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I have an attached garage on a house with a wood foundation in Minnesota, USA. The garage is not temperature-controlled.

On a roughly three foot long exterior wall, I discovered the drywall was disintegrating (white powder fell out from between the paper) near the floor (from the floor to about 10 inches above it). I pulled that piece of drywall off and I want to know how I should repair it. Everything was humid but not wet. The nails that held in the drywall were rusted near the bottom of the wall. I didn't see or feel any moisture in the insulated cavities of the wall. The floor in the corner slopes slightly toward the garage door. In the winter, snow and brine often pools a bit in this area as it melts off the snowblower and shovels. I'm guessing the disintegrated drywall is a result of moisture being wicked up into the drywall and then going through freeze/thaw cycles - but I really don't know.

picture of wall

How should I finish this wall? I figure if I just put of a sheet of drywall, I will get the same issue in the future. Here's some potential ideas I have:

  1. Replace the drywall but only down to the base plate - then put cement board from the floor to the bottom of the drywall.

  2. Replace the drywall but only down to the base plate - leave the bottom area covered with something else?

  3. Replace the drywall to the floor but then put some kind of water proof baseboard along the floor.

  4. Replace the entire piece of drywall that I teared off with cement board.

  5. Mount PVC trim board against the floor and run the drywall down to the top of the PVC board.

  6. Something Else?

I'd like my fix to meet Minnesota code and the scrutiny of a home inspector in a few years.

At the bottom of the wall cavities is sand. The piece of steel in the left wall cavity is c-channel shaped and someone sprayed a bunch of expanding foam into the cavity. I don't know what that might be about - I'm guessing a previous owner had problems with water intrusion at some point - especially if the garage roof gutter hadn't been installed yet. I've never noticed water from anywhere but the garage floor and vehicles.

Here's a picture of exterior of the wall:

exterior view of the wall

Eagle-eyed DIY-ers will recognize the dirt in the corner is a sign of improper drainage. I am having the concrete outside mud jacked later this week to fix the slope and the cavity between the garage and the gap between driveway and the garage re-sealed.

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  • #5 - PVC Trim boards, Drywall down to that.
    – Alaska Man
    Commented Jun 29, 2020 at 22:37
  • When you say "PVC trim board" are you talking about a trim board that goes over the drywall? Also, are you OK with looking for products that might not be obviously available at a bigbox store?
    – ThreePhaseEel
    Commented Jun 30, 2020 at 0:08
  • Once you've fixed this, either store the snowblower and shovels at a different place in the garage so their runoff doesn't make it to this low spot, or store them in a shallow plastic/rubber tray (like a "bed liner" for the back of an SUV) to contain the mess. If you do that, you would probably be just fine going with drywall all the way down.
    – FreeMan
    Commented Jun 30, 2020 at 11:44
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    @ThreePhaseEel I'm OK with considering products that aren't necessarily at a big box store. I was thinking a PVC trim board like this homedepot.com/p/… I would stop the drywall above the trim board.
    – Jon
    Commented Jun 30, 2020 at 15:36
  • @FreeMan - a cargo liner is a good idea. The snowblower really needs to be where it is - where it can get out without having to move a vehicle. It is also rather big and cumbersome - I store it by putting the large tires on a couple of carts so I can roll it into the nook. I wouldn't be able to roll those carts onto an bed liner or anything. Even with a mat, one should expect snow to blow into the area next to the garage door and later melt.
    – Jon
    Commented Jun 30, 2020 at 15:45

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I would use cement board. Since it comes 3x5 feet typically I'd use it for at least the bottom 3 feet, unless doing a larger area (or using a scrap you already have on hand) where I might cut it in half and just come up 18 inches from the floor. It takes both water and the sort of minor impacts common in garages with tools far better than drywall does.

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