Architects memo no. 112: August 2013
by a nose
When waterborne paints first started displacing
solventborne, oil-based alkyd interior paints, they
were welcomed, not only for their fast drying and ease
of clean up and application, but also because their
odour was so much lower and more pleasant than the
smells associated with the solvents and the curing of
How quickly times change and how quickly we
get ‘spoilt’! Those original waterborne paints are
nowadays considered far too odiferous, with too high
levels of VOCs.
Now, compared to the grizzly bear or the bloodhound,
the human nose is not considered overly sensitive but,
with several million olfactory receptors, it can detect
certain odours when present at less than one part
per billion in air! Studies have shown that olfactory
sensitivity peaks between the ages of 10-15 years and
that women are invariably better at ‘sniffing things
out’ than men. The state of one’s health impacts on
one’s olfactory sensitivity with one group of researchers
suggesting that smell tests should be part of psychiatric
disorder diagnostics! So, the perception of odour is not
uniform across the population.
Odour is often associated by chemophobes with ‘toxic’
chemicals but odour can be a real safety feature. The
sensitivity of the human nose is such that it can often
detect materials at levels well below the detection
power of present analytical techniques and way, way
below dangerous toxicity levels. So odour is often an
‘early warning system’.
Your scribe grew up in England where ‘coal gas’ was
reticulated to most urban houses. Now ‘coal gas’ was
the name given to carbon monoxide, an odourless and
toxic gas. As a safety measure, an odorous material was added so that gas leaks could be detected well before
gas levels became dangerous.
Responding to market demand to reduce odour levels
of waterborne paints has set the industry on a bit of a
rollercoaster ride with many unforeseen hurdles arising.
An obvious first move was to eliminate ammonia
(which is used to maintain the pH of the paint at a level
to promote maximum stability) with odour-free ‘fixed’
bases such as caustic soda or caustic potash. It turns
out, however that not only does a significant portion of
the population quite like the smell of a little ammonia,
but also the ammonia was effectively masking some of
the other odours in the paint.
This leads into the area of assessing odour, not just to
a level, but also to a degree of acceptability. It doesn’t
help that the population does not always perceive odour
uniformly and, in the case of androsterone, one man’s
‘floral bouquet’ may be another man’s ‘pissoir’.
Assessment of this feature is attempted by the concept
of a ‘hedonic tone’ of an odour. It scales from -10 (which
is bloody awful) to +10 which is very, very nice.
From a personal point of view, Resene put out a uniquely
good, niche product called Resene Waterborne Smooth
Surface Sealer. It contains an irreducibly low level (a
few parts per million) of a by-product called vinyl cyclo
hexane. I can’t stand it – literally gets up my nose –
and wouldn’t use it if there was anything else on the
market which works as well. It definitely gets a -10
on my hedonic scale, but most people find it very low
odour, which technically speaking it is.
The above is an example of the hurdles that we come up
against. Time and again, it appears that as the obvious
odourants are dealt with, very low levels of by-products
assume a ‘non-intuitive’ significance.
Download as a pdf. (You will need Acrobat Reader).