Mold? on deck railing and how to remove

[Teri Bennett]

I bought some 6' railing segments from Lowe's last year. They have vertical metal poles secured by horizontal wood (probably pine) beams on the top and bottom. I stained the railings with a Cabot outdoor stain and sealed it with Cabot poly. After 2 years, black stuff - assuming mold - has developed on the bottom beam. I've tried bleach and it doesn't budge. I'm really upset because I did what I though was right, the railing looks great, but now I have this black stuff to deal with. Any helpful advice is welcome!

[Lee Schierer]

You probably won't like this answer...if the black is under the finish, you will need to remove the finish and sand the wood until the black is gone. Sealing the wood with polyurethane has created an area where moisture can stay behind it. Any mold spores that are present will like the nice damp environment. Any rain or snow touching those vertical tubes will run down the tube into their sockets and get absorbed into the wood. You might be better off just staining the wood with no sealing finish.

[Ben Silver]

You probably won't like this answer...if the black is under the finish, you will need to remove the finish and sand the wood until the black is gone. Sealing the wood with polyurethane has created an area where moisture can stay behind it. Any mold spores that are present will like the nice damp environment. Any rain or snow touching those vertical tubes will run down the tube into their sockets and get absorbed into the wood. You might be better off just staining the wood with no sealing finish.

Exactly. The polyurethane prevents the moisture from escaping quickly, creating a very nice environment for the mold to grow. Outdoor stain is the best way to go (that I am aware of).

[John Schweikert]

All the Cabot poly, oil and water-borne are quite specific in use, "for interior and protected exterior wood surfaces". Deck railings are not protected exterior surfaces. I would not poly outdoor wood getting full weather year-round. There are other products which can be used for full exposure.

[Stan Calow]

my experience is that even if the mold is killed dead, the black will remain unless you physically remove it.

[Teri Bennett]

Thanks Lee, I figured I'd have to sand it down and re-stain, but hoped there was a miracle cure, lol. Didn't think about the poly causing a problem. I thought I was doing good and using it to seal the wood so I didn't have this problem! So it sounds like I sand down, re-stain and that's that?

[Teri Bennett]

Thanks John. I won't use poly outdoors anymore. I thought I was doing the right thing using poly to seal the wood. Oh well. Sounds like I'll be sanding the black stains off, re-staining and that's it. For the record, I used Cabot's Semi-Solid Deck & Siding Stain. I'm happy with that part.

[Bill Orbine]

Me thinks the black stuff is staining from the metal balusters. Perhaps some cleaners with oxalic acid will get it out.

[Teri Bennett]

I thought that too, Bill - but the staining is not under the balusters. It's pretty random.

Me thinks the black stuff is staining from the metal balusters. Perhaps some cleaners with oxalic acid will get it out.

[Teri Bennett]

Exactly. The polyurethane prevents the moisture from escaping quickly, creating a very nice environment for the mold to grow. Outdoor stain is the best way to go (that I am aware of).

Guess what, I didn't put poly on there after all - just the Cabot Semi Solid Deck & Siding stain, 2 coats. I expect to sand and re-stain like you have recommended, but now I'm back to wondering what the staining really is. The top beam doesn't have any black stains but it is sheltered by the top railing.

[Lon Crosby]

For mold removal, head over to the nearest beauty shop store (Sally's, etc.) and bur a bottle of "40 volume clear" stabilizing solution (i.e., 12% hydrogen peroxide for the rest of us) and a spray nozzle to fit the bottle. Spray away on the mold. Use plastic gloves and a respirator if working overhead if in a closed space. 12% H2O2 will burn like crazy on your skin. H2O2 and an anti-microbial used in swimming pools is the base of the standard solution used in building rehab after Katrina. Developed and patented by scientists at Los Alamos National Labs.

[Allan Speers]

Thanks Lee, I figured I'd have to sand it down and re-stain, but hoped there was a miracle cure, lol. Didn't think about the poly causing a problem. I thought I was doing good and using it to seal the wood so I didn't have this problem! So it sounds like I sand down, re-stain and that's that?

If you're willing to sand it down, then you might have good luck with 2 products from Sporicidin.

One is a mold killer, and is called "Disinfectant." It's the only product I know of that is proven in independent tests to absolutely kill the stuff, even on porous surfaces. (Where, for instance, bleach is useless as it only kills the top-layer of "flowers.") - Although the stuff Lon mentioned also sounds promising. Sporicidin, however, is non toxic. (It's the same stuff hospitals use, and is also found in that green sore throat gargle.

The other product they make is specifically a mold CLEANER, and is called "Enzyme Mold Cleaner." (I'm guessing it uses enzymes. )

When my basement flooded 3 years ago, there was black mold all over the sheet rock. I sprayed it with Sporicidin first, then once dry I sprayed on the enzyme cleaner. It never got completely white again, but I'd estimate that 80% of the black just flowed right off. I hardly had to scrub. It does the same thing to the green stuff that loves to grow on my (synthetic) deck, although slightly less effective there for some reason. What's really nice is that this stuff has absolutely no bleaching effect. I'd try it first, before anything that sounds like it uses oxygen in it's process.

[Bill Sutherland]

I had to contend with the same situation except my whole deck turned black after applying Penofin. After the 1st yr I sanded it and reapplied the Penofin per their instructions and the same thing happened. Had to sand it down again and this time I used TWP. Came out beautiful after a winter of snow and last summer 100 degree + summer days.

[Charles Wiggins]

I've had good results in the past with an Oxyclean solution. I've sprayed in on with a garden sprayer, let it sit for a few minutes, then rinse it off.

[Lon Crosby]

More on H2O2. Note that one needs to also consider preventing mold regrowth. This is an old summary so not certain that links are still current but patent number always works.
The bestdecontamination solution is a mix of 1) hydrogen peroxide with 2) n-alkyl(C12-C16) dimethyl benzyl ammonium chloride and n-dialkyl (C12-C16)benzyl ammonium chloride. A formula developed by Sandia National Laboratory todecontaminate biological weapons of mass destruction. It was the standard forthe reconstruction of New Orleans. The benzyl solution is available from manyplaces as a 50% algaecide concentrate for use in home swimming pools. Thehydrogen peroxide is more difficult to find as the stuff in the drug store is 3percent. It is easiest to use 12% hydrogen peroxide which is sold in beautysupply stores. The mix is a foaming disinfectant used after surfaces have beenwashed. Spray it on and let it dry. The algaecide has residual activity onspore, microbes, etc.
A number of patents– for example 6,723,890. Or read a summary http://www.sciencedaily.com/releases/2001/11/011101060423.htm
You want ~8%hydrogen peroxide and a similar percentage of algaecide in the final mix. Ifonly drug store hydrogen peroxide is available, you can create an equalconcentration of algaecide and just spray more. Available commercially here http://tionicon.com/default.aspxor in your local store as http://www.scottsliquidgold.com/mold-control-500/Default.aspx.The latter will be much more expensive.