Archive Record
Metadata
Collection |
Mouns Jones |
Archive Number |
MJHTXT12 |
Title |
Early Mouns Jones House Mortar Analysis |
Description |
X-ray analysis of the primary constituents of the early mortar{1} used in the foundation and walls of Mouns Jones's 1716 house has determined the precise chemical composition of its lime binder. According to qualitative ("elemental") tests performed at West Chester, PA, University, the ratio of calcium compounds to magnesium compounds in the Mouns Jones house mortar is approximately 4 to 3 (57% calcium carbonate, 43% magnesium carbonate), decisevely placing this mortar in the "dolomitic" or "magnesian" category, sometimes called "dolomite" in the nomenclature of standard geological literature. This magnesium-rich{2} rock was formed in the geologic period known as "Permian", occurring between 225 and 280 million years ago (Cfr. Clifton-Taylor, op. cit. in next par.). Higher-calcium limestone [80-90%, or even higher in calcium content as a percentage of calcium plus magnesium compounds by weight] was formed principally by organic marine shells and skeletal fossil remains under enormous pressure from oceans and geological solids deposited between 280 and 345 million years ago [see summary of these and other limestone types and their periods of origin in The Pattern of English Building by Alec Clifton-Taylor, revised 4th Definitive Edition, edited by Jack Simmons, Faber & Faber (1987), pp. 58, 59, et seq.]. "High Calcium" lime mortars consist of ratios in the range of 8-10 calcium compounds to 1 magnesium compounds; even higher proportions of calcium are found at some sites. An example of exceptionally high-calcium limestone is prevalent in the Tyson quarry, 6 miles east of Jacksonwald in Exeter Township, surveyed in the 1883 PA Geological Survey and analyzed by D'Invillers (cfr. Sloto, op. cit.), showing a ratio of 15 parts calcium to 1 part magnesium. Such very high-calcium formations, including most of the 1883 limestone-quarry sites in the Oley Valley, should not be considered as possible sources for the burned and slaked dolomitic "quicklime" used in the early mortar found in the Mouns Jones house, which has 5-10 times as much magnesium carbonate as is found in those high-calcium limestone sites. Numerous high-calcium Oley Valley quarry- sites, and some in the moderately magnesian range of "earth-metal" compounds, are detailed in Sloto, op. cit., at pp. 256-261. Quarry-site limestone in the Exeter-Oley-Earl region north of Mouns Jones' tract also typically includes measurable Silica in the range of 2 to 10%, with rare outliers as high as 20%. Silica in moderate proportions contributes to hardness after mortar "sets-up", but is not a significant factor in the cohesion, binding quality, permeability, or bearing resiliency of the mortar. Atypically, much higher Silica content (3 and 4 times more than either Calcium or Magnesium compounds, respectively, "very silicious" according to D'Invilliers in 1883), dominated the "limestone" extracted from the Miller Quarry in the Borough of Bechtelsville north of Boyertown, according to the 1883 survey [Sloto, op. cit., at p. 23]. The Silica content in the early Mouns Jones house mortar was about 12% of the combined Calcium Carbonate, Magnesium Carbonate and Silica weight calibrations, higher than average and higher than at some of the quarry-sites tested by D'invillers. Accordingly it may be inferred that Mouns Jones' mason used limestone from a nearby source other than the sites (referred to below) closest to his home-site 4 or 5 miles south on the Schuylkill River. Silica is only about 5% of the dolomitic mortar to be used in the 2018 Mouns Jones house masonry restoration campaign. The dolomitic quarry-sources closest to Mouns Jones 1716 house range from 2.5 to 6.4% Silica content. The limestone type used in the early Mouns Jones House mortar is nearly identical to dolomitic formations close to the northern range of the original Mouns Jones tract nearly four miles north of his surviving stone house. The vast majority of the accessible rock formation under the 10,000 acre 1701 "Swede's Tract" [now essentially Amity Township] is "New Red Sandstone", formed between 195 and 280 million years ago]. Thus it may be reasonably concluded that there was little or no limestone within Mouns Jones's original tract boundaries suitable for "quicklime" created by the centuries-old method of