Technical Procedures Disclaimer
Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.
We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.
A. This procedure includes guidance on raking out and repointing the deteriorated or inappropriately repointed horizontal and vertical joints on exterior marble.
B. See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- General Protection (Surface and Surrounding)
These guidelines should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from the Regional Historic Preservation Officer (RHPO).
A. American Society for Testing and Materials (ASTM) www.astm.org
1.03 QUALITY ASSURANCE
A. Regulatory Requirements: Marble Design Manual, ASTM C144-70, Aggregate for Masonry mortar; ASTM C150-74 Portland Cement; manufacturer's printed recommendations for product use and installation.
B. Certifications: Prior to delivery, submit certificates attesting compliance with applicable specifications for grades, types, classes.
C. Field Samples: Prior to raking out all areas, cut back joints at location selected by the Contracting Officer using the methods specified. Raking will continue at no additional cost to the Government, until an acceptable sample is achieved. This area will serve as standard for joint raking for the entire job. It will be marked and left unpointed until all other pointing is completed. Point when directed by the Contracting Officer.
1.04 PROJECT/SITE CONDITIONS
A. Existing Conditions: No stone work will be performed when the air temperature is 40 F and falling or when stone surface temperature is 40 F or below.
A. Portland cement: Type I, ASTM C150, gray and/or white as necessary to match mortar color specified.
B. Hydrated masons lime: ASTM C207.
C. Aggregate: See ASTM C144 (ASTM 1997a). Clean sharp sand free of loam, silt, soluble salts and organic matter. Sand color should match stone color as closely as possible. Aggregate shall conform to the size gradations specified as a result of laboratory analysis of an approved sample.
- Choose the color of the aggregate so that the dry mortar color matches specified color.
D. Water: Clean and free of deleterious amounts of oils, acids, alkalis and organic matter.
B. Joint tools
D. Stiff fiber bristle brushes
F. Rubber mallet
A. Proportions for Marble Pointing, or as determined by mortar analysis:
- Portland cement: 1 part by volume
- Lime: 2 parts by volume
- Aggregate: 9 parts by volume
- Water: To form a workable consistency
B Mixing Procedures:
- Measure materials by volume or equivalent height.
- Do not measure by shovel. Use known measure.
- Mix ingredients in clean mechanical batch mixer for 3-5 minutes.
- Let mortar sit for 20 minutes prior to use to allow for initial shrinkage. Use mortar within 1 hour of initial mixing.
3.01 ERECTION, INSTALLATION, APPLICATION
A. Rake out all stone joints in designated areas by hand using a chisel no more than width of the mortar joint. Clean all mortar from surfaces within the joint or crack so that the new pointing mortar bonds to the building material, not old mortar. Do not chip or spall edges of the marble. If work is found unacceptable, all raking will cease without additional cost to the Government until deficiencies in tools, workers or methodologies have been corrected to the Contracting Officer's satisfaction.
B. Raked joint depth to be at least 3/4" but in all cases rake back to expose sound mortar. Raked joint depth should be 2 to 2 1/2 times the joint width.
C. Brush, vacuum or flush joints to remove all dirt and loose debris.
D. Reduce initial absorption of the stone by thoroughly wetting (surface dry) with clean water just prior to repointing.
E. Pack joints with mortar leaving no voids. Place mortar in layers not exceeding 1/4 inch in depth. Apply succeeding layers only after preceding layer has taken initial set.
F. Use clean tools and equipment free from hardened or partially set mortar.
G. Clean excess mortar from stone and joints, removing splashed mortar and droppings immediately.
H. Do not retemper or use mortar which has partially set, is caked or is lumpy.
I. Finish horizontal and vertical face joints. Do not allow mortar to extend over the surface of the stone.
J. Curing: Keep joints damp (90% RH) for at least 72 hours or until surface is cured. Protect joints from rapid drying due to wind (i.e., covering tarps, enclosure on scaffolding).
A. At the time of repairing, pointing and resetting the marble, immediately remove mortar, grout and adhesives from the face of the masonry.
B. Use only tools and equipment which are clean and free of hardened or partially hardened material.
C. Clean marble only with fiber bristle brushes and water. Use no acids, detergents, or other cleaning agents.