Seepage above glass block in masonry wall

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This topic contains 1 reply, has 2 voices, and was last updated by  Kurt 4 years, 3 months ago.

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  • #653

    Mark Daugherty

    I’m experiencing an ongoing issue of seepage above a glass block. Following (very) heavy rains, the surrounding drywall has gotten wet enough to drip a few pints worth of water inside the house. There is a masonry arch above the block that was tuckpointed last year after the first instance of leakage; this has lessened the severity but not solved the problem. The moisture damage is only occurring on the drywall surface that is perpendicular to the top of the glass block (see photo).

    Given that the glass block sits flush with the exterior wall, would the brick arch absorb enough moisture in severe rains to be the sole cause of the drywall leak? Or is the water more likely to be infiltrating from elsewhere? (copings, parapet walls, mortar joints in the glass block, etc.) I suspect I’ll have to start removing drywall to confirm if the seepage is localized to that area and remediate the water damage, but I’d appreciate any feedback on these observations thus far – thanks!

  • #656


    First, I want to thank you for posting this excellent question, but first…..How did you find us? The site’s new, we have it up to work out kinks, but we’ve got the search engines deflected while we tune it up. If you could tell me how you found it, I’d be thankful.

    As far as your window, this one’s easy. If the world was divided into two wall types, there’d be water managed and barrier systems. All masonry is water managed. Some amount of water penetrates any masonry assembly and in a properly constructed wall, that water is collected and returned to the exterior through a system of flashing details. Barrier systems, as the name implies, are intended to prophylactically prevent water from entering the wall. In masonry, barrier systems don’t work.

    Your window is set up as a barrier system. The window has no apparent flashing system over the top of the window to deflect it to the exterior, so it soaks into the drywall. Setting the block flush with the outside of the wall makes it worse. The pointing repairs and touching up the masonry reduced the amount of water entering the wall but it’s never going to stop all of it. Remember, barrier systems don’t work in masonry.

    In a couple weeks, I’ll have drawings up to explain these points, but for now, I’ll stick with basics.

    You need to remove the brick over the wall and install flashing to prevent water from soaking into the drywall. The flashing should be set up in a sill pan arrangement with end dams and back dams to prevent the water from migrating inwards or sideways.

    Since your the first person to post, I’ll fill in some details.

    Old masonry was all solid (3 or 4 bricks thick) load bearing assemblies. Water was managed through the sheer mass of the thick wall and the miracle of lime mortar (more on lime mortar in a future blog post).

    Modern masonry is cavity wall; there’s a layer of brick on the exterior, one on the interior, and an air gap between the two layers. Water penetrates the wall, it wicks down the inside face of the outer layer in the air gap, and strategically located flashing diverts the water back to the exterior. You need to install flashing over the top of your window. You’re not going to keep the water out with pointing, caulking, or similar repairs.

    Here’s a simWindow-Head-Flashing1ple drawing of a flashing profile. You need to fabricate a flashing like this profile and install this over the top of the glass block, then fill in the space over the block with wood or other trim material. Yes, it’s a large job, but there’s no other way to get it right. Continuing with attempts at sealing water out of the wall (barrier systems) won’t work. You have to install flashing to make it work.

    • This reply was modified 4 years, 3 months ago by  Kurt.
    • This reply was modified 4 years, 3 months ago by  Kurt.
    • This reply was modified 4 years, 3 months ago by  Kurt.
    • This reply was modified 4 years, 3 months ago by  Kurt.
    • This reply was modified 4 years, 3 months ago by  Kurt.
    • This reply was modified 4 years, 3 months ago by  Kurt.

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