[Greenbuilding] adding borates?

JOHN SALMEN terrain at shaw.ca
Sat Nov 5 07:58:43 PDT 2011

The problem with borates and silicates is that they are water soluble and so
quickly lose their effectiveness. Mold is tenacious. It takes about 20%
moisture content to start mold forming - once the finish on wood windows
deteriorates enough (or at joints) to absorb and retain moisture it creates
the perfect environment for mold to grow which is why continuously moist or
wet window sills turn black. 

Once the mold is killed (vinegar, bleach whatever) the mold spores remain
and can become active again with only 15% moisture. The mold does not eat
the wood itself (it relies on it like a sponge to maintain a moist
environment) but thrives on what is on the wood (some finishes, dirt, dust,

Controlling the mold consists of eliminating the moist environment.
Primarily this means waterproofing the window sill to prevent it from
absorbing moisture. Oils (like pure tung oil) are effective in that they are
absorbed into the wood and fill the voids and also have an inherent
antifungal property. Some oils (like linseed) are not effective because they
are a food for mold. You have to be careful as some products marketed as
tung oil finishes actually are linseed oil with a small amount of tung oil.

Borates, salts, etc are effective because they are a mineral that fills the
voids and fibres essentially  mineralizing the wood so it can't retain
moisture. They are water soluble though so leach out over time. There is a
new form of potassium silicate that has been changed chemically to be
insoluble and that is marketed as 'timbersil'. This is about the only
effective mineralizing treatment that I know of.

So the idea is to thoroughly waterproof the wood (and joints) so that it
does not retain moisture and become a mold environment. I would recommend
stripping the wood and then either treating with timbersil or a pure tung
oil. For a wet environment I would treat the wood with timbersill - I would
fill open end grain joints with epoxy and then I would topcoat the whole
thing with a few coats of tung oil as the final finish. The nice thing about
tung oil is you don't have to refinish it - simply wipe another coat on. The
second thing is to remove the food on a continuous basis (wiping the
woodwork down with an enzyme or even tea tree oil is pretty effective). 

Eliminating the source of the moisture (reducing moisture content of rooms,
etc.) would be the best solution but not always achievable.

Ironically most of the wood windows from large manufacturers over the last
25 years have been dip treated with fungicide to begin with so be careful
with the sanding dust.

-----Original Message-----
From: greenbuilding-bounces at lists.bioenergylists.org
[mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of
Benjamin Pratt
Sent: November-05-11 7:19 AM
To: Green Building
Subject: [Greenbuilding] adding borates?

I have a couple of window frames in my house that were finished with
clear polyurethane. Every winter the condensation causes fuzzy mold to
grow and some of the wood had turned black. I'm thinking of sanding
those parts and touching them up. Can I add borates to the poly to
keep the mold from growing again? I do have some boric acid and borax.
Will either of these work?
  I think paint stores sell additives that may work--and I think some
of these contain zinc oxides. But i'm not sure if borates would be
better, cheaper, easier, etc.

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