century plasterwork at St Mary's, East Knoyle, Wiltshire.
Some of the figures were vandalised by Roundheads during the
Civil War, and the rector, Dean Christopher Wren (father of
the pre-eminent architect), narrowly escaped jail for creating
from enriched architectural surfaces is a sensitive area. Firstly,
removal erases the historic record embodied in the paint layers.
Secondly, physical damage to the underlying material can and often
is caused by either the cleaning agent or the tools used. Where
plasterwork is concerned, no matter how sensitively undertaken,
removal of softened paint with conservators' tools inevitably
damages surfaces. Leaving well alone is often more beneficial
to overall preservation. The harm caused to important underlying
decorative schemes and mechanical damage far outweigh the benefits
of any aesthetic reinstatement or dressing up. Nonetheless, excessive
paint build-up obliterates fine decorative detail, transforming
the finest ornament to dull and pedestrian shapes of little interest
to all but the most knowledgeable viewer. Removal can revitalise
and uncover technical virtuosity and re-ignite both public and
scholastic interest in decorative interiors that might otherwise
languish in obscurity or, worse, fall prey to neglect and decay.
As with all interventionist conservation, perceived benefits and
risks must be carefully weighed up.
On outer walls
and other surfaces subjected to persistent condensation or moisture
ingress, applied coatings may be acting as a barrier to evaporation.
As a result, evaporation concentrates at any cracks or gaps in
the paint and at the edges of the painted area, causing high local
concentrations of salts. Sulphate salts, for example, can be leached
from later cement renders and internally from gypsum, leading
to eruption of salt crystals at the plaster and paint interface.
moisture levels in the plasterwork may also lead to rusting and
expansion of ferrous armatures and possible fungal attack of organic
materials. In cases such as these, paint removal can be essential
to arrest the rate of decay and reduce loss of plaster enrichment.
Before undertaking such an irreversible step, it is essential
that a responsible programme of recording be undertaken using
photography and microscopic paint analysis. A small section of
the full paint thickness should also be retained in an appropriate
area of the plasterwork for future reference and investigation.
attack is particularly severe, it is worth undertaking salt analysis
prior to paint removal. In one instance the removal of paint from
early 17th century plasterwork led to the sudden crystallisation
of salts, hitherto in solution as the structure dried out. The
result was the rapid erosion of the plaster surface and the irretrievable
loss of decorative plaster. In such cases paper pulp poulticing
may be the only means of ameliorating damagingly high salt concentrations
without physical removal of the plaster.
removal is undertaken, the use of methylene chloride (such as
Nitromors Green Label) is controllable and effective on organic
coatings such as oil based paints and modern coatings, leaving
the inert lime and gypsum plaster chemically undamaged. The translucent
liquid and thickening waxes incorporated in these cleaning agents
do not obscure the work in hand, enabling the conservator to proceed
with care. Importantly, if this process is carried out with the
necessary care and skill, any particulate residues may subsequently
be removed with nothing more than a gentle dusting with a soft
in particular should be avoided, especially on porous historic
fabric. They can inflict great damage to plasterwork. Not only
does the plaster absorb potentially harmful soluble salts, but
there is also an increased risk of physical damage from tools
due to the thickness and opacity of the paste which blind the
conservator to the enrichment. Lack of chemical control and the
necessity to wash away residue with water should be enough to
suggest their use has no place in the treatment of historic surfaces.
fine detail of a Georgian cornice obscured by paint
such as casein-bound distempers, have little or no organic binder
and may prove particularly difficult to remove safely. In these
cases water and small tools may prove to be the only effective
method of paint removal. Other techniques such as the use of heat
and steam generally lack sufficient control for them to be considered
for use on delicate historic fabric. It must also be accepted
that no matter how desirable, in some cases paint removal is neither
practical nor feasible.
problems associated with paint removal include the uncovering
of poor repairs and previous intervention which must be subsequently
dealt with. Examples are poor cast reproductions of existing elements,
often reinstated on a shoe string budget following large scale
failure in the past, such as war time bomb damage.
