An initial render assessment together with mortar and paint analysis results.

Buttress Architects, working for Gregynog Hall, has asked M. Womersleys Ltd to undertake an initial render inspection, take mortar and exterior paint samples, and analyse the results.

An assessment of the render.

It appears that all but the eastern extension was rendered in the 1860s or early 1870s, creating a timber-framed pattern over relatively new brick walls. Relevant mortar analysis prepared by M Womersleys, shows the brickwork was built with lime mortars strengthened with cement, and that the renders were applied using what appears to be early Ordinary Portland Cement made with lime, shale, and clay, including waste produced during its manufacture. Early Ordinary Portland Cement production is well documented to have yielded large amounts of unreacted material within the crushed clinker, which was often not fine enough to be fully effective as a binder. Cement production in North Wales and the Liverpool area often used shales, not just clays, as sources of silica and alumina, and when they were burnt with lime slurry, they did not fully combine in a molten mix. It appears that at least some of the shale and fired clay residues found in the render samples applied up to the 1870s originated in cement production, and that this waste was supplied with the OPC, perhaps not requiring any additional aggregate in the mix. There were also often considerable amounts of unreacted calcium oxide that had to be air-slaked by storing the cement for some time before use. The resulting combination of calcium hydroxide and reactive silicas within the cement produced a strong but not completely impervious cement render.

This render appears to have survived well on Gregynog with no immediately obvious damage to the building. Unfortunately, many years of water ingress into the walls behind the render has damaged it, as shown in Blue in Figures 19 to 27, resulting in areas of render breakdown, as shown in red. The full extent of this damage, shown in red, cannot be determined until the building is fully accessible from the outside. The renders on the timber-framed clad extension that formed the Billiard and Music Rooms are more conventional in makeup, with lime, cement, and aggregate used separately in the mix, as would be expected after 1896 and especially after the 1920s.

An assessment of the paint.

The paint finishes applied to the fake timber frame and windows, as shown in historical photographs (Figures 1 to 7), consistently present a ‘black and white’ timber-framed house with cream-coloured windows. All the early paint finishes found in paint samples  1 (page  23), 6 (page 28)-the best example,  9 (page 31) and 10 (page 32), show the use of paint finishes recommended in painting manuals of the time with white lead primers, paints mixed from lead, pigments, double boiled linseed oils and turpentine.

The majority of the paint samples date from redecorating carried out from 1895 to the 1920s, when similar materials were used, but zinc white was replacing lead white. See samples 4, 8, 11, 12, 13, 14, 15, 16, 17, and 18 (on pages 26, 30, 33-40).  The only difference on the woodwork was the use of red lead priming coats and red oxide primers on the rainwater goods. Samples 2, 3, 5, 7, and 19 on pages 24, 25, 27, 29 & 41 all show more modern paints dating to the buildings' institutional use.

An assessment of the torching

The torching used under the slates comprises a very lime-rich, hairy mix gauged with some OPC, as might be expected where it was being used so extensively.