Photo Record

Images

1 of 1977

View Image Metadata

Additional Images [30]

Metadata

Collection

Michael Fulp House

Title

Restoration of the south gable chimney

Archive Number

MFHPH58

Description

Series of 36 digital photos taken during the restoration of the south gable chimney of the Michael Fulp (formerly "Bridge Keeper's") House.

Many years of infiltration by storm water and recurring freeze-thaw cycles had disintegrated the bed- and joint-mortar in the gable wall and chimney wall segments enclosing the flue(a). Lacking the crucial monolithic bond between the gable wall and chimney, portions of both masonry elements had delaminated and moved(b) from their reciprocal support and buttressing positions. Partially dismantling the chimney disclosed fractures and voids in the stonework [see photos #835 & #840], providing clear evidence of instability, and the need for immediate remediation.
(a) The walls of the chimney were called "wythes" in early documents; later this term was broadened to include the vertical outer and inner wall segments lining the wall's "core". The flue was called a "funnel" in the early English tradition and in a 1750 letter from Benjamin Franklin on the subject of fireplaces.
(b) in rotation, deflection, lateral shift, or a combination of these displacements.

The risk of catastrophic failure and the hazard inherent in any substantial structure was significantly increased by the sloped ["corbelled"]{1} construction of the chimney from above the smoke chamber to the penetration of the roof-planes near the vertical axis of the ridge. The rise to the chimney outlet above the roof-ridge is entirely west of the vertical alignment of the firebox and smoke chamber, thus the sloping chimney mass is not supported directly from below, but is borne obliquely by the stacked cantilever [also "cantilever in the British literature through the mid-19th century] effect of the overlapping corbels [see footnote {1}].

Large bond-stones [also "through-stones" in the 18th- and 19th-century British tradition] will be strategically "toothed" from the chimney walls into the gable wall to integrate the two structures, adding these "ties" as a redundant{2} measure of reciprocal support and restraint against the shearing forces imposed on the corbels.

The sloped chimney presented structural challenges to the original builders which were not confronted in the erection of the Mouns Jones House and its corner chimney 25 yards to the northwest and 65 years earlier. The Jones chimney projects straight upward from the diagonal corner fireplace through the roof, and extends above the horizontal ridge-plane to provide adequate draft. The fireplace and chimney breast support the chimney stack in compression.

The sloped Fulp chimney, structurally more demanding and not precisely centered on the ridge, nevertheless offers the rational benefits of a "crook'd" chimney. Those benefits were considered to be worth the structural hazard [see discussion of the functional advantages of "gathered" chimneys in MFHPH17--1005.01.018 and MFHPH21--1005.01.022]. A more acutely sloped chimney would increase the risk that the slope will exceed the "angle of repose," thus approaching the structural limits of a stable chimney in this "gathered-over" form.

The remediation plan designed to structurally stabilize the south gable wall and the chimney included:
A. Resetting displaced stone "units," and inserting stone "plugs" and "pins" in large voids
B. "Deep pointing" the core of the chimney walls and applying carefully formulated mortar{3} to all beds and joints
C. Projecting ("toothing") longer stones from chimney wythes into the gable wall as structural ties, and integrating the chimney with the gable masonry
D. Pargeting the flue interior, creating a smoother surface to inhibit turbulence, thus reducing back-draft and
E. Coating the re-contoured chimney interior with a refractory{4} cement.

DETAILED CAPTIONS
#835 & #840, 11/10/10: Unstable and displaced chimney stones in attic

#842, 11/10/10: Dislocated stonework in west face of chimney, and deflected window lintel and soffit board

#844, 11/10/10: view of the western face of chimney from attic, showing voids in joints, shored cavity, and dislocated stones

#843, 11/10/10: detail view of #844

#1467, 11/27/10: full height of fireplace and chimney interior after removal of south gable wall; three restored walls have been pargeted and projecting stones are positioned for bonding ["tying"] into gable wall

#1897, 12/22/10 is a detail view of a large bond-stone

#917, 11/13/10: disintegrated chimney stonework under roof in attic

#2604, 3/10/11 and #2670, 3/12/11 show the rough contour of the displaced stone "units" near the top of the chimney; this interior segment was re-configured and pargeted to create a smoother contour to reduce turbulence and back-draft in the smoke-exhaust [see photo #2117, 1/9/11 showing fully-coated chimney interior, and iron bar ["pot-hanger" or "lug-pole," see Long, A., The Pennsylvania German Family Farm, pub. by The Pennsylvania German Society as Volume 6 (2nd series) in 1972, at p. 98] embedded in the opposing wythes

#951 & #953, 11/15/10: Interior detail of displaced chimney stones

#970: west face of chimney from attic after deep-pointing and application of "scratch-coat"{5} to joints and edges ["arrises"] of stones

#972: detail of #970, showing cantilevered stone [projecting horizontal stone just above angled wooden brace] positioned to bear eastern end of oak lintel above window opening

#981: deep-pointed core of south wall of chimney, with two large stones set in position to be tied into the restored south gable wall under the terminal rafter (raking from upper left in photo to lower-right corner); such ties provide reciprocal mechanical advantages, bonding the structural ranges and components together to counterbalance and neutralize stresses and strains in the integrated walls

#2037, 1/1/11, shows corbelled segment of chimney prior to re-laying of gable wall across open southern wythe; temporary wooden bracing across flue; and stones projecting from eastern wythe for toothing into gable wall; blue electric blankets, electric heaters, and fiberglass batts kept daily stonework above 40 degrees Fahrenheit overnight to facilitate curing of the mortar

