Stucco humps

Dear Stucco Swami,

I love your name by the way!

We are very interested in a Craftsman house built in 1924, that has stucco siding (which we know nothing about)! In the back of the house there are several large, visible humps. We had a friend of ours, who is a home inspector, look at it and he felt it may be that the paper is crumpled. There is no visible water leaking, no rust, and the humps are not soft. Do you know what it could be?

Thank you so much. Kathy

The metal lath has deteriorated, usually because interior lath was used on the exterior.

These humps and bumps are hard enough to knock on, but break apart easily when hit with a hammer.

I have heard people say the wall is pregnant. Usually, this deterioration is accelerated by roof leaks, lack of drip edge, window flashing, etc.
Another indicator of lath failure is when a house has been patched umpteen times. A house like this will always be a patched up looking house until the lath and stucco is replaced.
Expanded metal lath was invented after the turn of the century, that is, the last century. The oldest building I have seen expanded lath used was a stable built in 1908. Welded wire lath also came out about this time, and is almost always in good shape today.
Expanded metal lath, even back in that time period, was available in galvanized for exterior use, and painted, or bare steel for interior plaster.
The gap between the stucco and the foundation forms a drip edge in Washington, DC.

This 1910 house in Chevy Chase had galvanized diamond mesh lath. The lath was in excellent condition after 110 years, so we reused it.

You can see the reason for the patch, The downspout was stopped up for some period of time.

The gap between the stucco and the foundation forms a drip edge in Washington, DC.

This galvanized expanded metal lath on this 1910 house in Washington, DC was still in like new condition. We recoated the house with the confidence the stucco will last.

More about the project here..

The gap between the stucco and the foundation forms a drip edge in Washington, DC.

This 1923 house we patched last summer had been patched 14 times. We counted 14 different textures. The lath was made for interior use and had deteriorated to a thin paper-like film. I couldn't talk the owners into replacing all the stucco. Stucco like this is a time bomb waiting to fail.

Interior lath was discontinued over 30 years ago, and only galvanized is available. My competition used interior lath outdoors back then because it was a lot cheaper.

Exterior lath was galvanized, and interior lath was painted. The paint was really some black coating that washed off. I remember my hands would be black after tying this so called painted lath om the ceiling all day.