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Historic Preservation - Technical Procedures

Spectitle:

Preservation Briefs: 28 Painting Historic Interiors

Procedure code:

0990001S

Source:

Preservation Briefs 28, National Park Service, Pad

Division:

Finishes

Section:

Painting

Last Modified:

09/05/2012

Details:

Preservation Briefs: 28 Painting Historic Interiors



PRESERVATION BRIEFS:  28

PAINTING HISTORIC INTERIORS

 

The link immediately below connects to the latest version of Preservation Brief 28:

 

http://www.nps.gov/history/hps/tps/briefs/brief28.htm


Sara B. Chase

This standard includes the bulk of information contained in the
original Preservation Brief developed by the National Park Service.
To obtain a complete copy of this brief, including figures and
illustrations, please contact:  

              Superintendent of Documents
              P.O. Box 371954
              Pittsburgh, PA  15250-7954

              GPO #024-005-01027-1
              $1.00

Please call the Publication Order Information Desk at 202/783-3238
to verify price and availability.  


***INTRODUCTION***

The paint Americans used in the past is undeniably part of a
technological and commercial record.  But beyond that, the colors
we have chosen and continue to select - for our interior living and
working spaces - bright and exuberant, purposefully somber, or a
combination of hues - reflect our nation's cultural influences and
our individual and collective spirit.  Paint color is a simple,
direct expression of the time, and of taste, values, and mood.  To
consider paint only as a protective coating is to misunderstand its
meaning as an important aspect of America's heritage.

This Brief is about historic interior paints and choosing new
paints for historic interiors if repainting is necessary or
desirable.  It addresses a variety of materials and features:
plaster walls and ceilings; wooden doors, molding, and trim; and
metal items such as radiators and railings.  It provides background
information about some of the types of paint which were used in the
past, discusses the more common causes and effects of interior
paint failure, and explains the principal factors guiding decisions
about repainting, including what level of paint investigation may
be appropriate.  Careful thought should be given to each interior
paint project, depending on the history of the building and its
painted surfaces.  Treatments may range from protecting extant
decorative surfaces, to ordering custom-made paint that replicates
the original paint color, to using today's paint straight off the
shelf and out of the can.

Finally, stripping old paints or applying new oil/alkyd paints
poses serious health and safety concerns; the State Historic
Preservation Officer should be contacted for current legal and
technical information on oval disposal and  health and safety
precautions.


***CONSTITUENTS OF HISTORIC PAINT: PIGMENT, BINDER, AND VEHICLE***

Paint is a dispersion of small solid particles, usually
crystalline, in a liquid medium.  Applied to a surface, this liquid
has the special quality of becoming a solid, protective film when
it dries.  Paint also enhances the appearance of surfaces.  A late
Victorian writer observed that the coming of a painter to a house
was cause for celebration.  Indeed, these statements not only
indicate the chemical and physical complexity of paint, but also
its emotional impact.

PIGMENT:

Pigment made the paint opaque, thus preventing deterioration of the
substrate caused by ultra-violet light, and added color, thus
making the paint attractive.   White lead, a whitish corrosion
product of lead, was most often used to provide opacity.  The white
pigment in a colored paint is often called the "hiding" pigment.
In addition to preventing the sun's damaging rays from hitting the
surface of the substrate, the white lead also helped prevent the
growth of mold and mildew.  Not until early in the 20th century was
a successful substitute, titanium dioxide (TiO2), patented, and
even then, it did not come into prevalent use by itself until the
mid-20th century (earlier in the century, titanium oxide and white
lead were often mixed).  Zinc oxide was used briefly as a hiding
pigment after 1850.

Early tinting pigments for house paints consisted of the earth
pigments - ochres, siennas, umbers made from ironoxide containing
clay - and a few synthesized colorants such as Prussian blue, or
mercuric sulfide (crimson).  From the early 1800s on more pigments
were developed and used to offer a wider and brighter variety of
hues.

BINDER:

The most common binder in interior paints was, and still is, oil.
Chalk was sometimes added to water-based paints to help bind the
pigment particles together.  Other common binders included hide
glue and gelatin.

VEHICLE:

The fluid component was termed the vehicle, or medium, because it
carried the pigment.  Historically, vehicles included turpentine in
oil paints and water in water-based paints, but other vehicles were
sometimes used, such as milk in casein paints.


