earth-sheltered home damp-proofing
Various damp-proofing methods are appropriate for use in earth-sheltered
homes. Damp-proofing products are those which will interrupt the capillary
draw of moisture into the walls of a building but are either too thin, have
too little resistance to bridging wall cracks, or deteriorate too easily
to be considered as a good waterproofing technique. Although damp-proofing
can help dampness problems in many instances, there are no guarantees with
it. It is not intended to stop water penetration and hence there is almost
no comeback for a system that doesn't work. Some of the techniques are discussed
Concrete mix design and additives
There is much that can be done to make concrete more impermeable than it
normally is, including keeping the water/cement ratio as low as possible,
using adequate vibration when placing the concrete and including well distributed
reinforcement to limit the size of the shrinkage cracks that occur when
the concrete dries out. Admixtures can fill the capillary channels in the
concrete, others react when they come into contact with water. All these
techniques will cut down the permeability of the wall, but as long as concrete
cracks and shrinks when it dries, which is always the case (unless very
expensive expansive cements are used), cracks will occur which destroy the
integrity of the seal. For limiting the flow through the wall which is the
primary goal in reservoirs, for example, the techniques can be very successful
but even very small amounts of leakage can make unsightly marks on the wall,
roof, or floor finishes.
This refers to the coating of the wall with a dense cement plaster or similar
material. This can be done on the inside or the outside of the wall, but
as with all waterproofing applications it is best done on the outside of
the wall so that any water pressure will not tend to force the coating off
the wall and so that the wall will be on the dry side of the waterproofing
(particularly important when reinforcing steel is contained in the wall
because if it were on the wet side of the waterproofing it could then rust
and spall the concrete). Cracking of the wall which almost inevitably occurs
will also crack these generally brittle materials, and hence, they cannot
be relied on as waterproofing materials.
These can be used applied hot or cold and can be sprayed, brushed, or trowelled
on. In general, trowelling gives a better job than spraying because a denser
layer with better adhesion is obtained. Hot asphalt applications become
brittle when they cool and the cold asphalt applications have some bridging
characteristics over cracks but not sufficient to bridge normal sized structural
cracks. Asphalt emulsions are slowly soluble in water.
This is a more stable material to use underground than an asphalt emulsion.
A special waterproofing pitch used to be available but was discontinued
to comply with health standards of fume release during application. The
major pitch available now is a general purpose pitch designed for roofing
applications. It has a softening point of about 150°F and hence underground
it will remain brittle with no resealing abilities.
This is a very cheap material use. It degrades when exposed to sunlight
but when completely covered underground it should last a long time. With
reasonable laps and care taken not to puncture the sheet during placement
and backfilling it will function as good barrier against capillary draw
and vapor transmission. No attempt is usually made to seal the laps completely
and hence it will not resist a water pressure on its own. It does have the
capability of bridging some cracking in the concrete. For the floor of an
earth-sheltered house that is above the water table, has a foundation drain
system and gravel layer under the floor, this type of damp-proofing protection
will usually be adequate.
These suffer from the same problems as most damp-proofing techniques. When
the walls crack the integrity of the seal goes with it.