Photo Record
Images
Additional Images [19]
Metadata
Collection |
Michael Fulp House |
Title |
Mortar details |
Archive Number |
MFHPH56 |
Description |
Series of 25 digital photos depicting the variations in composition and performance of the mortars in the walls of the 1780 Fulp ["Bridge Keeper's"] House. The building displays six or more varieties of mortar in its beds, joints, and exterior pointing applied periodically during its 230 years of existence. The wall mass reconstructed or re-mortared in this project, including restored and reinforced foundations, constitutes approximately half of the masonry volume of the entire building{1}. Careful comparative analysis, the experience of the historic restoration mason, and professional advice have provided the basis for selection of the composition, application method, and tooled profile of this traditional and structurally critical component of random rubble masonry. Criteria invoked in formulating the joint ["pointing"] mortar included color, texture and granular variety of the aggregate [sand], early traditional mortar types found in the walls, compatibility with the early pointing materials found in the structure, and harmony between the mortar color and the variable palette of the stones. The earliest "mud" in the masonry structure was a lime mortar with a slightly coarse aggregate texture, mostly sandy clay containing visible "lime chunks"{2}. This 18th-century mortar, containing no "cement," was applied in a slightly cambered ["crown"] profile, also called "weather" pointing because the convex bevel of the raised mortar shed moisture away from the joints. This early mortar is quite precisely confined to the spaces between stones, and is often slightly set-back from the wall-plane. Another early generation of pointing mortar, also "crowned" and having lime-sand or lime-clay content, had a more smoothly troweled ["tooled"] finish{3} and is also amber-brown in surface color, probably because of the local red clay. The loose residue in the core of the wall was a reddish-brown sandy aggregate including lime chunks, gravel, and miscellaneous local soils. The next material applied to the building, and still existing in substantial quantity on the south gable wall, is 19th-century "barn-dash" pointing which was spread beyond the narrow joints and overlaps the perimeters of the stone "units" composing the wall. The apparent purpose of this "flush" pointing was to create a partial sub-strate forming a plumb and vertically uniform wall-plane to receive coats of parging material as a full-coverage weather barrier. Large areas of pargeing residue survived into the 20th century [see photos of this material on the north gable wall in 1970 in MFHPH22--1005.01.023 & MFHPH37--1005.01.038]. The "barn-dash" mortar presented a partly browned and mottled surface, undoubtedly caused to some degree by contact residue picked up from the application, removal, and natural erosion of the pargeing material. The visible brown and white granules are, respectively, coarser particles in the aggregate, and lime chunks. Later generations of pointing shown in these photos include mortar which is high in gray or white "Portland"-type cement, creating a hard ["strong"] mortar which presents a less permeable barrier to moisture trapped in the core of the wall. The 1970s pointing formula, applied and tooled in a concave shallow-cove profile, seems to be in this category and has undoubtedly contributed to the deterioration of the wall through this eroding process. If moisture in a masonry wall cannot efficiently transpire through the mortar joints, it will act as "rising damp" through the core of the wall, causing gradual dissolution of binding elements and eventual destabilization as the mortar "padding" disintegrates. The moisture also expands and contracts during heat-freeze cycles, causing strain and fractures in the wall structure. A few surviving specimens of early pointing will be preserved in their current joint locations in the corner piers of the south gable wall. Since the vast majority of the pointing on both eaves walls and the north gable wall is shallow-cove in form, this profile will be adopted for the repaired segments of the east eaves wall, the north gable wall, and the extensively reconstructed south gable wall. The mortar to be applied to both bed joints and as pointing will be a mix of traditional ingredients of sand, lime, and Portland cement [see discussion of the history and role of Portland cement in photo record DTR09PH66--1001.01.150, footnote {2}]. The Trust's consulting engineer recommends a ratio of aggregate- [sand]-to-binders [lime and cement] within the range of 2-to-1 up to 3-to-1{4}. Although the 20th-century concave ["shallow cove"] profile will be the template for the form and method of application of the restored pointing, the 1970s mortar mix, which is too rich in binders (probably excessive Portland cement), will not be utilized. The mixture selected for the south gable wall bed and joint mortar, and the final pointing of the restored segment of the east eaves wall, consisted of 4 parts BP "Jersey Buff" sand [photo #1204], 2 parts BP White mason's sand [photo #1202], 2 parts white lime, and 1 part gray Portland cement, and sufficient water to maintain a moderately "stiff" consistency in the mortar as applied. For discussion of the structural function of bed mortar adequately applied to all voids, fissures, and joint spaces in the wall, see detailed captions to photos #580 & #581 in MFR10PH2--1005.01.058. Photos of mortar samples prepared for this project with numerous permutations