***OIL-BASED AND WATER-BASED PAINTS***

The two major types of paint are termed oil-based and water-based.
For oil-based paints, linseed oil was frequently chosen because it
is a drying oil.  When thinned with an organic solvent such as
turpentine for easier spreading, its drying speed was enhanced.  To
make the drying even faster, drying agents such as cobalt compounds
were frequently added.  Because the addition of driers was most
successfully done in hot or boiling oil, boiled linseed oil was
preferable.  The drying rate of linseed oil paints was relatively
rapid at first, for several days immediately after application, and
paint soon felt dry to the touch; it is important to remember,
however, that linseed oil paint continues to dry - or more
precisely, to cross-link - over decades and thus continues to a
point of brittleness as the paint ages.  Strong and durable with a
surface sheen, oilbased paints were mainly used for wood trim and
metal.

Whitewashes and distemper paints differed from oil paints 1 in
appearance primarily because the vehicle was water.  Water-based
paints were always flat, having no gloss of their own.  Because the
paint film dried to the touch as soon as the water evaporated,
driers were not needed.  Water-base paints were fairly strong, with
the pigments well bound as in hide glue distempers, but they did
not hold up to abrasion.  Wood trim, therefore, was rarely painted
with these types of paint historically, though interior plaster
surfaces were frequently coated with whitewash and calcimine.
Distemper paints were commonly used for decorative work.

RECENT CHANGES TO PAINT CONSTITUENTS:

Until the mid-20th century, almost all paints used in America could
be divided according to the type of binder each had. Chemists
sought to improve paints, especially when the two world wars made
traditional paint components scarce and expensive.  Modern paints
are far more complex chemically and i physically than early paints.
More ingredients have been added to the simple three-part system of
pigment, binder, and vehicle.  Fillers or extenders such as clay
and chalk were put in to make oil paints flow better and to make
them cheaper as well.  Mildewcides and fungicides were prevalent
and popular until their environmental hazards were seen to outweigh
their benefits.  New formulations which retard the growth of the
mildew and fungi are being used.  As noted, lead was eliminated
after 1950.  Most recently, volatile organic solvents in oil paint
and thinners have been categorized as environmentally hazardous.

A major difference in modern paints is the change in binder from
the use of natural boiled linseed oil to an alkyd oil which is
generally derived from soybean or safflower oil.  Use of synthetic
resins, such as acrylics and epoxies, has become prevalent in paint
manufacture in the last 30 years or so. Acrylic resin emulsions in
latex paints, with water thinners, have also become common.


***PRE-1875 PAINTS***

PRODUCTION AND APPEARANCE:

How were paints made prior to the widespread use of factory-made
paint after 1875? How did they look? The answers to these questions
are provided more to underscore the differences between early
paints and today's paints than for practical purposes.  Duplicating
the composition and appearance of historic paints, including the
unevenness of color, the irregularity of surface texture, the depth
provided by a glaze topcoat, and the directional lines of
application, can be extremely challenging to a contemporary painter
who is using modern materials.

The pigments used in early paints were coarsely and unevenly
ground, and they were dispersed in the paint medium by hand; thus,
there is a subtle unevenness of color across the surface of many
pre-1875 paints.  The dry pigments had to be ground in oil to form
a paste and the paste had to be successively thinned with more oil
and turpentine before the paint was ready for application.  The
thickness of the oil medium produced the shiny surface desired in
the 18th century.  In combination with the cylindrical (or round)
shaped brushes with wood handles and boar bristles, it also
produced a paint film with a surface texture of brush strokes.

GEOGRAPHICAL VARIATION:

The early churches and missions built by the French in Canada and
the Spanish in the southwestern United States often had painted
decoration on whitewashed plaster walls, done with early
water-based paints.  By the mid-17th century oil paint was applied
to wood trim in many New England houses, and whitewash was applied
to walls.  These two types of paint, one capable of highly
decorative effects such as imitating marble or expensive wood and
the other cheap to make and relatively easy to apply, brightened
and enhanced American interiors.  In cities such as Boston,
Philadelphia, New York, and later, Washington, painters and
stainers who were trained guildsmen from England practiced their
craft and instructed apprentices. The painter's palette of colors
included black and white and grays, buffs and tans, ochre yellows
and iron oxide reds, and greens (from copper compounds) as well as
Prussian blue.  That such painting was valued and that a glossy
appearance on wood was important are substantiated by evidence of
clear and tinted glazes which may be found by microscopic
examination.

