Question: I’ve been reading your column in the Free Press for a while now and appreciate all your advice and guidance. I have a bit of a similar situation to that addressed in an older article you wrote, about a void under stairs. I have water pooling under these concrete stairs, which came in after all the wet weather. Now the water is going across my foundation and finding its way to a couple of window wells, which are plugged, of course. It is leaking in there and from my chimney clean out, as well.
Is using mudjack material to fill the void a good alternative to shovelling in quarter down?
I appreciate any insight, as Google doesn’t offer any solutions, Greg Fast
Answer: Filling in eroded or shrunken soil under older concrete steps should work to prevent foundation seepage, no matter what is used for the fill. As long as the top of the fill is well above the surrounding grade it should prevent water from pooling in that area and sitting up against the concrete foundation wall.
Having written many times about the need for proper grading to prevent moisture intrusion into a foundation, I am not sure what exact recommendations I proposed in the noted column. I am sure that it was suggested that filling in any depressions adjacent to that area, especially underneath stairs, was critical. Any voids under older concrete stairs, porches, patios, or additions are particularly important because they are typically hidden from view. While it may be easy to see standing water, from a heavy rain or melted snow, collecting in uncovered areas, the opposite is true in these locations. Moisture may collect and remain in large amounts in any hidden voids, and can take a long time to disappear, due to the lack of airflow for quick evaporation. Any water sitting against an older concrete foundation wall is likely to find its way through.
Preventing pooling water, and oversaturated soil, in any location adjacent to your home may be accomplished by simple regrading. Building up the grade, so that a gentle slope is created away from the foundation, is the trick. Because water will flow to low areas, either through or above saturated soil, regrading is critical. The opposite is also true, that water will not collect in higher locations, especially if there are no impediments to good drainage. The area under your stairs will have neither of these positive qualities, so upgrading will be required to prevent your problem from reoccurring.
To access that hidden area, partial excavation outside the stairs is likely the initial step. Digging a small trench beside the stairs, large enough to look underneath, will give you a good idea how bad the issue is. Shining a flashlight, or trouble light, into the cavity will help determine how much lower the soil is than the surrounding area. Once that is known, measurements can be made to figure out how much fill will be required to correct the situation. Enlarging the trench will likely be required, to allow better access for shovelling in material into the small cavity. As you have stated, granular fill is easier than soil to keep in place, so quarter down, pea gravel, sand, or mixed gravel is often the choice for this job. While soil of similar composition to the surrounding area may be a better choice, it can be difficult to obtain and manually shovel in our local clay-based soil into that space.
Your alternative of filling the void under your front steps with the same material used for mudjacking may be a good option, but will likely be much more costly. That specialized expanding soil can be fairly expensive to produce and pump under the stairs. While it may give you a superior product, which should be resistant to shrinkage and moisture absorption, it comes at a cost. The main benefit would be that you could hire a company to complete the entire installation. That would save you a significant amount of hard labour. If you are planning on hiring a contractor or landscaper to do the job, anyway, the additional cost of the mudjacking slurry may be the only difference. The other concern would be any possible disruption to the foundation, stairs, or surrounding components, due to the strength of that material. Since it is used to lift concrete slabs and other heavy components, care must be taken not to overfill the void and cause additional pressure, or physical damage, to any of the items noted.
The final areas to address are the window wells, chimney clean-outs, and other locations where the seepage is occurring. Filling in under your front steps may help prevent this from happening, but may not be the complete cure. Digging down to seal the old chimney base under ground will likely be needed to prevent further leaking in that location. Also, lifting up and securing the window wells to the foundation, if they have settled, as well as regrading inside and around them may also be a requirement. Shovelling built up snow away from the foundation next winter and spring may also help stop next year’s water infiltration.
Hiring a contractor to pump in expanding clay into the void under your stairs may be a viable, but costly, solution to your moisture issue. Especially if it is done in conjunction with other regrading and water-proofing improvements at the window wells and chimney. Otherwise, any fill that will eliminate the void and remain well above the grade outside the stairs should also help minimize future seepage.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and a Registered Home Inspector (RHI)(cahpi.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.