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Project Prep

Different levels of slab damage require different solutions from a thin resurface to a complete tear-out and re-pour. However, there’s a lesser-known, third option for damage between 1/2” and 2” deep – capping.

The process of capping is essentially the same as pouring a new slab, meaning good results are easy to achieve at a fraction of the cost of a new pour or specialty resurfacing mixes.

  1. Ensure air temperature will remain between 40°F – 90°F for 24 hours before and after the project.
  2. Estimate the amount of material required. One 60# bag of Sand Mix will cover about 5 ft2 at 1” deep.
  3. Use the Slab Pour Calculator  for fast results.
  4. Make sure your slab is clean and free of any loose concrete – a pressure washer is a good way to get it ready for resurfacing.
  5. Build a form around the area to be repaired to simplify the project.
  6. The top of the form boards will indicate the height of the capped slab – anywhere from 1/2” to 2” higher than the area to be repaired.
    1. For example, if capping a sunken area of sidewalk, the top of the form should be level with the adjoining sidewalk slab.
  7. Confirm overall slab level by leveling edge to edge and corner to corner.
  8. Apply a bond enhancer such as Bond Strength Primer, Concrete Glue or Bonder & Fortifier to the repair area and allow to dry to a tacky texture.

Project Tip: Use the Sakrete App to measure, estimate and purchase materials for the job straight from your phone.

Mixing

Capping a slab with Sand Mix adds a minor step to mixing, replacing part of the mix water with a bond-enhancing admixture to achieve ultimate performance.

  1. When using bond-enhancing admixtures, DO NOT bring the slab to SSD before or after application—water can act as a bond breaker in this instance.
  2. Wearing respiratory protection, pour Flo-Coat into a 5-gallon bucket or wheelbarrow. If using a drum mixer, add a small amount of head water before adding the dry mix.
  3. Replace part of the mix water with a bond-enhancing admixture.
    1. If using Bond Strength Primer, use 1 part primer to 2 parts water.
    2. If using Concrete Glue, use 1 part primer to 1 part water.
    3. If using Bonder & Fortifier, use 2 parts primer to 1 part water.
  4. Mix for roughly three minutes until water is fully incorporated.
  5. When correctly mixed, concrete should hold together when packed together, but fall apart when released.

Project Tip: Be careful to avoid over-watering concrete mixes. Correctly-mixed bagged concrete is much stiffer than ready mix concrete – it should not “flow”!

Application

It’s time to pour! This stage is simple but ensure you move quickly. Results are best achieved with at least one assistant.

  1. Pour concrete into your form and begin consolidating with a trowel.
  2. Continue pouring until concrete reaches the top of the forms.
  3. Select a very straight piece of scrap lumber to use as a screed—ideally wide enough to span the entire slab.
  4. Drag the screed backwards in a back-and-forth sawing motion across the slab to level the surface.
  5. Capped area should be no higher than the adjoining surfaces—Sand Mix cannot be feather-edged.
  6. Use a bull float—or hand float for smaller repairs—to smooth out the surface. Technique is important here – keep the leading edge slightly elevated on the push, lift the handle to elevate the trailing edge on the return pull.
  7. Take a break! Floating brings bleed water to the surface which must evaporate before moving on to final finishing.

Project Tip: Be careful to not over-work the surface at this point. Making too many passes with a float can overwhelm the surface with water, weakening the slab and increasing the likelihood of cracking.

Finish

Bring it home! Once the surface bleed water has evaporated and the concrete is thumbprint hard, you’re ready to move into final finishing.

  1. Run an edging tool between the slab and form to encourage a clean release and create a rounded edge. Run the edger back and forth until the edge is smooth and fully separated from the form.
  2. Cut control joints between the capped slab and adjoining slab(s) using a groover tool and a 2×4 as a straight edge.
  3. Use a magnesium (mag) float to put a final smooth finish on the slab. This step will even out any imperfections left from bull floating, edging, control jointing, etc.
  4. Mag floating is complete when there is a slurry of cement brought back to the surface—the effect looks like the bleed water brought to the surface after bull floating.
  5. A hard troweled finish can be achieved by making additional passes with a steel trowel, allowing the slab to harden slightly between passes.
  6. A broom finish—popular in outdoor slabs—is achieved by dragging a concrete broom across the slab. Make light, smooth strokes—just enough pressure to make an impression on the surface.

Project Tip: Choosing when to start finishing is critical. Use the “thumbprint” test to ensure that the slab is hard enough – you should be able to press into the concrete about ¼”, but no further, when the slab is ready.

Curing

A critical but often overlooked final step to getting a great slab.

  1. Apply Concrete Cure ‘N Seal to the surface of the slab using a pump sprayer or a roller. Do not pour it directly on the slab!
    1. Cure ‘N Seal seals the pores in concrete to lock as much moisture into the slab as possible to ensure the slab doesn’t lose moisture prematurely, which could lead to cracking.
  2. Even when using Cure ‘N Seal, it’s critical to keep the slab moist for several days to promote a proper cure.
  3. Cover the slab with wet burlap, hose it down frequently throughout the day, or place a sprinkler next to the slab – just don’t skip this step!

Project Tip: Properly cured concrete can be up to twice as strong as un-cured concrete and will have a significantly longer lifespan.