[Greenbuilding] mold on timbers

[Maren Leyla Cooke]

> "Ken Beiser" <kbeiser at centurytel.net> wrote:
>
> The logs sat on the ground and in a pile for almost a year.  He had 
> them milled into some 8 by 8 timbers and they were obviously pretty 
> wet when they arrived at my shop.  Shortly after they were here, mold 
> started to grow on ONLY the corners of the timbers that still 
> contained sapwood.    I realize that WAS the live part of the tree but 
> it has been dead for a year.  I also realize that the most moisture 
> and possibly food for the mold could have been in the sapwood.
>
> I was hoping to get some information on how to kill the mold and 
> remove the discoloration in the process.  Bleach did not discolor the 
> wood much but the mold looks like it is still there but I suppose it 
> is dead.   How can I tell if it is dead?  Any input would be 
> appreciated.

I've had some very interesting experiences with mold on black locust 
logs.  They spent a while in a cool basement, open to the weather 
during a humid summer (bad combination!), and there was tremendous mold 
growth on the exterior of the logs where they had been peeled... but 
not on the exterior surfaces that had peeled themselves earlier, and 
not on the cut faces (some of the pieces were cut lengthwise, as well 
as the cut ends).  So it's not just sapwood/heartwood;  there may be 
something protective where the bark had naturally weathered free.  I 
mentioned the phenomenon to my miller, and he found it interesting as 
well.

So what did I do...  after much research and with great reluctance (I 
was never one for bleach), I did ultimately bleach the logs.  First we 
gingerly carried them outside to sun-kill the mold (since it was so 
extensive that some spores would become airborne with any cleaning 
method).  Had to bleach some of the cherry and maple logs in the 
interior as well as the locust going outside.  I also used a borate 
treatment on the exterior logs (Bora-Care, diluted appropriately and 
wiped on with a rag), and treated all my timbers with Land Ark, a 
staple of timber framers.  (Land Ark is a natural oil finish made by 
Mike & Nita Baugh in South Carolina, containing linseed oil, tung oil, 
limonene (citrus), pine rosin, and beeswax.  They make an exterior 
version by adding a UV protectant and an iodine-based mildewcide.)  
Neither the borate (supposed to be good for mildew as well as insects) 
nor the exterior Land Ark were complete proof against further mildew, 
but subsequent cases were much less extensive and didn't seem to be 
correlated with previous areas -- i.e., they may have been new 
infections vs. recurrence of old ones.  I don't recall regrowth from 
the stained areas (as you found, some of the stains did not respond to 
the bleach).  Bleach (diluted 1:3) is pretty good at killing fungi, 
though.

Will you be using the wood as is, or resurfacing it?  If you use bleach 
to kill the mold and then take the surface down, you should be fine.  
If the wood is subsequently kept dry, there should be no problem;  if 
it remains moist then even if the first mold is killed, some new spores 
may wander in and reinfect.  (my logs have had a rough life, where 
moisture is concerned).

Cheers,
	-- Maren.