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Blackish substance on siding


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Today found me at a 1912 home. I noticed a black/reddish substance on the north side of the home. Some spots looked as if they came straight through the wood siding, other stains appeared to run down the face of the siding and onto the wood trim of the windows below.

Just to the right of this window is a shower/bath that has been recently installed. Several pieces of new siding were installed on the top 1/3rd of the home at this location and the home was recently painted. The home has been vacant for approx. 6 months. Renters before that.

The friendly neighbor...gotta love 'em...said that the discoloration was much, much worse prior to the new paint job, and now this substance was bleeding through again, and no one has been living in the home to use the shower.

The window frame and sill plate below this location in the basement contained wood rot and carpenter ant damage. There has clearly been a leak in the shower/tub prior to the repairs and I'm sure water entered this wall, creating the need for repairs.

My question is, what is this stuff? I'm assuming some type of asphalt building paper behind the siding, but why would it continue to bleed through?

Any ideas would be great.

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Around here a house that old usually has a rosin paper WRB if it has any at all. If they used asphalt impregnated felt under the new siding above, any moisture in the wall will be driven out through the more permiable older areas of the wall. That kind of tannin stain is the result. I would wager that there is/was wet wood in the wall well up into where they new siding is.


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There was a leak for sure sometime in the past as indicated by the damaged/stained subfloor in the basement and the destroyed frame and sill around the window beneath.

I did test for moisture, however the home has been vacant for 6 months so I was told. As far as residing, portions were resided, but most of the new siding was above these stains. The neighbor also mentioned that the stains were there a long time and much worse prior to any repairs.

That's what has me puzzled.

- Orinally really bad stains

- Repairs made to bathroom (new tiled surround)

- Fresh paint at exterior

- Vacant for 6 months (no one using shower)

Maybe residual moisture in wall cavity is pushing resin/asphalt through siding?

I'll just report what I see on this one.


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In all the accounts listed above by you and other members, all seem like valid possiblities.

Sometimes I feel like our curiosity gets us to investigate further than we need to.

I personally would have used a moisture meter just to see if it was wetter than areas around it. Checked the eave and roof closely in this area, then written up that further investigation is needed.

If the sub structure was still wet when they made the repairs, and no one has lived in the home since, I could be condensation from a greenhouse effect of the house being sealed up and is now sweating. The damage before that could have been from the actual leak. but if moisture was sealed in, that could lead to sub structure rot. We can't do distructive testing to find out if that is the case but it should definately be looked into further.

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