ST CANICE S CATHEDRAL

Transcription

1 ST CANICE S CATHEDRAL KILKENNY A CONDITION SURVEY OF THE WEST DOORWAY Wells Cathedral Stonemasons West Doorway, St Canices s, Kilkenny

2 Wells Cathedral Stonemasons 2 West Doorway, St Canices s, Kilkenny

3 INTRODUCTION This report is compiled by Wells Cathedral Stonemasons Ltd on behalf of Paul Arnold Architects. The external elevation of the doorway was studied in detail from scaffold and from the ground, on 24 April The cathedral in Kilkenny was begun at the east end in the 1210s and the west end, with its door and singing gallery above, dates from the 1250s (below left). The form of the door, with its associated gallery, is very similar to that at the cathedral in Wells (below right), a building that was probably seen by many of the Irish bishops as they made their way to and from London via Bristol. The doorway is constructed using a local carboniferous limestone and an oolitic Bath stone, thought to be Dundry stone, from south of Bristol, imported through Waterford and shipped up the River Nore to the inland town of Kilkenny. Wells Cathedral Stonemasons 3 West Doorway, St Canices s, Kilkenny

4 CONDITION The two principal stone types in the door s construction have decayed, and subsequently been repaired, differently. The Kilkenny limestone has delaminated/spalled on protruding weathered courses, such as the outer arch hood mouldings and the inner hoods It is so severe in some places that the stone has begun to split (A) B A C Some of this decay has previously been repaired, by others, using a hard, perhaps cementitious, repair mortar (B). The quality of the craftmanship of these repairs is of a good standard. All the stone, including the repairs have had the joints repointed with a lighter coloured mix, again hard. (C) Wells Cathedral Stonemasons 4 West Doorway, St Canices s, Kilkenny

5 The robustness of the local limestone has meant that the carved elements, such as the column capitals have faired well. The protected areas of the capitals has led to a severe build up of sulphation however. Some of the relief carving, such as on the cusps, however, has been lost, possibly caused by face bedding of the stone. Wells Cathedral Stonemasons 5 West Doorway, St Canices s, Kilkenny

6 The Bath stone has weathed in a typical manner: a slow disintegration caused by a combination of factors, such as salt crystallisation, freeze/thaw etc. There are some areas where these damaging salts are present as dark, sulphation (A). Within the archivolt the joints have been previously repointed with hard, cementitious mortar. This has exacerbated the decay of the stone around these joints (B) A B All the Bath stone hood moulds have also previously been repaired with an overly hard repair mortar Wells Cathedral Stonemasons 6 West Doorway, St Canices s, Kilkenny

7 The elements within the spandrels of the arch, owing to their decorative nature, have lost much of their detail, and the remaining stone is very friable. There is a slight build-up of sulphation within the undercuts of the bosses (A). There has been a small amount of very unsympathetic repair (B). A B Wells Cathedral Stonemasons 7 West Doorway, St Canices s, Kilkenny

8 The original lime mortar in the joints to the surrounding rubble wall of the west is generally in good condition, with occasional open/defective areas. However the upper levels have been extensively repointed with hard cement pointing, dressed to a ribbon finish (below left). The juncture between the lower section of the west wall and the dressed stone of the doorway has been repointed with hard cement (below right). Wells Cathedral Stonemasons 8 West Doorway, St Canices s, Kilkenny