BRUSH MARKS:

Early paints did not dry out to a flat level surface. Leveling, in
fact, was a property of paint that was much sought after later, but
until well into the 19th century, oil paints and whitewashes showed
the signs of brush marks. Application therefore was a matter of
stroking the brush in the right direction for the best appearance.
The rule of thumb was to draw the brush in its final stokes in the
direction of the grain of the wood.  Raised-field paneling, then,
required that the painter first cover the surface with paint and
afterward draw the brush carefully along the vertical areas from
bottom to top and along the top and bottom bevels of the panel
horizontally from one side to the other.

In the 19th and early 20th centuries, for very fine finishes,
several coats were applied with each coat being rubbed down with
rotten stone or pumice after drying.  A four to five coat
application was typical; however nine coats were not uncommon at
the end of the century for finishes in some of the grand mansions.
Generally, they were given a final glaze finish. Though expensive,
this type of finish would last for decades and give a rich, smooth
appearance.

COLOR:

Color matching is complicated by the fact that all early paints
were made by hand.  Each batch of paint, made by painters using
books of paint "recipes" or using their own experience and
instincts, might well have slight variations in color - a little
darker or lighter, a little bluer and so on. The earliest known
book of paint formulations by an American painter is the 1812 guide
by Hezekiah Reynolds.  It gives instructions for the relative
quantities of tinting pigments to be added to a base, but even with
proportions held constant, the amount of mixing, or dispersion,
varied from workman to workman and resulted in color variations.

Knowing all of the facts about early paints can aid in microscopic
paint study.  For example, finding very finely and evenly ground
pigments, equally dispersed throughout the ground or vehicle, is an
immediate clue that the paint was not made by hand but, rather, in
a factory.

By the first decades of the 19th century more synthetic pigments
were available chrome yellow, chrome green, and shades of red.
Discoveries of light, bright, clear colors in the plaster and
mosaic decoration of dwellings at Pompeii caught the fancy of many
Americans and came together with the technology of paint to make
for a new palette of choice, with more delicacy than many of the
somewhat greyed-down colors of the 18th century.  Of course, the
blues which could be produced with Prussian blue in the 18th and
19th centuries were originally often strong in hue.  That pigment
- as were a number of others - is fugitive, that is, it faded
fairly quickly and thus softened in appearance.  It should be
remembered that high style houses from the mid-17th to late 19th
centuries often had wallpaper rather than paint on the walls of the
important rooms and hallways.

GLOSSY/FLAT:

Another paint innovation of the early 19th century was the use of
flatter oil paints achieved by adding more turpentine to the oil,
which thus both thinned and flatted them.  By the 1830s the velvety
look of flat paint was popular.  Wherever decorative plaster was
present, as it frequently was during the height of the Federal
period, distemper paints were the coating of choice.  Being both
thin and readily removable with hot water, they permitted the
delicate plaster moldings and elaborate floral or botanical
elements to be protected and tinted but not obscured by the buildup
of many paint layers. (The use of water-based paints on ceilings
continued through the Victorian years for the same reasons).

Unfortunately, flat paints attract dirt, which is less likely to
adhere to high gloss surfaces, and are thus harder to wash.
Victorians tended to use high gloss clear (or tinted) finishes such
as varnish or shellac on much of their wood trim and to use flat or
oil paints on walls and ceilings.

DECORATIVE PAINTING:

In interiors, paint could be used creatively and imaginatively,
most often to decorate rather than to protect. Decorative forms
included stenciling, graining and marbleizing, and trompe l'oeil.

Stencilling:

Stenciled designs on walls were often used in the first half of the
19th century in place of wallpaper.  Old Sturbridge Village, in
Massachusetts, has paintings showing the interiors of a (c.
1815-1820) farmhouse which has both stenciled walls - imitating
wallpaper - and painted floors or oiled and painted floor cloths,
imitating fine carpets.  By 1850 and for the next 60 years
thereafter, stencilled and freehand-painted decoration for walls
and ceilings became a high as well as a humble art.  Owen Jones'
Grammar of Ornament, published in 1859, provided the source for
painted decoration from Portland to Peoria, Savannah to San
Francisco.

