Building with Pumice (GTZ, 1990, 86 p.): 4. Instructions for Building Pumice-Concrete Houses: 4.1 House with In-situ Pumice-concrete Walls

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Building with Pumice (GTZ, 1990, 86 p.)

4. Instructions for Building Pumice-Concrete Houses

		(introduction...)
		4.1 House with In-situ Pumice-concrete Walls
		4.2 House with Pumice-concrete Solid-block/brick Walls
		4.3 House with Pumice-concrete Cavity-block Walls
		4.4 House with Pumice-panel Walls
		4.5 House with Wall-length Reinforced Pumice-concrete Hollow-core Planks as Self-supporting Wall Members

4.1 House with In-situ Pumice-concrete Walls

Technical description:

This house has load-bearing walls made of in-situ cast pumice concrete. It rests on a reinforced concrete strip footing (normal -weight concrete, not pumice concrete) or on a natural-stone masonry foundation. The in-situ pumice-concrete walls are erected directly on the foundation. They are 15 to 25 cm thick and, to the extent necessary, reinforced with steel to provide protection against earthquakes. The massive walls can be rendered/plastered or smoothed with several coats of paint. The door and window openings are simply left free, and the door -and window cases are embedded in the concrete. In-situ concrete walls have the advantage of not requiring prefabrication (like bricks or panels). On the other hand, they do require the installation of wooden form work to contain the concrete - which in turn involves extra expense, work and prior knowledge (Fig. 50). The roof substructure consists of lattice steel or wooden beams. The roof skin can be made of galvanized corrugated sheeting screwed down on wooden laths, although any other kind of roofing would also be suitable, e.g. clay roofing tiles, straw and reed, etc. The solid walls are strong enough to accommodate a ceiling for the possible subsequent addition of a second story. The floor is made of thin concrete screed on a layer of sand and gravel. Wooden or steel frames hinged to the concrete - embedded cases are recommended for the windows and doors.

Figure 50: Wooden formwork for in-situ pumice-concrete walls

This type of construction is most suitable for building new homes. Since it requires a substantial amount of formwork, it is appropriate for countries with adequate supplies of wood. Putting up formwork is no job for beginners, so the aid of specialists should be enlisted.

This type of house lends itself well to the construction of sizable housing developments by self-help cooperatives. The use of prefabricated forms that can be used repeatedly, together with the aid of trained specialists, can help maximize the effectiveness of the building effort.

The following list is a rough bill of quantities for the subject type of house. Local prices can be entered in the "price" column, thus allowing comparison with other house -building systems.

Bill of quantities

Quantities	4.1 House with pumice concrete walls	Walls	Prices
ca. 50 m² wall area	walls comprising 7.5 m³ pumice concrete for a wall thickness of 15 cm. A concrete mixing ratio of 1:4 will yield about 7.5 m³ pumice concrete for 1000 kg cement (20 bags weighing 50 kg each). The same walls with a thickness of 25 cm require 12.5 m³ pumice concrete. For a mixing ratio of 1:4, about 1750 kg cement (35 bags weighting 50 kg each) are needed for 12.5 m³ pumice concrete.		...
70 m	reinforcing rods (approx. 10 mm diameter) for a peripheral tie beam, if the house is located in an earthquake area.
30 m	reinforcing rods for around the doors, windows and corners.
ca. 50 m²	wooden formwork, at least 2 cm thick for casting the walls. Suggestion: prepare forms with height of roughly 1.10 m and cast the formwork and pour the upper part. Wood for forms can often be borrowed, not necessarily bought.

Figure 51 and 52

Figure 53 and 54

Figure 55: Section

Figure 56: Isometric view