SGM-SF_2017with 12/20 Revisions

4 SGM-SF Gravel or crushed stone Abundant hydraulic conductivity exists with mostly 3/4 inch stones in aggregates classified in ASTM C33 numbers 5, 56, 57 or 6. These products are commonly used in new building construction. The size of pores you see between stones or aggregates is an indication of how permeable that aggregate layer is. Where the total size of the pores represents an open area smaller than the open end of a suction pipe, system airflow is inhibited. Sands, fine gravels and soils Advisory — Sands that contain more than 10% fine sand, silt and clay should not be as gas permeable. Expansive soils or soils that contain more than 35% sand, fines, clay and silt should not be as gas permeable. Solid clay is impervious to air movement. Unified Soil Classification System (ASTM D 2487) This table helps illustrate various soil compositions. Areas NOT highlighted with gray background are the most permeable. PFE Measurements: All mitigators will encounter situations that require, in addition to “qualitative evidence” indicating airflow and direction, “quantitative measurements” that tell you exactly how much air volume and vacuum is needed. This an important tool to not disregard. Some seasoned mitigators immediately create pilot holes for PFE testing at 4 locations to evaluate each outer quadrant of a slab. Such practice can enhance PFE characterization of the sub-slab condition and save a lot of grief.