Graining and Marbleizing:

If floors, walls, and ceilings were decorated by paint in a variety
of styles, the wood and stone trim of rooms was not omitted.  The
use of faux bois, that is, painting a plain or common wood such as
pine to look like mahogany or some finer wood, or faux marble,
painting a wood or plaster surface to look like marble -
realistically or fantastically - was common in larger homes of the
18th century.  By the early 19th century, both stylized graining
and marbleizing adorned the simple rural or small town houses as
well.  Often baseboards and stair risers were marbleized as were
fireplace surrounds. Plain slate was painted to look like fine
Italian marble.  In many simple buildings, and, later, in the
Victorian period, many prominent buildings such as town halls and
churches, the wood trim was given a realistic graining to resemble
quarter sawn oak, walnut, or a host of other exotic woods.

Trompe L'oeil:

Churches, courthouses, and state capitols frequently received yet
another remarkable use of paint: trompe l'oeil decoration. Applied
by skilled artists and artisans, painted designs - most often using
distemper paints or oils - could replicate three-dimensional
architectural detailing such as ornate molded plaster moldings,
medallions, panels, and more.


***FACTORY-MADE PAINTS AFTER 1875***

An enormous growth of the paint industry began in the 1860s,
stimulated by the invention of a suitable marketing container - the
paint can.  The first factory-made paints in cans consisted of more
finely ground pigments in an oil base; after purchase, additional
oil was added to the contents of the can to make up the paint.
Such paints saved the time of hand-grinding pigments, and were
discussed at length by John Masury in his numerous books.  After
1875, factory-made paints were available at a reasonable cost and,
as a result, greater numbers of people painted and decorated more
of their buildings, and more frequently.   The new commercial
market created by ready-mixed paint became the cornerstone of our
modern paint industry.


***20TH CENTURY PAINTS***

By the early decades of the 20th century, popular taste turned away
from exuberant colors and decoration.  Until the late 1920s both
the Colonial Revival and Arts and Crafts styles tended toward more
subdued colors and, in the case of Colonial Revival, a more limited
palette.  The use of faux finishes, however, continued.

Residential architecture often featured stencilling, such as
painted borders above wainscoting or at ceiling and wall edges to
imitate decorative wallpaper.  Institutional buildings in both
cities and small towns used wood graining on metal-clad doors, door
and window frames, and staircases, and had stencilled ceilings as
well. Many high style public buildings of the 1920s had painted
ceilings which imitated the Spanish and Italian late medieval and
Renaissance styles.

Although stenciling, gilding, and faux finishes can be found, they
did not express the modern style of the time.  On the other hand,
glaze treatments were often used in the early 20th century to
"antique" walls and trim that had been painted with neutral colors,
especially in Spanish Colonial Revival and Mission architecture.
The glazes were applied by ragging, sponging, and other techniques
which gave an interesting and uneven surface appearance.  Colored
plasters were sometimes used, and air brushing employed to give a
craftsmanlike appearance to walls, trim, and ceilings.  During the
same period, Williamsburg paint colors were produced and sold to
people who wanted their houses to have a "historic Georgian look".
Churches, country clubs, and many private buildings adopted the
Williamsburg style from the late 20s onward.

Often decorated with simple molded plaster designs of the Art Deco
and Art Moderne styles, interiors of the 1930s and 1940s were
frequently accented with metal flake paints in a full range of
metallic colors, from copper to bronze.  And enamels, deep but
subdued hues, became popular.  Paint technology had progressed and
varying degrees of gloss were also available, including the
midrange enamels, variously called satin, semi-gloss, or eggshell.
In contrast to Victorian paint treatments, this period was
characterized by simplicity.  To some extent, the Bauhaus aesthetic
influenced taste in the 1950s; interior paints were frequently
chosen from a palette limited to a few "earth" colors and a "nearly
neutral" palette of offwhites and pale greys.

While the trend in colors and decorative treatments was defined by
its simplicity, paint chemists were developing paints of increasing
complexity.  Experimentation had started early in the 20th century
and accelerated greatly after World War II.  Of greatest
significance was the manufacture of the latex paints for consumer
use.  Synthetic resin emulsions carried in water offered advantages
over the traditional oil paints, and even over the oil/alkyd
paints: they did not yellow; they permitted water clean-up until
dried; and they emitted no toxic or hazardous fumes from solvent
evaporation.


***PAINT INVESTIGATION***

Understanding each project's historic preservation goal and knowing
what level of information needs to be collected to achieve that
goal is an important responsibility of the purchaser of the
service.  Before someone is hired, the owner or manager needs to
decide if a thorough investigation of painted surfaces is actually
needed, and how to use the results when one is done.

