The Washington herald., 1912-08-28
CEMENT MORTAR
Is WATER-TIGHT
Bureau of Standards Issues Bulle-
tin After Making Exhaust
i've Tests.
GOOD MIXTURES ARE NEEDED

Portland cement mortar and concrete
may be made practically water-tight. II
has been determined through tests made
by the Geological Survey and the Bureau
of Standards, according to officials of the
survey. They told yesterday Of the re-
suits which had been obtained from ex-
periments made of the laboratory OF the
survey at st. Louis and at the Bureau of
Standards.
The general conclusions are summarized
in a bulletin as follows, the first series
of tests on plain mortar and concrete be-
ing correlated with those made with
mortar and concrete that had been treat
ed with the various waterproofing and
damp-proofing compounds.
Portland cement mortar and concrete
made be made practically water-tight or
impermeable (as is defined below to any
hydrostatic head up to forty feet with
out the use of any of the so-called in
tegral' waterproofing materials. but In
order to obtain such impermeable mortar
or concrete considerable care should be
exercised in selecting good materials as
aggregate and proportioning them IN
such a manner as to obtain a dense
mixture. The consistency of the mixture
should be wet enough SO that 1t can be
puddled, the particles flowing into posi-
ton without tamping. The mixture
should be well spaded against the forms
when placed so as to avoid the formation
CT pockets on the surface.
The addition of so-called integral
waterproofing compounds will not COM
pensate for lean mixtures, nor for poor
materials, nor for poor workmanship in
the fabrication Of the concrete Since in
practice the inert integral compounds
(ecting simply as void-flling materiaD
are added in such small quantities. they
have very little or no effect on the per-
meability Of the concrete.
Where Portland cement Is used as a
plaster coat, If sufficient cement be used
and the sand contain sufficient fine ma
terial (or a fine material be added and
the mortar be placed without Joints and
well troweled tcare being taken not to
cyertrowel, which may cause crazing).
the coating will be effective as an i'm
permeable medium without the use Of
any waterproofing compound.
As a precaution, under certain condi-
tions, II is undoubtedly desirable tc use
bituminous or similar coatings, even on
new work, as protection where cracks
may occur due to the settling of the
foundation or expansion or contraction
caused by temperature changes. In large
or exposed work it is practically impos-
sible to prevent some cracks, but where
cracks can be prevented no coating
whichever Is required to make the struc-
ture impermeable.
The importance of testing cement Just
before using it is generally recognized by
large consumers, but II is entirely over
looked by the great majority of those
who employ cement on a small scale, as
in building sidewalks and small houses,
cementing cellars. &C. These suggestions
are therefore addressed only to con-
sumers who have never looked into the
matter Of having tests made. A few i'm
portant reasons why tests are essential
are as follows: On account of the nature
of the manufacture of cement from raw
materials which are rarely constant in
composition, he resulting product can
hardly be expected to be invariably uni
form. Manufacturers generally take pre-
cautions to prevent the shipment of de-
fective cement. but the tests made at
the mill cannot always reveal imperfec-
tions in manufacture. The properties in
cement are subject to alteration after
leaving the mill. Cement that is found
slightly inferior when tested at the mill
may be sold where II Is not likely to be
tested Cement that is tested by large
purchasers at the mills and rejected by
In order best to ascertain the quality of
cement shipped the tests should be made
after the cement arrives on the work. |
and they should be made with the great
est care and only by responsible and
instruments have been properly stand
ardixee
For the purpose Of correcting any mir