Tech Alert: Hot Rubberized Waterproofing Systems

March 16, 2017 in Tech Alert


Hot Rubberized Waterproofing Systems


By: Frank Kaligis - Field Consultant, Level 4

Hot rubberized waterproofing systems are fluid-applied waterproofing membranes.  These systems have been used for many different applications in construction, including; below grade waterproofing, tunnels, parking decks, balcony decks, podium decks, roofs (including vegetative roofs), and planters.  Hot rubberized systems consist of a blend of asphalt and modified rubber polymers containing mineral stabilizers. These systems are fluid-applied and can create a monolithic membrane covering a large surface area that can be used on both horizontal and vertical surfaces.  Hot rubberized membranes are as the name suggests - applied while hot.  The material is heated in kettles following the manufacturer’s instructions and delivered to the area of application either by a pump or by hand carried in buckets.

Hot rubberized waterproofing systems serve three (3) main functions:

  1. Eliminates seams thus reducing potential issues with detailing transitions on systems such as roofs.
  2. Reduces the risk of leaks.
  3. Provides for more aesthetically pleasing finishes.

There are specific precautions to take when preparing and applying hot rubberized asphalt. For one, working with such hot materials can prove to be dangerous. Additionally, overheating the product or applying the product to a damp or contaminated surface can result in construction risk, as the sealing properties will have been tampered with.

Be Careful Not to Overheat the Product!

Hot rubberized asphalt is typically heated in a jacketed kettle that is gas fired. There are several different brands of hot rubberized product available. Not all brands call for the same preparation methods. It is therefore extremely important that the temperature of the product in the kettle be maintained within a range that is as specified in the manufacturer’s instructions.  For most manufacturer’s, the product is not to be exposed to temperatures above 400o F.  Exposure to excessive amounts of heat can cause the product to break down in the kettle and therefore be unable to cure properly once installed. If the hot rubberized product is unable to cure properly, this can result in a major failure of the waterproofing system application.

“In one instance, the rubberized asphalt waterproofing system began to ooze out from under the concrete topping slabs, onto the fascia and into the deck drains. Not only did this create an aesthetic problem of staining of the fascia, but the drains ultimately became clogged and caused severe leaks in various locations on the project.”

The use of a jacketed kettle can reduce the risk of overheating the product at the bottom of the kettle. Utilizing an agitator to move the product can also reduce the risk of overheating.  Another suggestion is to have an upper and lower thermometer to monitor the temperature at the bottom and top of the kettle simultaneously. If you do not utilize an agitator then we recommend periodic manual agitation of the product to prevent overheating of stagnate product.

It is vital when applying a hot rubberized waterproofing system on a deck surface that the drains are protected and plugged. Also, when steel railings are involved, rust inhibitors are to be applied to steel railing plates to prevent corrosion, and rust bleeding onto the deck. Another item to consider in the applications is that it is not to be done in inclement weather conditions…humidity and cold weather can greatly affect the outcome.

Not Heating the Product Up Enough Can Be Just As Bad!

Although overheating the product can prove to have a number of issues associated with it, not heating the product up enough reduces its working time and can create problems with adhesion as well. The product solidifies as it cools and thus will become impossible to apply when the temperature drops below a certain level which will vary by brand.

For application areas where buckets are used to transfer materials, the use of insulated buckets to keep the product at the proper temperature when transporting would be advisable.  A best practice would be to take temperature readings at random times and keep a written record of the temperature and time when it is taken. This record should track temperature for random samples both in the kettle as well as at the application site.

Safety Precautions

Never leave the kettle unattended, it is unsafe and can’t be monitored for proper temperature.  Experienced installers will also advise that you do not rely on a permanently installed kettle temperature probe, as the reading can be off due to improper handling or faulty storage conditions. Instead, it is suggested to use a handheld kettle thermometer for conducting these random samples. These readings can be compared to the permanently installed temperature probes and used to gauge the accuracy of these probes. Superintendents should not assume that the Trades are monitoring temperature of the product and should therefore be verifying that they are.

