Moisture in Concrete - Part 1
June 26, 2019
This post focuses on the moisture phenomenon in concrete and the difference between lightweight and normal-weight structural concrete. Curing versus drying and the standards used to determine relative humidity levels are also addressed. Part II will address design recommendations and roof assembly selection.

Moisture in Newly Poured Structural Concrete Roof Decks
When investigating roofs for leaks, invariably, moisture is found beneath the roof membrane. However, the source of moisture is not always a roof leak. Newly poured structural concrete could be a contributor to the presence of moisture beneath a new or a replacement roof.

Concrete is a mixture of several components that reaches its optimum strength through a chemical reaction induced by water. Concrete needs water to allow for flowability and workability, however, water also has adverse effects. Once the concrete has cured, the remaining water is considered “free water”, or moisture which is no longer consumed by the curing process. Rain and snow add moisture to exposed concrete roof decks and further prolong the drying. As an example, a 4” slab of structural concrete contains as much as 200 gallons of free water per 1,000 square feet.

Structural Concrete Mix Ratio
The ratio for both normal-weight and lightweight structural concrete (LWSC) is generally the same:
• 10-15% cement
• 60-75% aggregate (fine and coarse)
• 15-20% water

The difference is in the aggregate; the lightweight aggregate is pre-saturated prior to mixing. The lightweight aggregate, which is made up of shale, slate slag, or clay, can absorb 5-25% of its mass. Normal-weight structural concrete, however, utilizes aggregates such as sand and stone, which are not as porous and do not need to be wetted before adding to the mix.

The popularity of LWSC is increasing due to:
• Lower building structural cost;
• Lesser density for reduced dead loads; and
• Environmental and sustainability claims.



Drying Time
To reach a 75% relative humidity for normal-weight structural concrete, it will take approximately three months. However, achieving the same 75% relative humidity for LWSC will take twice as long. According to the Portland Cement Association, the dry-down time for LWSC is more than normal-weight structural concrete.


Standards for Moisture Testing
For many years, the roofing industry has used a curing time of 28 days after the concrete is poured. However, there are test methods published by ASTM for determining the moisture content in concrete.

Qualitative tests, such as the plastic sheet test and electrical resistance and/or impedance are good indicators of the presence of moisture in a given area but are not as accurate as quantitative tests.

Quantitative tests, such as the moisture vapor emission rate test, surface humidity, or in-situ relative humidity tests demonstrate levels of moisture present in the concrete.

The recommended quantitative test is the in-situ relative humidity test (ASTM F2170), in which a sleeved probe is placed in a drilled hole in the concrete and left in place for 24 hours. After the 24 hours, an electronic reader is attached, and the information is read directly from the sensor. The relative humidity reading should be less than 80% at a depth of approximately 40% of the thickness of the slab.

The moisture values and test duration stated above have been slightly modified to better suit outdoor roof conditions. 

Site Considerations
The concrete pour schedule can affect moisture testing and provide inaccurate moisture values. Therefore, in phased construction, the field testing and the roofing installation should be aligned with the concrete pour schedule and ICRI-Certified Concrete Inspectors should be commissioned.

For in-depth information, the International Concrete Repair Institute (ICRI) offers various resources that can aid with the proper steps required for testing and evaluation. Stay tuned for part II for recommendations on design and the selection of an appropriate roofing assembly.


October 16, 2019
Electronic Leak Detection for Roofing Systems

A building’s roofing system separates the damaging outdoor environment from the valuable interior contents. To be effective, it must be watertight. Although roof systems are inspected and sometimes flood tested prior to warranty issuance, small, difficult-to-see breaches in the membrane system can go unnoticed until damaging water leaks occur inside the building. Moreover, once a leak has developed it can be extremely difficult to locate the leak and perform the necessary repair, especially when overburden materials are installed. Enter Electronic Leak Detection, otherwise known as ELD. ELD systems have been around for 20+ years and are gaining popularity due to some revolutionary new products that have expanded testing capabilities. ELD systems come in two main varieties: low-voltage and high-voltage, with low-voltage being the most common. ELD systems work by creating an electrical potential difference between a non-conductive roof membrane and a grounded conductive structural deck or substrate. Testing is performed by applying water, which is conductive, to the surface of the roof membrane. The roof membrane will isolate the potential electrical difference between the deck and the water, but when a breach is present, the water will create an electrical connection to the grounded deck, pinpointing the exact leak location to the testing technician. A major benefit of ELD testing is that it can be performed at any time, even after overburden materials are installed. For ELD systems to be effective, a conductive substrate must be present directly below the membrane’s surface. Due to this requirement, membrane choice and application method can be limited. Two ELD companies that Carlisle has experience with are International Leak Detection (ILD) and Detec Systems. Products from either of these companies are permitted for use in a Carlisle warranted roof system but are not covered in the Carlisle warranty. ILD has been around since 2001 and promotes a conductive mesh that must be installed directly below the membrane for accurate testing of membrane systems over non-conductive decks. Due to the design of the conductive mesh, it is only acceptable for use under thermoplastic FleeceBACK® membranes adhered with FAST™ or Flexible FAST Adhesive. Detec Systems promotes a conductive primer called TruGround® that is roller-applied over the top layer of insulation, prior to adhesive application. Once dried, the membrane system can be installed as usual. TruGround conductive primer expands ELD testing capabilities, as it is suitable for use with bareback membranes and even black EPDM, which historically has not been compatible with ELD testing. Carlisle SynTec Systems has secured FM approvals for Detec’s TruGround in a number of different roofing assemblies. Those assemblies include: EPDM and TPO with CAV-GRIP® III adhesive over SecurShield®, SecurShield HD, DensDeck® Prime, and SECUROCK®. PVC with Low-VOC Bonding Adhesive over InsulBase®, SecurShield, SecurShield HD, and SecurShield HD Plus.  Contact Chris Kann with questions regarding ELD systems.

