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How do I replace brick mortar with something more insulating?

wcpriest | Posted in Green Building Techniques on

I was an associate of an energy consulting firm in 1973.

A Canadian study showed the virtues of insulating basement walls well below the frost line because of heat flow into the wall, up, and out at grade.

From then on I always insulate basement walls, as the first step in reducing energy costs. I typically use 2″ Styrofoam, mastic to concrete, brick or rock. One job, 1893 Victorian, we would put up the panels against a craggy rock wall, hammer with rubber mallets to cause high spots to indent the foam, then apple mastic there. It worked fine. Finished with 5/8″ sheet rock, just 2 long screws to the sill for fire code, then tape and popcorn finish. Eighteen years now, it is a fine way to finish a basement with no studs and no other vapor barrier.

Now. I am to insulate an existing brick building. This is not the multi-brick type as described

The owner wants to expose the brick on a side that faces a cold room of a later addition to the building.

So, I can use Styrofoam again and fasten the sheet rock using lead inserts at the top.


I want to stop heat flow from this interior brick wall to the outside wall to which it is linked with mortar. This means to drill out a zig-zag of mortar near the cold outside wall and filling the gap with an insulating binder.

As an engineer, I know that polyurethane foam and Styrofoam have enormous load-bearing capabilities. I could also consider a 2-part urethane caulk or a 2-part epoxy. Of course, we want the load-bearing and locking to be as good as mortar.

So. Has anyone done this? If so, using what? If not, comments are most welcome.


Curtiss Priest

P.S. picture of the building is attached. The addition is on the rear side, so looking at the picture, beyond a grade-level entrance on the left side.

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  1. GBA Editor
    Martin Holladay | | #1

    If I understand you correctly, you have a building with uninsulated brick walls. You want to insulate just a portion of the building, using interior wall insulation, and you are worried about the thermal bridging through the bricks.

    There is no solution to this problem. You need to either insulate the entire building, or you have to learn to live with thermal nose-bleeds.

    The best way to insulate the entire building is on the exterior. Of course this requires you to cover up all of the bricks with rigid foam. The EIFS system is the easiest way to do this. Most clients hate the thought of hiding the bricks, however.

    You can also insulate the entire building on the interior. This is tricky, but possible. You need to maintain continuity between your floor insulation, your wall insulation, and your ceiling insulation. Basically, you build a big six-sided foam box inside your brick building. That works. One big disadvantage of this approach is the loss of interior space.

    But you can't just insulate a portion of the building, because heat will flow through the brick wall and bypass your insulation.

    Your idea of removing mortar in a zigzag pattern won't work, for two reasons: it would be incredibly time-consuming and expensive, and the R-value of the caulk you install would be trivial. Even if you inject spray foam in the gaps after you remove a mortar joint, all you get is 3/8 inch of spray foam. That's not much.

  2. wcpriest | | #2

    What if I replace the zig-zag of bricks with Styrofoam bricks cut from 2" board
    A brick is 7.5*3.5 sq. in.
    The compressive strength of Styrofoam SM is 40 psi
    The weight of a brick is 4.25/ (7.5*3.5) psi = .161 psi, so styrofoam can take 40/.161 bricks stacked = 248 bricks
    As I am replacing half the weight with Styrofoam, the stack could be 496 bricks above.

    And, we are only talking about doing this to the 1st floor wall of a 2 story wall, and even with roof and snow weight the compressive strength will not be exceeded.

    A 9 ft. wall has 2" (brick) + 3/8" mortar, so (9*12)/2.375 bricks high, or 45 bricks, which is really equivalent to 22.5 bricks high, accounting for almost zero weight of Styrofoam.

    I can shim the height by taking brick and diamond sawing them.

    My R value is minimally 11.5 and more like R 15 due to the zig-zag.

    One would trowel mastic onto the Styrofoam block to reestablish tensile strength. The tensile strength of Styrofoam is 60 MPa which probably exceeds the grip of mortar to brick.

    To drill out mortar and remove a brick takes about 2 minutes. To hammer in the Styrofoam block takes about 10 seconds.

    So to remove and replace the 45 bricks will take about 45 times 5 minutes, or 3.75 hours.

    Isn't disconnecting the wall with an R of 15 worth this ?



  3. GBA Editor
    Martin Holladay | | #3

    It's not worth it to me, but it might be to you. Good luck with your project.

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