Why Mold is Attracted to Oil Based Stains  4.6/5 (10)

This post was updated on May 1, 2024

Why Mold and Mildew is Attracted to Oil-Based Stains

Mold or mildew growth is a common problem during deck staining when using an oil-based stain. Today we talk about what causes your deck to turn black during the staining process and how to prevent it. If you have encountered mold during your deck staining project, we want to hear from you. Feel free to leave a comment below with pictures of your deck stain projects.


Moldy_Deck_StainMost any exterior surface subjected to the elements is prone to natural occurrences like mold growth. Oil-based stains are no different. Although they can provide years of protection to exterior wood surfaces, they can be prone to mold in some circumstances. There are however some reasons that can increase mold attraction to oil-based stain.

Over applying oil-based deck stains can increase the chance of mold attraction. When over-applied, oil-based stains will not cure right away. The stain can remain sticky and tacky for several days allowing dirt and tree pollen to become embedded. With the intrusion of natural contaminants prior to fully curing, the stain is more prone to mold growth.

Best Cleaner to Remove Mildew on Oil-Based Deck Stains

The RAD Guard will remove the black mildew and green algae stains from your wood and deck stains and will prevent them from returning for 1-2 years: RAD Guard Mildew and Algae Cleaner and Preventer

Mildew on Deck Stains

Mold can also be attracted to oil-based stains that are cheap or inexpensive. Inferior deck stains have cheaper ingredients in them that may lack the mildewcides that help deter mold growth. In the case of the mold being attracted to oil-based stains, you get what you pay for.

In some instances, the mold is more attracted to oil-based stains like in areas of humid climates or when close to a body of water. The extra humidity and moisture can cause mold to grow on the surface of oil-based stains ruining the appearance of the wood. Even with high-quality oil-based stains, mold can still be a problem in humid climates. To avoid a mold attraction problem, use an oil-based stain that protects against mold and mildew. Also, increase the amount of regular wood maintenance.

To combat the attraction of mold to oil-based stains; use a quality stain that has added mildewcides and algaecides. Be extra careful not to over-apply oil-based stains. Apply only enough stain that can be absorbed into the wood. Wipe away any excess stain that does not penetrate. Increase wood maintenance in high humid climates.

If you have any Questions. Please Post a Comment Below!

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Scott Paul ~ Restoring Wood & Decks Since 1993 Owner
As an article and comment contributor to the site, Scott has been around the pressure washing industry since attending college. In 1993 he started his first company called Oakland Pressure Wash specializing in exterior pressure washing and deck staining. That company evolved into OPW L.L.C. shortly thereafter concentrating more on exterior wood and deck restoration. Scott and his Deck Cleaning Michigan company have restored over 10,000 decks in the Metro Detroit area since the early years. He has become an authority in the deck restoration industry and has contributed to numerous wood restoration forums and informative sites. All the products he suggests through this site are sold through online sites and in retail stores, allowing the consumer to choose their own means of purchase. Scott’s eCommerce sites do sell many top brands he endorses and if you appreciate any of the help he has offered then feel free to purchase from one of them.

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Ron
Ron
1 year ago

We just finished rubbing back our outside bar table and use Cabot’s outdoor deck oil, after a couple of days black spots started to appear . How do we get rid of these black spots

Bill Keane
Bill Keane
2 years ago

We have a Sikkens-coated Kwila deck, laid approx 6 years ago, with exactly the mould appearance and pattern in your top photo. Currently only 4 boards (out of 25) have been infested after an extended rain period this year. Scrubbing and surface mould treatments haven’t had any positive impact, so it appears the mould is below and into the layers of the sealant. I’m concerned the mould may worsen / spread and may weaken the integrity of the deck – and this is apart from the aesthetic of mouldy boards? Does the issue need to be addressed, and what would you recommend? The deck has proud studs which would prevent sanding, so if these boards need to be stripped back are you able to advise the easiest / best approach?

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Bill Keane
Bill Keane
2 years ago

Will this mould cause issues if nothing is done?

Tania
Tania
2 years ago

I have an in inbuilt wardrobe that for some reason attracts mould and mildew. I have cleaned it multiple times, but will find mould in shoes that I haven’t worn in less than a month.

I also have a shelving unit that keeps getting mould on the wood. How can I fix this? I thought about using wood oil but I firstly I put clothes on the shelves and I read that bacteria grows on the wood because of the oil.

Please help.

David Brown
David Brown
4 years ago

I live in central Florida and am considering installing stained wood on the ceiling of my open air lanai w/a pool in close proximity, but not under the roof area. I’m a little bit concerned w/possible mold growth and don’t want to waste my time or money if this is not a good idea and could be a future health problem source. The area above the ceiling is in the roof area so it would be exposed to high temperatures from the heat during the summer months. Any advice would be greatly appreciated!

Mari Etta McEachern
Mari Etta McEachern
4 years ago

Our cedar log cabin has been stained with Behr oil. The South side has mold. How do we restore it to a nice cedar stain?

Bill George
Bill George
5 years ago

what about oil base paints ?

Shelley Grellner
Shelley Grellner
6 years ago

If you do begin to see black mold on a newly stained fence, can you remove it without harming the stain? It is an oil stain on a one year old thoroughly cleaned and prepared cedar fence. We did have
some very humid days after staining. The mold is on 3 panels of the fence.

Linda
Linda
6 years ago

My deck has been installed but not stained yet. It is KDAT lumber and has the black spots everywhere! What do I need to do to clean it and insure the mildew/mold is gone before it is stained?

Paula
Paula
6 years ago

how do you get rid of the black mold???

Paula
Paula
6 years ago

I have tried a deck cleaner and power washer. Someone told me that i had to sand it is that correct? or would the stain stripper work? If the stain stripper would work which one and where do I get it?

john g. mcmaster III
john g. mcmaster III
7 years ago

I live on a lake in a humid environment. I used a tinted oil stain in the past. I applied a deck cleaner which turned the deck black. I pressure washed the deck, reapplied the cleaner and pressure washed again and again. The process works fine, it's just that I miss little spots here and there and can't tell until it's dry. It's still a little splotchy. I really need to know which product and brand is best. The deck is treated wood and I really would like something that allows the wood to show through. The deck builder recommended the tinted stain

Dani
Dani
9 years ago

I live in Arkansas and have problems with black mold on the pressure treated deck I stained with Cabot wood preservative finish. I was planning to strip the old stain and apply the TWP 100 series this year but wondered if I should use a water based stain instead. What product do you recommend ? Also when is the best time of year to strip and stain. We get a lot of green pollen in the spring.

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