Specialists with both training and field experience conduct paint
investigations.  These experts use sophisticated instruments and
procedures such as field sampling, cross section analysis, and
fluorescent and chemical staining to learn about the components and
behaviors of historic paints.  In addition, they utilize written
documentation, verbal research, and visual information about past
painting in the building in conjunction with findings in the field.

Paint investigation can make several contributions to a project.
A complete analysis of the paint layers on surfaces within a
structure can tell a great deal about the sequence of alterations
that have occurred within a building, as well as potentially
providing ranges of dates for some of these changes. By
establishing a full sequence of paint layers (termed a
chromochronology), together with other research, alterations of
various building spaces and features can be associated with
specific paint layers.  It is by establishing this association that
the correct layer is identified; when the correct layer has been
identified, the color may be matched.

In addition to its archeological value, paint analysis can
determine the types and colors of paint on a given surface
(identification of thin glazes, decorative paint schemes, binders
and pigments).  Beyond color identification, then, paint analysis
is also recommended to diagnose causes of paint failure.  Knowing
a paint binder can often explain causes as well as guide
appropriate preservation or conservation treatments.

Owners and managers should identify all of these needs before
deciding on the extent of analysis.  For example, a complete paint
investigation is usually recommended as part of an historic
structure report.  For buildings with little documentation,
additions and alterations can often be identified, and possibly
dated, through analysis.  Often the use of such seemingly expensive
techniques can save money in the long run when determining the
history of building change.

It is possible to do some analysis on site; this is a much simpler
process that can be undertaken for less cost than the complex
laboratory procedures described above.  However, the usefulness of
on site analysis is limited and the results will not be as precise
as results from samples that are analyzed in a laboratory with a
good microscope.  Any short-cut approaches to paint analysis that
do not follow scientific procedures are generally not worth the
expense.  In summary, if preservation and restoration treatments
are being undertaken, a complete investigation is recommended; for
a rehabilitation project, on site analysis and color matching may
provide an adequate palette.


***CHOOSING A TREATMENT***

Most projects involve repainting.  It is the historic appearance of
the interior and the visual impression that will be created by new
paint treatments that must be considered before choosing a
particular course of action.  The type and colors of paint
obviously depend on the type of building and the use and
interpretation of its interior spaces.  A consistent approach is
best.

PRESERVATION:

When the treatment goal is preservation, a building's existing
historic features and finishes are maintained and repaired, saving
as much of the historic paint as possible.  Sometimes, cleaning and
washing of painted surfaces is all that is needed.  Or a coating
may be applied to protect important examples of history or art.  If
repainting is required, the new paint is matched to existing paint
colors using the safer, modern formulations.  Re-creating earlier
surface colors and treatments is not an objective.

REHABILITATION:

In a typical rehabilitation, more latitude exists in choosing both
the kind of new paint as well as color because the goal is the
efficient reuse of interior spaces.  Decisions about new paint
often weigh factors such as economy and durability - use of a high
quality standard paint from a local or national company and
application by a qualified contractor. Color choices may be based
on paint research reports prepared for interior rooms of comparable
date and style.  More often, though, current color values and taste
are taken into account. Again, the safer paint formulations are
used.

Interiors of institutional buildings, such as university buildings,
city halls, libraries, and churches often contain rich decorative
detailing.  During rehabilitation, careful choices should be made
to retain or restore selected portions of the decorative work as
well as match some of the earlier colors to evoke the historic
sense of time and place.  At the least, it is important to use
period-typical paint color and paint placement.

RESTORATION:

In a restoration project, the goal is to depict the property as it
appeared during its period of greatest significance. This may or
may not be the time of its original construction. For example, if
a building dated from 1900 but historians deemed its significance
to be the 1920s, the appropriate paint color match would be the
1920s layer, not the original 1900 layer.

Based on historical research, on site collection of paint samples,
and laboratory analysis, surface colors and treatments can be
re-created to reflect the property at a particular period of time.
It should be noted that scholarly findings may yield a color scheme
that is not suited to the taste of the contemporary owner, but is
nonetheless historically accurate.  In restoration, personal taste
in color is not at issue; the evidence should be strictly followed.

In the restoration process, colors are custom-matched by
professionals to give an accurate representation.  If an artist or
artisan can be found, the historically replicated paint may be
applied using techniques appropriate to the period of the
restoration.  Although custom paint manufacture is seldom
undertaken, color and glazing are capable of being customized.  In
some projects, paint may be custom-made using linseed oil and, if
building code variances allow it, white lead.  For example, the
repainting of a number of rooms at Mount Vernon demonstrates that
it is possible to replicate historic paints and applications in all
aspects; however, as noted, replication of historic paint
formulation is not practical for the majority of projects.