9 CONSERVATION In this section is a marked up photograph showing individual interventions. This will outline the essential conservation/repair work needed for each stone element, but there are a couple of more general areas that may need to be considered for the long-term care of the doorway. Cleaning The sulphation on the underside of sheltered stone needs to be removed. A combination of gentle scraping and poultice may be sufficient. Localised use of nebulous sprays could also be trialled. Stone repairs The previous repairs to both the Kilkenny and Bath stone are well executed and are showing no signs of failing. They could, however, be too strong for the original material, certainly on the Bath stone. Consideration must be made to removing these and either repairing with a more sympathetic repair mortar or replacing the stone. All the Bath stone within archivolt needs a combination of repair and restoration, especially around the joints. The carved elements will require a careful clean and consolidation with a sheltercoat. Consideration should be made to the extent of repair: how much of the carved detail is to be reinstated if any? Repointing All open and defective joints require repointing. Consideration should be made to removing hard cementitious pointing, both within the door way and on the main west elevation. This would be dependent upon trials. Mortar samples were taken and analysed (see Mortar Samples below). Wells Cathedral Stonemasons 9 West Doorway, St Canices s, Kilkenny

10 MORTAR ANALYSIS Four samples were taken from the doorway, lettered A D on the marked up photograph. It is possible that the sample mortar has been affected by environmental conditions and therefore appears weaker than mortar remaining in the walls. A more durable mortar can be made with St Astier NHL3.5 required to suit the environment but further information about the strength of the stone and remaining mortar should be taken into account first In order to establish a suitable repair mortar we must take into account the original mortar along with the stone strength, function of mortar, site conditions, seasonal working, location and environment Mortar sample A Bath stone joint SUMMARY The sample mortar is a weak dark cream bedding mortar. The sand/ aggregate is yellow/ brown graded, it is graded from 0-3mm and is just 18% by weight. See enclosed sievings. A similar strength of the mortar can be achieved with a mix of 1 part St Astier NHL2 to 2.5 parts sand. It is possible that the sample mortar has been affected by environmental conditions and therefore appears weaker than mortar remaining in the walls. A more durable mortar can be made with St Astier NHL3.5 if required to suit the environment but further information about the strength of the stone and remaining mortar should be taken into account first. FINDINGS INITIAL OBSERVATION The sample is made up of 80% powder and 20% small pieces of 3 to 10mm. Dark cream coloured. A relatively weak mortar. The sample was tested with phenolphthalein, which showed it had fully carbonated. DISAGGREGATION ANALYSIS The sample was separated from the aggregate by dissolution in hydrochloric acid and the relative proportion of sand was determined. DISAGGREGATION SAMPLE A. DRY WEIGHT OF SAMPLE: 32.05g B. DRY WEIGHT OF SAND: 5.29g C. DRY WEIGHT OF LIME AND CALCAREOUS MATERIAL (less 10% CO2): 24.08g D. PERCENTAGE SAND BY WEIGHT 18% E. PERCENTAGE LIME AND CALCAREOUS MATERIAL 82% BY WEIGHT: Wells Cathedral Stonemasons 10 West Doorway, St Canices s, Kilkenny

11 THE AGGREGATE GRANULOMETRY AND GRADING Magnification of the sievings showed the aggregate is made up of sharp and sub-rounded sand graded from 0-3mm. Aggregate Weight Retained (g) % Aggregate Weight BS Sieve 5.00mm % 2.36mm % 1.18mm % 0.60mm % 0.30mm % 0.15mm % Fines % 30.0% Mortar position A 25.0% 25.1% t 20.0% h ig e w 15.0% te a g r e 10.0% g a f o % 5.0% 7.3% 17.1% 14.1% 17.6% 18.8% 0.0% 0.0% 5mm 2.36mm 1.18mm 0.6mm 0.3mm 0.15mm Fines sieve mesh size SAMPLE COLOUR AND AGGREGATE MATCHING Suitable sand/ Close colour match: Yellow/ brown aggregate see sievings. Wells Cathedral Stonemasons 11 West Doorway, St Canices s, Kilken-