composition or other fragile and organic-rich applied decorative
elements may also be present, especially on 19th century work,
which might be destroyed by an otherwise acceptable paint removal
technique, so it is vital to investigate what is being dealt with
prior to specifying work, let alone commencing work.
and trials of any suggested technique are essential to ensure
the suitability of any chemical agent, the skill of the operatives,
the quality achievable and the effect on the plasterwork and adjacent
related substrates and coatings. Programme time available can
also be a decisive factor and should not be dismissed from the
coatings fulfil two particularly relevant functions. One is purely
aesthetic, relating to colour, texture and overall visual qualities,
like opacity and transparency. The other is performance related
and how the coating functions physically. Factors of relevance
here include permeability, compatibility, durability, flexibility,
reversibility, protection, weight, thickness, surface tension,
drying, ageing, preparation requirements and the number of coats
required. Added to this are the means of application and the cost.
In the field
of conservation it is usual for historic fabric to be repaired
and reinstated on a like-for-like basis, using materials and techniques
that match those used originally as closely as possible. However,
where plaster is concerned, renewing the original finish may be
desirable, but it may also be impractical for a number of reasons.
In some cases the choice of coating is dictated by circumstance;
in others, the options may be less clear cut. In any event, the
conservation and preservation needs of the fabric should be foremost.
soft distemper (a chalk-based paint with a binder of size) can
be applied by brush to a newly stripped ceiling of especially
deep and fragile modelled plasterwork to recreate its original
colour and texture authentically, using water soluble reversible
materials. The bonus is a surface that can be readily cleaned
when its details eventually become clogged with paint again. Such
an approach presents a beguilingly straightforward, ideologically
sound conservation solution.
water soluble stains that inevitably accumulate in the plaster
from persistent moisture ingress may be impossible to cover without
the use of an impermeable solvent-based sealing coat. Yet impermeable
paints are generally undesirable, particularly where future risk
of moisture ingress cannot be precluded. Moreover, brush application
carries a high risk of further mechanical damage to delicate and
fragile ornament. At least three coats of distemper may be required
to achieve satisfactory decoration. What of later maintenance
or redecoration? Water soluble reversible coatings like distemper
will, at some stage, require mechanical removal with brushes prior
to further redecoration. This too subjects fragile modelling to
the certainty of further damage and loss. It also imposes a responsibility
and duty of care that the owner of the building may not wish to
shoulder. This can result in the later overcoating of all the
good work with a totally inappropriate, easier to use coating
that starts off the cycle of decay all over again.
In many instances,
it may be more beneficial to spray using a variable 'high volume
low pressure' (HVLP) turbine. Spraying precludes further unnecessary
physical contact. Coating thickness can be better controlled on
intricately detailed plaster and redecoration intervals may be
extended by specifying a coating with the most appropriate attributes.
removal of paint does not always reveal the fine
expected. Bad repairs may also lurk beneath
paint removal systems can damage fine
plasterwork by introducing
harmful salts, and the thickness
and opacity of some pastes
blind the operative to the
enrichment beneath, reducing control
and making them
difficult to remove safely.
needlessly emphasise 'breathable' coatings in the misguided belief
that this equates to conservation and a responsible approach.
Although vital when applied to bare surfaces subject to continued
moisture vapour movement, permeability is an irrelevant attribute
when applied over impermeable systems.
is also frequently specified, and in general specifications the
term is taken to mean soluble in water. This attribute may not
be a good thing when used in close proximity to fragile existing
coatings that may be easily damaged or altered by water, and it
can easily be avoided by using a non-traditional coating which
is soluble in a synthetic solvent. Advice should be sought to
ensure that specifications adequately account for the real needs
of the historic fabric. Oil
paints may be less than a fifth of the thickness of modern emulsion
paints. At Castletown House near Dublin, microscopic paint analysis
has revealed two modern emulsion decorations accounting for more
than 70 per cent of the total thickness of the previous oil painted
schemes since the house was begun in 1722. Generally, much of
the heavy paint build up on plasterwork today is a product of
the late 19th and 20th centuries.
