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Community and Q&A

Proposed approach for fixing brick/poly wall issues

MarkJeantheau | Posted in Green Building Techniques on

My house was built in Kentucky in 1996. Exterior walls were built with the following order/characteristics:

— Full brick siding – rope-style weeps but no vents
— 1/2-inch air gap between brick back and Tyvek – there’s lots of trash mortar, much of it smushed flat against Tyvek; gap is open at top, good air flow in soffit
— Tyvek – probably lapped not taped ()
— OSB sheathing
— 2×6 studs with R-19 Fiberglas bats
— poly
— drywall with latex paint

After we took of the perimeter drywall, we observed moisture droplets on the insulation side of the poly in areas where windows had leaks but not in areas where windows did not have leaks. I assume this means vapor drive from the outside has been a minimal issue compared to water injected into the tight walls via the leaks. Minor mold and staining was found on the bottom plates and OSB under some windows and the next 2-3 stud spaces.

Moisture was NOT observed on the drywall side of the poly, and we saw no water damage on the back of the removed drywall.

My planned remediation steps are:
— Replace windows (which have other problem too), improve flashing and caulking
— Redo brick ledges to ensure adequate slope for water shedding
— Add venting to brick layer at or just above weep line.
— Add sealant to face of bricks — MAYBE
— Tear out all the perimeter drywall, remove poly and insulation.
— Remediate mold — remove or abrade damaged or overtly moldy wood, spray everything with vinegar, let dry; then spray with Borax solution, let dry thoroughly.
— Add 2″ of closed-cell spray foam insulation
— Add unfaced R13 Fiberglas bats in remainder of stud space
— Add drywall with latex paint — no poly!
— Clean or repaint all interior walls and surfaces
— Clean/disinfect HVAC ducts

Questions and comments on logic:

(1) Does the above approach look sound?

(2) Brick venting: I’ve looked at brick-sized vents — intended to replace an entire brick every so often. Some products are not very well designed; others are well done but for various reasons won’t work for me. My current thinking is to take out a vertical mortar line every second or third brick — setting the bottom of the gap on an angle to keep water from running in — and then add stainless steel wool, brass wool, or a tube of aluminum screen in each hole to keep wasps and mice out. Any thoughts on how many mortar joints I should take out to foster the needed air flow, given the restricted air gap I’m stuck with?

(3) Brick sealing: In the few spots where we’ve removed test patches of OSB, the brick itself (or at least the air-gap space) has a slightly moldy smell, though there is no visible mold. Perhaps this is due to moisture from vapor drive? It seems to me that sealing the surface of the brick and simultaneously improving the air flow behind the brick will help keep the body of the brick from getting damp, thus reducing the tendency to mold, and will minimize the amount of moisture getting to the OSB as well. Agree?

Thanks for any insights you can share.

Mark Jeantheau
Berea, KY

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  1. GBA Editor
    Martin Holladay | | #1

    Q. "Does the above approach look sound?"

    A. Yes. Make sure that you properly flash the window rough openings before installing new windows. I don't like brick window sills, even if they are sloped, because bricks and mortar aren't roofing. If you can afford it, copper window sills make more sense than brick-and-mortar window sills.

    Q. "Any thoughts on how many mortar joints I should take out?"

    A. The standard advice is one open head joint every 24 inches.

    Q. "It seems to me that sealing the surface of the brick and simultaneously improving the air flow behind the brick will help keep the body of the brick from getting damp, thus reducing the tendency to mold, and will minimize the amount of moisture getting to the OSB as well. Agree?"

    A. Your planned remedies should help. If I were you, however, I wouldn't install any sealer on the brick. Leave the bricks unsealed.

  2. MarkJeantheau | | #2

    Thanks for the comments, Martin. Can you expand on your stated preference for no brick sealer. I did a little reading about Siloxane-based sealers, and the spin is that they work a lot like Tyvek -- they greatly reduce bulk water absorption into the brick but still let the brick breathe. This is from the first product sheet I ran into when I googled siloxane:


    They claim 90% reduction of water intrusion. If it really does still let the brick breathe, that seems like a win in fight against vapor drive, with no downside.


