Evening star., 1942-06-06
Of Stars, Men
And Atoms
Notebook Of Science Progress
In Laboratory, Field
And Study
By Thomas r. Henry.

Huu Stouy
By Thomas r. Henry.
Specifications for "armored attics," as
q protection against both fire bombs
and penetrating bombs, are being set up
by the United States Bureau Of Stand
ards.
BY following these, it may be possible
for the neighborhood mechanic to turn
the average home into 4 fort against
air raids.
Even lighter bombs, the bureau ex-
perts say, can be expected to 60 through
an ordinary wood frame roof and prob
ably also an attic or upper floor. How
ever, they have determined, a covering
applied to such attic floors would great
ly increase the resistance to penetra-
ton, besides afiording protection against
fire.
The amount Of "armor" 1t Is pointed
out. must be determined by local build
ers and by the money the house owner
feels justified In spending There will
be progressive gain in safety with in
crease In thickness.
But they have determined. the govern
ment experts point out, that an inch to
lh-inch thickness of portland cement
mortar or concrete, cast in place or used
as precast slabs, will prevent ignition
Of . wood floor from a bomb such as
one OF the 1-kilogram thermine mag
nesium type which were used by the
Germans over London.
Lesser thicknesses would give tempo
rary protection, and the incombustible
finish would help in extinguishing or
removing q bomb without setting on fire
the floor beneath.
Says the Bureau OF Standards report:
~Slabs made with cinders, Stag and
other lightweight aggregates are some
what more resistive than those made
with sand and gravel, although the
latter do not depreciate appreciably
under the heat Of bombs. Precast slabs
may require . finish consisting of port
an even-wearing surface.
The wearing properties of portland
cement mortar can be greatly increased
by the addition of emulsified asphalt in
the mix. The precast slabs should pref
erably have beveled edges to enable the
mortar to fill the joints fully, and they
can be nailed in place through such
joints. An alternative to mailing might
be to bed them in mortar. Where the
traf1Ic Is light and surfaces are fairly
even, 1t might serve the purpose to fill
the joints with mortar and apply a
rubber base concrete paint.
slabs of burned clay are another
possibility-a development that deserves
attention OF the clay products industry.
Present stock sizes in solid or near solid
units, of thickness from inches up.
might be used II other considerations
permit. Where the ceiling construction
has no floor above, the most practical
method probably would be to floor it
over with boards. not necessarily
matched, on which the covering is ap-
piled.
The bomb is likely to ignite any
combustible contents near it. As pro-
lection, the side walls and roof rafters
can be covered with boards made largely
or wholly OF incombustible materials.
such as cement-asbestos or gypsum wall
boards. or with plaster. metal or gypsum
lath. Some degree of protection can
also be obtained with heavy coats of
sodium silicate. whitewash, borax paints
or other f1re-retardant coverings applied
with brush or spray. Spaces along the
walls into the construction beneath
should be blocked with the floor cover
ing material or other incombustible fill.
protection also can be applied on
wood frame fiat roofs, but preferably it
should not be more than or 4 inches
thick to give the needed additional re-
sistance to penetration. The advantage
within limits of using lightweight ma
terials is apparent in decreasing the
load on the structure and increasing
heat insulation, particularly for ordi
nary temperature conditions.
The protecting layer should be an
chored into the masonary and be water
proofed or otherwise covered. to form A
weather-tight covering. Sloping roofs
require less thickness, but introduce
greater dificulties in application.
Between the stopping layer and any
refuge room floor equivalent to impact
resistance of a single board wood floor
should intervene"