12 Mortar sample B dressed Kilkenny stone joint SUMMARY The sample mortar is a weak dark cream bedding mortar. The sand is graded from 0-3mm. The mortar is made up of approximately 1 part lime and other calcareous material to less than 1 part sand by volume. The sand is poorly graded from 0-1mm with 46.9% below 150 microns A large proportion of fines in lime mortars can lead to longer setting time, shrinkage, lime leaching, and are more sensitive to adverse weather conditions. The sample can be matched in colour with a site mix using a grey 0-3mm aggregrate similar to the enclosed sievings. A similar strength of the mortar can be achieved with a mix of 1 part St Astier NHL3.5 to 2.5 parts sand. FINDINGS INITIAL OBSERVATION The sample is made up of 50% powder and 50% small pieces of 3 to 25mm. Dark cream coloured. A medium strength mortar. The sample was tested with phenolphthalein, which showed it had fully carbonated. DISAGGREGATION ANALYSIS The sample was separated from the aggregate by dissolution in hydrochloric acid and the relative proportion of sand was determined. DISAGGREGATION SAMPLE A. DRY WEIGHT OF SAMPLE: 41.15g B. DRY WEIGHT OF SAND: 13.80g C. DRY WEIGHT OF LIME AND CALCAREOUS MATERIAL (less 10% CO2): 24.62g D. PERCENTAGE SAND : BY WEIGHT 36% E. PERCENTAGE LIME AND CALCAREOUS MATERIAL 64% BY WEIGHT: F. MIX RATIO BY WEIGHT: 1 : 0.56 G. MIX RATIO BY VOLUME : (calculated approx.) 1 : 0.22 Wells Cathedral Stonemasons 12 West Doorway, St Canices s, Kilkenny

13 THE AGGREGATE GRANULOMETRY AND GRADING Magnification of the sievings showed the aggregate is made up of sharp and sub-rounded sand graded from 0-3mm. BS Sieve Aggregate Weight Retained (g) % Aggregate Weight 5.00mm % 2.36mm % 1.18mm % 0.60mm % 0.30mm % 0.15mm % Fines % Mortar position B 50.0% 46.9% 45.0% 40.0% t h35.0% ig e w30.0% te a g25.0% r e g 20.0% a f o15.0% % 10.0% 5.0% 0.0% 26.4% 18.0% 5.0% 1.3% 2.4% 0.0% 5mm 2.36mm 1.18mm 0.6mm 0.3mm 0.15mm Fines sie ve mesh size SAMPLE COLOUR AND AGGREGATE MATCHING Suitable sand/ Close colour match: Frithend Blend (0-3mm) Wells Cathedral Stonemasons 13 West Doorway, St Canices s, Kilken-

14 Mortar sample C rubble stone joint SUMMARY The sample mortar is a weak dark cream bedding mortar. The sand is graded from 0-3mm. The mortar is made up of approximately 1 part lime and other calcareous material to less than 1 part sand by volume. The sand is poorly graded from 0-6mm with 46.9% below 150 microns A large proportion of fines in lime mortars can lead to longer setting time, shrinkage, lime leaching, and are more sensitive to adverse weather conditions. The sample can be matched in colour with a site mix using a dark grey 0-3mm aggregrate similar to the enclosed sievings. A similar strength of the mortar can be achieved with a mix of 1 part NHL3.5 to 2 parts sand. FINDINGS INITIAL OBSERVATION The sample is made up of 80% powder and 20% small pieces of 3 to 0mm. Grey coloured. A medium/ strong mortar. The sample was tested with phenolphthalein, which showed it had fully carbonated. DISAGGREGATION ANALYSIS The sample was separated from the aggregate by dissolution in hydrochloric acid and the relative proportion of sand was determined. DISAGGREGATION SAMPLE A. DRY WEIGHT OF SAMPLE: 40.03g B. DRY WEIGHT OF SAND: 18.05g C. DRY WEIGHT OF LIME AND CALCAREOUS MATERIAL (less 10% CO2): 19.78g D. PERCENTAGE SAND:BY WEIGHT 48% E. PERCENTAGE LIME AND CALCAREOUS MATERIAL 52% BY WEIGHT: F. MIX RATIO BY WEIGHT: 1 : 0.91 G. MIX RATIO BY VOLUME (calculated approx.) 1 : 0.36 Wells Cathedral Stonemasons 14 West Doorway, St Canices s, Kilkenny

