Filling a cavity under a slab
Some nasty runoff eroded a cavity under the edge of my concrete patio, and I became concerned about the lack of bearing along its edge. Sooner or later, the slab would break off where the soil had been washed away. To remedy the situation, I used the apparatus shown in the drawing to pack mortar into the cavity. The rig consists of a length of 2-in. PVC pipe with a 90° elbow glued to one end. The plunger is a length of 1-1/2 in. PVC pipe with a gasket made of an old inner tube on its end. The gasket is held fast by a screw and a washer driven into a wooden plug in the end of the plunger.
To use the rig, I put the elbow at the opening of the cavity and packed dirt around it to keep the mortar from escaping. Then I poured a runny mortar mix into the 2-in. pipe until it rose to the top. By using the plunger, I was able to push the remaining mortar into the cavity until it was full.
David L.Johnson, Clinton, IA