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September 18, 2019
Fire Performance of Polyiso

All construction materials, including foam plastics such as polyiso insulation, must provide a suitable margin of fire safety. Polyiso possesses a high level of inherent fire resistance when compared to other foam plastic insulations due to its unique structure of strong isocyanurate chemical bonds. These bonds result in improved high-temperature resistance (up to 390°F [199°C], more than twice that of other building insulation foams) which in turn leads to enhanced fire resistance. In addition, because polyiso does not melt or drip when exposed to flame, but rather forms a protective surface char, its fire resistance is further enhanced, especially in terms of flame spread and flashover potential. Polyiso passes both the ANSI UL 1256 and FM 4450 fire tests without a thermal barrier. Polyiso, a thermoset material, stays intact during fire exposure in the ASTM E84 or "Tunnel Test.” It forms a protective char layer and remains in place during the test, thereby meeting all building code requirements and contributing to a fire-safe building. For more information on polyiso’s performance in fire tests, visit the 'Technical Bulletins’ page on the PIMA (Polyiso Manufacturers Association) Website where you can find the following papers: Technical Bulletin 103: Fire Performance in Walls and Ceilings Discusses polyiso insulation as it relates to building codes in construction and fire tests in walls and ceilings, including ASTM E84 and ASTM E119. Technical Bulletin 104: Fire Performance in Roof Systems Provides an overview of polyiso insulation requirements for roof systems and key issues in fire performance, including the importance of the FM 4450 Calorimeter Tests and the UL 1256 Resistance to Interior Spread of Flame test. Technical Bulletin 105: Fire Test Definitions Provides an in-depth look at fire test procedures for building applications. Technical Bulletin 111: Class A and Class 1 Roof Assemblies Are Not the Same Explains why Class 1 and Class A are not the same. Technical Bulletin 111C: Roofing Regulations in Canada – Class A and Class 1 Roof Assemblies Are Not the Same Explains why Class 1 and Class A are not the same. Technical Bulletin 405: Fire Resistance Properties of Polyiso Foam Plastic Insulation Used in Wall Assemblies – Facts and Comparisons Looks at the minimum fire resistance properties required for foam plastic insulation and compares data on polyiso with other recognized combustible materials. Product Stewardship Paper 100: Polyiso Insulation and Flame Retardants New Product Stewardship report on polyiso and flame retardants. Contact Craig Tyler at [email protected] with questions.

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September 4, 2019
Alternative Uses for Roofing Membranes

All single-ply membranes make for great roofing systems, but they can be used for a variety of other purposes too. EPDM, TPO, and PVC can be used in the lining of underground tunnels and can serve as liners for water retention ponds, irrigation canals, and other water containment systems. For years, EPDM membranes were used as pond liners – even before they were utilized for commercial roofing. You could see EPDM pond liners being used in agriculture for irrigation canals and ditches, by municipal water systems for retention ponds and spillways, and even in backyards as small ponds and water features. This is still true today, and EPDM has expanded into additional markets such as tunnel waterproofing. The number of large underground transportation tunnels used for vehicle traffic or metropolitan railways has certainly increased in the last few decades as traffic and access needs continue to outstrip the supply of existing infrastructure. These tunnels have to keep water out, whether they’re underneath a river or traversing through a mountain, and single-ply membranes meet their waterproofing needs with the same technology used on the roof. Different types of membrane offer specific benefits, from EPDM’s large sheet size to thermoplastics’ (TPO/PVC) seam weldability. Regardless of whether the tunnel is a boring project or a “cut and cover”, lining the tunnel can be accomplished using several different installation methods and can utilize EPDM, TPO, or PVC. For more information, please consult the links for the products or specifications on the Carlisle SynTec website below. Tunnels – Conventional Blindside Method Consult the Tunnel Waterproofing System – Conventional Specification and Details on the Carlisle SynTec website.  Tunnels – Cut and Cover Method Consult the Tunnel Waterproofing System – Cut and Cover Specification and Details on the Carlisle SynTec website.  Pond Liners Consult GeoMembrane Page for Pond Liner Products and Brochures on the Carlisle SynTec website.   Contact Craig Tyler at [email protected] with questions.

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