15 THE AGGREGATE GRANULOMETRY AND GRADING Magnification of the sievings showed the aggregate is made up of sharp and sub-rounded sand graded from 0-6mm. BS Sieve Mortar position C Aggregate Weight Retained (g) % Aggregate Weight 5.00mm % 2.36mm % 1.18mm % 0.60mm % 0.30mm % 0.15mm % Fines % Mortar position C 35.0% 30.0% 28.7% t h 25.0% ig e w 20.0% te a g r e g15.0% a f o 10.0% % 10.4% 11.3% 15.3% 15.6% 15.9% 5.0% 0.0% 2.8% 5mm 2.36mm 1.18mm 0.6mm 0.3mm 0.15mm Fines sieve mesh size SAMPLE COLOUR AND AGGREGATE MATCHING Suitable sand/ Close colour match: Grey aggregate see sievings. Wells Cathedral Stonemasons 15 West Doorway, St Canices s, Kilken-

16 Mortar sample D rubble stone joint SUMMARY The sample mortar is a weak dark cream bedding mortar. The sand /aggregate is dark grey, it is graded from 0-5mm and is 52% by weight. See enclosed sievings. A similar strength of the mortar can be achieved with a mix of 1 part NHL2 to 2.5 parts sand. A soft strength premixed mortar with St Astier NHL will be similar in strength. It is possible that the sample mortar has been affected by environmental conditions and therefore appears weaker than mortar remaining in the walls. A more durable mortar can be made with St Astier NHL3.5 required to suit the environment but further information about the strength of the stone and remaining mortar should be taken into account first In order to establish a suitable repair mortar we must take into account the original mortar along with the brick/ stone strength, function of mortar, site conditions, seasonal working, location and environment. FINDINGS INITIAL OBSERVATION The sample is made up of 90% powder and 10% small pieces of 3 to 0mm. Grey coloured. A weak mortar. The sample was tested with phenolphthalein, which showed it had fully carbonated. DISAGGREGATION ANALYSIS The sample was separated from the aggregate by dissolution in hydrochloric acid and the relative proportion of sand was determined. DISAGGREGATION SAMPLE A. DRY WEIGHT OF SAMPLE: 33.65g B. DRY WEIGHT OF SAND: 16.67g C. DRY WEIGHT OF LIME AND CALCAREOUS MATERIAL (less 10% CO2): 15.28g D. PERCENTAGE SAND BY WEIGHT : 52% E. PERCENTAGE LIME AND CALCAREOUS MATERIAL 48% BY WEIGHT: Wells Cathedral Stonemasons 16 West Doorway, St Canices s, Kilkenny

17 THE AGGREGATE GRANULOMETRY AND GRADING Magnification of the sievings showed the aggregate is made up of sharp and sub-rounded sand graded from 0-5mm. One rogue 12mm particle. BS Sieve Aggregate Weight Retained (g) % Aggregate Weight 5.00mm % 2.36mm % 1.18mm % 0.60mm % 0.30mm % 0.15mm % Fines % Mortar position D 30.0% 27.6% 25.0% t h 20.0% ig e w te 15.0% a g r e g 10.0% a f o % 5.0% 4.8% 9.1% 12.3% 11.0% 17.0% 18.3% 0.0% 5mm 2.36mm 1.18mm 0.6mm 0.3mm 0.15mm Fines sieve mesh size SAMPLE COLOUR AND AGGREGATE MATCHING Suitable sand/ Close colour match: Grey aggregate 0 to 5mm see sievings. Wells Cathedral Stonemasons 17 West Doorway, St Canices s, Kilken-

18 A B D C Wells Cathedral Stonemasons 18 West Doorway, St Canices s, Kilkenny