***IDENTIFYING DETERIORATED AND DAMAGED PAINT SURFACES***

Because painted surfaces are subject to abrasion, soiling, water
damage, sunlight, and application of incompatible paints they
generally need to be repainted or at least reglazed appropriately
from time to time.

ABRASION:

From the baseboards up to a level of about six feet off the floor,
wood trim is constantly subjected to wear from being touched and
inadvertently kicked, and from having furniture pushed against it.
Chair rails were in fact intended to take the wear of having chairs
pushed back against them instead of against the more delicate
plaster wall or expensive wallpaper. Doors in particular, sometimes
beautifully grained, receive extensive handling.  Baseboards get
scraped by various cleaning devices, and the lower rails of
windows, as well as window seats, take abuse.  The paint in all of
these areas tends to become abraded.  Two things are important to
bear in mind about areas of abraded paint.  Samples taken to
determine original paint colors and layer sequences will not be
accurate except at undamaged edges.  Also, dirt and oil or grease
need to be removed before applying any new paint because new paint
will not adhere to dirty, greasy surfaces.

DIRT:

Soiling is another problem of interior paint.  Fireplaces smoked;
early coal-fired furnaces put out oily black soot; gas lights and
candles left dark smudges.  Sometimes the dirt got deposited on
plaster walls or ceilings in a way that makes the pattern of the
lath behind the plaster quite clear.  Another source of dirt was
polluted outside air, from factories or other industries,
infiltrating houses and other nearby buildings.  Until smokestacks
became very high, most air pollution was caused by nearby sources.

In paint investigation, dirt on the surface of paint layers, as
seen under the microscope, can be very useful in suggesting the
length of time a given paint layer remained exposed, and in
distinguishing a finish layer from a prime or undercoat layer.
This kind of soiling can happen on any painted surface in a room,
but may be slightly heavier in the recesses of moldings and on
upward-facing horizontal edges.  Using dirt as a sole measure,
however, may be misleading if the surfaces have been cleaned.  The
fracture or bonding between paint layers is often used by
professionals as a better means of indicating time differences
between layers as well as indicating those layers that are part of
a single decoration or painting.

WATER:

Water, the usual source of deterioration for many kinds of
material, is also a prime cause of interior paint failure.  As a
liquid, it can come from roof leaks, from faulty plumbing or steam
heating systems, or from fire-suppression systems that have
misfired.  As a vapor, it may come from such human activities as
breathing, showering, or cooking.  Plaster walls sealed with
unpigmented hide-glue are notably susceptible to water damage
because it forms a water-soluble layer between the plaster and the
paint.  This can cause the paint to lose adhesion when even small
amounts of moisture come into contact with the water-soluble
sealer.

AGE/SUNLIGHT:

Finally, in historic interiors, especially where there is heavy
paint build-up, paint can weaken and fail due to chemical or
mechanical reasons.  For example, the older linseed oil is, the
more brittle it is.  It also darkens when it is covered and gets no
ultra-violet exposure.  In rooms where there is more sunlight on
one area than on others, the oil or even oil/alkyd paint will get
discernibly darker in the less exposed areas in as short a time as
six months.  Painted over, the oil medium in older paints gets
quite yellow-brown, thus changing the color of the paint.  Prussian
blue is one of the tinting pigments that is particularly vulnerable
to fading.

INCOMPATIBLE PAINTS:

Understanding some basic differences in the strength of various
paints helps to explain certain paint problems.  Paints that dry to
a stronger film are incompatible with those which are weaker.
Acrylic latex paints are stronger than oil/alkyd paints.  Oil or
oil/alkyd paint is stronger than water-based paint such as
calcimine.  When a stronger paint is applied over a weaker paint,
it will tend to pull off any weaker paint which may have begun to
lose its bond with its substrate.  Thus, on many ceilings of older
buildings where oil/alkyd paints have been applied over old
calcimine, large strips of paint may be peeling.

Oil or varnish glazes over older paints become brittle with age,
and can make removal of later paints rather easy. Sometimes it is
possible to take advantage of this characteristic to reveal an
earlier decorative treatment such as graining or marbleizing.
new paint will not remain well adhered.


 


Preservation Brief 28, painting historic interior, painting interior, historic interior, historic interiors