I noticed the following mold in a corner of my garage. Where is it coming from, air flowing around the door or hinge? Could the garage door (right), contribute to this? How does one stop this from happening?

At this time, my plan is to cut out the sections that have mold and replace them with mold resistant drywall that I have on hand.

Mold in corner of garage

Here is a pic of the outside.

Outside of garage

I'm on the East coast in Canada (ie. Maritimes). This issue has appeared a while back, just getting to it now. It doesn't seem to have expanded.

We use the garage a few times a day as the car is always parked in it. The ride-on lawn mower and snow blower are typically parked near the corner for easy usage which might bring in excess moisture to the corner?

Update 2

I had the chance to open up the walls. It seems superficial. Noting the black strips along the edges look to be some sort of caulking.

Removed drywall from corner

Back of the drywall shows some traces of mold.

Back of drywall

Maybe all I need to to put a mold resistant drywall patch, which I conveniently have sitting in the garage?

I wonder if the line on the moulding isn't due to air circulating via the hinge?

Update 3

I should have posted these earlier. A closeup of the hinge and both front and back of moulding. At this point, this seems to be surface only?

The green drywall is the new patches that I cut and haven't installed yet. They're from an old piece cut out from left overs used in the bathroom a while back at another house.

Closeup of hinge

Front of moulding

Back of moulding

  • 1
    please add a photo of the exterior
    – P2000
    Aug 31, 2022 at 20:31
  • 1
    Your exterior photo lacks context. Show us the roof as well, please. It's all relevant. The water came from the sky, after all. Even the slope of the surrounding area could be a factor, if the concrete is perpetually soaked.
    – isherwood
    Sep 1, 2022 at 12:59
  • 1
    If water was pooling in the corner per @HotLicks I think 1) it would be more evident in staining of the floor there and the pattern of the debris and 2) OP would see the pooling water and hopefully would have mentioned it! But IF that is the case it's easy to fix, drill a 2 inch by 18 inch hole at the low spot and fill with gravel. That's adequate drainage for vehicle snow melt.
    – jay613
    Sep 1, 2022 at 13:12
  • 1
    Update 2 has me stumped.
    – jay613
    Sep 3, 2022 at 21:53
  • 2
    Yes, looks like you have a humid area there, not water ingress. Mold resistant drywall could be all you need. Perhaps just install it, leave it unmudded for a year, and re-evaluate. It's possible there is moisture entering through the concrete or between foundation and sill due to a missing or inadequate sill plate gasket. Could also be humid summer garage air condensating around the cooler concrete (e.g. shade/cool side of house)
    – P2000
    Sep 4, 2022 at 18:37

3 Answers 3


The service door is suspicious. If the siding installers didn't lap the flashing, house wrap (if present) and J-molding correctly it can result in a funnel. I'd look that over carefully. Could be that it's been leaking for years and only recently accumulated enough moisture on the inside to result in mold.

"Maintenance-free" siding isn't always the miracle that folks think it is, especially if it's not done perfectly.

Your updated photos don't change much for me. You don't get concentrated mold like that without either regular damp air movement or a leak.


Here's a guess. The downspout is leaking in one of the indicated locations. Go look at it during heavy rain fall. Here's an even more specific guess: The green pipe is blocked, the downspout is filling up with water creating pressure and so where it joins the green pipe it's spewing forcefully backwards underneath the last row of siding towards the door.

There are other possibilities. If you add another exterior picture showing the top of the door, the roof and eaves, maybe other guesses could be made.

enter image description here

  • Thanks! Green spout isn't blocked, that's for sure. It may be spewing backwards though. When you say, "top of the door", which door? The side entrance one? We had heavy rainfall yesterday afternoon, would have been perfect to inspect this.
    – TechFanDan
    Sep 1, 2022 at 12:27
  • 1
    Yes the people door not the overhead door. Water may be finding its way from a roof or gutter fault down the inside of the wall and collecting near the door. You usually can't SEE the cause of that but it's worth a look.
    – jay613
    Sep 1, 2022 at 12:29
  • I wonder, ice forms at the bottom of the garage door during the winter as snow/ice from the car melts and drains towards the door. It sometimes makes it hard for the door to come up. Maybe this has an impact? I'll try to open up the walls over the weekend.
    – TechFanDan
    Sep 1, 2022 at 12:44
  • I don't think your problem is runoff from vehicles. The pattern of mold suggests something else. You mentioned parking the snow blower, I had that EXACT problem, I was parking it butt up against the wall and I developed something like in your photo. But the pattern of the mold was vaguely where the blower was touching the wall. Yours doesn't look like that at all, you surely are parking it on the other side of the people door.
    – jay613
    Sep 1, 2022 at 13:08
  • Yes, it's parked inside, in front of the door to some degree. It's always a few inches from the wall and door.
    – TechFanDan
    Sep 1, 2022 at 13:41

You've got a water leak in there somewhere. It's probably behind the drywall so it's a good think you were planning on cutting that section out, the whole corner from door trim to garage door track about 2" high. You might be able to save the door trim by cleaning it off with some hydrogen peroxide or vinegar. Clean out the whole area and then observe the area during/after rainfalls for leaks. Might be nice to post a picture of the outside of that corner.

  • Added picture to the original post
    – TechFanDan
    Sep 1, 2022 at 11:26

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