How To Patch Dirt Section of Concrete Slab in Basement?
downingarts
| Posted in General Discussion on
We have a large damp spot in our basement which upon further examination appears to be largely dirt. The rest of the basement is a concrete slab, except for a crawlspace which is on the other side of the wall from the damp spot. The dirt/damp spot is weird because there appear to be some corner blocks buried and filled and also some places where there is a thin layer of concrete (1/4”). Perhaps a botched repair job in the past?
We are in the process of beginning to mitigate our mild radon issue and this dirt spot will be in the vicinity of the sub slab depressurization system, which is why we need to address the basement floor issue soon.
Does anyone have any ideas or suggestions? I am thinking we might just pour a new section of concrete over the dirt spot, or maybe some kind of vinyl quikcrete patch but I don’t know what would bond to the clay/dirt.
Thanks!
Replies
Those photos look more like a small oil spill. If you dig up some of that dirt, does this dirt happen to smell like old petroleum or fuel oil? Perhaps a fuel oil tank resided in this area at one point and some of the fuel oil leaked out over time or when it was removed. The legs for the tank may have rested on those concrete blocks. Look for any holes in the foundation or rim joist in the area for evidence of a fill pipe (since removed) that may have been used to fill the oil tank. At this point, I would just dig up the soil and replace it with clean sand leaving enough space for 4" of concrete. Determine where your radon mitigation will be placed and get that installed. Then drill holes into the surrounding slab to install some rebar pins to avoid settling, moisten the sand and pour new concrete in the patch area.