#1028, 11/19/10 & #1623, 12/4/10: pargeted interior of chimney, prepared for refractory{4} coating; angled wooden braces support eastern wythe of chimney pending restoration of gable wall, which will cover opening at upper-left in photo, and which serves as the southern wall of the chimney, tying the chimney walls together

#1412, 11/26/10 shows a forged iron pot-hook anchored in a mortar joint at the lower edge of the parge-coat [center-left]

#1161, 11/21/10 shows both "lug" bars, which will be bedded in the reconstructed south gable wall; also seen in this view is smoke chamber above the timber lintel, and the sloping segment of chimney, braced during re-stabilization

#1405: detail view of 1161, 11/26/10, upward from the western end of the lintel level, with hanger-bars

#1196, 11/22/10: detail of smoke chamber above fire-box

#1197, 11/22/10: view up the chimney prior to final pargeting and application of refractory coating

#1031, 11/19/10: detail of the upper segment of the eastern chimney wall from the sloped ["corbelled"] segment to the vertical range extending to the roof level

#1158, 11/21/10 shows the open gable and corbelled chimney prior to completion of the upper masonry wall reconstruction

#1734, 12/11/10: first few courses of south chimney wall, laid up from grade and pointed

#1778, wall laid-up several courses [in modern terms one "lift," commonly used regarding concrete slab construction but sometimes referring to the courses of "walling" laid between each raising of the scaffolding] higher than in #1734

#1780, 12/14/10: detail of western wythe of chimney after "mudding-in" of bed and joint mortar; electric heater in fireplace facilitates curing of interior chimney pargeting

#1794, 12/14/10: plastic insulated sheet over blankets and batts helps conserve "heat of hydration" during curing ["setting-up"] process in fresh mortar

#2142, 1/10/11 is view up chimney after pargeting of interior walls

#2461, 2/28/11: eastern segment of stepped(a) ["corbelled"] chimney structure from attic after application of "scratch" coat of mortar preparatory to finish plastering [sample plaster patch on interior gable wall]
(a) the masonry mass of the "steps" provides counterweight to restrain the oblique or rotational stress on the corbelled western wythe of the chimney;

#2546, 3/6/11 & #2591, 3/7/11: fully reconstructed, pargeted, and plastered upper chimney, from attic; note preserved early plaster [red-brown color from local clay content] in lower-right corner

#2552 is a detail view of #2546

#2766, 3/18/11: completed gable wall, integrated with southern chimney wythe; mason is inside chimney, re-contouring and pargeting upper flue

FOOTNOTES
{1} Constructed by extending ["cantilevering"] each non-uniform "rubble" course of the sloped chimney stonework beyond the edge of the bearing stones below. This method (called "gathering-over" in the English masonry tradition) forms a structure which is in stable compression provided that the load supported by each overhanging range is relatively close to the fulcrum (the supporting edge of the bearing stones), and the mass bearing on the embedded segment of the cantilevered stone is adequate to offset the "outboard" load. Even though the lines of force in cantilevered structures are oblique and supported at some horizontal distance from the load, the chimney mass is borne "in compression". The loads imposed by the masonry mass of the chimney are conducted to the support-base of the structure, in this case the gable foundation and the fireplace jambs and lintel. As a rule-of-thumb, the length of the load-bearing "overhang" should be no more than half the stone segment embedded in the bearing-mass inside the fulcrum. The sub-grade foundation under the fireplace, carrying the fireplace and chimney stack, is wider than the foundation ranges set plumb ["flush"] with the above-grade wall dimensions [see photo #736, 11/8/10, in record MFR10PH3--1005.01.059]. This expanded base forms a "plinth" intended to provide more support on a larger bearing-plane for the immense loads imposed by the fireplace and chimney masses, thus serving the same mechanical function as a foundation "footing." In some buildings (Mouns Jones House, e.g.), the plinth extends above grade to the offset ["water table"] where it returns to the normal wall-plane.
{2} "Redundancy," a technique developed within the "art and mystery" of medieval masonry, encompasses complementary structural measures which utilize the mass and material strength of building components to reciprocally counterbalance, buttress, or support other components or segments in the same building.
{3} See restoration record MFR10PH4--1005.01.060.
{4} Heat resistant (having a low coefficient of thermal conductivity), and not deformable at high temperatures.
{5} The fresh mortar was "scratched" with a series of recessed lines, randomly incised with the tip of the trowel into the mortar, "stucco," or other "pargeting" material to facilitate the adhesion ["keying-in"] of the next layer of material. This long-standing traditional sequence includes a "brown" coat (sometimes with a binder consisting of straw, grass, or animal hair), then a scratch coat, and finally the finish plastering [often "plaistering" in the 18th-century English tradition].

Larry Ward

Search Terms

MFHPH
MFH
MFR10PH
Michael Fulp House
Restoration
Restoration Photo
Bond Stone
Chimney
Chimney Wythe
Toothing
Sloped Chimney
Cantilever
Corbel
Plinth
Scratch CoatChimney Restoration
Deep Pointing
Through Stone

People

Fulp, Michael

Object Name

Print, Photographic

Accession number

1005.01

Date

11/10/10 thru 3/18/11

Photographer

Ward, Laurence

Catalog Number

1005.01.064