rust spots on exterior walls

[Flank]

Hello, I am new to this group. I just bought a recently remodeled house, and I have noticed that there are small sort of round dark spots on some of the exterior walls. These spots are about 5 inches above the floor, and they are randomly scattered. The spots are about 1 to 2 inches in diameter. It seems that they are the result of rusting nails. I immediately considered water damage, and so I went outside and inspected the exterior of the wall, and there is no apparent damage at all. The part of the house that has this problem is an addition, on a slab foundation. Based on what I can see, the guys who put this place together cut every possible corner. Has anyone out there ever dealt with this before? Is this an indication of interior water damage. Or could the rust be from a one time wetting event, such as painting?

thanks flank

[m Ransley]

It might be the nails get cold in winter and condense, maybe there is no insulation in the wall.

[Hopkins]

Yeah, could be condensation. Could be moisture wicking from the surrounding ground. Is there a sprinkler that sprays in the affected areas? Or do the areas hold moisture?

[Flank]

It is an odd problem. One wall does have a sprinkler spraying nearby, but the other two walls don't. And one of the walls is a shared wall with the garage, and so it is not even an exterior wall. So, let's consider the wicking moisture/condensation problem. Why would the rust spread out to a circle of 2" diameter? Does that seem right? It seems to me that the rust would stay isolated to the nail head, or it may streak down the wall like nails in a fence. I don't understand why the rust spot should spread. Any ideas?

flank

H> > Hello,

[Hopkins]

right? It seems

the wall like

I'm not sure I have a good response. Rust spots bigger than the nail head aren't uncommon -- I've seen them in bathrooms with lousy circulation. I could see relatively large spots if the moisture is a repeat problem (ie, if there was a one-time moisture problem I'd probably expect smaller rust spots).

For rust to run down, it seems there would need to be so much moisture that it reaches or passes the saturation point (given that the moisture is coming from the outside or the bottom). A fence gets rained on and water runs down -- the water carries the rust down.

Is the room in question on a slab? If one of the trouble walls is not even an exterior wall I'd look at the slab. Maybe someone with more experience will comment, but that seems like a lot of wicking moisture. I dunno.

The easy thing to do right now is to make sure the ground is sloped properly to allow drainage, and to make sure the soil/mulch is not in contact with the walls outside.