A preliminary study of stone decay in the Victoria Memorial Museum in Ottawa

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Technical Note (National Research Council of Canada. Division of Building Research), 1952-10-01

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A preliminary study of stone decay in the Victoria Memorial Museum in Ottawa

Ritchie, T.

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-NATIONAL RESEARCH COUNCIL OF CANADA

DIVISION OF BUILDING RESEARCH

No.

'f

E

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_{1HIN ][}

CAlL

NOT FOR PUBLICATION

130

NOTlE

FOR INTERNAL USE

PREPARED BY T. Hi tc rie CHECKED BY APPROVED BY

PREPARED FOR the record October,1952

SUBJECT _{A Preliminary Study of Stone Decay in the}

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-A Preliminary Study of Stone Decay in the Victoria Memorial Museum in Ottawa

In the course of an investigation of settlement of the ｖｩ｣ｴｯｲｾ

Memorial Museum in Ottawa, an interesting case was noticed of decay of certain of the stones used in the walls of the building. A brief des-cription of the occurrence, and some notes considered relevant to the case, are given here.

The Victoria Memorial Museum is a large, four-storey, monumental-type bUilding on which construction began in 1905 and which was completed about 1910. The walls are natural stone masonry, and are load-bearing, in conjunction with many large buttresses. Much of the stonework is of ornate character, especially in the high parapet walls.

The building is shown in the photograph of Figure 1.

The source, and some properties, of the stones used in this

building, have been recorded by W.A. Parks (1). Stones from two quarries _ were used.

The stones used in the walls proper were obtained from a local quarry (Bells Corners, Nepean Township, Carleton County) and belong to the ttNepean Sandstone" type of stone which has been extensively used in bUilding construction in the Ottawa area. Parks has listed the Parliament Buildings, the Observatory, the Archives Building and the refinery to the Mint, as examples of the use of this stone in building construction.

As trim stone for the Victoria Memorial Museum (around window openings, at the foundation, and in parapets, and buttresses), Wallace sandstone has been used. The quarry is located at Wallace, Cumberland County, Nova Scotia and its products have been very Widely used thrOUghout the Maritime provinces, and, as in this case, often very far afield.

Some physical properties of these two stones have been determined by Parks; some .of these are given in Table I.

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TABLE I

Some Properties of Nepean and Wallace Sandstones as determined by Parks (1).

Wallace Sandstone Ne ean Sandstone

Pore Space, per cent

13.038

5.958

Ratio of Absorption, per cent

5.58

2.31

Crushing Strength, psi

15,633

21,621

The pore space of the stones was determined by Parks from water absorption experiments, the pore space being taken as the weight of stone which would be required to fill the pores of the sample, expressed as a percentage of the weight of the stone if it had no pores.

The ratio of absorption was determined as the total amount of water absorbed by the stone (on

36

hours immersion in warm water under

reduced pressure) expressed as a percentage of the dry weight of the stone. Table I shows the differences in some properties of these two

stones, the Wallace stone apparently possessing a more porous, open, structure.

The chemical composition of these stones has not been recorded by Parks.

Very noticeable decay is apparent on many stones of the walls of the Victoria Memorial Museum. Only the Wallace stoms, however, seem to have been affected.

The decay appears as extensive areas which have undergone flaking, exfoliation or crumbling of the surface.

A white ｳ｡ｬｴｾ deposit discolours most areas where deterioration has taken place.

Some photographs showing representative examples of the decay are given in Figures 2 to

9.

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3

-Figure 2. The foundation stone, and the dressed stone belt course and window and buttress trim are Wallace sandstone. The rough-faced stone above the belt course is Nepean sandstone. Decay can be seen in the dressed stones of the buttress, in the belt course, particularly at the

junction of the buttress and the wa 1, and at the window opening in the foundation.

The appearance of the decay is shown in greater detail in Figure

3,

the belt course at a buttress being shown here.

More example of decay in the belt course are shown in Figures

4,

5,

and

6.

The foundation, at a window opening, is shown in Figure

7.

The decay around the window and the dressed stone above the window is very noticeable.

Severe decay of stone around a window opening in the foundation wall (similar to that window opening in Figure

7)

is shown in Figure

8,

the long slab of stone splitting off at the top, and the exfoliation at the sides presenting a very striking appearance.

The general appearance of the decay in the stones is shown by the photograph in Figure

9.

The mortar joint shown is about

1/4

inch in width.

The mortar on the exterior surface is apparently a pointing mortar, extending only a half-inch or so into the joint. It has been coloured red. The mortar has become detached from the joints in many places, as can be seen in several of the photographs, and, as well, in many places it can be removed from the joints with little difficulty. However, it is hard and strong,probably a cement type mortar.

It was observed, and is shown in the photographs, that the decay is more pronounced in those parts of the building where the stones are somewhat sheltered (e.g. in the window openings, in corners, beneath projections).

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ＭＭＭＭＭＭｾＭＭＭ

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I

The cause of decay of stone masonry has been the subject of

4It

considerable investigation, particularly in Great Britain, where the preservation of very many buildings and monuments is additionally desirable because of their great historic or artistic value.

It has been suggested (2), that decay in stone may be the result of one or more of several agencies, inclUding chemical attack

(which includes the solvent action of rain), biological ｡ｴｴ｡｣ｾ (bacteria, lichens, etc.), movements due to temperature or moisture changes, and frost.

