Expert Field Advice on Cedar Siding Mold Removal

Black mold – we have all seen wood sided homes that turned that death black color. It just looks bad.

In wooded or shaded areas mold is going to present itself insidiously. The problem is that for many years the only semi-transparent wood stains on the market were oil based.

Oil based stains actually feed mold. They contain natural resins like linseed, vegetable, tung oils and animal fat which make a scrumptious dinner for mold spores.

black mold on western red cedar siding

Learn how to remediate mold on your wood siding – both removing mold and then preventing mold from returning.

We interviewed one of our callers (Jim) who was deciding whether or not to replace the cedar he had on his house for the last 30 years. He was the original owner and has been “meticulously maintaining” (as he put it) the wood the entire time.

We asked him how he handled mold on his wood siding – both removing mold and then preventing mold from returning.

How To Clean Mold Off Cedar Siding

Jim qualifies as a special kind of expert because he knows what it takes to maintain wood long term.

He got 4 or 5 good years with that first coat of clear oil based stain before the “darkening” set in.

“The mold got considerably worse when we put the mulch in to grow our shrubs.”

“The key is remove the mold and clean the siding the year BEFORE you think you need it. You could look at it and say- ‘I could wait till next year’ and that’s how you know it is time to do it THIS YEAR!”

“If you wait you will be sorry!”

I could hear the pain of experience in his voice.

wood siding mold damage

When should you clean your moldy siding? Soon – don’t wait till the mold looks like this!

“OK – so how do you remove mold from cedar?” I asked

“The first thing is what you don’t do:

Do NOT pressure wash the wood! It can force water through the cracks and seams and cause moisture damage inside your home.

Do NOT clean wood mold with Chlorine Bleach products! It will eat the fibers that hold the wood together and discolor the siding.”

In order to avoid cleaners that contain chlorine bleach you can check the product label. The chemical name for chlorine bleach is sodium hypochlorite. It is highly toxic to vegetation.

Removing the Wood Mold with Oxygen Bleach

“The safe and effective way to clean the wood is oxygen bleach. The oxygen bleach comes as a granular powder that mixes with water. It is nontoxic to trees and vegetation and will not remove natural color from the siding.

I used double the concentration on mine because I got tired of scrubbing. It said to use 4 to 1 on the Oxy Bleach and I did 2 to 1. I tested on a small area and it worked and really cut down on the elbow grease.”

(We advise testing a small section before trying modifications of any sort.)

wood siding mold removal

“You removed the wood mold by HAND?” I asked.

“Yup. You need a garden pump sprayer and a scrub brush. You let the oxy bleach solution set on the wood for about 15 minutes and then scrub it off.”

Cleaning & Restoring Wood Siding

“Then we used Wolman’s Deck Brite to clean it – to get rid of the dark stains left by the mold. You can’t get it all but you can really improve the overall look and reduce the dark areas considerably.

Next, we applied the wood restorer- I use Wolman’s Deck and Fence Brightener. The Deck Brightener we let sit 20-30 minutes.” Jim said.

“Those two things – cleaner and brightener – really worked well for us. “

cedar siding mold removal cleaning and brightening

Staining the Restored Cedar Siding

Now the cleaned and brightened cedar wood siding is ready to stain.

In the past he had used oil based wood stain products but found the mold and mildew returning within a few years each time.

“So, after the last round of mold cleaning and wood restoring we decided to use a newer wood stain product on the market called DEFY. It is a water-based wood stain that has synthetic resins which block water but do not feed mold spores. I have gone 7 years and counting and no black mold!”

Synthetic Resins to Prevent Mold

Synthetic resin-based products are the most expensive wood protection products on the market but compared to the value (and replacement cost) of your wood siding it is a minimal price to pay. If it lasts twice as long it can justify its own costs.

DEFY Water Repellent Wood Stain

Factory Finish to Prevent Mold

Factory finishing all four sides of your wood siding before installation – and sealing the ends during installation – continues to be the single best protective measure you can take towards long term wood siding and decking performance. Factory finishing continues to be the most economical way to achieve a multi sided finish.

A factory finish floods the wood. If you were to request an expensive product like Defy for a factory pre-finish it would cost a fortune. I have always said it makes sense to use a lower cost finish for multi-sided factory coating and then upgrade protection in the field – a 2nd finish coat during installation and then follow-up maintenance coats during the lifetime of your wood siding.

That way you are only paying for the good stuff (synthetic resin) on the face of the wood where it is needed to prevent mold.

If you have a heavily shaded area I would recommend a water-based stain as the technology seems to have improved to the point where they are equal to or greater than their oil based contemporaries.

In the case of factory application Sherwin Williams WoodScapes is a reasonably affordable water-based stain and can be run through factory machines at a reasonable cost.

Then when it is time to clean and maintain your wood you can come back with Defy or another synthetic resin-based stain and get your long term protection. This is maximum value for the wood protection dollar.

Just remember that 99% of all reported siding problems are installation and maintenance related. If you take care of your wood- it will take care of you.

cedar siding on home
Cedar Siding Home After Mold Removal, Cleaning, Brightening and Staining

That is the truth as we know it.

Good luck out there! Buffalo Lumber Co

Send us your stories – your triumphs and tragedies – anything you think might help future wood lovers achieve their dreams and we will share them here. Sign-up for our Lumber Newsletter and read our latest customer projects and discoveries.

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