I am trying to figure out what is inside of my exterior plaster wall that the brick is attached to. The house was built in 1946, has no insulation in the walls, and (oddly enough to me), has drywall with plaster on top of the drywall. I was actually expecting wood lathing of some kind. I'm assuming the sheathing is some kind of gypsum or fiberboard sheathing but wasn't sure if that was even around in 1946.

The first shot shows the sheathing through the hole in the plaster. The second shot has the sheathing on the left (with water damage). When you push on it with your finger, it is a little "squishy" and not firm like regular drywall.

Click photo for full size

enter image description here enter image description here

  • My house looks the same. The bizarre plaster-upon-drywall concept is called "rock lath." Commented Apr 17, 2013 at 14:22
  • Good to know, @ArgentoSapiens! "rock lath", eh?
    – BradLowrey
    Commented Apr 19, 2013 at 1:30

1 Answer 1


A better question would be, why is my sheathing getting wet?

The grain of the sheathing suggests to me it is Homosote Homasote. It should not be squishy, rather firm and resilent.

Something is allowing water past your brick barrier, and then, past what was vapor barrier (for the time, 15-30# tar embedded felt paper. I would look up, overflowing gutters can get behind fascia boards and run down the inside of the bricks, soaking the sheathing if the vapor barrier was broken during the bricking (as sometimes happened, also mortar bridging can cause this). In no case is it normal for the sheathing to be wet. Poor tuck pointing (especially around windows) can also allow water intrusion.

Once the water intrusion is corrected, all stud bays in the affected areas should be opened and the sheathing evaluated for viability. Also, opening the cavity will allow faster drying out and possibly see where the intrusion is starting.

enter image description here

As an aside, my 1941 house used a gypsum lath board for plaster.

  • Thanks, @HerrBag. I'm pretty sure I know where the water is coming from as there is a door just to the left of the opening that was never fully caulked/sealed on the edges. I am actually planning on removing the door and converting to a window so it will all be opened up soon. I'm in my planning phase now, hence the question on what kind of sheathing it is so I know what to add/replace it with.
    – BradLowrey
    Commented Apr 17, 2013 at 4:01
  • You are not limited to reusing Homosote, although it is available in some markets.. Wiki it, pretty interesting history.
    – HerrBag
    Commented Apr 17, 2013 at 4:06
  • To help others with searching for the product, I note that it's spelled "Homasote." Commented Apr 17, 2013 at 23:58
  • Thanks Argento, google must have corrected my phonetic spelling.
    – HerrBag
    Commented Apr 18, 2013 at 0:29

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