Resetting Limestone

Procedure code:
446013S
Source:
National Capitol Region Specifications
Division:
Masonry
Section:
Limestone
Last Modified:
03/03/2017

RESETTING LIMESTONE

 

 

PART 1---GENERAL

1.01 SUMMARY

 

A. This procedure includes guidance on removing displaced

   limestone panels, repairing the substrate and re-

   installing the panels.

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. Certifications: Prior to delivery, submit certificates

   attesting 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 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.

C. Sample Stone Pointing and Repair: Repoint joints, re-

   attach stone fragments and patch stone using materials

   and methods specified at a location selected by the

   Contracting Officer. The samples accepted by the

   Contracting Officer will serve as standard for the entire

   job. They will be marked and left undisturbed.

 

1.03 PROJECT/SITE CONDITIONS

 

A. Environmental Requirements: No stonework will be

   performed when the air temperature is 40 F or below

   during and for 48 hours subsequent to the work.

 

PART 2---PRODUCTS

2.01 MATERIALS

 

A. Stone: To match existing in grade, color and finish.

B. Lime: Should conform to ASTM C207, Type S, high

   plasticity, Hydrated Lime for Masonry Purposes.

   1. Lime which meets this standard will "work" well,

       resists drying during curing, and is sufficiently

       strong for the purpose of repointing.

   2. Lime expands as it hydrates, making high lime

       mortars more resistant to crack formation.

C. Cement: Should conform to ASTM C150, Type I, White. It

should not have more than 0.60% alkali nor more than

0.15% water soluble alkali. Use gray portland cement

ONLY if a dark mortar is to be matched.

   1. Cement meeting this standard should increase the

   workability of the mortar, accelerate the setting

   time and slightly increase the strength of the

   mortar.

   2. The low alkali content will prevent efflorescence.

D. Sand: Free of impurities and conforming to ASTM C144.

   1. Sand color, size, and texture should match the

       original as closely as possible. Provide a sample

of the sand for comparison to the original, and

       have it approved by the RHPO before beginning

       repointing work.

   2. When possible, use bar sand or beach sand rather

       than crushed sand for the repointing mortar.

       NOTE: BAR SAND OR BEACH SAND SHOULD BE WASHED TO

       REMOVE THE SALTS BEFORE USING.

       a. Crushed sand has sharp edges, which makes it

           more "sticky" and difficult to work into the

           joints.

       b. Bar sand, on the other hand, has rounded edges

           and flows easily during the mortar

           application.

       c. The working characteristics of mortar made

           with crushed sand may be improved by adding a

           slight amount of portland cement. The amount

           of cement should be determined by

           experimentation, but should not exceed 20% of

           the total lime/cement binder. 20% OR LESS OF

CEMENT HAS MINIMAL EFFECT ON THE HARDNESS OF

THE MORTAR. CEMENT CONTENT ABOVE 20% WILL

MAKE THE MORTAR TOO HARD.

 

E. Clean, potable water: If the water must be transported

   or stored in a container, the container must not impart

   any chemicals to the water.

F. Stone dust finely ground from the same stone as that to

   be repointed.

G. Additives: NO antifreeze compounds or other admixture

   shall be used.

 

NOTE: DO NOT USE ANTI-FREEZE COMPOUNDS. THESE COMPOUNDS

ARE DESIGNED FOR USE WITH CEMENT MORTARS, AND THEIR

EFFECTIVENESS WITH HIGH LIME MORTARS IS QUESTIONABLE.

FURTHERMORE, THE COMPOUNDS CONTAIN SALTS WHICH CAN LEAD

TO SERIOUS PROBLEMS IN THE MASONRY AT A LATER TIME.

