SILCOR® 900HA/900MP Waterproofing Plywood Substrates Technical Bulletin

Plywood/Design Requirements:

  • Use plywood panels meeting the American Plywood Association (APA) Exposure 1 or exterior exposure durability classification. According to the APA, Exterior 1 panels are designed for applications where long construction delays may be expected prior to providing protection, or where high moisture conditions may be encountered in service.
  • Use plywood panels with B-grade or better veneer to minimize surface preparation.
  • Apply Plywood according to building code requirements and APA recommendations. APA recommendations are outlined in the APA’s Design/Construction Guide: Residential &Commercial, Form E30.
  • Plywood must be installed per manufacture’s requirements and fully supported at all butt joints with blocking between joists.
  • Joints in plywood panels should be minimized and butt joint spacing must comply with manufacturer’s requirements.
  • Ensure the assembly is adequately vented if applicable and complies with all building code requirements.
  • Oriented Strand Board (OSB) is not an acceptable substrate for SILCOR® applications.


  • Substrate must be clean, dry and free of dust and other contaminants.
  • All horizontal joints between plywood panels must be filled flush with a Polyurethane Sealant and allowed a min. 24-hours to cure.
  • All vertical upturns, inside corners, deck to wall junctions must receive a fillet of BITUTHENE® Liquid Membrane.

Primer Application:

  • Apply SILCOR® EPS or EPF Primer to the horizontal and vertical plywood, Polyurethane Sealant and BITUTHENE® Liquid Membrane per the applicable data sheets/installation instructions.
  • Allow SILCOR® Primer to cure to a tack free condition.
  • When SILCOR® Primer is tack free, install a 2” wide self-adhesive bond-breaker tape over each horizontal plywood joint. (Do not install bond-breaker tape at deck to wall junctions or over the fillet of BITUTHENE® Liquid Membrane.

Silcor 900HA/900MP Application:

  • Apply SILCOR® 900HA/900MP within 24-hours of the SILCOR® Primer application at a minimum thickness of 80-mils per applicable data sheets/installation instructions. | North America Customer Service: 1 877-4AD-MIX1 (1 877-423-6491)

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: 2022-05-16