Questions on teak deck mold

Trying to learn as much as a I can on teak decks so I can judge things when I am looking at trawlers. The attached picture shows the teak decks on an older Grand Banks. The black staining is what I am trying to learn about. Is this staining indicative of surface mold that can be cleaned fairly easily or is it the sign of bigger issues associated with moisture below the deck? I know that no absolutes can come from a simple picture but is something like this generally a danger sign? Thanks in advance for any comments.

It's hard to say what it is from the picture.

Give the deck a good wash with say Dawn soap to get the dirt and oil off the deck if the deck has not had a good cleaning in a while.

Then wash again with a mild powdered teak cleaner/brightener.

That should get most of the mold out.

If the teak is very dirty you may have to use a two part two step cleaner/bleach system. That will get the teak the cleanest. But you need to use it carefully and only say once a year or so.

I have a home brew recipe for two part cleaner/bleach that is far cheaper than the store bought stuff if you want it.

Thanks Bill. Just seems odd to me that the mold is centered in that area, I believe right by the cabin door. Almost looks like dirt and wear from foot traffic going in and out. Other pictures show slight signs of mold on other parts of the deck but it is more of a general darkening and not so defined as this picture. Just wondering if it could be a sign of something more significant going on in that area. I have a healthy case of teak deck paranoia I guess. Probably not a bad thing when they are old. My other mental health issue is in regards to fuel tanks on Grand Banks but that another thread!

Sometimes you get mold in a specific area of the deck because direct sunlight doesn't get there very often. Perhaps the way it's moored, roof of a boat house, boat in an adjoining slip or even poorly ventilated shrink-wrap.

Wash it with salt water. That usually kills the mold, plus salt water is good for the teak.

jleonard said:

Wash it with salt water. That usually kills the mold, plus salt water is good for the teak.

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That's great to do on a regular basis after you get the teak clean.

firstbase said:

Thanks Bill. Just seems odd to me that the mold is centered in that area, I believe right by the cabin door. Almost looks like dirt and wear from foot traffic going in and out. Other pictures show slight signs of mold on other parts of the deck but it is more of a general darkening and not so defined as this picture. Just wondering if it could be a sign of something more significant going on in that area. I have a healthy case of teak deck paranoia I guess. Probably not a bad thing when they are old. My other mental health issue is in regards to fuel tanks on Grand Banks but that another thread!

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I doudt it's the sign of anything bad under the decking.

I had an older GB motor yacht and that area always seem to get/stay dirtier.

As to the fuel tanks. On GBs there tends to be far less issues with them than on other lesser brands. And on the ones where I've seen issues the likeliest cause was from water getting in around and under the deck fills.

So I would poop those up, clean out under them and re-bed them. And also check/change the O-ring for the cap.

If that is where you are boarding the boat most of the time, you step on with dirt still attached to your shoes. Maybe this gives mold a little extra nourishment to flourish?

I guess so...with the rest of the boat showing a darkening could be as simple as the owner just wasn't in to keeping the decks clean I guess. Glad to hear it's not necessarily a bad sign..just general maintenance.

Several of the affected areas look to correspond with longitudinal joins in the planks, I`d be looking hard at the joints. What looks the darkest area is adjacent to the cabin, water should drain away from, not towards the house; if it is draining towards sometimes the house has dropped slightly, or maybe it`s how it was built. Look to check the sealant caulk is adherent and not leaking.

I haven't seen this boat in person but would be interested to see if there is any moisture issue at the base of the cabin door. It looks like that darkest area or mold line is right in front of the door. Have seen several older GB's with that issue, water staining and peeling/curling veneer along the bottom of the door.

Hi, this is Halsberg rassy factorys offical tips over 20 yars old. Boracol!


boric acid kill black mold, is gentle does not consume the wood, such as teak, many commercial cleaning. The product name is boracol!


https://www.acslimited.co.uk/teak-deck-maintenance-boracol/


In the long run the best way to treat the teak deck against
mildew is to use Boracol. Boracol is a liquid that is uncoloured and thin like water. It is sold in normal
chemist shops and hardware dealers. It is marketed as a treatment against mildew for garden furniture.
Use a normal paintbrush and paint the deck with Boracol. Never use a normal brush on the teak! Do
the work on a dry dray. If it rains too much Boracol will be washed away. It does not matter if it is
drizzling the next day but if it rains the complete day or over splashing waves washes over the deck, the
Boracol will make no effect. That would flush the Boracol way too early. If it does not rain, spray the
deck a little with water. This little amount of water only helps the Boracol to penetrate into the teak.
After three to seven days you wash the deck with a sponge and cleaner, for example green soap. Please
do not be afraid if you do not see any positive result immediately. On the contrary, the deck looks
worse than it did before the treatment. After about ten days things will start to happen. The mildew has
disappeared and the deck is clean. The mildew will not recur for some time. Do not be afraid to repeat
the treatment now and then."

firstbase said:

I haven't seen this boat in person but would be interested to see if there is any moisture issue at the base of the cabin door. It looks like that darkest area or mold line is right in front of the door. Have seen several older GB's with that issue, water staining and peeling/curling veneer along the bottom of the door.

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this can be due also traveled the most and dirt absorbed into the wood and cause black mold or grime

Thanks for the Boracol info. I don't understand this line though...

North Baltic sea said:

Use a normal paintbrush and paint the deck with Boracol. Never use a normal brush on the teak!

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What do you mean by this?

firstbase said:

Thanks for the Boracol info. I don't understand this line though...



What do you mean by this?

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based paint brush, apparently the idea of ​​a normal brush with handle scrubbing brush too hard and damage the teak. or another option to get further spread of the liquid. Pressure Sprayer will I think of another image in my back and knees might like to congratulate this choice in the evening





i think this is easy way

Ah, thanks. Use a paint brush to spread it not a normal cleaning, bristle brush. Those are pretty bad ALL of the time! I appreciate your comments.