Best practices for
self-adhesive and cold adhesive installation
These membranes
require different application techniques than traditional roofing systems
By RINO THERIAULT,
Soprema Inc.
Advances in
self-adhesive technology, installation tools and methods are pushing the growth
of this application method as roofing contractors reap the benefits of
completing SBS modified bitumen projects with greater ease, speed and
cost-effectiveness. Along with cold adhesive installation, they are more
commonly being used where hot asphalt odors are a concern or site conditions
preclude the use of open flame, whether torch or kettle.
However,
techniques for application of these roofing systems are different from those
used for hot asphalt and heat-welded membranes. It is highly recommended that
installers take advantage of the training programs offered by roofing
manufacturers to become familiar with the procedures required for completion of
a high performance, long lasting roofing system. This article, while not
intended as a substitute for attending a training program, looks at these
installation methods to illustrate the different techniques required.
A review of the
types of reinforcement options for modified bitumen membranes – glass mat,
non-woven polyester or a composite polyester/glass grid – will help in
understanding how product selection impacts on the finished project. Glass mat
performs the function of a bitumen carrier, while non-woven polyester
reinforcement adds strength to withstand in-service stresses. Composite
reinforcements of polyester and glass grid combine the best properties of each
in a membrane with excellent mechanical properties and dimensional stability.
The latter is key to achieving effective installation of self-adhesive and cold
adhesive products. However, it should be remembered that all membranes,
independent of their reinforcement, need to be relaxed before installation.
Temperature will indicate the length of time the unrolled membranes should be
relaxed.
WEATHER-SENSITIVITY
Both self-adhesive
products and membranes installed in cold, mastic-type adhesives are temperature
sensitive and generally not recommended for use below five degrees Celsius. The
installer should also be aware that the temperature of the substrate and the
membranes themselves must be considered in addition to the ambient temperature.
The membranes and adhesive may actually be colder than the ambient temperature,
if for example, they were stored on the roof and the overnight temperature
dipped to below five degrees Celsius. They should ideally be stored at a
minimum of 10 degrees Celsius. Moisture must also be considered and appropriate
measures taken to ensure both the roofing products and substrates are dry.
TWO-PLY
SELF-ADHESIVE SYSTEMS
Self-adhesive
membranes should more appropriately be referred to as pressure-sensitive, in
the same way as we think of labels, since the application of pressure to the
membranes is a key step in the installation process. When observed closely,
self-adhesive membranes tend to bond only to the high points on the surface of
the substrate. The application of pressure using appropriate weight rollers
maximizes the actual contact area between the self-adhesive bitumen and the
substrate, increasing the ultimate bond strength. The base sheet membrane
should be rolled with a 20-inch, 33 pound roller or the appropriate size and
weight of roller recommended by the manufacturer. The membrane should be rolled
from the centre to the outside edges for effective adhesion. The same method is
used for the cap sheet, but with a heavier roller. On the parapet, the
self-adhesive membrane should be applied with a flat-edged aluminum applicator
at the 90-degree T-junction angles to ensure adequate bonding, and the vertical
surface rolled from top to bottom, a reverse installation technique to that
used with heat-welded application. Although self-adhesive, the finishing
touches may require some extra help at the side and end laps for proper
sealing. Adhesive can be applied with a 3/16-inch notched trowel to the recommended
width at the end laps, and the edge of some laps may be sealed with an electric
hot air gun.
MOISTURE
With self-adhesive
products, moisture on the membrane or the substrate will lead to a lack of
adhesion and will create wrinkling and blistering. Let’s deal with the membrane
first. When products are delivered to a job site they should be covered and
protected from the possibility of rain. If they do happen to get wet, they must
be rolled opened and the membrane dried before installation, and it should be
remembered that a sanded surface will be more susceptible to moisture-retention
and require longer drying time.
Moisture in the
substrate, as well as the condition of the surface itself, are critical to
successful installation. Wood substrates must be dry, smooth and free of
irregularities. Improper construction methods or left over materials following
the removal of a previous roofing system will result in an uneven substrate
(especially in un-insulated roofing assemblies). This can create unbonded areas
and result in substandard performance. The installation of a low-cost asphaltic
recovery board is recommended to eliminate surface irregularities.
