TL-0010 — Use Over Georgia-Pacific DENSDECK® and DENSDECK® Prime Technical Letter

Technical Letter 10

DENSDECK® and DENSDECK® Prime are fiberglass-faced gypsum roof boards manufactured by Georgia-Pacific as nonstructural thermal barriers and membrane substrates for commercial roofing applications.

GCP’s self-adhered underlayments (GRACE ICE & WATER SHIELD® , GRACE ICE & WATER SHIELD® HT, GRACE ULTRA™, GRACE SELECT™, Roof Detail Membrane™ and GCP granular underlayment) maybe applied to Georgia-Pacific DENSDECK® and DENSDECK® Prime. There is no chemical incompatibility. However, because of the nature of the fiberglass surface, the level of membrane adhesion may not be as high as when it is applied to a monolithic surface like plywood.

  • When GCP’s underlayments are applied to DENSDECK®, they adhere very well to the fiberglass fabric surface. However, when the adhesion is tested, the fiberglass fails cohesively. This means that part of the fiberglass remains adhered to the membrane and part of the fiberglass remains bonded to the DENSDECK®. The adhesive bond strength of the GCP underlayment is greater than the internal cohesive strength of the fiberglass fabric surface of the DENSDECK®. Therefore, the bond between the DENSDECK® and GCP underlayment is limited by the fiberglass fabric. This is expected to be an issue only while the membrane remains uncovered before the metal roof is installed.

It is not expected that the use of primers will significantly improve the bond strength between GCP underlayments and the fiberglass fabric surface of DENSDECK®.

  • When GCP underlayments are applied to DENSDECK® Prime, they adhere well to the “treated” surface. If adhesion is marginal, the use of PERM-A-BARRIER® WB Primer will improve the adhesion. Apply the primer at a rate of 250–350 ft2/gal (6–8 m2/L). PERM-A-BARRIER WB Primer is slippery when wet. Allow primer to dry before walking on the DENSDECK® Prime substrate. Cover the membrane with the exposed roofing material as soon as possible. | North America Customer Service: 1 877-4AD-MIX1 (1 877-423-6491)

We hope the information here will be helpful. It is based on data and knowledge considered to be true and accurate, and is offered for consideration, investigation and verification by the user, but we do not warrant the results to be obtained. Please read all statements, recommendations, and suggestions in conjunction with our conditions of sale, which apply to all goods supplied by us. No statement, recommendation, or suggestion is intended for any use that would infringe any patent, copyright, or other third party right.

ICE & WATER SHIELD, GRACE BASIK, GRACE ULTRA, GRACE SELECT, and GRACE ROOF DETAIL MEMBRANE are trademarks, which may be registered in the United States and/or other countries, of GCP Applied Technologies Inc. DensDeck is a registered trademark of Georgia-Pacific. This trademark list has been compiled using available published information as of the publication date and may not accurately reflect current trademark ownership or status.

© Copyright 2018 GCP Applied Technologies Inc. All rights reserved.


GCP Applied Technologies Inc., 2325 Lakeview Parkway, Suite 450, Alpharetta, GA 30009, USA
GCP Canada, Inc., 294 Clements Road, West, Ajax, Ontario, Canada L1S 3C6
This document is only current as of the last updated date stated below and is valid only for use in the United States. It is important that you always refer to the currently available information at the URL below to provide the most current product information at the time of use. Additional literature such as Contractor Manuals, Technical Bulletins, Detail Drawings and detailing recommendations and other relevant documents are also available on Information found on other websites must not be relied upon, as they may not be up-to-date or applicable to the conditions in your location and we do not accept any responsibility for their content. If there are any conflicts or if you need more information, please contact GCP Customer Service.

Last Updated: 2022-05-06