Architects memo no.
13: September 1981
another paint failure
We were recently asked to inspect a pair of semi detached houses
that were due for repainting. The invitation to us was extended by a
painter who had repainted the houses previously and was concerned that
there were problems in the recoating that he couldn't handle.
The initial inspection of the structure tended to provoke the comment
"another paint failure".
Paint peeling on the tops and bottoms of the weatherboards, from edges
of wooden joinery and from ends of weatherboards. Ends of weatherboards
were also cracked about 2" back from any cut. One could think that this
was a typical case where surface coatings were simply not proving adequate
and were letting down the rest of the building. Two factors tended to
refute this however. Firstly, the areas where the paint was not broken
down were in excellent condition, maintaining good gloss and film integrity
and secondly the tradesman involved was known to us to be one of the
finest exponents of his craft, the fact that he called us in to discuss
the latest repainting indicating his responsible attitude to his craft.
We then started to look for the reasons for the failure and several
things became apparent that not only precluded the painter from doing
a satisfactory job but precluded this dwelling ever having a satisfactory
painting system applied to it.
The first point which showed itself was that this weatherboard construction
had no soffit and the protection that the soffit provides against rain
and UV light was totally lacking.
The next contributing factor to failure was that the wooden joinery
used, had no facing timbers protecting the joint of the weatherboard
to the joinery; the joint was open to the weather. The weatherboard
used on the dwelling was of a shiplap profile with absolutely sharp
edges top and bottom of the board. The timber joinery equally had razor
It is worth dwelling a little further on this aspect because it is
a phenomenon of all liquids that, due to surface tension effects, they
will pull away from sharp edges resulting in a decrease in thickness
at those edges.
In paint systems this can result in sharp edges being only half as
thick as the rest of the paint system. As sharp edges also tend to become
drip points for water, they can easily be identified as weak spots in
the system. The radiusing of sharp edges, even by as little as a 5 millimetre
radius, can increase paint durability by a more significant amount than
all the formulating principles known to the paint industry at present.
The final problem besetting this structure was that the builder had
done no end priming of cuts made in the preprimed weatherboard. Moisture
uptake via end grain is an order of magnitude greater than uptake through
the faces and consequently priming of end grain is absolutely vital
to maintain timber stability. In fact two coats of primer on the end
grain would be preferable.
The consequence of the above meant that before the painter even came
on to the job, his efforts were doomed to premature failure and the
rectification of the problems were outside his scope. The problem in
fact lay with the designer, the timber miller, the joiner and the builder.
It is interesting to note that at this stage in the life of the building
(about 10 years) it is only the painter who remains involved with the
building. It has become the easy thing to do, to blame failures on paint
and painters, whereas the truth of the matter is that for a successful
paint job, all of the above mentioned disciplines have a vital part
Download as a pdf. (You will need Acrobat Reader).