Focus on Roofing: Sealant and Adhesive Products used in Water Proofing Low-Slopped Roofing Membrane Joints, Laps and Penetrations

Posted on 10/26/2012 8:29:00 AM By Bob Braun

This blog continues the ASC Building Products series for roofing which began with ASC Blog #10. This blog will delve into perhaps the most highly demanded criterion for low-slopped roofing: It should not leak!   In earlier blogs I emphasized the industry norm to test roofing as an assembly for wind and fire resistance.  To a large extent this norm is not practiced for waterproofing.  The membrane must be completely sealed at all joints from any possible water ingress which depends on a thorough adhesive and sealant application.  The links below will embellish this point.

First let’s discuss adhesives which are needed to adhere most roofing membranes to the roof deck or underlying insulation board (as discussed in Blog #13) and to water proof the numerous joints created by butted or overlapping sheets.  The membrane attachment to parapet walls at the roof perimeter will often use rolled on adhesives and tube mastics or sealants for flashing details. Manufacturers formulate to the best possible adhesion and will determine the effectiveness by lap shear testing before and after aging.  Additionally they specify sufficient membrane or membrane-tape over-lap to insure that a water proof seal is obtained.  Visual inspection of joint seals is also a common installation QC procedure and also employed at the time of premature failure to identify the source of roof leakage.  Often a primer is employed to further insure well sealed membrane joints (see links below).

Of course a manufacturer guarantees a leak free roof for a specified period and this depends to a large extent on the performance and durability of the numerous joint adhesives (and sealants) in the assembly. I have listed related ASTM Standards from Committee D08 below. 

ASTM Adhesive Relevant Standards:

ASTM D7053/D7053M-11 Standard Guide for Determining and Evaluating Causes of Water Leakage of Low-Sloped Roofs

ASTM D1079-10 Standard Terminology Relating to Roofing and Waterproofing

Now let’s discuss sealants.  At the top of this Blog, I have again displayed the photo of a low-slopped roof and the many penetrations in the roof for the numerous utilities such as HVAC equipment, electrical conduit and plumbing penetrations, vents, elevator shaft access, etc. etc. etc.  These are often the primary points of both water and air leakage into the building in addition to the membrane butt or lap joints discussed above.  As with adhesive inspection, sealant inspection is equally important in indentifying the source of any roof leaks.  In all sealant applications a failure can usually be traced to an installation, application, or design problem.  Incorrect material selection can of course lead to early failure as well.  Guidance for roofing sealant selection is also based on testing smaller sized lab specimens per ASTM C24 Standards (See ASTM 1193).  Below I have listed a few additional related standards from ASTM Committee D08 and C24.


ASTM Sealant Relevant Standards:

ASTM C1193-11a Standard Guide for Use of Joint Sealants

ASTM D7349/D7349M-11 Standard Test Method for Determining the Capability of Roofing and Waterproofing Materials to Seal around Fasteners

Here are a few short video links to roofing applications for adhesives and sealants:


Installing curb flashing.

Re-seaming membrane with primer and adhesive membrane tape.

Visual Inspection example.     

In Blog #15, I plan to leave low-slopped roofing and begin focus on the slopped roofing applications and the diverse variety of adhesives and sealants that are used. 

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