Mold and Mildew on Lumber
Mold & Mildew on Lumber TIPS
- Mold / mildew can happen on any lumber
- Rot is rare when building
- Use Stain Solver oxygen bleach to clean
- No vapor barrier until lumber is dry
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DEAR TIM: I'm having a new room addition built and while inspecting the framing lumber I noticed black mildew and mold on different pieces of wood. One joist is totally black with it. Is the structural integrity of the wood compromised? Should the lumber be replaced? What causes this to happen as some of the lumber looks perfect? What's a sensible course of action at this point? Tracy K., Chicago, IL
DEAR TRACY: You're not alone. Many homeowners experience mold and mildew on their lumber as houses are built or room additions are constructed. The good news is the lumber is going to be fine and there's rarely any damage to the wood. If it's just surface mildew, it will clean off using a certified organic oxygen bleach like Stain Solver.
Wood rot can weaken wood, but it's easy to tell if wood is rotten. What's more, wood will not rot in the short time it takes to build a new home or room addition. It typically takes years for wood rot to advance.
Any Lumber Anytime
There are many reasons why the black mildew and mold appeared on the lumber. Understand that it can happen to just about any lumber any time.
Lumber that's treated with chemicals that contain copper or borates are less susceptible to mold and mildew growth because these elements and chemical compounds are natural biocides. But mold and mildew can, and does, grow on treated lumber.
The mold and mildew spores are just about everywhere. They're on the wood surfaces or can be transported there by wind and rain. Once in place, all they need is water to start growing and flourishing.
Sugar aerosols broadcast by trees and bushes is food for mildew. Dust is also a food. It's nearly impossible to keep the lumber clean as you build. Some lumber provides plenty of food for the mold and mildew to grow rapidly.
Mildew Within 48 Hours
When you see the black mold cover wide areas of lumber, usually this happens because the wood got wet and stayed wet while it was being stored. If it's warm and humid, the growth of the mold and mildew can be rapid.
Mildew can start to grow in as little as 48 hours if conditions are favorable.
Construction Food & Drink
Spotty outbreaks can sometimes be traced to food or liquids that are food for mildew or mold. For instance, if you shake up a bottle of soda containing sugar or high fructose corn syrup and spray it randomly on the lumber, you'll probably see black spots appear in short order wherever the liquid contacted the lumber and dried.
Test For Rot
You can test for structural integrity yourself. First make sure the lumber is dry. Once the room addition is under roof, the wood should dry pretty rapidly unless you're in a very long damp spell.
Take an 8-penny nail with a sharp tip and see if you can push it into the wood with just your hand. If you meet immediate resistance, the wood is fine. If the nail, using hand pressure, penetrates deeper than one-quarter inch, then you could have wood rot.
Stain Solver Cleaner
Cleaning the mildew and mold from the wood is a good idea. You don't want it covered up. Cleaning can be accomplished in several ways.
I recommend you use Stain Solver certified organic oxygen bleach mixed with a little bit of liquid dish soap
The Stain Solver is a pure powder Made in the USA with USA ingredients. It dissolves in warm or hot tap water with a little bit of stirring.
Once mixed and all the powder is dissolved, just pour the solution into a garden hand-pump sprayer and squirt it on all the lumber that's got mildew and mold on it.
Allow it to soak for about 15 minutes keeping the lumber wet with the solution the entire time.
Don't worry, the water is not going to harm the wood since it's able to dry rapidly.
Toxic Chlorine Bleach
Chlorine bleach is also very effective at cleaning up the mold and mildew. You can mix a 50-50 solution with regular chlorine bleach and water.
Some people don't do well with the fumes, so be careful. Wear old clothes as the chlorine bleach will ruin dyed fabrics. Wear goggles and gloves when using chlorine bleach or any chemical.
The other issue with chlorine bleach is that any solution that gets on, or near, trees, flowers, grass, bushes, etc. will kill it. Chlorine bleach is very toxic.
Don't Cover It
You do not want to cover up this contaminated wood. It needs to be cleaned before any insulation is installed. Never cover this stained wood with drywall or paneling. Anyone with asthma or other respiratory challenges could suffer from the hidden spores.
If you're building during a wet spell and the builder is trying to move the job along, never allow him to cover up the wood if it's still wet. Trapping water and moisture in wood will cause mold and mildew to grow.
Air Dry Is Fast
It doesn't take long for wood to air dry, especially once the roof is on and there are high-performance vapor barriers in place in crawlspaces and under concrete slabs. Don't be fooled by a builder that says the wood will dry out on it's own in the wall.
IMPORTANT TIP: Don't allow a builder to apply a vapor barrier on wet lumber. This will trap moisture and mold and mildew will become a huge issue. A vapor barrier traps the moisture in the wall cavity.