Repointing Marble

Procedure code:
445520S
Source:
National Capitol Region Specifications
Division:
Masonry
Section:
Marble
Last Modified:
03/03/2017

REPOINTING MARBLE

PART 1---GENERAL

1.01 SUMMARY

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:

1. Safety Precautions

2. Historic Structures Precautions

3. Submittals

4. Quality Assurance

5. Delivery, Storage and Handling

6. Project/Site Conditions

7. Sequencing and Scheduling

8. 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. 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.

PART 2---PRODUCTS

2.01 MATERIALS

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.

1. 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.

2.03 EQUIPMENT

A. Chisels

B. Joint tools

C. Hawks

D. Stiff fiber bristle brushes

E. Trowels

F. Rubber mallet

2.04 MIXES

A. Proportions for Marble Pointing, or as determined by

mortar analysis:

1. Portland cement: 1 part by volume

2. Lime: 2 parts by volume

3. Aggregate: 9 parts by volume

4. Water: To form a workable consistency

B Mixing Procedures:

1. Measure materials by volume or equivalent height.

2. Do not measure by shovel. Use known measure.

3. Mix ingredients in clean mechanical batch mixer for 3-5 minutes.

4. Let mortar sit for 20 minutes prior to use to allow

for initial shrinkage. Use mortar within 1 hour

of initial mixing.

PART 3---EXECUTION

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).

3.02 ADJUSTING/CLEANING

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.

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