R. A. LAWRENCE ENGINEERING LTD.
STRUCTURAL ENGINEERS
61 UNION ST., SAINT JOHN, N. B. E2L 1A2
PHONE: 506-634-8259 Fax: 506-634-8353 email: [email protected]
June 30, 2010
School District No. 2
1077 St. George Blvd.
Moncton, N.B.
E1E 4C9
Attention: Mr. Jacques Gervais
RE: Exterior Stone Masonry
Moncton High School
Gentlemen:
As requested, we have undertaken a site review of the exterior stone masonry for
the purpose of identifying the extent of deterioration in the past 6 months.
1. Lintel Beams
As noted in our previous report, distress in the exterior stone masonry is mainly
the result of "corrosion jacking", from the deteriorating lintel beams embedded in the
walls. With exterior cladding constructed as solid masonry, moisture will penetrate the
walls. In the presence of moisture, the embedded lintel beams over the windows have
corroded. With the corroded metal expanding, the stone masonry has been displaced,
causing cracks in the mortar joints. The fractured joints allow moisture to enter the walls;
which increases the rate of deterioration of the steel members.
At the lower levels, horizontal fractures in the mortar joints exist above virtually
all of the windows and to a lesser extent at the upper level. The extent of deterioration is
related to the direction of the prevailing winds during storms; with the South and East
sides showing the most distress.
The rate of deterioration and expansion of the corroding metal is relatively slow.
Over a 6 month time span, the extent of further deterioration was found to be almost
undetectable. The one exception being at a rear entry in the Courtyard, (adjacent to the
Library). The crack width in the mortar joints has increased, with a portion of the mortar
missing. See Photos No. 1 & 2. In the same area, the stone lintel above the window has
been displaced outward. See Photo No. 3. These signs of distress are indications of
ongoing deterioration in the embedded steel members. With the beam concealed, it was
not possible to assess the extent of deterioration. In this area of the Courtyard, the wider
mortar joints near the level of the embedded beams are an indication of past remedial
work to prevent water leaks. It would appear that the beams in the Courtyard are
deteriorating at a faster rate.
2. Caulked Joints
In the past 8 months, District staff have carried out work on the exterior in an
effort to stop water leaks. Above many windows, caulking has been applied to the mortar
joints. The caulking will help prevent moisture entering the building. Unlike mortar, the
caulking will reduce the amount of water entering the fractures, but it will also trap
moisture within the walls. In a solid masonry wall concept, moisture is allowed to
partially penetrate the walls during inclement weather. The water will eventually
gravitate to the lower levels and seep out of the walls. Moisture trapped in the walls will
contribute to the corrosion and deterioration of the beams. Entrapped moisture will result
in a higher degree of saturation of the mortar. When subjected to freeze thaw cycles, the
saturated mortar will deteriorate and displace the masonry stone units. Caulking should
only be used as a last resort to stop water leaks, as it will have a detrimental effect on the
stone masonry.
3. Loose Stones
Around the perimeter of the windows and doorways, a decorative red sandstone
has been employed. For the most part, the stones have weak bedding planes and a high
absorption rate of moisture. In various locations, portions of the stones are missing and
assumed to have fallen to the ground. Under a window in the tower, a small section of
stone has fallen, (since our previous review). See Photo No. 4. At a theatre window along
the side, a portion of sandstone has separated from the main jamb and remains in an
unstable condition. See Photos No. 5 & 6. With the deterioration of the red sandstone, an
annual inspection should be carried out at the start of the school year. At such time, all
loose or separated portions of the stones should be removed.
4. Side Entrance
Over an entrance on the North side, deterioration of the sandstone continues.
Fractures are evident in the bedding planes. See Photos No. 7 & 8. To stabilize the
stonework, we recommend the drilling and installation of epoxy dowels in such a manner
as to intersect the fractures and bedding planes. The dowels are to be fabricated from 1/4"
diameter stainless steel rods.
5. Gymnasium Wall
Constructed in the late 1980's, the exterior walls of the Gymnasium are also
constructed with stones. The stone masonry was installed without control joints. With
shrinkage and thermal movement, near vertical cracks have occurred in the walls. See
Photos No. 9 & 10. Over the years, the fractured joints have been repaired with mortar,
which continues to crack due to thermal expansion and contraction. Repairing the joints
is addressing the symptoms, but not the cause. Corrective action would entail the
introduction of control joints at various intervals in the perimeter walls.
At the Southwest corner of the Gym, thermal forces in the exterior stone occur
from 2 directions. Near the corner, cracking has occurred in the mortar joints of both
walls. Near the top, a stone unit has been displaced outward. See Photos No. 11, 12 & 13.
Remedial action will be required to reset the displaced stones back to their original
position. Constructing vertical control joints near the corners will relieve the thermal
stresses in the walls and stabilize the stone units.
6. Steps at Side Entrance
At the 2 entrances along the North side, stone masonry walls act as rails along the
sides of the steps. Presently, the walls are showing signs of distress. The outer walls have
been displaced outward; up to 1 1/2" laterally. See Photos No. 14 & 15. Cracks exist in
the thickened mortar joints which have been previously repaired. Near the ground level,
some of the stones have deteriorated; due to a water and salt environment combined with
freeze thaw cycles. In the future, consideration should be given to reconstructing the
steps and the displaced masonry.
Summary
With the ongoing corrosion of the lintel beams embedded in the walls, the stone
masonry walls will continue to show signs of distress. With the rate of corrosion being
relatively slow, deterioration in the stone masonry walls was not apparent; the exception
being the West wall of the courtyard, adjacent to the Library. In the future, the rate and
extent of corrosion in the embedded steel members will increase; with the fractures in the
mortar joints allowing more moisture to enter the walls. Under such conditions, both
vertical and lateral displacement of the masonry stones is anticipated along with
additional water leaks within the building. Corrective action will require the removal and
replacement of embedded steel beams over the windows at all 3 levels.
The remaining items noted in this report, including the loose portions of stones,
displacement of exterior stones in the Gym walls, and deterioration in the stone masonry
at the North side entrances are localized items which should be addressed in the very near
future.
If further discussion and/or assistance is required, please contact the undersigned.
Yours truly,
R. A. LAWRENCE ENGINEERING LTD.
Raine Lawrence, P. Eng.
Photo No. 1
Courtyard: Deterioration in the Joints
Photo No. 2
Courtyard: Deterioration in the Joints