The Mount Holly news. [volume] (Mount Holly, Burlington Co., N.J.) 1891-1942, 1911-08-15
He MOUNT HOLLY NEWS
TUESDAY, AUGUST 10, 1911.
WATERPROOF CONCRETE.
How to Prepare Mixture 80 Il 10 I'm.
pervions to Moisture.

How to Prepars Mixture 80 Il 10 Inn
pervio1s to Moisture.
Concrete is very largely employed
Ii many building constructions, and
II some situations It Is very important
that II should be at least practically
waterproof. There are several methods
Of rendering concrete more or less I'm,
permeable to water. some simple and
free TO anyone. and some involving
the use OF secret OF patented com.
pounds. OF the former the simplest
method Is to mix hydrated lime or
finely divided clay with the concrete
thus at least partially filing the voids
or interstices in the concrete and de-
creasing the percolation Of water.
Another simple method is to mix
powdered alum with the cement and
dissolve ordinary soap in the water to
be used in mixing the concrete. Al
though the latter materials have been
used for more than sixty years as a
wash for rendering masonry impervi-
GUS to water. and although In recent
years they have frequently been en-
ployed MS ingredients of concrete to
make the entire mass impermeable, the
proportions to be employed and the
reason for the effect seem to have had
little or no scientific consideration; at
least the proportions used In practice
vary very widely.
TO use. the alum and soap method
Of decreasing the permeability of NOR
tar or concrete the alum In powdered
form may be mixed with the dry CO.
ment or the sand. and the soap may be
dissolved In the water employed in
mixing fl1e concrete. or both the alum
and the soap may be dissolved in the
water The former is probably the
safer method In practice. since with
the latter method the water must be
thoroughly stirred while the two are
being mixed. or the precipitate may
form In large masses, which 1t Is prac-
ticnily impossible to break up: and
further, the water must be kept stirred
10 prevent the compound from ac-
cumuIating on the surface These are
conditions that 1t In not always easy
TO be certain Of securing. However.
the alum Is more easily dissolved than
the soap. and hence the alum may be
dissolved in. say. one-ffth of the water.
aud the soap 10 the remaining four
fifthR and then the two portions may
be mixed together. being careful to stir
them ms the mixing progresses The
alum and the soap combine and form
finely divided. fiocculent. fnsoluble,
water repeling compound. which ills
the pores OF the concrete and decreases
its permeability
The best proportions are. alum one
part and hard soap two parts. both by
weight Soap varies In its chemical
composition. and hence a single pro
portion cannot be stated which wifi be
chemically exact for all cases The
above proportion Is In round numbers.
the relative combining weights of
alum and average hard soap. and
hence 1t is the best. proportion to use.
although widely different proportions
have been used IN practice with sue
cess. ANY REASONABLY pure soap will
u.s. H1t n sui sup Is tllllD}GQ IL
greater amount should be used in pro
portion to the amount of water In IT..
1t Is difficult to dissolve more than
about 3 per cent of hard soap in cold
water. and hence this practically I'm
Its he amount of alum TO Id per cent
and of the soap to 8 per cent. These
amounts will give precipitate equal
to about per cent of the weight Of
the total water The amount OF precip-
ifate formed In the pores of the NOR
tar or concrete will depend upon the
amount of wafer used In the mixing
OF course. II Il he dissolved In small
er quantity OF soap and alum the soap
could be first dissolved In smaller
quantity ct hot water. which Is after
ward mixed with the water used In
making the mortar. but this is hardly
practicable or necessary.