GEORGE WASHINGTON MEMORIAL PARKWAY Patowmack Canal and Locks (Great Falls Section) Historic Structures Report — Architectural Data Section

(Memorandum from John Barrow)

MAY, 23, 1986

Memorandum

To: Superintendent, George Washington Memorial Parkway

From: Preservation Specialist, George Washington Memorial Parkway

Subject: Patowmack Canal

Enclosed is an architectural report which identifies preservation projects at the Patowmack Canal. This report is the result of numerous site visits, consultations with Paul Goeldner, Hank Snyder, Tony Donald, and others.

The preservation of the Patowmack Canal depends on a continual program of actions which are planned and co-ordinated in relation to the Historic Structures Report, past work accomplished, and future needs which may be identified. This report represents a preservation approach intended to initiate well considered actions that will retard deterioration of canal structures.

Nine project areas are identified, representing a variety of work. Currently the conservation portion of the program is underway including stone survey and analysis, herbicide study and soils testing. This work will assist in realizing long-term preservation goals.

The construction aspects of the project (relaying stone, reconstructing walls, repairing walls, and grouting) depend on our ability to incorporate an experienced stone mason and/or develop labor or project contracts to accomplish these tasks.

This project represents a rare opportunity to interact with a significant part of 18th century history and care must be taken that our goals coincide with the best interests of conserving this antiquity.

Enclosure

cc: Paul Goeldner/NCR Professional Services
Tony Donald/DSC
H. Osborne/GWMP
Dan Muller/Great Falls Park
Hank Snyder/GWMP

bcc: IRRM Files

JBarrow:emb 5/28/86

ARCHITECTURAL REPORT

1986 Preservation Project Plan for the Patowmack Canal

The preservation plan for the canal project is based on the legislation (the Capper-Crampton Act), the National Park System Advisory Board Recommendation, the Nomination to the National Register, the Patowmack Canal Preservation Alternatives (May 1985, NPS), the Memorandum of Decision (1985 NPS). and the draft and research work accomplished to date on the Historic Structures Report. The plan is also based on numerous site inspections.

The initial effort for the 1986 season is twofold — it is designed to increase the visitor awareness and enhance the landscape by selected removal of vegetation (trees and shrubs) and to take action to retard and reverse active deterioration of stone structures. As stated in the Memorandum of Decision, the highest priority is in Lock 1 and Lock 2 and that "Preservation techniques for those structures will be determined by investigation of their condition and structure". The initial phase also calls out for Lock 1 to be provided with stairs and a walkway. It is recommended that this action be postponed for further analysis and discussion due to the complexity of this treatment and the effect it will have upon the structure. Furthermore, the area of highest priority should be extended to include several other actively deteriorating areas. These are: Lock 3 walls; wall failures along the foundry area; the sluice gate; and Matildaville ruins.

This report addresses only the structural and material aspects including the environment immediately adjoining the structural elements. The clearing of shrubs and trees from the holding basin will significantly alter the status quo of that historic area and will open a vista towards the entrance of Lock 1 from the main recreational area of the park. This action will only affect the structure of the canal in stimulating more visitor interest in the ruins.

Prior to a presentation of projects to be accomplished at the canal, it is necessary to critically examine previous interventions in order that problems and difficulties encountered in the past will not be repeated. There are five areas of work which require examination and discussion. Future projects may profit from a thorough understanding of the successes and failures of past work. The areas of past work are: treatment of ruins in Matildaville; the end capping of Lock 1; the reconstruction of the gate cavity in Lock 2; the use of steel reinforcing to stabilize the walls; and the infill treatments (repairs rendered to replace lost and deteriorated stone). Each of these actions solves problems but also creates others. Generally speaking, they were independent responses to individual problems that represent diverse preservation approaches. In order to avoid a further proliferation of decisions and actions representing yet another philosophical context of preservation, it is incumbent that professionals involved develop a unified approach or preservation umbrella under which specific actions may be taken. Consensus and understanding is essential to develop a continuing program of intervention and documentation which can avoid the political pitfalls encountered as a result of previous work.

