Conservation & Heritage Issue 49 October 2025 - Flipbook - Page 108
Cleaning Terracotta and Faience
Before any cleaning is carried out, sample test panels
will be undertaken to ascertain the correct cleaning
approach and to define a benchmark. It is also important
to investigate the building fabric before commencing with
samples. When carrying out sample panels temporary
protection to the fabric of the building and to the general
public are put in place.
Given the ease with which faience can generally be cleaned
there are typically three key approaches.
1. A simple water wash by hand and soft bristle brush
2. DOFF or steam cleaning.
3. More heavily stained areas can be cleaned using
a non-acidic detergent applied in line with
manufacturers guidelines.
Abrasive methods of cleaning such as wet abrasions, JOS/
TORC are not suitable for use on faience and will damage
the surface of the material. Equally, no form of acidic
based chemical cleaning should be used on faience as it
might compromise the fire skin or glaze.
Faience and Terracotta Repair
The outward signs of decay on terracotta and faience do
not always reveal the extent of decay within. Sometimes it
is necessary to inspect each unit at close range, methods
can include drilling a small hole and using an endoscope.
In situ repairs can be undertaken providing the damage is
not too extensive. A colour matched lime-based mortar is
produced incorporating brick dust and/or natural earth
pigments .The damaged area is prepared and cleaned
incorporating stainless steel armatures where required.
The repair mortar is then built up in successive layers,
allowing each coat to dry and harden sufficiently before
applying the next coat. The final coat is left to match the
existing line and detail of the original stone.
Crack Repair
Where a crack has occurred in an otherwise sound block,
it may be repaired. The intention is to adhere parts of the
block together to restore its strength and/or to prevent
moisture ingress into the crack and further deterioration
due to frost or ‘pivot’ action. The crack will be carefully
cleaned by use of an etching tool. The method of repair
will be by carefully drilling 3mm holes at 100mm intervals
along the line of the crack to approximately half depth
of the crack. Small hollow tubes will then be set in the
holes and the face of the crack filled with non-stain plastic
or river clay. Starting at the lowest hole, the crack will be
injected with glue using a hypodermic syringe until full
and the process repeated upwards. The material to be
injected will vary according to the application. A flexible
epoxy resin or an acrylic glue with varying viscosity will
be utilised. On completion of the fill and initial set, the
‘putty’ will be removed and the face filled with a mortar
developed to match the block.
In the case of hairline cracks, it may not sometimes be
possible to use face putty and a colour matched glue can
be used instead. Where the block is structural, it may
be necessary to carefully introduce reinforcement across
the crack using stainless-steel rods of an appropriate
size. These will be inserted into holes drilled into the
block, preferably at opposing angles for strength and to
prevent rotation.
Repointing
Repointing of faience is only done using an appropriate
mortar which will be lime based with a fine sand aggregate.
Cement mortar and waterproof caulking of joints should
not be used with faience as they are both non-breathable.
A sample of pointing should be offered for approval before
commencement. Joints will be filled and consolidated by
pressing in mortar with appropriate tools and finished
flush. The joint will be wiped with a damp sponge to finish
flush with surrounding stone.
Replacement of Faience Units
Historic faience facades backing structures are typically
brickwork incorporating structural steel supports which
were historically built up together and any cavities
were generally filled with clinker and cement. Faience
replacement is becoming more frequent, typically due to
the corrosion of the embedded or underlying steel which
subsequently causes irreversible damage to the surrounding
masonry. Faience units that have lost their structural
integrity and waterproof quality, should be removed and
replaced with like for like units. The new elements are
hand crafted to match the original colour and profile. In
some cases, new clay models will be made from scratch
by an artisan. New moulds would then be created ready
to cast the new units. Only specialist companies can
undertake this, and there are a few in the UK.
Modern faience facades are now usually designed
incorporating a cavity where the stones are fixed
back to the new structure using stainless steel or non
ferrous fixings.
Above, Battersea Power Station Before
Above, Battersea Power Station After