of sands, lime, and Portland cement appear in this series. A record will be kept in the Archives listing the ingredients and proportions of each sample. DETAILED CAPTIONS #242 & #250, 9/27/10: The web of pointing of diverse composition and application seen here in the south gable wall is a virtual sampler of pointing methods and materials representing over two centuries of rural masonry practice. All of the mortar varieties mentioned above appear in this stonework. Swaths of "barn-dash" pointing appear in the upper-right quadrant of photo #250. #254, 9/28/10 & #528, 11/2/10: Chunks of pointing and bedding mortar from various sites in the walls{3}, and two mortar-sample "medallions" with the constituent proportions of sand, lime, and Portland cement, and the Roman numeral sample number incised into the surface. The medallion samples in #254 and #528 also included coloring agents, which will not be considered in this mortar analysis or in formulating an approved mix for this project. The ingredient codes are as follows: #1- "CS"= BP White "Concrete" sand, a variant of "WB" with a small component of slightly coarser aggregate; light beige. #2- "BS"= BP "Buff" sand, light yellow-beige [see photo #1204]. #3- "BB"= BP "Brown bar" sand [also "dark bar" or "Pocono" brown sand]. #4- "WB"= BP "White bar" mason’s sand, light beige [see photo #1202]. #5- "MD"= BP Mason’s sand. #6- "YB"= "Yellow bar" sand. "L"= Lime. "C"= Portland cement [gray]. In samples "A" & "B" of 11/8/10, white Portland cement was substituted for gray Portland, in order to eliminate the gray hue which permeated earlier samples. The colors and proportions of the aggregate constituents will determine the ambient shade and speckling of these samples. The types of sand and permutations in further samples will produce the final pointing mortar. #658, 11/6/10: Twelve medallion samples of possible mortar to be applied in the masonry restoration of the Michael Fulp House. The challenge of matching the color and granulation of new pointing to historic mortars is complicated by the fact that white or gray Portland cement, even at low concentrations of 10-20% of the mortar by volume, is a significant color agent which was not an ingredient of early lime mortars. In the early [prior to mid 19th-century] periods the primary determinant of color and texture in the mortar was the sand, clay, and other local "aggregate" content, with a lesser tinting contribution from the lime. The intense gray in modern cement dominates the lighter lime tones, and combines with the aggregate to produce color shades not found in mortars from the early periods. In this instance, seven different sands were included in the permutations of ingredients, together with variable proportions of lime and cement. In all samples, the minimum ratio of two parts aggregate to one combined part of binders [lime and cement] was maintained. Ten of the twelve sample medallions shown in this photo included constant amounts of two parts lime and one part cement. The variable elements in these ten samples were limited to the proportions and colors of sand from the types listed in the caption to #254 above. #248: 1970 shallow-cove pointing in the south bay of the west eaves wall, applied during the restoration of the partially collapsed wall segments. This mortar is in a higher proportion of the "cementitious" [Portland cement] ingredient than is recommended by the Trust’s mason and consulting engineer, even though the stones in these walls are quite durable. The slightly recessed joint configuration in this wall range will be replicated in the three walls to be restored, despite the fact that the earliest pointing, as represented by small surviving runs in the south gable wall, is "crowned" [cambered in a convex "V" profile]. Although there is evidence of the color and texture of early mortar, this decision will avoid a large-scale repointing of the entire building in a somewhat conjectural replication of an 18th-century pattern. The new pointing material will be of slightly darker earth tone and slightly coarser aggregate granulation than the 1970 patina, which will reduce the emphasis on the "web" of light gray joints which tends to present a distracting contrast with the color values and variegated palette of the stones. #255 & #256, 9/28/10: Detail views of "barn-dash" pointing; the tape measure locates the joint positions relative to the electric junction box outside the south gable wall. #258, 9/28/10: masonry joints in the south gable wall broadly applied in the barn-dash pattern; white bits in the mortar are "lime chunks," mentioned in footnote {1} below. The darker gray-green pointing several inches to the right of the measuring tape is a modern "Portland-patch." The southwest quoin corner pier in the south gable wall was reconstructed after the 1970 partial collapse using a coarse mix high in Portland cement, producing a harder mortar than is healthy for random rubble stone masonry. #259, 9/28/10: lime-chunk riddled barn-dash mortar residue and a small segment of early pointing [just right of center in the upper third of the photo] confined within the joint and displaying transverse cracks across its coarse finish. #260, 9/28/10 & 269, 9/29/10: south gable wall range displaying (a) two generations of early "crown-pointed" lime mortar; (b) 19th-century barn-dash ["flush"] pointing; (c) modern gray Portland; (d) modern white Portland; and, deeper in the joints, (e) bed mortar residue consisting of a disintegrated mixture of sandy clay, coarse gravel, and local soils, with no apparent surviving lime residue. This