Surface Preparation

One of the most important things in installing a hot rubberized membrane is surface preparation.  Improper surface preparation can result in lack of adhesion or pin-holing of the membrane.  Oils, curing compounds, and debris can prevent proper adhesion of the membrane to the substrate.  The other major concern, especially with concrete and masonry substrates, is the presence of moisture in the substrate.  Moisture vapor escaping from the substrate causes bubbles and pinholes in the membrane that can result in water intrusion.  The industry has evolved to address the water vapor issue and many manufacturers now include a reinforcing fabric as well as a thicker overall application to reduce the risk of pinholes occurring and allowing water intrusion.

To reduce the risk of pinholes from moisture vapor, concrete should be allowed to cure for a minimum of 14 days (21 for lightweight concrete). Cure time is essential to allow water to dissipate from the concrete.

Beware of the Possibility of Delamination

The surface preparation is critical, even a surface that is too smooth can cause delamination when the product is unable to bond to the substrate. Some manufacturers require concrete substrate to have a wood or broom finish. This is because a steel-troweled finish or a smooth finish resulting from formwork can inhibit the bond, whereas a broom or wood-float finish will enhance the bond.

Hot fluid-applied rubberized asphalt can blister or delaminate at the concrete deck substrate due to a vapor drive toward the roofing or waterproofing assembly, improper surface preparation, or other sources. Delamination can occur when the internal pressure exerted by a water vapor or solvent vapor (primer) exceeds the bond forces between the membrane and the substrate. The membrane can also fail to initially bond to the substrate, causing delamination if the substrate is too smooth or includes a bond inhibitor.

When heated by the sun, hot fluid-applied rubberized asphalt can become soft and pliable. If the membrane is not fully adhered, it will delaminate from the substrate. Upon cooling, the blistered or delaminated area remains plastically deformed and if reheated can expand even further. If left uncorrected, the delamination can lead to building leakage. Fluid-applied waterproofing membranes develop small discontinuities that resemble pinholes prior to curing. The areas of discontinuity are gaps in the membrane and are often circular in shape. The gaps then become potential water-entry locations after the membrane sets.

Working With Primers

Primers to help promote bonding to the surface must be used with caution. Applying a thick layer of primer will increase the required drying time and will therefore make it so that the primer is more likely not to be cured by the time the membrane is applied. Although a thick primer application may feel dry to the touch, the solvent in the primer might not have fully flashed off and can result in problems with adhesion. Conversely, applying a thin layer of primer will make it so it is unable to adequately cover the substrate. Both conditions may result in reduced adhesion to the substrate.

Applicators must also pay careful attention to the duration that the primer is being exposed to weather and construction traffic. Primers left on overnight can accumulate moisture in the form of dew or pick up dirt and debris from construction traffic. Manufacturers might suggest applying an etching agent or another chemical agent to the surface of the concrete deck or conducting a form of mechanical abrasion (i.e., sandblasting, short-lasting, diamond grinding, etc.) to enhance the bond in areas with poor adhesion due to the presence of a curing compound or smooth finish.


Hot rubberized membranes were designed to provide effective waterproofing for large surface areas and to help with conditions with intricate transitions. When prepared and applied correctly, the benefits of the product can prove to be outstanding. However, not only is dealing with such a hot product dangerous, but there are also a great number of factors that can affect its sealing properties thus leading to construction risk and potential water intrusion issues. Best building practices and following the manufacturer’s specifications are always essential rules to follow. Hot rubberized products are sensitive to overheating or not being heated enough, inclement weather conditions, and damp or contaminated surfaces. A number of tips were provided in this Tech Alert, however, in order to help combat these issues on the field, we recommend that you involve a third-party independent consultant such as Quality Built to take a look over your design details by conducting a Technical Plan Review (TPR) in an effort to pinpoint inconsistencies in product compatibility. Also, it is advised to have a consultant observe and inspect the installations. Lastly, as with all systems that are a part of the building envelope, it is recommended that a consultant performs water testing of the waterproofing at random locations.


Frank Kaligis has over 40 years of experience in the construction industry, with 14 years of specialized experience in housing and commercial building inspections for FEMA at the Federal, State, and Local agency levels. Frank’s experience includes scheduling on-site appointments with applicants for rental, residential, and commercial properties to determine the extent of damage and costs to repair and or replace real and personal property. Frank is sure to provide detailed feedback during inspections in order to aid builders in building structures to code and habitability per FEMA and county guidelines. Frank also has experience in interpreting engineering and architectural plans, drawings, specifications, and cost sheets in order to pinpoint areas for improvement.

You can reach Frank at [email protected]

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