a simple dilution of lime putty with water, coloured with the
addition of alkali resistant pigments, is eminently suited to
lime renders, externally or internally. It should be applied sparingly
as a wash, as a thick paint-like coating is liable to fail and
flake. Water based and equally vapour permeable is soft distemper,
which is for internal use only. Although perhaps the most common
plaster finish well into the 19th century, and easy to remove,
it may not always be the best choice for conservation work. In
particular, the use of oil and casein bound distempers are precluded
by their thickness and the difficulty of subsequent removal. Their
additives are intended to decrease dusting while increasing permanence
and durability rarely suiting them for use on pure conservation
thickness, there is much to recommend the use of 'contract' emulsion
paints particularly when applied to patch repairs in plain run
mouldings and flatwork, where sharpness is not an issue. These
materials have the highest vapour permeability and are specifically
formulated for use on new plaster. Not only are they relatively
cheap and widely available, crucially they are alkali resistant.
This makes them eminently suitable where the use of lime repairs
precludes the use of oil paints for a minimum of 12 months: the
time necessary to ensure sufficient carbonation of lime and reversion
of the surface to a neutral ph to avoid a reaction (saponification).
Vinyl emulsions do not have the higher vapour permeable qualities
of contract emulsion. Invariably vapour permeability decreases
with an increase in gloss and weather resistance for modern water
thinned products of this nature.
may be restricted by programme time, as noted above, requiring
a full 12 months before application direct to any new surface
containing lime. This also applies to modern alkali resistant
primers whose use will not generally be endorsed by manufacturers
without a similar time lapse. Another alternative is Classidur
Super Classic, which originates from Switzerland. This is a non-conventional
solvent-based system which has a number of attributes that suit
it particularly well as an alternative to distemper for interior
decorative plaster. Chiefly these include lack of surface tension
with high vapour permeability, a very matt finish, which can be tinted
to the same intensity as distemper, and the minimal number of
coats required. Indeed, soot, nicotine and most other water and
oil soluble stains can be painted over without priming or sealing
coats, and its high opacity allows strong colour changes in only
two coats. The minimal preparation required and lack of tension
especially suit it to badly stained substrates and fragile existing
coatings. Care should be taken for persistently damp areas as
mould resistance may not match that of less organic coatings such
as whitewash and limewash, especially in relation to large volume
spaces like churches.
such as Keim mineral paint, is another coating originating from
overseas, appearing in Germany in the late 19th century where
its use has a strong tradition. Although there is no tradition
of its use in the UK, the material is widely specified, particularly
for use on external renders. It is irreversible and so should
be specified with care in situations where its particular attributes
will be beneficial to the conservation of the fabric. It should
not be used simply as a low-maintenance substitute for limewash.
of any culturally important historic building or artefact is necessarily
encumbered with a multiplicity of opposing needs. Ultimately,
preservation is paramount to serve the needs of enlightenment,
education and the wider enjoyment and appreciation of the past.
Inevitably, the very act of conservation is interventionist, having
far reaching consequences on the continued survival of an object,
so all unnecessary alterations should always be avoided.
this issue is especially pertinent when considering the removal
of paint from plasterwork. An easy decision when coatings are
actively assisting decay, the pros and cons are much less defined
when removal is proposed for largely aesthetic grounds. Damage
is inevitable, yet when undertaken sensitively for appropriate
reasons, the effects can be startling. Plasterwork detail can
be dramatically revealed, enhancing appearance and bringing important
attention which may itself be sufficient to ensure continued investment
and survival. Conservation should never be purely prescriptive.
Each case must be carefully balanced to ensure an appropriate
response that best addresses the many conflicting needs of preservation.
article follows on from Richard Ireland's introduction to the conservation
of historic plaster in The Building Conservation Directory 2005, 'Conserving Decorative Plaster', and is reproduced from Historic
IRELAND undertakes conservation on buildings as diverse as
castles and farm houses to the Entrance Hall decoration and
Reading Room at the British Museum. He operates chiefly around
the British Isles and Ireland as both consultant and practitioner
and lectures widely.
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