either a delamination of the concrete’s upper surface (often caused by freeze-thaw) or loss of the subgrade’s base material (often caused by erosion) removing needed support for the concrete. Either condition requires your attention, before repairing the concrete.
- Look for differences in elevation between concrete panels at either control joints or entry points. Sunken concrete is usually caused by poorly compacted subgrade, poor water drainage (check the gutter down spouts) or soil erosion. Slabs can be raised back to their original position by pumping a mixture of sand, cement, fly ash, and other additives beneath the slab—a process called slabjacking. This should be completed prior to the repair process.
- With all this in mind, step back and look at the entire concrete surface for a bird’s eye view. Despite what you might do, repair materials may not match the concrete surface’s texture or color. Often the best thing to advise to the owner is that following your repair of the cracks, popouts, and discolorations, you should consider applying a thin concrete overlay. An overlay can help protect the concrete by creating a surface that better drains stormwater and achieves a consistent, renewed appearance.
How should you patch popouts and small cracks?You should use a “dry packing” technique to repair popouts and very small cracks.
The repair process for popouts and small cracks begins in a similar way.
Popouts are shallow and cone-shaped holes often with a deteriorating material at the bottom. First, use a rotary-hammer drill and drill out the remaining deleterious substance and unsound concrete to create a hole with a minimum depth of ½ inch. Then shape the hole’s edges so that they are vertical to the surface and extend down out a ½ inch. Don’t feather the edges, and be sure to remove all unsound concrete, dirt, and debris.
For small cracks, clean the entire opening and remove all unsound material. The more vertical the final edge, the better.
Then before placing the dry-pack repair material in the holes, scrub the repair area with a thick and creamy bonding grout consisting of one-part cement and one-part fine sand. This layer can help bond the repair material to the concrete. Finally, immediately tamp the repair mortar into place and finish or texture to match the surrounding surface. Do not place or smear the repair mortar over a larger area on the concrete adjoining area than is necessary.
When dry-packing deep or wide popouts, fill the opening by layering in the repair material. Each layer should only be about ¼ to ½ inch thick when dry. Consolidate each layer thoroughly before adding the next layer of material. If there’s room, you should also try to scratch small grooves into the top of the compacted layer to help it bond with the next layer. When the filling is completed, be sure to cure all repaired areas using wet burlap, plastic sheeting, or a spray-on curing compound.
How should you repair larger cracks?You need to approach the repair of wide and/or long static cracks a little differently. The clean out approach is the same, removing all loose material, worn concrete, and any old repair material to expose a new surface on each crack side. Sometimes you might use a small walk-behind floor saw that “chases” the crack, or a hand-held diamond crack chaser tool with a diamond tuck point or chaser blade. But most often you use a rotary hammer or small chipper for clean out.
If you are concerned about any future movement along the crack, you might consider stitching and/or dowelling. Start by saw cutting small slits into the floor, perpendicular to the crack’s centerline, spacing them out about 2 feet. Then insert either steel rebar dowels or pre-cured carbon fiber into the slits across the crack.
Next, fill the crack with materials such as epoxies, urethanes, silicones, polysulfides, asphaltic materials, or polymer mortars. Cement grouts should be avoided due to the likelihood of cracking. Choose a repair material that is sufficiently rigid to support the anticipated traffic but not so hard that it’s brittle.
How should I approach treating large areas following repair?A common approach on small projects is to add a new look to a concrete surface that has been repaired. Refinishing with an overlay provides a longer lasting and more aesthetic repair than patching. In recent years, spurred by the interest in decorative concrete, there are a wide variety of overlay systems available for refinishing concrete flatwork. These products range from ultra-thin systems (also called "microtoppings" or "skim coats") that can be applied in layers as thin as a credit card, to floor underlayments that go on at thicknesses of up to an inch or more in one lift.
Each overlay type offers different decorative options and performance attributes. Your White Cap experts can provide you with information on the type of overall system that works best in your part of the country and matches the type of look you want to achieve.
Regardless of the type of overlay you choose; you will need to surface-prep the area. To help contractors prepare the existing floor for the overlay, a product manufacturer will specify the roughness of the surface preparation. In simple terms the roughness of a properly prepped floor is matched to the eventual thickness of the overlay to insure bonding.
In most cases, the manufacturer will refer to the ICRI Surface Profile Chip number. These are a set of rubber plaques (chips) numbered 1 through 10 that show properly prepared concrete ranging from almost smooth to extremely rough. The chips, along with the accompanying booklet, establish a third-party guideline for what properly prepared concrete should look like, how to achieve the desired level of surface preparation, and which profile is best for a particular overlay or coating system.
How do I repair concrete joints?Repairing these man-made cracks requires a different approach than cracks caused from other reasons. In most cases, you are trying to correct the situation referred to as spalled joints. The joints aren’t spalled in the same way that a slab spalls from freeze/thaw issues.
A spalled or rounded edge also can’t help restrain joint sealant, which may cause it to pop-out of the control joint.
Repairing the joint is simple. Start with two saw cuts, each perpendicular to the floor’s surface, positioned at the far edges of the distressed area, extending 3/4” deep into the floor. Then chip out any high spots between the new saw cut edges and existing joint with a chisel or similar tool to establish a shelf. Remove all loose material with a vacuum. Then, slightly overfill with a repair material system that is mixed to the manufacturer’s directions.
Protect the repair by following the curing procedures outlined in the manufacturer’s directions. And when the repair is fully hardened, grind, sand, or cut the repair material to be level with the floor on each side of the joint.