loose material in the wall was easily brushed or troweled ["raked"] out of the voids in the stonework, indicating that it currently contributed minimal structural stability. Such disintegrated ["friable"] bedding material fails to perform the crucial function of solidly filling all voids and thus facilitating the uniform distribution of compressive loads and oblique thrusts within the wall structure. #512, 11/2/10: mortar sample medallions with incised ingredient proportions and sample number in Roman numeral. #546, 11/2/10: mixing measured ingredients for medallion sample. #547, 11/2/10: incising sample ingredient proportions in medallion. #548, 11/2/10: finished medallion and extra "mud" from same mix for sample to be tooled into wall joint for optimal visual comparison after it sets-up to its lighter tone. #469, 10/29/10: The mortar strip to the left was applied during the 1970 reconstruction of portions of the eaves walls and smaller areas in the gable walls. The light gray chunk in the center is new troweled ["tooled’] pointing from the cellar foundation restoration. The piece to the left is the same material left un-tooled in order to present a slightly coarser texture, which leaves the surface pores of the joint more permeable to moisture. The mortar in the lower-center of the photo is early pointing material from the south gable wall, which has visibly more aggregate of varying sizes and colors than the other specimens. The in-wall portion of this remnant has become browned by the dried mortar residue from the core joints of the wall. #1202: BP White Mason's sand. #1204: BP Jersey Buff sand. #965: sample selected for bed, joint, and pointing mortar. #964, #987 & #1002: Coded mortar sample medallions, some with acid wash to lower portion or edge. #1240: Pieces of early crown pointed joint mortar from south gable wall. #1242: Barn dash pointing chunks from south gable wall. FOOTNOTES {1} It is estimated that approximately twenty tons of new mortar will be applied to this modest-size structure during the course of the current stabilization project. {2} The clay-lime mortar found both deep in the bed joints and in a few of the surviving runs of early pointing in the south gable wall is essentially a "lime mortar" with no cement or other 19th- or 20th-century additives. It is of a color and texture consistent with the pervasive reddish-brown virgin clay found 18-24 inches below grade all around the building and westward to the river bank. In some of the photos of excavated areas this clay is visible below the fill material blackened by coal silt deposited by the Schuylkill River during periodic flooding. This upper stratum gradually deepens as it approaches the river bank, reflecting the greater sediment penetration in the flood-plain elevations subjected to more frequent saturation. Photo #XX shows a small nugget of original mortar found deep in the junction of the western fireplace pier ["jamb" or "leg"] and the south gable wall [this early mortar is visible in the exposed core masonry in photos #1435 & 1438, 11/26/10; the gray patches locate new bed mortar(a) packed into the core of the wall [by a technique sometimes called "back pointing"] to replace disintegrated ["friable"] early mortar raked or swept out during the current restoration campaign. The material applied as "mortar" in the core of the walls during original construction has either deteriorated from moisture and stress, or was intentionally applied as a dry "rubble" mixture of clay, sand or a coarser aggregate, and probably lime. The fragmented condition of this material, found throughout the walls and often concealed by modern "veneer" pointing, increases the difficulties in stabilizing the structure for the long-term without reconstructing all wall ranges. (a) compounded as 5 parts yellow bar sand, 2 parts white lime, and 1 part gray Portland cement. {3} Tooling the exposed surfaces of the pointing mortar is not solely a cosmetic technique. This finishing method also helps close the pores near the surface of the mortar joint, thus allowing less moisture penetration into the core of the wall. Acid-washing and similar modern "finishing" applications{a} which dissolve the lime film ["milk"] extruded to the surface during the curing process also re-open the pores of the mortar compound. The degree of expedited erosion of the mortar depends on the concentration of the acid solution and the amount of time until the applied acid is washed away with water, a critical step necessary to minimize corrosion of stones in the wall. {a} intended to simulate a naturally weathered appearance by exposing the color and granulation of the aggregate. {4} Examples of mixtures which qualify under these parameters would include: *6 to 9 parts sand with 2 parts lime and 1 part cement ["Portland"]. *8 parts sand with 2 parts sand and 2 parts cement; this "strong" mix would be appropriate in unusually wet conditions. *The proportions in footnote {2}(a) above, used in the foundation and some destabilized wall-core segments, do not precisely meet the guidelines, but were considered an acceptable deviation due to the unstable condition of portions of the foundations and the pervasive wall-core deterioration. Larry Ward |
Search Terms |
MFHPH MFH MFR10PH Barn-dash Pointing Pointing Pargeing Pargeting Lime Mortar Crown Pointing Portland Cement Bed Mortar Michael Fulp House Mortar Mortar Joint Wall Core Aggregate |
People |
Michael Fulp |
Object Name |
Print, Photographic |
Accession number |
1005.01 |
Date |
09/27/2010-11/02/2010 |
Photographer |
Ward, Laurence |
Catalog Number |
1005.01.060 |