Dear Mr. Marantz:
There is a crack with a width of greater than one quarter of an inch, or 16mm, in the bottom-most step of the concrete stairs attached to my 47 year-old house. Apparently, the bottom half of the stairs shifted with the ground while the upper steps did not. The stairs are attached to the house, which is built on piles. The last repair was professionally done, over ten years ago, and none of the contractors consulted at the time were optimistic that any concrete patch job would last for long. In fact, the crack reappeared two years later and has gotten worse, since. The appearance is unsightly and wasps use the crack as an entranceway to their nest beneath the steps.
I understand that cracks in house foundations can be repaired with an injectable, flexible resin that leaves a closed cell rubber gasket in the entire crack. Can this be used for my cracked step? If so, is this an easy do it yourself project? Where can such a material be acquired and would it’s colour match the concrete? If not, what are the alternatives?
Thank you, in advance, for any assistance you can provide in this matter.
There may be several considerations in attempting a repair on a damaged set of concrete steps other than patching the crack itself. If the crack continues to enlarge due to ground movement, the bottom step may be dropping, increasing the rise between this and the next step. This will create a greater chance of tripping on the steps, which may be a significant safety concern.
Repairs to cracks in concrete can often be effectively done using injection with compounds like you mentioned, or more commonly epoxy-based adhesives. These materials will fill the crack and seal it to prevent moisture and pest intrusion. Some may even help to bond the two surfaces together, preventing some movement, but not eliminating it. This may be effective for a short period of time, perhaps up to a few years, but will eventually lose its adhesion to one of the moving surfaces and the crack will again open up. This is what has happened in the past with the other repair.
The cause of the crack must be addressed before attempts at repairs are done, to ensure success. The cause of the crack is movement and settlement in the bottom step, which has broken away from the main stairs, due to soil erosion and seasonal expansion and contraction. There is likely a void developed beneath the steps that the wasps have used to create a nice dry home for their nest. This void may be several feet deep and will allow the soil surrounding the stairs and beneath the bottom step to slowly sink toward this pit. This will cause the bottom step to sink, while the upper part of the stairs remain attached to the foundation of the house with bolts or reinforcing steel. To fix the problem properly, the bottom step will have to be broken up and removed to allow backfilling the void beneath the stairs.
Once this pit and the surrounding soil has been filled and built up to prevent further erosion, the steps can be repaired. Compaction of a good base of granular fill below the old bottom step is essential to prevent further movement. Once this has been done, a new bottom step may be formed and concrete poured to replace the settled one. If the sidewalk or landing in front has sunken significantly, two new steps may be required to retain the proper rise. This new step should be secured to the remaining old concrete with re-bar or steel bolts, installed before re-pouring.
If a new bottom concrete step is not desired, or two difficult, a pressure treated wooden step may be installed with less effort and cost. This could be bolted to the old stairs and would be less likely to pull away with soil expansion and contraction. It will not match the upper stairs, but may provide a simpler solution. Care must be taken to prepare the soil beneath the steps and the new stair similar to the concrete repair suggested previously.
This issue may seem like a small item that may be moderately costly to properly repair, considering the size of the crack. This cost will be minor compared to the damage if someone happens to stumble and fall due to the uneven surfaces between the stairs. In this case, serious injury may occur to family or friends. Patching the crack to keep out nasty stinging insects may be a legitimate concern, but proper repairs to prevent dangerous falls is much more of a reason to do the job right.