Washington standard. [volume] (Olympia, Wash. Territory) 1860-1921, 1911-11-17
WATERPROOF CONCRETE.
How to Prepare Mixture So It 10 I'm.
peryious 70 Moisture

How to Prepare Mixture So II 10 I'm.
pervious to Moisture.
Concrete is very largely employed
In many building constructions. aud
In some situations it is very important
that 1t should be at least practically
waterproof. There are several methods
Of rendering concrete more or less i'm
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 filling the voids
or interstlces 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-
BUS to water, and although in recent
years they have frequently been en-
ployed rs 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
ar or concrete the alum In powdered
form may be mixed with the dry &C.
ment or the sand, and the soap may be
dissolved In the water employed In
mixing the 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-
tically impossible to break up; and
further, the water must be kept stirred
to prevent the compound from ac-
cumulating on the surface. These are
conditions that It is 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-flfth Of the water,
and the soap in the remaining four
Hfths, and then the two portions may
be mixed together. being careful to stir
them us the mixing progresses. The
alum and the soap combine and form
finely divided. focculent. insoluble.
water repelling compound, which oils
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 will 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
do. but II soft soap is employed a
greater amount should be used In pro-
portion to the amount Of water I'm II.
1t Is difficult to dissolve more than
about 3 per cent Of hard soap in cold
water, and hence this practically linn
Its the amount Of alum to 1.5 per cent
and Of the soap to per cent. These
amounts will give a precipitnte equal
to about 3 per cent Of the weight Of
the total water The amount Of precip-
itate formed in the pores Of the NOR
tnr or concrete will depend upon the
amount Of water used in the mixing.
OF course. II 1t be dissolved in small
er quantity Of soap and alum the soap
could be first dissolved In a smaller
quantity Of hot water. which Is after
ward mixed with the water used In
making the mortar. but this is hardly
practicable or necessary.