NATIONAL RESEARCH COUNCIL
DIVISION OF BUILDING RESEARCH
INFLUENCE OF SILICONE TREATMENT OF
BRICKS ON MOISTURE PENETRATION AND
BOND STRENGTH OF
Division of Building Research
Work done as part of a continuing program of masonry
studies has shown the importance of the suction characteristics
of the brick upon the excellence of the bond obtained.
is more difficult to obtain good bond when the brick has a
high initial rate of absorption.
the silicone treatment of bricks upon the moisture penetration
and bond strength of brickwork subsequently made with them.
One paper on this work has been published (1).
from a further series of tests is now presented.
This led to a study of
The author is a research officer with the Building
Materials Section of the Division engaged in studies of
N. B. Hutcheon,
INFLUENCE OF SILICONE TREATMENT OF BRICKS ON MOISTURE PENETRATION
ANTI BONI> STRENGTH OF BRICRWORK
A previous paper (1) described tests which had shown
that improved resistance of brick masonry to moisture
penetration was obtained when high-suction bricks were treated
with a water-soluble silicone before being laid in mortar"
The tests had been made on laboratory-constructed panels
of brickwork consisting of five bricks laid one above the
other with mortar joints between them"
secure additional information on the subject was provided in
October 19599 when outdoor test piers were being constructed
of untreated and
cence"The piers were constructed by a bricklayer and in the
course of the work he was asked to construct, in addition to
the piers9 small panels of brick masonry that could be tested
in the laboratory for moisture penetration and bond strength
An opportunity to
silicone~treated bricks to study efflores-
Two types of bricks and two mortars were used"
The bricks were used in their normal dry conditiong and
also after they had been treated by being dipped in a solution
of water-soluble silicone9which reduced greatly the property
of initial rate of absorption"
the extruded wire~cu
press type"Properties of the bricks are given in Table I"
One of the bricks was of
t type9 while the other was of the dry-
One of the mortars was composed of a masonry
cement and sand in proportions by volume of one part to three
parts respectivelY9 while the other mortar was made of
portland cement9lime and sand in proportions by volume of
one part oement 9 one part lime and 6 parts of dry sand"
lime was a dry hydrate soaked overnight before use"
mortars were mixed on the job site by the bricklayer9s
helper9 by hoeing the materials together in a mortar trough"
PANEL CONSTRUCTION ANI> TESTING
The panels were constructed by placing a bed of
mortar on a brick9 setting a brick directly over the brick
- 2 -
below and tapping it into placeo
followed closely that normally used by the bricklayer in
his worko The only controlled factor in the cons"truction
was the time interval between placing the mortar bed on a
brick and setting a brick in ito
oontrolled at either ~ - m i n u t e
the manner of construction duplicated as closely as possible
the normal technique of the bricklayero
The method therefore
This period of time was
or 1 minute. In other respects,
The panels were stored in the laboratory for
several weeks at 73°F and 50 per cent relative humidity
before they were tested. The moisture penetration properties
were determined by the method described in DBR Internal Report
160 (2).After this test they were dried for about 2 weeks
(at 73°F and 50 per cent relative humidity) when the strength
of bond between brick and mortar in direct tension was
d e t e r m i n e d ~
using the method described in DBR Internal Report
The results of the tests are presented in Table II.
The third column indicates the average bond strength of all
the joints of the panel; in brackets is shown the average
bond strength of all the joints of the 3 panels of each seto
The last four columns of the table show the
results of the leakage tests.
that passed through the panels in the first hour of test and
in 24 hours of test are shown 9 along with the maximum rate
of leakage recorded during the test (expressed as ml per
minute). The final column shows how long it took for dampness
to appear on the back of the panel.
The amounts of water (in ml)
It can be seen that for the pressed brick used
with both mortars the strength of bond was considerably
higher when the brick was treated with the silicone solutiono
The treatment applied to this brick also resulted in brick-
work which was much superior in resistance to moisture pene-
when compared with panels of the untreated brick.
Bond strength of the extruded brick, however, was
clearly reduced as a result of the silicone treatment when
the brick was used with the masonry cement mortar and was
slightly reduced when the brick was used with the 1:1:6
Moisture penetration tests of panels of the extruded
brick did not reveal significant differences between those of
- 3 -
The effect of treating bricks with a water-soluble
silicone solution on the bond strength and moisture pene-
tration properties of brickwork panels was studied.
For one brick, of the dry-press type, both bond
strength and resistance to moisture penetration increased
greatly as a result of the silicone treatment.
brick of lower suction, however, reduced bond strength and
insignificant change in resistance to moisture penetration
resulted from the silicone treatment.
(1) Ritchie, T.Influence of silicone pretreatment and
wetting of brick on moisture penetration
of brick masonry. Brick and Clay Record,
Vol. 136, April 1960, p.84-88 (Reprinted
as NRC 5686).
(2)Ritchie, T.A small-panel method for investigating
moisture penetration of brick masonry.
DBR Internal Report 160, September 1958,
Hodgins, P.T.Small brick panel tests at Ottawa.
Apparatus and techniques for study of
bond strength. DBR Internal Report 175,
March 1959, 9 p.