A brief introductory examination of the past actions follows:

Although a good bandaid, the steel stabilizing system requires renewed evaluation. The aesthetic quality of this work as well as its lack of flexibility renders it questionable for continued long term stabilization. Often monument stabilization systems become semi-permanent systems, remaining in place for many years as this has. It is questioned whether a system of point pressure provides generalized support to the loosely tied masonry walls of the locks. Beyond this consideration is the fact that this system is inflexible and does not allow for movement or redesign as the loading, bulging, or shifting of the stone alters the requirement. Heavy timber bracing should be considered as it would offer a stabilization solution — allowing flexibility and at the same time not requiring extensive engineering. Another possibility is an adaptation of the existing system design that is more easily adjusted and changed

The construction at the east end of Lock 1 to stabilize the deterioration of the end of the lock walls presents a solution which imitates stone work in the style and quality of the historic period. The end is finished with a cement capped stepping which then sets it apart from the original historic work. This solution requires active discussion by professionals in order to develop a consensus concerning the future treatment of the end walls at Lock 2 which are in a state of active deterioration. Should a similar treatment be given to unify the solutions or should other answers be sought? Perhaps a modified version could serve the purpose — a reduction in the longitudinal dimension of the stone work end to limit the visual effect of the new work but maintain the end stepping and stylistic quality of the Lock 1 end cap, thus clearly indicating that it is new work.

The total reconstruction of the gate pocket at Lock 2 is an example to be studied critically. The construction has left its end section dangling in an unconnected and disorienting manner requiring immediate attention. In this reconstruction it should be noted that the stones were not replaced as they had been taken out and in this solution it is difficult to see how the intersection of the pocket to the quoin could have been built. This reconstruction is in complete contrast to the rest of the canal and demonstrates clearly the effect of preservation interventions without a general plan. Does this action mean that reconstruction (dismantling and relaying stones with modern cements) in this manner becomes acceptable?

This intervention into the fabric of the canal is irreversible and it limits the solutions available to preserve the remaining 'dangling end' adjoining this reconstructed section. This end section is in an active state of structural deterioration and a refined version of the reconstructed section may be the only practical solution to save this end. Repairs to this area must address the loss of definition at the junction of the quoin and cavity. A carefully considered reconstruction of the end section would solve the disunity and reverse the deterioration processes.

The Memorandum of Decision states that "Lock 2 (will/may) require earth filling due to its major structural failures." While a good stabilization measure, the earth filling removes the interpretive value of the mason's marks found in this lock. It is hoped that solutions resulting from studies called for in the next section of this report would offer a more positive alternative than filling in the canal Lock 2.

The use of plastic to cover sections of the ruins at Matildaville has the general effect of making the area look like a trash dump. Although moisture will not penetrate the plastic from above. neither does it allow moisture to migrate up; rather it traps condensation and creates a negative environment on the tops of wall ruins. A renewed treatment for these walls and the standing ruins is indicated in the project section which follows.

Finally the infill treatments are causing negative and destructive effects in areas. There are two types of infill treatments seen: one is brick and the other pargeted masonry cement. A modified consistent solution to this problem is desirable and necessary to correct the destructive processes.

The brick sections are constructed with a hard Portland cement mix and this work possesses a higher comprehensive strength and a lower porosity than the adjoining sandstone. As a result, when stress is applied through loading and freeze/thaw cycling the sandstone is caused to crack and spall under pressure from the infill. In contrast the cement plastered infills have aesthetic superiority over the brick and they appear to be designed mortar mixes. This technique should serve as a model and replace the destructive brick units. Two alternatives to this treatment are to use cast stone or similar sandstone tooled in a manner indicating it as a replacement. Stone of a similar mineral content to the Seneca stone is currently being imported into the U.S. and is locally available.

In addition to recognition of the above specific areas of concern and a presentation of specific recommended preservation policies and actions, it is necessary to focus on the general causes and characteristics of deterioration using the HSR as a guideline for detecting deficiencies, defining the problems and diagnosing causes. From these findings, remedies may be determined and programs instituted to eliminate and correct these deficiencies. The initial evaluation process includes on site investigation and documenting research which when completed will yield the preliminary analysis. Such studies are supplemental to the HSR. From these analyses, specific lab and field tests are developed which provide basis for field evaluation on structural problems and fabric conditions. As stated, this report is focusing particularly on areas requested in the Memorandum of Decision and the additional areas of immediate concern which have been recognized from site visits.

