a condition survey of the west doorway · sieve mesh size mortar position a wells athedral...

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

ST CANICE’S CATHEDRAL

KILKENNY

A CONDITION SURVEY OF

THE WEST DOORWAY

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


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 2012.

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.


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)

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)

A

C

B


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.


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)

All the Bath stone hood moulds have also previously been repaired with an overly hard repair

mortar

B

A


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).

B

A


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).


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).


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 Asti-

er 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 11 West Doorway, St Canices’s, Kilken-

THE AGGREGATE GRANULOMETRY AND GRADING

Magnification of the sievings showed the aggregate is made up of sharp and sub-rounded sand grad-

ed from 0-3mm.

SAMPLE COLOUR AND AGGREGATE MATCHING

Suitable sand/ Close colour match: Yellow/ brown aggregate – see sievings.

BS Sieve

Aggregate Weight Retained

(g) % Aggregate

Weight 5.00mm 0.00 0.00%

2.36mm 0.39 7.32%

1.18mm 0.91 17.07%

0.60mm 0.75 14.07%

0.30mm 1.34 25.14%

0.15mm 0.94 17.64%

Fines 1.00 18.76%

0.0%

7.3%

17.1%

14.1%

25.1%

17.6%18.8%

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

5mm 2.36mm 1.18mm 0.6mm 0.3mm 0.15mm Fines

% of aggregate weight

sieve mesh size

Mortar position A


Mortar sample B—dressed Kilkenny stone joint

SUMMARY


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


Dark cream coloured.

A medium strength mortar.



The sample was separated from the aggregate by dissolution in hydrochloric acid and the relative

proportion of sand was determined.





D. PERCENTAGE SAND : BY WEIGHT 36%


BY WEIGHT:

F. MIX RATIO BY WEIGHT: 1 : 0.56

G. MIX RATIO BY VOLUME :

(calculated approx.) 1 : 0.22



Magnification of the sievings showed the aggregate is made up of sharp and sub-rounded sand

graded from 0-3mm.


Suitable sand/ Close colour match: Frithend Blend (0-3mm)

BS Sieve Aggregate

Weight Retained (g) % Aggregate

Weight

5.00mm 0.00 0.00%

2.36mm 0.22 1.30%

1.18mm 0.41 2.42%

0.60mm 0.84 4.96%

0.30mm 3.04 17.97%

0.15mm 4.47 26.42%

Fines 7.94 46.93%

0.0%1.3% 2.4%

5.0%

18.0%

26.4%

46.9%

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

45.0%

50.0%



sie ve mesh size

Mortar position B


Mortar sample C—rubble stone joint

SUMMARY


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


Grey coloured.

A medium/ strong mortar.



The sample was separated from the aggregate by dissolution in hydrochloric acid and the relative pro-

portion of sand was determined.





D. PERCENTAGE SAND:BY WEIGHT 48%


BY WEIGHT:

F. MIX RATIO BY WEIGHT: 1 : 0.91

G. MIX RATIO BY VOLUME (calculated approx.) 1 : 0.36



Magnification of the sievings showed the aggregate is made up of sharp and sub-rounded sand

graded from 0-6mm.


Suitable sand/ Close colour match: Grey aggregate – see sievings.

Mortar position C

BS Sieve Aggregate


Weight

5.00mm 0.51 2.78%

2.36mm 1.91 10.41%

1.18mm 2.08 11.34%

0.60mm 2.81 15.31%

0.30mm 2.86 15.59%

0.15mm 2.92 15.91%

Fines 5.26 28.66%

2.8%

10.4%11.3%

15.3% 15.6% 15.9%

28.7%

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%



sieve mesh size

Mortar position C


Mortar sample D—rubble stone joint

SUMMARY


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 ap-

pears 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 remain-

ing 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


Grey coloured.

A weak mortar.



The sample was separated from the aggregate by dissolution in hydrochloric acid and the relative propor-

tion of sand was determined.





D. PERCENTAGE SAND BY WEIGHT : 52%


BY WEIGHT:



Magnification of the sievings showed the aggregate is made up of sharp and sub-rounded sand graded from 0-5mm. One rogue 12mm particle.


Suitable sand/ Close colour match: Grey aggregate 0 to 5mm – see sievings.

BS Sieve Aggregate


Weight

5.00mm 0.80 4.78%

2.36mm 1.52 9.09%

1.18mm 2.06 12.31%

0.60mm 1.84 11.00%

0.30mm 2.84 16.98%

0.15mm 3.06 18.29%

Fines 4.61 27.56%

4.8%

9.1%

12.3%11.0%

17.0%18.3%

27.6%

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%



sieve mesh size

Mortar position D


C

B D

A

a condition survey of the west doorway · sieve mesh size mortar position a wells athedral...

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