Aberdeen herald. [volume] (Aberdeen, Chehalis County, W.T.) 1886-1917, 1911-08-24

Concrete K" yer. iargo,y eDl0!cye+
In many building constructions. ana
In some situations it is very important
that it should be nj least practically
waterproof. There are several n!"t!o"
of rendering concrete more or less iii
permeaDe to water, some simple anG
free to anyone and some involving
the use of secret of patented com
rouhds. 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 nter>tite, i'll the concre,e and ut-
crcasing the percoation 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 imrervl-
GUS to water and although in recent
years they have frequently been en-
ployed rs ingredients of concrete to
make the entire mass impermeable. the
B
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
! l,n ~, l,.
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 witt
the latter method the water must be
thoroughly stirred while the two are
being mixed. or the prccipitate may
| form in large masses, which it 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-fifth of the water.
and the soap In the remaining four
! tifths, and then the two portions may
be mixed together, being careful to stir
them as the mixing progresses. The
alum and the soap combine and form
/ a finely divided. hocculent. insoluble
water repeling compound. which fills
! 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 it 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 il soft soap is employed n
greater amount should be used In pro-
portion to the amount of water in 1t.
1t IS difficult to dissolve more than
about per cent Of hard soap in cold
water and hence this practically lin
its the amount of alum TO is per cent
and Of the soap to 3 per cent. These
amounts will give precipitate equal
to about per cent Of the weight Of
the total water The amount Of precip-
itate formed In the pores Of the NOR
tar or concrete will depend upon the
amount of water used in the mixing.
OF course. II It 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.