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Is veneer plaster considered an air seal?

JFBasnett | Posted in Energy Efficiency and Durability on

I run a remodeling company in Littleton, MA that has become very focused on builiding envelope efficiency and durability. We (myself, project develper, production manager, and project supervisors) are working on standard specifications for air sealing and as we were discussing interior air sealing, one of the project supervisors asked if sealing the perimeter of the wallboard at inside corners was really necessary if we were properly sealing the framing joints behind the wallboard and skimcoat plastering all those inside corner joints. His reasoning was that if it is necesarry to seal these joints then why aren’t we sealing other seams in the field of the wall. This got us all wondering if veneer plaster was considered an air seal or if we’ve been missing a step in good air-sealing practices.

Jim Basnett
BASENTT Design/Build/Remodel

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Jim,
    As far as I know, veneer plaster is an excellent air barrier.

    Here's why we usually caulk the top and bottom plates -- and sometimes the far left and far right studs -- behind drywall when adopting the Airtight Drywall Approach: Most exterior walls (and, for that matter, most partitions) allow some air movement. The most common way for interior air to enter stud cavities is at electrical boxes, but it can also enter through cracks around penetrations of the bottom plate. By caulking the seam between the drywall and the top plate, we prevent that warm interior air from escaping into the attic.

    For more information, see Airtight Drywall.

  2. JFBasnett | | #2

    I get the bottom plate idea, but if the inside corner at the top plate and far right and left are plastered, aren't they effectively sealed?

  3. GBA Editor
    Martin Holladay | | #3

    James,
    Indoor air can enter the stud bays of a partition at the gaps around an electrical outlet. The indoor air can then escape into the attic through the crack between the plaster (or drywall) and the partition top plate.

  4. JFBasnett | | #4

    Ok, that makes more sense. We use gasketed electrical boxes and also seal the holes in the boxes, but I like the sealed wallboard edges for added insurance. Thanks for addressing this with me Martin.

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