In the first of these - decay bW chemical processes - of especial interest is decay brought about by the crystallization, or change in

crystal form, of salts in masonry. This has been studied in considerable detail in Great Britain at the Building Research Station, and by other

Ie

workers.When a stone or other masonry material becomes wet, soluble salts in it may be taken into solution; the salts may have been initially present, or later formed in the material. The solution of salts in the material will move, depending mainly on the conditions of evaporation. When eva-poration, or temperature change, occurs and the solution becomes saturated with respect to a particular salt, crystallization of that salt can start, and the resulting growth of crystals may exert sufficient force within the material to lead to its disintegration.

Similarly, volume changes may result from the conversion of a salt into different states of hydration, or from the anhydrous to the hydrated form. The experimental work of D.G.R. Bonnell and M.E. Nottage (3) at

the Building Research Station of Great Britain has shown that such hydration taking place within the pores of normal porous building materials may set up stresses sufficiently high to overcome the tensile strength of these materials.

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•

5 -An

interesting earlier study of decay in many stone and brick

masonry buildings in Great Brltain was made by A.P. Laurie and J. Milne

(4).

From ehemical analysis of samples of the masonry of buildings affected by decay, they found in very many instances large amounts of sulphate of lime in the decayed masonry. They stated that, " •••••••• it is generally admitted that the main cause of the rapid decay in

modern buildings is the action of the sulphur oxidation compounds, such as sulphuric acid and sulphate of ammonia in the air and rain, due to the combustion of coal. These compounds combine with lime to form sulphate of lime, which crystallizes within the stone or brick and breaks it up."

The lime sUlphate, they found, formed,in many cases, in the

mortar. If the rate of evaporation from the surface of the masonry units was then faster than that of the mortar surface, the lime sulphate would be drawn from the mortar into the units, to be crystallized in the masonry units on evaporation of the moisture.

However, if the rate of evaporation from tm units was less than that from the mortar, there would be a tendency for the moisture to move from the units into the mortar. Laurie and Mnne pointed out that the use of dense, cement-type pointing mortars (with very low rate of evaporation) generally forces the movement of moisture with salts in solution from the mortar into the masonry units, where they can crystallize and disrupt the units.

A few p'reliminary chemical analyses of samples of masonry from the Victoria Memorial Museum were made. These show that calcium sulphate may be a factor in the decay of this building.

Samples of masonry from the Victoria Memorial Museum included: (a) the decayed, crumbling stone at the exterior surface of some Wallace

sandstones;

(b) a piece of Wallace stone taken from the exterior surface of an apparently sound stone;

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•

6

-(c) a piece of Nepean Sandstone taken from an interior exposed surface (in an attic); and

(d) a piece of mortar taken from an interior exposed surface (in an attic). No samples of the red, exterior pointing mortar were analysed.

The results of chemical analysis of the samples are shown in Table II (made by E. C. Goodhue, Division of Applied Chemistry, National Research Council).

- ｾ Table II

-Analysis of Masonry Materials from Victoria Memorial Museum, Ottawa (by E. C. Goodhue, Division of Applied Chemistry, N. R. C.)

Sample Acid Oxides of

Insoluble Iron

&

Alumina SulphateCalcium CalciumOxide

Decayed Wallace

e

Sandstone

90.5

6.0

1.5

(a) Sound Wallace Sandstone

92.8

5.8

0.4

(a) Sound Nepean Sandstone (interior)

6 9•2

0.4

0.08

(a) Mortar ttnterior)

9.0 _4·4

1.00 _9.9

(a) Not determined.

The relatively high concentration of calcium sulphate in the decayed stone, as compared with the sound Wallace sandstone, which is ,shown in Table II, indicates that this salt may be the cause of the

decay. In addition, the analysis shows that the source of lime sulphate may be the mortar, although it should be mentioned that no damp-proof

course was seen between the foundation and the walls of this building

ｾ｢ｯｶ･ grade, which if present, would rule out the possibility of passage

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•

.. 7 ..

The Victoria Memorial Museum illustrates the problem of decay of certain, and not others, of apparently identical stones in similar locations, as well as the problem of decay in certain more or less sheltered areas of the building and not others. In regard to these problems, it may be mentioned that the pore structure of materials,

(size of pores, distribution, connection, etc.) and of stones in

particular has been shown to influence to a considerable extent their resistance to decay

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The decay of stones in the Victoria Memorial Museum, which has been briefly described here, is considered worthy of further study.

Therefore, if circumstances permit, it is hoped to continue this preliminary study with more methodical and more complete analyses,

chemical and physical, of the masonry materials used, and of the adjacent soil of the building.

REFERENCES:

(1)

w.

•

Parks "Report on the Building and Ornamental Stones of Canada" .. Volumes I and II, Government Printing Bureau, Ottawa,

1912

and

1914.

(2 ) Report of the Director, Report of the Building Research Board of Great Britain for the year

1926;

H. M. S.

o.

(3) D. G. R. Bonnell and M. E. Nottage "Studies in Porous Materials with Special Reference to Building Materials .. The

crystallization of Salts in Porous Materials"; Jour. Soc. of Chem. Industry Vol. _LVIII,

1939.

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A. P. Laurie and J. Milne "The Evaporation of Water and Salt Solutions from Surfaces of Stone, Brick and Mortar", Proc. Royal Soc. of Edinburgh Volume XLVII, Part I,

1926 - 1927.

R. J. Schaffer "Some Aspects of Investigations in the United Kingdom on the Weathering and Durability of Building Materials", Building Research Congress, Division 2,