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Vapor open lead encapsulate?

finePNW | Posted in General Questions on

Anyone know of a lead encapsulate product OK’ed for exterior use with reasonably high vapor permeability? I’m going to use it on old (flat shiplap) wood lead-painted siding before covering it with WRB and cement fiber board siding (in climate zone 4 coastal).

Insul-X Lead Block technical support says they have no test results but assume it is probably a Class III permeability based on its composition and should be OK for my use case.

LeadX states a permeability of 5 perms, but I’m still looking into whether it’s OK for this exterior application.

Anyone have any experience? Thanks!

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  1. finePNW | | #1

    Come to think of it, and based on a comment in this Q&A, perhaps lead paint is typically so vapor impermeable that this line of inquiry is pointless? Anyone with experience have thoughts?

    HUD does specify that vapor permeability should be considered in order to prevent peeling (page 13-14 here:, but does not specify appropriately "open" perm rating values.

    Another product is FiberLock LBC rated at ~ 0.28 perms grains/ft2/hr (which I think is equivalent to 0.28 perms?). Perhaps this is worthwhile?

  2. finePNW | | #2

    In case it might help others in the future, Benjamin Moore tech support has told me that:

    "The lead block is similar in composition to acrylic elastomeric coatings we produce which have perm ratings of 32 perms. While we have never submitted Lead Block for perm testing, we would suspect it would be similar."

    Take it with a major grain of salt given it's only one product rep's guesstimation, but figured I'd share.

  3. Expert Member
    Michael Maines | | #3

    Thanks for the info. I'm curious why just covering the existing lead-coated siding with a WRB wouldn't be enough?

    1. finePNW | | #4

      That's a very reasonable point / question. For me, I hope to never have to re-side this house, and it seems the most responsible thing to do before I cover the lead paint up with siding is to spend a little extra time and money now to ensure that the paint stays in good condition and properly & thoroughly encapsulated for decades to come. I'm more trying to understand my options than necessarily support the premise of my question, but the premise is that an elastomeric encapsulation would be more reliable in keeping the underlying paint in good condition than a standard WRB would be, and I'm curious about adhesives potentially damaging/aerosolizing the underlying paint if any future work requires its full or partial removal and/or the chemicals or pH levels in the adhesive potentially causing Lead ion movement/leaching through the WRB (to be clear, I don't have any reason to believe adhesive chemicals would cause leaching; I'm simply curious).

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