Much like a piece
of adhesive tape, pressure-sensitive self-adhesive membranes will not stick
well to a dusty surface. Insulations and cover boards must be properly stored
on site and adjacent work minimized to avoid dust during membrane installation.
Work should be staged, if possible, with the self-adhesive cap sheet applied on
the same day as the base sheet to minimize the risk of surface contamination.
COLD ADHESIVES
The adhesives used
are typically solvent-based and require several to many days to achieve full
cure. The roofing system must therefore rely on the initial “green” strength
and the waterproofing properties of the adhesive to provide good performance
until the adhesive is fully cured. Because of this slow curing, the use of
glass or composite reinforced membranes with superior dimensional stability
reduces the risk of movement and wrinkling during curing. Even then, the rolls
should be laid out and relaxed.
Precise
distribution of the cold adhesive is important for good bonding – more is not
better. Brush grade adhesive should be applied to the field with a 3/16-inch
notched squeegee for consistent volume, and trowel grade adhesive on the end
laps should be applied with a 3/16-inch notched trowel. Too much adhesive can
lead to blistering, delaminating and possible slippage. The membrane should be
pressed into the adhesive bed with an 18-inch, 90 pound roller from the centre
of the membrane roll to the outer edge as full adhesion at the seams and end
laps is critical in preventing fishmouths. All products used should be from one
manufacturer to ensure compatibility.
Fumes and odors
may be a concern with solvent adhesives, and cautions need to be implemented.
The area should be well-ventilated for safety, and air intakes closed to
prevent discomfort to building occupants. In a confined area, a self-adhesive
product should be considered. And, an open flame should not be present in the
installation area as fumes can be highly flammable.
MIX AND MATCH
OPPORTUNITIES
Self-adhesive and
mechanically-fastened base sheet membranes provide the opportunity to select
cap sheet installation methods suited to specific conditions. A
semi-independent base sheet membrane, with discontinuous self-adhesive strips
or spots covering approximately 50 per cent of the bottom face of the membrane,
is used as part of a roofing system. This discontinuous adhesion allows stress
distribution from the substrate as the roof system contracts/expands with
thermal cycling, and allows venting of the membrane underface to eliminate risk
of blistering or wrinkling. More than a membrane, it is part of a system
applied to a specific insulation substrate, possessing a dimensionally stable
glass fleece facer with an acrylic coating that eliminates the need for cover
board. It simplifies roof system installation and provides a suitable substrate
surface for the self-adhesive base sheet. The cap sheet can be applied with
cold adhesive or heat-welded, with self-adhesive flashings used on parapets.
Mechanical
fastening is another alternative, either as a single-ply roofing system for
roofs with slopes greater than three per cent 3/8-inch in 12 inches) or as base
sheet in the roofing assembly. With the single-ply system, overlap joints can
be sealed with adhesive or can be heat-welded if conditions warrant. As part of
a two-ply roofing system, cold adhesive can be used for cap sheet application over
the mechanically-fastened base sheet, as well as self-adhesive or heat welding.
In a
mechanically-fastened roof system, the quantity and spacing of the fasteners
are critical in preventing movement of the components, and most importantly in
withstanding wind uplift. Ensure that the proper type, size and length of screw
fasteners, and the proper size and shape of plates are used. Also use the
proper installation equipment. Power screw drivers should always be equipped
with a depth-sensitive nosepiece for consistent fastener depth to prevent the
screws and plates being driven into the substrate. The resulting indentations
will prevent proper adhesion of the self-adhesive cap sheet at these locations.
For adhesive installed systems, the adhesive would pool in the indentations and
take much longer than normal to cure. For maximum adhesion of the
mechanically-fastened base sheet, the pattern and spacing of the fasteners
should meet manufacturer’s guidelines.
BACK TO SCHOOL
By following
manufacturer recommendations, these installation methods provide high
performance roofing systems, and in the hands of trained applicators can result
in easier, faster and most cost-effective projects. The payback for attending a
training program provided by a modified bitumen manufacturer will be immediate.
ABOUT THE AUTHOR
Rino Theriault is
a senior technician with Soprema Inc., providing on-site technical support for
installation of the company’s SBS modified bitumen roofing systems. He has 33
years of experience in the roofing industry, the last 18 years with Soprema
Inc.
