Black staining on a log home is one of the most common problems homeowners notice — and it usually means the wood is holding moisture. While some stains look like “dirt,” most black discoloration comes from mildew, algae, tannins, or trapped moisture breaking down the wood surface.
The good news is black logs can often be cleaned and restored. However, if you ignore the problem too long, it can lead to deeper staining, stain failure, and eventually rot.
If your logs look dark or uneven, start here: LOG HOME CLEANING
What Causes Black Staining on Log Homes?
Black staining doesn’t come from just one thing. In most cases, it’s a combination of moisture and organic growth.
Here are the most common causes:
1) Moisture + Shade (The #1 Cause)
North-facing walls and shaded sides stay wet longer, especially in wooded areas. When logs don’t dry out, mildew and algae grow on the surface.
Common signs:
- dark streaks near gutters
- blackening under rooflines
- stains on shaded or tree-covered walls
- black growth near the bottom course
If the wall stays damp most of the day, black staining comes back quickly unless the moisture source is fixed.
2) Mildew / Algae Growth
Mildew and algae feed on organic material on the log surface. They thrive where:
- there’s shade
- humidity is high
- pollen and dirt build up
- water runs down the same area repeatedly
Mildew can look like:
- black specks
- dark streaks
- gray-black film on the wood
Professional log cleaning removes this safely without damaging the wood. LOG HOME CLEANING
3) Failed Stain (The Wood Has Lost Protection)
When stain fails, the logs lose UV protection and water resistance. As a result, moisture soaks in faster and holds longer, which creates the perfect environment for black staining.
Signs stain is failing:
- fading or graying logs
- patchy or uneven color
- water no longer beads on the surface
- peeling or flaking stain
If stain has failed, cleaning alone won’t fix the problem long-term. You usually need staining after cleaning. LOG HOME STAINING
4) Tannin Bleed (Dark Streaks That Look Like Stains)
Some black or dark staining is caused by tannins in the wood. This happens when water runs over logs repeatedly and pulls tannins to the surface.
You’ll often see tannin bleed around:
- metal fasteners
- window and door frames
- water runoff paths
- log ends
This can be removed in many cases, but it requires the right cleaning system. Using the wrong chemicals can make it worse.
5) Water Runoff Problems (Gutters, Rooflines, Splashback)
Most black staining comes back because water keeps hitting the same area.
Common water problems include:
- missing gutters
- clogged downspouts
- roof valleys dumping water on a wall
- soil or gravel splashing water onto bottom logs
- decks holding moisture against the home
If you fix the staining but not the moisture source, the black will return.
If you suspect moisture issues, start with a professional evaluation: LOG HOME INSPECTION
Is Black Staining a Sign of Log Rot?
Not always — but it can be.
Black staining is often a surface issue at first. However, when moisture stays trapped in the wood, rot can develop.
You should be concerned if:
- logs feel soft under pressure
- the black stain is deep, not just surface
- wood crumbles or flakes
- you see cracking combined with softness
- stain keeps returning quickly
If you suspect rot, read this next: LOG ROT REPAIR
How to Remove Black Staining Safely
The safest way to remove black staining is to use log-safe cleaning methods that kill organic growth and restore the wood surface without damaging the grain.
Good cleaning includes:
- correct cleaner for mildew/algae
- proper dwell time
- gentle rinsing (not destructive pressure)
- drying before staining or sealing
- treating recurring moisture areas
Most homeowners make it worse by using heavy pressure washing or strong bleach.
The best first step is professional cleaning, especially if staining is widespread. LOG HOME CLEANING
How to Prevent Black Stains From Coming Back
To prevent black staining long-term, focus on two things:
- stop moisture problems
- keep the stain system maintained
Prevention checklist:
- trim vegetation away from walls
- improve airflow around the home
- fix gutter and drainage issues
- wash and inspect annually
- re-stain before the finish fails
- seal gaps and cracks where water gets in
For long-term prevention, follow this guide: LOG HOME MAINTENANCE GUIDE
When Cleaning Isn’t Enough
If the stain is failing or the logs are already exposed, cleaning alone won’t keep the home protected. In that case, you’ll likely need restoration-level prep and staining.
Start here: LOG HOME RESTORATION
Get Help With Black Staining on Your Log Home
If your log home is turning black, we can inspect the cause, clean it correctly, and recommend the right plan so the staining doesn’t return.
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