Briefly, the deterioration of the canal is caused by three factors: human, environmental, and inherent. The site is in ruins and has been so for a period of history significantly longer than its actual use (ca. 1802-1825). It is well known that maintenance of the canal was difficult during the historic period when it was in use for some of the same reasons today — particularly, flood damage. It is also recognized that human interaction has accelerated the loss of fabric — first using the ruins as a quarry for stone and in recent times vandalism. Inherent faults are in the methods of construction, particularly the lack of tie back stones (headers). More recently problems have been generated by the excavations which have altered the environment of the base stones radically and thus accelerated deterioration, as well as the reconstruction in Lock 2 pocket which preserves the pocket but threatens the end of the lock.

PART II

STRUCTURAL FACTORS/MATERIAL FAILURES

Work Projects

1. The HSR provides a basic format in an on-the-job system of documentation for evaluating the movement of stone. It provides a photographic elevation view of the stone walls. These documents need to be supplemented with plan views and perspective views as well as measurements and notations which may be compared after time. This process provides for a basic continuing documentary plan. The use of infrared aerial photographs to locate subsurface structures and provide additional documentary evidence would be very helpful. This is accomplished in the winter months when vegetation is minimal.

2. Restoration and/or stabilization of recently collapsed and actively deteriorating walls. This deterioration is due to the recent flood and other active factors and constitutes basic preservation maintenance. The areas requiring treatment are the foundry, top stones of the wasteweir, the west end of Lock 1, the east end of Lock 2, and the bulge in Lock 3. These projects require the service of stone mason with a preservation background to ensure the sensitive and careful replacement of fallen and deteriorated stone. In several areas the walls have been affected by foot traffic and the creation of trails. Where stones can be identified as clearly knocked out of place, replacement may occur, otherwise minimal stabilization should be rendered to maintain these walls as they are; and other methods should be developed to discourage traffic on these corners, i.e. vegetation development, constructing bridges and new steps should be carefully considered from the point of view of structural impact (the necessity of constructing foundations adjoining historic walls) and the aesthetic impact (the historical effect of a new construction dominating the view of the ruins and their composition). If resources permit (staffing or under contract) the reconstruction of the Lock 2 end may be accomplished. This project requires the use of a backhoe and a movable crane. The earth will be removed from behind the stone wall and the stones will be lifted in a sling, one by one, (documented and recorded) and placed in a staging area. The wall will be then reconstructed in a similar fashion to its original construction (rubble masonry backing) correcting design deficiencies and using modified strengthened mortars (hydraulic limes with measured percentages of Portland and historically matching aggregates).

3. In selected and identified areas, vegetation (vines, trees, and scrub growth) is affecting the structural stability of the stones. This is particularly evident at the overflow gate (wasteweir). Where young root systems are developing now in the joints between stones, these should be removed. Until testing is complete on the use of herbicides as it affects the stone, this growth should be manually extracted. Usually it is necessary for the ground to be wet to remove roots without damage to structures. Roundup (glyphosate) is environmentally safe for use but the effect of this herbicide on sandstone is unknown. The Center for Urban Ecology has agreed to assist in testing the effects of this herbicide, and the others listed below, on the stone. This testing process has been initiated. The vegetation on Lock 5 is acting to support the arrangement of stones and situations such as this should be identified/documented and allowed to persist.

4. Action must be taken to reduce the problems caused by standing water at the base of walls. Along the south side of Lock 1 a small drainage ditch is allowing water to stand continuously in contact with those stones. The surfaces or these stones are very degraded, a situation clearly aggravated by the presence or water. This ditch should be redirected to the center of the canal and likewise positive drainage needs to be achieved in all areas of Locks 1, 2 and 3.

5. In association with these active projects, areas of continuing research are essential. These are: (1) the determination of the liquid and plastic limit of the soils which adjoin the stonework and (2) a load analysis of the stone walls. The liquid/plastic limit tests are relatively simple and can be accomplished at C.U.E. This leads to the possibility of using pump grouting systems to stabilize/strengthen the rear side of walls (soils modification). The load analysis provides a basis for understanding the active stresses and forces and thus the appropriate type and size of stabilizing elements.

