Pumice Defined

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How Pumice-Crete® Works

Mostly buildings have been cast on site using forms to create walls. Pumice-Crete® is mixed, either at a central plant and delivered in standard mixer trucks, or right on site, and poured into forms. It is always used over a concrete footing or slab and once the pour reaches roof elevation another structural concrete bond beam is poured over that has connectors to fasten the roof system to the walls. Once poured the forms are removed and the rest of construction takes place. Walls are plastered with two coats of any kind of interior and exterior plaster to finish. No further insulation is used in finishing. Stucco netting is not required to adhere plaster surfaces to the wall because of the uniform coarseness of the poured wall.

Walls are poured to a thickness of at least 14 inches to obtain adequate thermal protection and structural integrity. We have mostly done I5 and 16 inch thick pours because we feel this is the optimum efficiency for structure and thermal performance. The reason this low density mix can be used with no additional structural members and additional insulation is because the walls are poured thick. This can be seen as a disadvantage but most clients I have worked with like the fact that the walls of their building have a massive look and feel to them. Many projects I have been involved with choose even thicker walls for added performance and massive appearance. This of course increases the cost.

Pumice window sill design. Windows and doors and all openings are defined at the time of pouring and the Pumice-Crete® pours around them as the pour progresses. 2x wood frames are installed in the pour to define the rough opening of the windows and doors. They are formed in such a way that once the forms are removed all the openings have been installed and shaped to their final appearance. Only minor shaping needs to happen before the final plaster coats go on.

Any roof system can be built on these masonry walls. Anchor bolts are left out of the bond beam on top of the wall that wood plates can be bolted to. Rebar can be extended out of the bond beam to connect to masonry roof systems. Wood framing is often used but more and more I am seeing roof systems such as precast structural slabs or steel systems being installed. The advantages of these can be improved fire resistance, larger spans can be accommodated, and greater variety of architectural choices. We have poured complete Pumice-Crete® domes that span 30 feet across and two stories high that need no interior support.

The forms used to pour walls can be lighter than typical concrete forms. Our standard form is constructed of 1/2" plywood with 2x4 frame backing at 2ft. spacing. Spreaders, ties, and fasteners are all made from common locally available materials. All components can be used for a number of years and dozens of pours. If managed properly there is next to no waste as a result of forming and pouring walls.

Pumice-Crete® has proven to be a cost effective, reliable alternative to conventional building methods. Low density concrete wall mixes can be made from other lightweight aggregate sources with similar performance structurally and thermally. It is a system that uses no manufactured materials since all components are usually locally available and assembled at the site of construction. It can be reinforced to increase its resistance to seismic stress and is an appropriate material for many climates.

This material has found acceptance here in New Mexico mainly because of the similarity of it with adobe construction. It is an earth based material that is very compatible with adobe styles of building.

Pumice-Crete® Building Systems of New Mexico has been building cast on site Pumice-Crete® buildings for 21 years. We offer assistance and training to builders and contractors wishing to use this technology in their locales. We help designers to determine if Pumice-Crete® is an appropriate building system for their area and provide construction details, information, and consulting services. Builders wishing to be trained in the use and installation of pumice- crete building systems can come and train with us and learn the tricks of the trade first hand.

PO Box 539, EL Prado, New Mexico 87529



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