Infilling glazed ceramic tiles

Vanessa Wiggin <vanessa [at] artworksconservation__com> writes

>...  I am interested in hearing about what others have used to
>infill losses in tiles in an outdoor context.  Also, if replacement
>tiles have been used instead how were these sourced?

We carried out extensive restoration of the Crown Bar in Belfast, a
National Trust owned property but very much a working public house.
The Exterior and Interior of the Bar were highly decorated in glazed
ceramics, made by the Craven Dunnil Jackfield factory in the 1880's.
Past treatments had included infills with epoxy resins and dental
plaster, both of which had deteriorated.   Epoxy resins are well
known for their instability in UV light, cross-linking and changing
colour, in our case darkening to an unacceptable hue and pulling
away from the substrate.

In addition to needing to find a suitable fill material for the tile
body, we also wanted to seek a suitable way of mimicking the glaze
and depth of colour, which again would not suffer under UV light. We
used a white cement fill, coloured with cement pigments which if the
surface coating failed would at least retain some colour akin to the
original tile, the surface of the fill was then painted using Keim
paints colour-matched to each individual tile.  Cement fill trials
carried out ten years previously were seen to be in good condition
and had not faded, plus they have the advantage of being of a
similar porosity and flexural strength to the original tiles.  It
goes without saying that you will need a clean surface of the loss
prior to using any fill material, and experience of tending mortars
is an advantage!

After extensive accelerated aging tests on a variety of commercial
products as surface coatings (to mimic the glazed surface), we
selected Incralac.  Whilst this may well need replacing in due
course, this proved to be the most stable of all the products tried
and relatively straightforward to reverse in a regular maintenance
cycle.  On applying the coating this did darken the underlying Keim
colour slightly so this needed to be considered during the initial
colouring.

In terms of replacement tiles, we contacted Craven Dunnil Jackfield
directly.  One of the difficulties is that many of the colours are
not easy to replicate as they were originally lead based glazes,
which was frustrating for all concerned, but the end results were
satisfactory.  A decent tile manufacturer used to replicating
historic tiles should be able to assist.

Berenice Humphreys
Cliveden Conservation
+44 1761 420300


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                  Conservation DistList Instance 24:40
               Distributed: Wednesday, February 23, 2011
                       Message Id: cdl-24-40-003
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