6. Deterioration of individual stones within the structural framework is also in evidence and requires attention. Fracturing is seen at various locations and it is important to understand whether the fracturing is the result of structural stress or failure in the stone resulting from inherent factors and/or environmental factors. The engineering assistance required to define the load stress factors will assist in determining individual stone failure. Also it will be necessary to examine the stone from a mineralogical viewpoint. The U.S.G.S. has been contacted and they are assisting in this process. In certain cases the deteriorated stones may be replaced in kind, recorded and documented. The importance of the individual stones is particularly enhanced by the mason's marks (of which there are ca. 13). One is very uniquely carved at the head of Lock 1 (cross-hatching carved). At least one of the mason's marks (see sketch)

appears on a stone at the White House and this is a clear indication of a connection between the construction of the two structures which are of the same time period. This mark is very unusual because it is formed with a curve. The loss of this mark and the others would be significant and every effort must be made to preserve these features. Edward Miller writes in his article "Problems in the Deterioration of Stone": "The decay of stone in a building or monument is an extremely complex process or combination of processes that may have several independent factors. Every variable should be fully understood before preservation of any kind is attempted. The first and foremost important step should be to identify the origin of moisture, if present, and its channels throughout the masonry." The problem of stone deterioration at the canal can be examined and actions are necessary to initiate a program directed at retarding this deterioration. The stone failure is generalized in the canal structure and cannot be isolated to one specific area (low on the wall, or adjoining other failures).

The nature of the deterioration may be itemized as the following:

A. Fracturing of the surface, cracking
B. Spalling of the surface
C. Stone dissolution, advanced friability

The causes for these failures may be itemized as the following:

A. The high porosity (5% — 26%) of these stones indicates that moisture is a factor major; aggravated by:

* acidity of rain water (measured recently at 4.5 ph)
* freeze/thaw
* erosion

B. Microbiological attack (5 types of green growth) which causes one or more of the above. The acidic products of these algaes in their natural life processes works to dissolve the binders of the sandstone, and the root development which transforms the sandstone back into soil elements (dissolution).

Obviously the canal cannot be protected from rain water and flooding but keeping runoff and natural springs flowing away from the walls and redirecting rain away from those stones with the markings is desirable. Also various chemicals are recommended to control low spectrum biological growth. These herbicides (short chain fatty acids, triazines, and alkylbenzene sulphanate) will require testing prior to application. These tests are aimed at measuring the dissolution effects of the herbicide on the binders of the stone (thus changes in porosity and mass of stone). Other factors are the friability of the stone (which depends on the intergranular bond) is measured by an abrasion hardness test. Also, the mineralogic quality of the stone can define the parameters of treatments. "Seneca is limonite cemented and in a dry climate will season to a harder, stronger rock. resistant to weathering and chemical disintegration." (From E. Robertson in 'Physical Properties of Building Stones'.) This mineralogic description defines the negative association with water and the stones weakness to acidity. Another important factor is the attention paid to the quarrying processes in regard to setting the cut stone in conformity with its geologic setting bed. If not laid in this manner, weaker stones will spall and disintegrate from the surface more rapidly. Fracturing can be caused by the pressures of freeze/thaw cycling. This is particularly evident where the holes (constructed for connecting iron pins) are collectors for rain water. Where they are not self-draining they should be packed with lead wool to absorb the expansion of freezing water.

In order to initiate the conservation effort a thorough inspection identifying, itemizing, and locating the problems is necessary (i. e. stone spalling due to vertical placement of setting bed requiring replacements or stone dissolving from vegetative threats, requiring cleaning).

Also, beyond developing an assessment of the quality of the stone it is necessary to know the characteristics of the mortars to define replacement mortar and test for reactions to herbicides. There are at least three types of mortar present and the character and aesthetic quality of this material requires description as well.

7. As stated the brick infills are causing disruption to the materials around them. These should be removed where this damage is seen and replaced with pargeted stone-masonry utilizing high content lime mortar (i.e. 1.1.4 mix). These infills should replicate other plastered infills which are more agreeable in appearance.

8. Masonry structures in Matildaville are in need of preservation treatment. The standing ruins are in an active state of deterioration. Pointing and grouting these structures may begin immediately under the direction of a preservation mason. An archeological conservation effort is required to correct problems associated with the plastic covering of the ruined foundations. Standardized treatments of vegetation removal and site cleaning, masonry capping, wall consolidation, and minor excavation may be accomplished. These systems must be designed to divert rain water as much as possible from the erosion processes. It is required that the Regional Archaeologist be involved with this project and any other earth disturbing activities.

9. Aside from these active repair projects continuing research is necessary to complete an understanding of the history of the Canal to date. For example the CCC records of the 1930's have not been located and Army Corps of Engineers Restoration Plans from the same period are available but unresearched. Visitor impact on the structures requires an in depth study. Essential to these efforts is the development of a library research center which contains in one location all of the documents relating to the canal.