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WARNING: Chemicals
known to the State of
California to cause cancer,
birth defects, or other
reproductive harm are
created by the combustion
of propane, use of hot tar
kettles and tar products.

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Concrete Block Insulation

Insulated concrete blocks can accommodate many walls in a home. Their
cores are filled with insulation (except for those cells requiring structural
steel reinforcing and concrete infill), which raises the average wall R-value.
The better concrete masonry units reduce the area of connecting webs as
much as possible.

Types of Concrete Block Insulation

There are several ways to incorporate foam insulation—such as polystyrene,
polyisocyanurate or polyiso, and polyurethane—into concrete blocks. The
hollow cores of concrete blocks can be filled by pouring and/or injecting
loose foam beads or liquid foam. Some manufacturers make concrete
blocks that accommodate rigid foam inserts.
Some block makers coat polystyrene beads with a thin film of concrete. The
concrete serves to bond the polystyrene while providing limited structural
integrity. The most common group of ingredients are expanded polystyrene
mixed with Portland cement, sand, and chemical additives. These make
surface-bonded wall assemblies with a wall R-value of R-1 per inch
thickness. Polystyrene inserts placed in the block cores increase the unit
thermal resistance to about R-2 per inch.

In the United States, two varieties of solid, precast autoclaved concrete
masonry units are now available: autoclaved aerated concrete (AAC), and
autoclaved cellular concrete (ACC). This class of material has been
commonly used in European construction since the late 1940s. Air makes
up 80% (by volume) of the material. Autoclaved concrete has ten times the
insulating value of conventional concrete. The R-1.1 per inch blocks are
large, light, and have a flat surface that looks like a hard, fine sponge.
Mastic or a thin mortar is used to construct a wall, and the wall then often
gets a layer of stucco as the finish. Autoclaved concrete is easily sawed,
nailed, and shaped with ordinary tools. Since the material absorbs water
readily, it requires protection from moisture.

Precast autoclaved cellular concrete uses fly ash instead of high-silica sand
as its distinguishing component. Fly ash is a waste ash produced from
burning coal in electric power plants. The fly ash is the material that
differentiates ACC from AAC.

Hollow-core units made with a mix of concrete and wood chips are also
available. They are installed by stacking the units without using mortar (dry-
stacking). Structural stability comes from the concrete fill and appropriate
rebar throughout for structural walls. One potential problem with this type of
unit is that the wood is subject to the effects of moisture and insects.
Concrete blocks are also sometimes filled with vermiculite or perlite pellets.

Concrete block insulation is typically installed for new home construction or
in homes undergoing major renovation. Since installation involves masonry
skills, it's best to have a certified cement mason do it.

When using masonry blocks for a foundation wall, filling the block cores with
high-pressure foam works better than most poured-in insulations, like
polystyrene beads or vermiculite or perlite pellets.

Note that even though filling the block cavities and special block designs
improve a block wall's thermal characteristics, it doesn't reduce heat
movement very much when compared to insulation installed over the
surface of the blocks either on the exterior or interior of the foundation walls.
Field studies and computer simulations have shown that core-filling of any
type offers little fuel savings since the majority of heat is conducted through
the solid parts of the walls such as block webs and mortar joints.
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