Westcoat WP-40 Waterproofing Sheet Membrane | 36” x 75’
About
Self-Sealing Waterproof Protection for Plywood Decks
Westcoat WP-40 is a 40 mil rubberized asphalt sheet membrane designed primarily for waterproofing plywood seams. Its self-sealing, self-adhering construction provides a reinforced waterproof barrier while the white polyester carrier allows light foot traffic and short-term UV exposure during installation.
WP-40 can also be used as a secondary waterproofing membrane in critical situations or other areas requiring a self-sealing, self-adhering waterproof membrane.
Specs
Why Choose Westcoat WP-40?
- Self-sealing waterproof membrane
- Self-adhering for user-friendly installation
- Reinforced with a white polyester carrier
- Withstands light foot traffic during installation
- Designed primarily for waterproofing plywood seams
- Can be used as a secondary waterproofing membrane in critical areas
How WP-40 Fits Into Westcoat ALX Systems
WP-40 Sheet Membrane is used throughout Westcoat’s ALX waterproofing systems as a waterproofing membrane and reinforcement over plywood. In the Standard and Custom Finish systems, 6-inch WP-40 is required over plywood seams, while 36-inch WP-40 can be installed over the entire deck for maximum protection. Full-deck WP-40 installation also allows these systems to meet the listed Class I Vapor Retarder ASTM E96 performance.
WP-40 is specified for use with the following Westcoat ALX systems:
- ALX™ Standard Finish
- ALX™ Custom Finish
- ALX™ Waterproofing Underlayment
- ALX™ Pro Standard Finish
- ALX™ Pro Custom Finish
- ALX™ Pro Waterproofing Underlayment
Product Specifications for Westcoat WP-40
| SPECIFICATION | DETAILS |
| Roll Size | 36" x 75' |
| Coverage | 225 sq ft per roll |
| Thickness | 40 mil ± 5 mil |
| Tensile Strength | 1,400 psi, reinforcing only (ASTM D882-A) |
| Elongation | 500% minimum, ultimate failure of SBS mass (ASTM D412) |
| Pliability | Pass |
| Shelf Life | 1 year in unopened packaging |
Instructions
Application Instruction Overview for Westcoat WP-40
IMPORTANT! Before You Begin: Review the complete Westcoat WP-40 Technical Data Sheet (TDS) and Safety Data Sheet (SDS), linked above, before installation. The information below is a brief overview and does not replace Westcoat’s complete application instructions.
STEP 1 — INSPECT AND PREPARE THE SUBSTRATE
- Surface must be clean, dry and free of grease, paint, oil, dust and other material that could prevent proper adhesion
- Nails and screws must be flush with the surface
- Plywood should be dry, typically defined as less than a 10% moisture reading or showing no moisture with a plastic sheeting test
- Concrete must be cured for a minimum of 28 days and scraped or ground to remove protrusions
- Pre-patch divots or holes as needed
STEP 2 — PRIME AS REQUIRED
- WP-43 Sheet Membrane Primer is highly recommended with WP-40 to promote maximum adhesion to plywood
- Primer is especially important in cooler climates or covered projects with limited sun exposure
- WP-43 Sheet Membrane Primer is required when installing over concrete
STEP 3 — MEASURE & POSITION
- Starting at the outside edge of the deck, roll out WP-40 fabric side up
- Measure and cut the membrane to the required length
- For best results, Westcoat recommends installing WP-40 under sheet metal flashing
- When installed under flashing, align the finished edge of WP-40 with the deck edge
- When installed over flashing, extend WP-40 at least 1 inch onto the sheet metal flashing without extending past the lath
STEP 4 — ADHERE THE MEMBRANE
- Fold the bottom half of the membrane back onto itself and remove the bottom portion of the split release backing
- Carefully position and firmly adhere the bottom half to the deck
- Fold over the top half and remove the remaining split release backing
- Carefully position and firmly adhere the remaining membrane to the deck
STEP 5 — CONTINUE INSTALLATION
- Repeat the installation method across the remainder of the project
- Maintain a minimum 2-inch overlap between layers of sheet membrane
- Dispose of release film in an appropriate trash container
INSTALLATION LIMITATIONS
- Do not leave exposed to UV for more than 7 days
- Do not install below 40°F or above 90°F
- Do not store rolls on end
- Do not allow Westcoat products to freeze
