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The log home is doing fine with Woodguard that we put on originally and when necessary since we built it. The problem I have is with our new cedar deck. I replaced the old deck which was treated boards. They warped and wouldn't keep the stain very well. I didn't like the look either. The new cedar deck gets mold on it and I can't seem to get rid of it. Tried cleaning it with a wash that was supposed to keep the mold in check. I attached a picture.
Any suggestions will be appreciated.
Thank you.

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Hi, Rodney.

Is your deck stained? Your photos look to be showing tannin staining more than mold/mildew. Cedar is especially susceptible to tannin staining when a chemical is used to clean it. Those chemicals change the pH of the wood and draw the tannins to the surface. They follow the grain pattern and can look dark blue, black, or gray. You may have gotten rid of the mold, while at the same time bringing out those tannins. It usually takes a neutralizer wash of some kind to get rid of the stains, but can sometimes require sanding to get rid of them. What kind of cleaner are you using to get rid of the mold?

As for the problems with mold, is your deck exposed and in the sun a lot? It's possible some of what you're experiencing is algae, not mold. Not sure where you are in the country, but we're finding more and more of the mold-looking issues are actually algae. Do you have any pics before you washed?

--- Charis w/ Sashco - - 

I put a colorless preservative on. Sitkins. I will do some research on tannins. I don't know anything about it. The deck is on the south of the house. I don't think it can be algae.
Than you for the advice and will attack it with a vengeance this summer.

Sure thing. When you do get around to things this summer, be sure to keep in mind that most cleaners will discolor cedar. It usually takes a secondary neutralizer to bring the color back to normal. Check with the manufacturer of the cleaner for specific advice when using on cedar.

And, of course, let us know how things work out.

Good luck!

--- Charis 

Charis, I see you work for Sashco. Do they have a first step cleaner, and neutralizer I can start with? I don't think it's mold because it faces South with no tree obstructing it. The only time it's wet is when it rains. As soon as it stops snowing I want to start.
Thank you for the help. I have been researching tanning and I'm now convinced that is what is on my deck.

We have an oxygenated bleach cleaner call CPR that might do the trick. On most cedar surfaces, it's fine, but it can discolor red cedar some. I'd recommend you do a test in an inconspicuous area (maybe on the underside of a board or a hidden corner) to see what happens. If it brightens the wood some and doesn't turn it dark, you'll be good to go. If it does turn dark, you'll need to hit up your local paint store for a deck cleaner and neutralizer.

Let me know where you are in the country and I can direct you to the reseller nearest you.

--- Charis

I am in Northern NY. The snow is gone. The deck, when dry, doesn't look too bad. When it rains the black color comes out.
As I understand, I start with a neutralizing cleaner. Then do I reapply the finish. I have Sikkens Cetol SRD RE . I use a natural color. Should I sand before either step?

Hey, Rodney. I ran your pics by our R&D team, just to make sure about what we were seeing in them.

Really, what you're seeing is typical of a clear deck stain. It wears very quickly, leaving parts of the wood bare and others protected. The bare wood gets degraded by the sun, darkening it some. Then, when the wood gets wet, you see it darken (very similar to when concrete gets wet). Where the wood was exposed, that is even more pronounced.

You have a couple of options:

* Clean the deck good and coat it again with a deck stain. Those sunburned areas that have gotten darker will soak up the stain and stay a bit dark, but you'll be protected. (This is the less-work-now-more-work-later option.) OR

* Take everything down to bare wood with a floor sander and refinish. This should help alleviate the darkening quite a bit (although not completely). We'd recommend you use a pigmented stain that will erode over time, rather than a clear that will simply get burned off and offer no protection within a matter of months. A pigmented, eroding type of stain will wear better over time for easier maintenance. It won't completely deteriorate (as a clear often will), nor is it too thick to cause peeling. And just keep in mind: you'll likely need to do maintenance every 1-2 years on a deck that's fully exposed to the elements. :-) Nature of the beast. (This is definitely the more-work-now-less-work-later option.)

That should be enough for you to chew on for a bit. Let me know what other questions you might come up with. Definitely wait to do any work until you can guarantee dry, warm weather (above 40, including overnight temps) to give the stain enough time to dry.

Thanks! --- Charis

I will definitely go the second option. When it rains it gets black and the tannin can be washed off. When we walk on it, it leaves foot marks. I attached a picture that shows the deck after it rains. Notice the part that looks lighter. There was a floor mat over it when it rained.
Before I sand it back to bare wood, do I use a neutralizer first to stop the tannin from reappearing?
I will start it as soon as my other project is fininished. A ice damm caused a water leak and ruined the wood flooring enough making it necessary to replace it. Plus I need to fix the roof so it doesn't happen again.


No need to use a cleaner or neutralizer first. As I mentioned in my previous response, we're pretty sure that's not tannins but actually just UV damaged wood that turns dark when it gets saturated. Sanding will help reduce that and even things out again, as will using a pigmented deck stain. 

So sorry to hear about your wood floor! We recommend folks try to seal roof penetrations from both sides, along with checking their insulation levels, to prevent ice dams. Do you have an attic, or vaulted ceilings with T&G boards? If you have the vaulted ceilings, you might consider having your local energy provider do an energy audit for you since installing insulation isn't really an option. They can often pinpoint where the air leaks are happening so you can seal those up, thus preventing the heat escape and subsequent ice dams. (And I would be remiss if I didn't mention that we make a great roof sealant called Through the Roof that is great for sealing roof penetrations.)

Hope that helps for now. Best wishes with both projects.

Enjoy the Easter weekend!

--- Charis

How long should I wait after I sand it to apply the stain. Also is there a floor sander type that would be better? I am hoping that I can add a tint to the preservative I already have.

Wait no more than 2 weeks, if you can. The wood can start building up the sunburned wood fibers in as little as 7 days, so 2 weeks is a max. 

Yes, a floor sander will make everything go faster, though not necessarily a brand. Stick with an 80-100 grit sand paper to remove everything. You can usually rent those from home improvement stores. I would think that the Sikkens can have universal pigments added to it to tint it and give you the UV protection you need.

--- Charis

I'm getting ready to work on the deck. I will be using an orbital sander to get most of it. I don't think it will fit under the rails, so a palm sand will have to work.

As for the roof job. I had a energy audit and he said i need more insulation. I knew that. He's going to shoot cellulose insulation in-between the rafters from the top and the soffits.
As soon as it looks like a few days of nice dry weather we are starting that too.

I will let you know the results. Thank you for your experts guidance.


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