burning and hydrating limestone of the appropriate characteristics to produce workable, non-friable, and stable lime mortar. However, several sources of dolomitic limestone approximating the 57% calcium-43% magnesium proportions{3} of the Jones house mortar lay within very few miles of the northern boundary of the original 480 acre Jones tract, and within a few more miles from the home and masonry works of Samuel Savage, a "Manatawny stone mason" as he was described in a 1715 Deed, at Pine Grove, only a few miles north of the Mouns Jones 1716 stone house site: A.Earl Township: 1.D. Davidheiser Quarry site: 56% Calcium, 44% Magnesium {3}; 2.Mengel Quarry: 56.5% Calcium, 43.5% Magnesium; B.Douglas Township: 1.J. Davidheiser Quarry site: 59% calcium-41% magnesium; 2.Henry Keely Quarry site: 56.6% calcium-43.4% magnesium. What can be reasonably inferred from this data is that limestone of nearly the precise relative proportions of calcium and magnesium found in the Jones house mortar was readily available from outcroppings or shallow formations within an hour or two wagon-ride northward from the 1716 Jones home-site. Given the relatively high Silica content of the early Mouns Jones mortar, it is quite possible that his limestone came from a nearby site other than the four cited above. An American source has been located for geologically, chemically, and functionally equivalent, (and decidedly dolomitic){4}, lime-mortar{5} that will be used in the masonry re- building campaign in 2018. Tests have reasonably demonstrated that this product is structurally sound for the masonry, flooring, framing, and roof loads to be imposed on the reconstructed wall ranges of the 1716 house. The selected mortar mix contains no Portland cement, artificial coloring, or other modern additives, and is not in the high-calcium range of the dolomite-limestone spectrum. The ultimate and decisive field-test for structural mortar is its contribution to the static nd dynamic stability and durability of the structure over time. It is evident that substantial ranges of the early walling of the Mouns Jones House have functioned in stable equilibrium, bedded and bonded with dolomitic lime-mortar, for over three centuries. None of the manifest primary causes of partial failures of segments of the masonry in the structure, including one or more probable tectonic events and numerous ground- and masonry-saturating floods, can be attributed to the magnesian chemistry of the mortar. There seems to be no empirical or statistical evidence that high-calcium mortar performs at levels superior to the experience with dolomitic formulations, including but undoubtedly not limited to the mix used in the 1716 house . End-Notes: {1} taken from the interior of the 2d story northern gable wall, which appears to be undisturbed walling from the first period of the house, c. 1716. {2} relative to the much lower magnesium content in "high calcium" limestone. {3} These proportions are derived from the 1883 D'Invilliers analyses cited in Sloto, op. cit. and the quarry-location maps reproduced by Sloto from the 1883 PA Geological Survey cited above. {4} The published relative proportions between calcium and magnesium in this domestic lime mortar are: Calcium: 57-58%; Magnesium: 42-43%. These proportions are nearly identical to the calcium-magnesium ratio of the early Mouns Jones house mortar determined by the x-ray spectroscopy process discussed above, within a 2% margin of error compared to the local dolomite-limestone cited above. Dolomitic limestone and marble in western Connecticut, near East Canaan, has been analyzed to consist of: Calcium compounds-54.4% average; Magnesium compounds- 44.6%; Silica-1%: "Marbles and Limestones of Connecticut" by Fred Holmesly Moore, M.A., CT State Geological and Nat. Hist. Survey, Bulletin No. 56 (1935), at p. 24. {5} This "lime-mortar" (defined for purposes of this paper as mortar with its largest elemental component consisting of calcium carbonate), is nevertheless "dolomitic", defined here as having a proportion of magnesium carbonate relative to calcium carbonate higher than 1 to 2, i.e., magnesium compounds greater in weight than one-third of the combined weight of calcium and magnesium compounds in the sample. Laurence F. Ward, March 2018 |
Object Name |
Lime Mortar |
Catalog Number |
1000.01.129 |
Search Terms |
Lime Mortar Dolomitic Limestone Dolomite Magnesian MJHTXT MJHTXT12 |