  3. GBA Editor
    Martin Holladay | | #3

    Here's what Jerry Carrier wrote on the topic:

    "Some coatings are breathable, which means that the coating allows moisture to exit the wall as vapor. But remember — if a coating is applied, the pore structure of the brick has been altered. The pore structure directly affects the durability of the brick. There must be enough pore space in the brick to allow any absorbed moisture to freeze and expand. If the pore structure is altered and the room for expansion is no longer available, the brick may deteriorate. If you decide to try a coating, choose a breathable coating. While some types of silanes and siloxanes have proven to reduce moisture penetration without reducing the durability of the masonry, siloxanes appear to be more successful [than silanes] with brick. Siloxanes are fairly expensive, but you get what you pay for when it comes to coatings. If it costs $5 a can, you can do without it. In any case, properly installed brickwork should not require coatings to prevent moisture penetration."

    [-- Jerry Carrier, "Keeping Water Out of Brick Veneer," Journal of Light Construction.]

  4. MarkJeantheau | | #4

    Martin -- Thanks for the pointer -- I read Jerry Carrier's excellent article in its entirety.

    Based on my improved understand of how brick veneer is supposed to be installed, I'll summarize the "wrong" things I have going on and ask a couple more questions.

    (1) Jerry's article recommends a minimum 1-inch air space between the brick veneer and the sheathing, and preferably a 2-inch air space whenever possible. My air space is only 1/2". Two issues:

    -- Because of my paltry air-gap depth, and even more so because of the high amount of trash mortar in there, drainage at the back of the brick is impeded and there is too little air flow in the air space.

    -- The areas where we took out test patches of OSB from the inside show that the trash mortar from most bed joints is smushed flat against the Tyvek. The article says we are not sure how water moves from the front of the brick face to the back, but logically there is a pretty good chance that my trash mortar can create a capillary bridge for the water to migrate to the face of the Tyvek. The Tyvek SHOULD stop capillary migration, but a mason I talked to this week said he has seen numerous examples where water coming across mortar bridges eventually caused mold on the sheathing.

    (2) There is no visible flashing anywhere. The best case scenario is that they added flashing but did left the edge buried behind the brick face -- better than not at all, but still wrong, allowing any intruded water to run into the brick holes rather that out the front. Should I cut out a piece of OSB/Tyvek by the base plate and see if there is flashing? If it's not there, what then?

    (3) My cotton weeps, which are a second-best solution in the first place, are on 32" centers vice the recommended 16". I also don't know how much tail the masons left in the wall (more tail = better). Regardless, if there is no through-wall flashing, the cotton weeps will be much less effective anyway. Lack of proper flashing and air flow could explain why the wall smells slightly moldy -- i.e. water is getting trapped inside more than it should.

    (4) The lack of open head joints reduces the opportunities for water to flow out and air to flow in, convect, and exit at the top, taking moisture with it.

    So, that's what I learned from reading the article last night. This morning, I was actually able to speak with Jerry for about 10 minutes and pick his brain a little. After hearing my description, he thinks:

    (A) Adding weep holes by taking out head joints is not likely to improve air flow. A half-inch air gap with lots of trash mortar is never going to breathe properly, with or without weep holes.

    (B) He was not totally opposed to adding siloxane as a sealant, but he said he didn't think it was likely to improve things. Since vapor drive does not seem to be the main factor for me (leaks are), he thinks the brick is breathing well enough and I shouldn't do anything that might mess with that characteristic.

    (C) He recommended completely redoing the brick ledges under the windows in a way that incorporates flashing that goes under the window, with a lip protruding under the new ledge.

    (D) He thought the flash and bat approach was fine, regardless of the fact that I'm not able to do anything to improve air flow (and water ejection) in the air gap.

    Bottom line: He said the place to focus is to get the windows right and make sure I don't have any future leaks.

    I will also point out that I have had the drywall and insulation out for 6 weeks now -- "love your new OSB decor, Mark! -- and have not seen any sign of moisture on the OSB, under the windows, or anywhere else, despite higher-than-usual rainfall here in Kentucky.

    If anyone has any additional ideas or thoughts, I'm all ears.


  5. GBA Editor
    Martin Holladay | | #5

    I worked with Jerry Carrier on that article years ago, when I was an editor at JLC. Jerry has far more experience with the type of problems you are facing than I do, so I have nothing to add beyond his advice.

    Good luck.

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