|Building with Pumice (GTZ, 1990, 86 p.)|
|2. General Information on Pumice|
Most pumice is found on the downwind side of volcanoes (Fig. 6).
Figure 6: Pumice deposits on the downwind side of a volcano
The average deposit is loose, with a layer thickness ranging from 50 to 300 cm. Pumice should always be extracted under expert supervision and not haphazardly; otherwise, the results will look like Figure 7. The thickness of the pumice strata decreases with increasing distance from the center of the eruption.
The size of pumice particles ranges from superfine powder (0-2 mm) to sand (2-8 mm) to gravel (8-65 mm). The particle porosity can reach 85%, meaning that 85% of the total volume consists of "air" and only 15% of solid material. Its high porosity gives pumice good thermal insulating properties and makes it very light.
Old pumice deposits in areas with once-active volcanoes are covered with a 0.2-1 m thick layer of humus. When quarrying it, care must be taken to ensure that no humus is mixed into the pumice. If a large area is being mined, e.g. for a housing project, the humus should be replaced afterwards to prevent erosion and consequent ecological damage.
Additional site-specific information on pumice deposits is available from the various national geological institutes and/or soil research offices.