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- All retaining walls need to be installed on some type of layered base that is made up of a rough, pebble-stone base underneath a layer of sand or stone dust for cushioning. This foundation layer is usually 6 to 8 inches deep and is made up of fingernail-sized fragments that help the soil around and underneath the wall to drain during the wet season so freezing does not occur and upheave the wall. Limestone is one of many types of rock that can be used.
- The traditional cushion layer is usually some type of sand because it has superior draining capabilities compared to most types of stone dust. While limestone dust is still susceptible to nature and should not be used in wet climates or clay soils, it is more than acceptable to be used as a cushion layer on top of the gravel layer for retaining walls. The 2 to 4 inches of sand acts as a cushion for the stone wall as it settles over the years, keeping the original wall’s structure intact.
- While limestone dust cannot be used as a grout to fill the vertical joints, it is an acceptable joint filler for horizontal joints on top of a retaining wall. You can also mix in limestone dust with grout if you want to adjust the color somewhat, as the light nature of limestone dust can help lighten traditional gray grout into something a little more neutral in tone. You can also use limestone dust to fill the joints on walkways and patios.
- While the pebbled sections of limestone are fine for any type of retaining wall, stone dust has weaknesses. If you live in an area where the soil is wet or claylike or you experience heavy amounts of rainfall or moisture during the freeze/thaw cycle of the year, you will not want to use limestone dust as the padding layer. Instead you should use sand. This is because stone dust readily retains water and when water freezes it will buckle upward, which can knock the wall out of place and upheave it in sections.
Foundation Layer
Cushion Layer
Joint Filler
Considerations
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