Pointing Granite And Filling Cracks
- CSI Division:
- Division 4- Masonry
- Last Modified:
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 pointing deteriorated joints on vertical granite surfaces. The procedure described may also be used to fill minor cracks in granite.
B. This procedure should be used in conjunction with 04520- 02-R, which describes in more detail the purpose of repointing in general, the materials required and precautions that should be taken.
C. 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). 1.02 REFERENCES A. American Society for Testing and Materials (ASTM), www.astm.org
1.03 QUALITY ASSURANCE
A. Certificates: Prior to delivery, submit certificates attesting to compliance with applicable specifications for grades, types and classes.
B. Joint Raking: Prior to raking out all areas, cut back joints at location selected by 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 with masking tape and left unpointed until all other pointing is complete. Point when directed by the Contracting Officer.
C. Sample Stone Pointing: Repoint joints, using materials and methods specified at a location selected by the Contracting Officer. The samples accepted by the Contracting Officer will serve as a standard for the entire job. They will be marked with tape and left undisturbed. Pointing mortar should match historic in appearance, strength and composition.
1.04 PROJECT/SITE CONDITIONS
A. Environmental Requirements: No stone pointing or repair shall be performed when the air temperature or stone surface temperature is 40 degrees F, and falling during and for 48 hours subsequent to laying.
A. Mortar For Granite Pointing: Follow manufacturer's= printed recommendations for product use and installation. 1. Portland Cement:
1. ASTM C150, gray or white as required to match existing color.
2. Hydrated Masons Lime: ASTM C207, Type S.
3. Aggregate: ASTM C144; clean, sharp sand free of loam, silt soluble salts and vegetable matter. Aggregate shall conform to the following size gradations: Sieve Size Percent Passing No. 4 100 No. 8 100 No. 16 85 - 95 No. 30 40 - 60 No. 50 15 - 20 No. 100 1 - 5 4. Water: Clean and free of deleterious amounts of oil, acid, alkalis and organic matter.
A. Proportions for Granite Pointing: Mix/proportions for aggregate color and texture should closely match historic.
- Portland Cement: 1 part by volume.
- Lime: 1 party by volume.
- Aggregate: 3 parts by volume.
- Water: to form a workable consistency.
B. Mixing Procedures: (see also 04100-03-S for additional guidance)
- Measure materials by volume or equivalent weight.
- Do not measure by shovel. Use known measure.
- Mix ingredients in clean mechanical batcher for 3-5 minutes.
- Let mortar sit for 20 minutes prior to use to allow for initial shrinkage. Use mortar within 1=AB hours of initial mixing.
3.01 ERECTION, INSTALLATION, APPLICATION
A. Rake out all stone joints in designated areas by hand using a chisel no wider that 3/4 (three fourths) joint width. Remove all un required metal fasteners from granite and granite joints.
B. 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 stone. More than one chip per square yard will be unacceptable. 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.
C. Joint depth to be at least 3/4", but in all cases rake back to expose sound mortar.
D. Brush, vacuum or flush joints to remove all dirt and loose debris.
E. Reduce initial absorption of the stone by thoroughly wetting stone surface with clean water just prior to repointing. Do not allow water to pool on surface of the stone.
F. 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.
G. Use clean tools and equipment free from hardened or partially set mortar.
H. Clean excess mortar from stone and joints, removing splashed mortar and droppings immediately
I. Do not retemper or use mortar which has partially set, is caked, or is lumpy.
J. Tool horizontal and vertical face joints flush, dense and smooth after mortar has taken initial set. Do not allow mortar to extend over the stone surface.
K. 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 pointing of the stone, immediately remove mortar, grout and sealant 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 stone only with fiber bristle brushes and water. Use no acids, detergents, or other cleaning agents.