Mark Meshulam is an expert witness and consultant for window sealant failures.
Since sealant (caulk) is usually the primary means of sealing elements of a window system together and to the
surrounding condition, sealant failures are often part of a window leakage problem.
Email me for a great caulking contractor at email@example.com
To the uninitiated, sealant is gooey stuff you buy in a tube at Home Depot and smear on cracks. To window-ologists,
however, sealant is a science.
Window leaks related to sealant failures
1. Perimeter Sealant Failure
Windows must be caulked to the surrounding conditions or they will surely leak. I did see a job once where an inventive
contractor tried to use the EIFS coating of the exterior wall overlapped onto the edge of the window, instead of using
caulk. Of course this brittle material cracked at the first thermal movement. Water leaks in this building filled 5
gallon buckets and the wall became the worst mold colony I ever saw. Lesson: use caulk around your windows, not
2. Sealant deterioration or reversion
In this type of sealant failure, old caulk or a “bad batch” of caulk never fully cures. It might have a gummy quality,
or turn into a disgusting liquid. This is a bad problem and will require removal and cleaning or full encapsulation to
3. Sealant failure: adhesive
Adhesive sealant failure occurs when the sealant does not stick to one or both substrates. Ironically, the adhesive bond
can release days, weeks or even months after application. It probably will not be known during application. The best way
to prevent this type of sealant failure is to perform adhesion tests on substrates before performing all of the caulk
work. Perform the tests with and without the recommended primers. This will flesh out potential adhesive
incompatibilities. Equally important is the use of proper cleaning techniques immediately prior to sealant application.
And always “tool” the joints! Carefully follow manufacturer’s instructions and recommendations for cleaning methods and follow them religiously.
4. Sealant failure: cohesive
Cohesive sealant failure occurs when the caulk shows a rupture or tear within its boundaries as opposed to where it
sticks to something else. Cohesive sealant failure can occur as a result of sealant deterioration or poor joint design.
Caulk joints must be installed according to manufacturer-approved designs in order to function well. Generally, the
design will include the use of a foam backer rod, creation of an hourglass shaped sealant cross section, a specified
ratio of width to thickness, a minimum amount of area of adhesion at each substrate, and “tooling” of the joints.
5. Sealant failure: discontinuity
Sealant is only as good as the person who installs it, and the substrate that si being sealed. If the caulker misses a
spot, even a small one, the building will leak and possibly quite a bit. Sometimes the window, flashing, or adjacent
wall has overlaps or cracks which penetrate the caulk joint. These cracks or overlaps will conduct water into the
building even with a world-class caulker on the job.
6. Sealant failure: immersion
Unless your building is caulked with aquarium sealer, I would be willing to bet that your warranty will be void, and
sealant failure will occur prematurely, if the caulk is subjected to immersion in water. The most classic example of
this is at “back-pitched” sills or balconies. If you see your sealant joints immersed in puddles of water, find a way to
either correct the pitch (slope) of the sill, or create a drainage path which will carry water away from the caulk.
7. Sealant failure: incompatibility
Caulk utilizes fairly complex chemistry which includes the actual solids involved, the solvents, the cure chemistry, the
crosslinking of molecules as cure takes place, the release of by-products of cure, the development of adhesion. If the
caulk is in the presence of other materials which also have a reactive nature (as opposed to being inert), you might
find that these two materials will react to one another, possibly not in a good way. They might degrade one another, or
fail to adhere to one another, or prevent the cure of one or both materials. Or, they might simply discolor one another
while continuing to otherwise perform.
Take sealant compatibility very seriously and test all substrates with the caulk you want to use. Also be sure to use
the cleaning solvent which is compatible with the sealant. Do not improvise with your solvent selection. If the
instructions say to use isopropyl alcohol (IPA) for example, don’t use denatured alcohol, grain alcohol or vodka. Use
what the manufacturer specifies. The wrong solvent can be incompatible with and cause seal failure.
Separating incompatible sealants
One of the frustrating ironies of waterproofing is that the two best and most frequently used waterproofing materials
don’t like each other. I am referring to the silicones, which are generally regarded as the best window and wall
sealants, with the bitumastic family, frequently used on roofs and flashings.
Bitumastic, or bituminous materials are derived from coal or oil. They are almost always black. They might be in a
liquid or mastic form, or heated and rolled on, or manufactured into a roll with an adhesive backing. They are great
waterproofers because they repel water, but they tend to either remain in a somewhat liquid state or release oil at
their surface. Few caulks will stick to them as a result.
I have spent many sessions with design professionals who grapple with this incompatibility. They generally devise an
intermediate substrate that both sealants will adhere to, such as a metal flashing. This approach can yield success,
however it can also fail. Failures will typically occur at corners, splices or intersections of the flashing, where
maintaining sealant continuity (while also maintaining separation) through that location is nearly impossible.
Great resource: Dow Corning Contractor’s Handbook. A contractor’s guide to Dow Corning construction products and
For a good sealant job, involve an expert
If you have a project which involves either failures involving sealant, or a project which will utilize a significant
amount of sealant, make sure you are doing it right. A good sealant job will last 20 years or more. A bad job can fail
during the next rainfall. It does not cost much more to do a good job. Involve an expert (call me, for instance) to
ensure that your sealant performs and gives you the value and water-tightness you bought. And if you just need a great
caulker, let me know.
Email me for a
great caulking contractor at firstname.lastname@example.org
Have sealant problems?
No matter where you are,
contact me, Mark Meshulam,
the Chicago Window Expert
For the expert attention you deserve
Download Mark Meshulam’s CV
Download Field Testing Credentials
- Air Infiltration Testing for Windows & Curtainwalls
- Condensation Investigation & Testing for Windows and Buildings
- Expert Witness & Investigation of Window Falls
- Expert Witness & Investigation of Glass Injury
- Glass Consultant for Building Professionals
- Insulating Glass Dewpoint Testing
- Insurance Claim Investigation
- Masonry Moisture Testing
- Window Consultant for Building Professionals
- Window Water Leak Testing
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