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  • By Mark Meshulam

    Information to help you find and manage your caulking contractor

    Mark Meshulam is an expert witness and consultant for caulk installation and failures. He has extensive experience working with caulking contractors.

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    Since caulk is usually the primary means of sealing the window system together and to its surrounding condition, caulk failures are often part of a window leak problems. To avoid caulk failures and to get the best from your caulking contractor learn here what can go wrong and how to avoid it.

    To the uninitiated, caulk is gooey stuff you buy in a tube and smear on cracks. To window-ologists, however, caulk is a science.

    Window leaks related to caulk failures

    1. Perimeter caulk 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. This brittle material cracked at the first thermal movement. Water leaks filled 5 gallon buckets and the wall became the worst mold colony I ever saw. Lesson: use caulk around your windows installed by a reputable caulk contractor, not creativity.

    Caulk joint is not tooled, is used in insufficient amount, has gaps and poor joint design. It was clearly not installed by a knowledgeable caulking contractor

    Caulk joint is not tooled, is used in insufficient amount, has gaps and poor joint design. It will leak! This is a classic caulk failure. No decent caulk contractor would do this

    2. Caulk deterioration or reversion
    In this type of caulk 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 rectify it. A good caulking contractor uses fresh materials and can quickly spot a bad batch.

    Caulk failure can occur when it has exceeded its expiration date. Use a good caulking contractor to ensure the freshest products are used

    A good caulking contractor would not use caulk which has exceeded its expiration date

    This caulk failure is characterized by detaching from one or both substrates. This is called caulk adhesive failure. A good caulking contractor will test for adhesion before starting the job

    This caulk failure is characterized by having detached from one or both substrates. This is called caulk adhesive failure.

    3. Caulk failure: adhesive
    Adhesive caulk failure occurs when the caulk does not stick to one or both substrates. Sometimes the adhesive bond can look good at first, but release days or weeks after application. The best way to prevent this type of caulk failure is to have a good caulking contractor perform adhesion tests on substrates before performing all of the caulk work. This caulking contractor will perform the tests with and without primers.
    Equally important is the use of proper cleaning techniques prior to caulk application, and good “tooling”. A good caulking contractor will always clean correctly and tool the joints! This good caulking contractor will carefully follow manufacturer’s instructions for cleaning and tooling.

    4. Caulk failure: cohesive
    Cohesive caulk failure occurs when the caulk shows a rupture or tear within its boundaries as opposed to where it sticks to something else. Cohesive caulk failure can occur as a result of sealant deterioration or poor joint design. Caulk joints must be installed by a reputable caulking contractor according to manufacturer-approved designs. 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.

    When a rupture occurs within the sealant itself, this is called cohesive caulk failure

    When a rupture occurs within the caulk itself, this is called cohesive caulk failure

    Caulk adhesion and cohesion failures in tension and shear

    Everything you wanted to know about caulk failure, both adhesive and cohesive, in shear and tension, in one richly illustrated graphic. A solid caulking contractor will help you avoid these pitfalls.

    5. Caulk failure: discontinuity
    Caulk is only as good as the person who installs it, and the substrate that is being sealed. If the caulking contractor 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. Caulk failure: immersion Unless your building is caulked with aquarium sealer, I would bet that your warranty will be void, and caulk failure will occur prematurely, if the caulk is immersed in water on an ongoing basis. The most classic example of this is at “back-pitched” sills or balconies. If you see your caulk 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. A good caulking contractor should advise you if such conditions exist.

    7. Caulk failure: incompatibility
    Caulk utilizes fairly complex chemistry which includes solids, solvents, the cure chemistry, crosslinking of molecules as cure takes place, the release of by-products of cure and the development of adhesion. If the caulk is in the presence of other materials which are reactive (as opposed to inert), you might find that the two materials will react to one another adversely. They might discolor, degrade one another, fail to adhere to one another, or prevent the cure of the caulk.

    A good caulking contractor will take caulk compatibility seriously and test any suspiciously reactive substrates. They will also make sure to use the cleaning solvent which is compatible with the sealant. If the instructions say to use isopropyl alcohol (IPA) for example, they will know to not use use denatured alcohol, grain alcohol or vodka.

    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 procedures

    For a good caulking job, involve an expert and a good caulking contractor

    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 caulking contractor, let me know.

    Mark Meshulam, Chicago Window Expert inspects sealant from scaffold on highrise building

    Mark Meshulam, Chicago Window Expert inspects sealant from scaffold on highrise building

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