If existing exterior paint on wood siding, eaves, window sills,
sash, and shutters, doors, and decorative features shows no
evidence of paint deterioration such as chalking, blistering,
peeling, or cracking, then there is no physical reason to repaint,
much less remove paint! Nor is color fading, of itself, sufficient
justification to repaint a historic building.
The decision to repaint may not be based altogether on paint
failure. Where there is a new owner, or even where ownership
has remained constant through the years, taste in colors often
changes. Therefore, if repainting is primarily to alter a building's
primary and accent colors, a technical factor of paint accumulation
should be taken into consideration. When paint builds up to
a thickness of approximately 1/16~ (approximately 1630 layers),
one or more extra coats of paint may be enough to trigger cracking
and peeling in limited or even widespread areas of the building's
surface. This results because excessively thick paint is less
able to withstand the shrinkage or pull of an additional coat
as it dries and is also less able to tolerate thermal stresses.
Thick paint invariably fails at the weakest point of adhesion--the
oldest layers next to the wood. Cracking and peeling follow.
Therefore, if there are no signs of paint failure, it may be
somewhat risky to add still another layer of unneeded paint
simply for color's sake (extreme changes in color may also require
more than one coat to provide proper hiding power and full color).
When paint appears to be nearing the critical thickness, a change
of accent colors (that is, just to limited portions of the trim)
might be an acceptable compromise without chancing cracking
and peeling of paint on wooden siding.
If the decision to repaint is nonetheless made, the "new"
color or colors should, at a minimum, be appropriate to the
style and setting of the building. On the other hand, where
the intent is to restore or accurately reproduce the colors
originally used or those from a significant period in the building's
evolution, they should be based on the results of a paint analysis.(5)
(5) See the Reading List for paint research and documentation
information. See also "The Secretary of the Interior's
Standards for Historic Preservation Projects with Guidelines
for Applying the Standards" for recommended approaches
on paints and finishes within various types of project work