SubSeal Foundation Water Barrier - Siding Moisture Barrier

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Subseal Self-Adhearing Waterproofing Membrane
MFM SubSeal is a 40 or 60 mil thick, (depending on the model #) prefabricated self-adhering sheet-type waterproofing membrane. It is composed of a tough multi-layer high-strength polymer film that is coated with a layer of specially formulated rubberized asphalt adhesive. A release sheet protects the asphalt and is removed as the membrane is installed. Mastic selvedge on both edges for improved sealing. SubSeal is engineered to be a multi-purpose waterproofing sheet suitable for use under siding, exterior plaster, as a through wall flashing or in sub-grade applications where the membrane is protected from long-term ultraviolet exposure. SubSeal adheres aggressively to most clean, dry substrates including metal, wood vinyl and masonry. SubSeal may be used in foundations and other below grade structures, plaza decks, balcony waterproofing, under siding, exterior plaster and as a through wall flashing. SubSeal complies with ICC-ES AC148 (ICC-ES ESR-2783) and ICC-ES AC38 (ICC-ES ESR-3980).

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subseal 40 self-ahearing waterproof membrane
subseal 60 waterproof membrane
SubSeal™ is designed for Extreme Moisture ProtectionSubSeal is engineered to be a multipurpose waterproofing sheet suitable for above and below grade, as well as vertical or horizontal applications. Intended uses include:

- Foundation walls
- Through-wall flashings
- Plaza and balcony decks
- Parking garages
- Sills, pot shelves, pony walls and parapets
- Floor and planter structures
- Under stucco
- Sealing SIPS building panels or DensGlass®
- Around windows and door frames


Prior to installation on concrete, the surface must be primed with an asphalt based primer. The following are a list of asphalt based primers approved by MFM:

- APOC 103
- Bulldog Asphalt Primer
- Karnak 108
- Lucas 315

(download the approved primer guide above for additional options)
When installed over a wood or metal surface, a primer is not required.


If installing SubSeal in temperatures below 50 degrees, a spray adhesive is recommended for optimal adhesion. The following adhesives are approved by MFM:

- 3M 77


  • 5
    Installed the product today & I'm very impressed with how it stays in place & seals the wall

    Posted by Dan Stewart on Nov 5th 2020

    Easy for two people to apply My neighbor helped me with the application. He has it on his foundation & his basement is totally dry.

  • 4
    Seems like an excellent product

    Posted by Unknown on Apr 28th 2020

    Can be a little tricky to apply - definitely a 2 person job, but very sticky backing creates a great seal. We used our to waterproof the joint between our SIP panels and the pier-and-beam foundation. Adheres very well... but be careful applying it.

  • 5
    Even better than expected

    Posted by Unknown on Oct 24th 2017

    I used this product to seal my basement foundation due to vaious cracks/openings in block. The adhesion was very tacky and easy to apply. The thicknesss was just right, easy to cut with razor knife, yet thick and durable and will not tear. The paper backing peeled cleanly for a simple transition onto the wall.

  • 5
    Good stuff

    Posted by Charles on Feb 7th 2017

    Company responded in timely manner regarding my check on status and updated me as status changed. Product was as advertised and easier to install than I expected. I believe it will provide the barrier I was looking for.