Mold Growing On North Facing Deck

By Todd Fratzel on Decks & Porches

Deck Mold Growth

Our new home has maintenance free siding, trim, windows and doors. However, we decided to “splurge” a bit on the decks so we installed beautiful Cambara decking (Cambara or Erbina uncinatum is a beautiful hardwood with straight clear grains similar to mahogany). In fact we installed the Cambara on the farmers porch and the large rear deck. Needless to say this has left me with a significant amount of wood to maintain (over 1,500 sq ft).

Cambara decking stained with mold.The problem we’re having right now is our rear deck is located on the north side of our house. Our new home is a very tall 2 story colonial with a high pitched roof so the sun is blocked from this deck most of the day. This has resulted in quite a mold problem on the decking.

Cambara has a natural reddish color. If you look at the adjacent photo you’ll see that our deck has a very dark brown to black color. This is a result of the mold that’s been growing on the decking.

Cleaning Deck Mold

I’ve decided that I need to remove the mold and try a new deck sealer. The best way to remove the nasty mold growth is to use a pressure washer. I’ve been wanting to buy my own pressure washer for some time now so I finally went out and bought one this weekend. Thanks to the guys over at One Project Closer I had a nice Home Depot gift card so I ended up buying a new gas pressure washer (I’ll write a review on it after I’ve used it for awhile).

Cambara decking after pressure washing.It’s been my experience that  you’ll need a pressure washer with at least 1500 psi or more to remove this type of mold. I used the medium nozzle on my new pressure washer and held it about 2-inches from the surface. As you can see from the photo I was able to remove all the black colored mold from the decking.

The key is to go slow and keep the pressure washer nozzle a constant distance from the decking. If you’re not careful you can create really bad gouges and defects in the decking. It took me about 2 hours to completely clean this 24 ft long by 8 ft deep deck.

Refinishing Cambara Decking

I’ll be writing at least one more post that focuses on refinishing the Cambara decking. The previous sealer (Penofin) was horrible. This deck is only 3 years old and it’s been sealed twice with Penofin so I need to try something new. I’ve actually decided to take the “One Time Challenge” and apply a deck sealer that claims to last 7 years! So stay tuned in the coming weeks for my review of the One Time product.

About the author

Todd Fratzel

I'm full time builder for a large construction company in New Hampshire. I run their design-build division that specializes in custom homes, commercial design-build projects and sub-divisions. I'm also a licensed civil and structural engineer with extensive experience in civil and structural design and home construction. My hope is that I can share my experience in the home construction, home improvement and home renovation profession with other builders and home owners. I'm also the Editor-in-Chief and Founder of Tool Box Buzz. Please feel free to contact me if you have any questions, suggestions or you'd like to inquire about advertising on this site.

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  1. Why S?` says:

    1,500 sq ft! Wow, that is a lot of wood to maintain. That’s bigger than our house. But it is a lovely wood, though.

  2. Baba says:

    I am sure it will be wonderful when you are all done. It looks like a great space to enjoy your summer.

  3. Jerry says:

    Todd, what a fantastic result! I too have a Cambara wood deck that I installed myself last year. I’m sharing this because after just 1 year there are patchy areas of mold (black fungi) appearing and it bugs me. Not just because of all the effort installing and treating (with Penofin I might add), but because of all the great pictures and promise of what a Cambara wood deck looks like and I’m not able to achieve that. Our conditions are a rooftop deck in Boston therefore 24x7x365 exposure to the elements and of course all 4 seasons. I chose Cambara for the look, ease of maintenance, and ability to exist in damp conditions. Using Penofin Finish for Hardwood {which they claim is used for all fine hardwoods such as IPE), I treated each board on 3 sides (+ ends) prior to installation and once installed, applied to the topside 1 initial coat and a 2nd coat ~3 months later. Last year the deck looked great. This year the color of the deck has darkened considerably and there are black mold patches everywhere. Wondering your thoughts and conditions and also how did the ‘One Time Challenge’ turn out?

    • Todd says:

      @ Jerry – Well with the rain we’ve had this summer I’ve yet to try the “One Time Challenge”. I’m waiting for things to dry up here. I think the problem is Penofin and I’m hoping that a different sealer will cure this. Be sure to sign up for my RSS feed so you’ll know when I finally seal it.

  4. I have part of my deck that get’s no sun to dry out. How it is green and black..How can I keep this from happening

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