I removed a wall panel next to the window in my garage and removed the wall insulation to expose a particle board (think that's the right term) panel that's behind the exterior brick facade. The particle board looks darker than expected, as if it is or was damp at some point. How can I tell if it is damp or had moisture damage?

I don't see any blatant signs of fungal growth.

Updated: Added an image. This is to the right of a window. The entire length of the panel looks like this.

enter image description here

  • OSB exterior sheathing is probably the product yours seeing. A picture may help us judge the appearance of the sheathing as normal or abnormal. Particle board is not used as exterior sheathing typically.
    – Kris
    May 20, 2018 at 12:57
  • @Kris Added a picture to help with sleuthing.
    – Alan S
    May 22, 2018 at 10:46
  • That looks like fiberboard building sheathing. inspectapedia.com/structure/Fiberboard_Sheathing.php
    – Kris
    May 22, 2018 at 12:14
  • It looks normal for fiberboard in coloration.
    – Kris
    May 22, 2018 at 12:18

1 Answer 1


Seems like there are a couple of things going on here:

First, you say, “next to the window.” Typically, I see a lot of leak problems around windows and particularly at the corner of the sills. This is a “leak” issue and not a lack of moisture barrier issue, as implied by your title question.

Yes, darkened wall sheathing is an indication that moisture has been there, but has dried out. If the sheathing is solid (not punky) and stained on the surface only not throughout, then it would indicate that not much moisture has entered or not very frequently.

Second, you don’t mention a moisture barrier between the wall sheathing and the brick, but if there isn’t one, then You have a bigger problem. Hand-in-hand with the moisture barrier is the need for “weep holes”. I’d check to see if there are weep holes and if they’re “open”.

Where I live, brick veneer is installed with a 3/4” to 1” air space to the wall sheathing with a moisture barrier on the face of the sheathing. The brick veneer extends down about 4” below the top of the floor line (finish floor) with weep holes at the bottom to allow water that gets behind the brick to drain out.

Third, brick is porous and needs to be sealed with a clear liquid sealer from time to time. Wind driven rain will “push” the rain water through the brick veneer. That is why a moisture barrier and weep holes are required.

I’d verify if the “leak” problem is at the window only or lack of moisture barrier and weep holes. If the darkened sheathing is punky or darkened throughout the sheathing, then it could have mold and you may want to have it tested.

If the brick wall is 8” thick and not 4” thick, then it’s a structural wall and not a veneer wall. We usually don’t use a moisture barrier for structural walls.

  • How do I test if the fiberboard sheathing is punky? Should I hire someone to take a look, and if so which type of specialist? How often does brick need to be sealed, and which type of specialist can do that type of work?
    – Alan S
    May 28, 2018 at 17:29
  • @AlanSzlosek We take a screwdriver and poke at the wall. If it “flakes” off, it needs to be replaced, unless it’s small (a few inches square). If it’s larger than a few inches square and is delaminated, it should be replaced too. If it’s fiberboard, it’s non-structural. Fiberboard is often used for sound control or for a backerboard to hold building paper, etc. Brick sealers have different guarantees and various length of service. You’ll need to re-coat as per the manufacturer’s recommendation, usually 3 years. It’s a clear coating, so it’s usually installed by a painter.
    – Lee Sam
    May 28, 2018 at 19:05

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