Architects memo no.
63: May 2000
water water everywhere - but the boards didn't
The drive to move from solventborne paints to their waterborne
analogues remains as strong as ever. If the rate of change has slowed,
it is indicative that all of the easier changes have been accomplished;
and the remaining solventborne systems are simply more difficult to
Penetrating wood stains are not only technically difficult to match
with water, they have also an emotional hurdle to overcome. "Everyone
knows that timber is a living material which needs oils to feed and
nourish it, don't they?" The reality is, that the tree died when the
chainsaw went through, and it lost its appetite at that point.
What timber is, however, is a unique fibre-reinforced polymer system
which is adapted to an internal aquatic food delivery system. These
channels for sap, render the timber continually open to ingress by water,
especially through the end-grain. Fluctuations in moisture levels cause
changes in the dimensions of the timber (possibly fuelling the living
Obviously then, it is beneficial to have a treatment that excludes
water. Typical waterborne acrylics are good at this. Their particulate
form blocks the pores of the timber, and forms a tough durable film
over the surface. Their very durability, however, leads to problems
in semi-transparent stains.
Even the best semi-transparent stain allows some UV light to percolate
through. The natural polymers of the timber degrade under UV light at
a rate, far faster than the acrylic stain. The degradation of the timber,
which is faster for the less dense timbers, leads to a failure at the
stain/timber interface with the dreaded "flaking" scenario ensuing.
Having flirted with film-forming stains, the industry realises that
penetrating stains, with little to no film forming ability, are the
best compromise for long term ease of maintenance. Penetration is best
accomplished using solutions of low molecular weight polymers and waxes
and solvent systems are king.
To design a waterborne penetrating system obviously needed a new
paradigm as materials that dissolve in water can often get washed-off
The approach Resene took, was to hybridise the desired oil component
so that it behaved like a waterborne material in the can and during
application. Following a period of exposure to the air, a phase change
occurs which sees the product take on a completely hydrophobic nature.
It penetrates deeply into the timber, at the same time conferring water-repellent
The product, Resene
Waterborne Woodsman, dries to a pleasant low gloss waxy finish.
It develops water-resistance in minutes and develops full film properties
after a month.
So does it form a film? Well yes, sort of - where it hasn't penetrated
the latewood bands. But it is designed to have low cohesive strength
so that preparation for recoating is straightforward.
It is available in the Resene
Woodsman colour range and in testpots.