 

NOTE: AIR ENTRAINING AGENTS ARE NOT RECOMMENDED. THESE

AGENTS ARE DESIGNED FOR USE WITH CEMENT RATHER THAN LIME,

AND THEY RESULT IN DECREASED BONDING OF THE MORTAR AND

THE MASONRY. AIR ENTRAINING IS NOT NECESSARY WITH HIGH

LIME MORTARS BECAUSE OF THE NATURAL ABILITY OF THESE

MORTARS TO FLEX WITH TEMPERATURE CHANGES.

H. Epoxy grout

I. Reinforcement/Anchors: Stainless steel type 302/304 3/8"

   in diameter threaded rods, length as required.

 

2.02 EQUIPMENT

 

A. Natural fiber or nylon bristle brushes

B. Wire bristle brush for cleaning anchors

C. Mixing Vessels

D. Joint tools

E. Chisel

F. Hammer

G. Hawk (plywood or steel mortar board)

H. Trowel

I. Hoe

J. Mesh screen

K. Putty knife

L. Wooden mortar boxes

 

2.03 MIXES

 

A. Some factors to consider when mixing lime mortar include

   durability, color and texture, and workability.

   1. Durability: Repointing and resetting mortar should

       be softer than the masonry units and the original

       mortar to reduce stresses at the edge of the

       masonry and, in the case of lime mortar, to reduce

shrinkage which can cause cracks in the mortar.

       a. If the new mortar is harder than the masonry

           or the original mortar, it can cause serious

           stresses within the wall during thermal

           expansion and contraction, which can lead to

           deterioration of the masonry units rather than

           the mortar.

       b. If the mortar is softer, any deterioration

           which occurs will take place in the mortar,

           which is easier to replace than the units

           themselves.

   2. The repointing and resetting mortar should allow

       the passage of water, both liquid and vapor. If

       the mortar does not allow water to pass freely

       through it, the water can become trapped inside the

       wall, freeze and cause serious deterioration to the

       masonry.

   3. Color and texture: The repointing mortar should

       match the original mortar in color, texture and

       physical characteristics.

A. Obtaining an accurate color match is best

   achieved by selecting an appropriate sand.

   1. Use sand which is similar to the original

       in color and gradation. Sand from more

       than one source may be required.

   2. For repointing of natural stones, use

   finely ground stone "dust" in the mortar

   to match the joints as closely as

   possible to the stone.

 

B. If the original mortar was tinted, or if it is

   impossible to obtain a color match through the

   use of sand, it may be necessary to use a

   special mortar pigment.

 

CAUTION: PIGMENTS MAY REACT WITH OTHER

INGREDIENTS IN THE MORTAR TO FORM

EFFLORESCENCE. THEY MAY ALSO WEATHER AT A

DIFFERENT RATE THAN NATURAL COLORING AND CAUSE

A COLOR VARIATION IN THE MORTAR.

 

NOTE: IF PIGMENTS MUST BE USED, PURE MINERAL

OXIDES SHOULD BE USED BECAUSE THEY DO NOT FADE

OR LEACH OUT OF THE MORTAR. AMOUNT OF PIGMENT

SHOULD NOT EXCEED 2% OF THE MORTAR MIX BY

WEIGHT.

 

C. Many mortars used before the twentieth century

   have small lumps of incompletely burned or

   ground lime, or other impurities. To match

   the original appearance of the masonry, these

   impurities must be included in the new

   repointing mortar. Use identical materials

   such as ground oyster shells (obtained at feed

   stores) or lumps of lime, to duplicate

   original lumps.

   4. Workability: The workability or plasticity of the

       mortar is a direct result of the selection of

       materials.

B. Mortar Mix:

   1. Have the existing mortar completely analyzed to

       insure that the repointing mortar will not be less

       permeable/harder than the masonry units or the

       original mortar. IT IS BETTER TO HAVE MORTAR THAT

       IS MORE PERMEABLE THAN LESS.

   2. Measure all ingredients by cubic volume using a

       pre-established uniform measure, such as a small

       bucket, rather than a less uniform measure such as

       a shovel.

   3. For historic masonry set in lime mortar, use the

       following mortar mix:

       1 part portland cement

       3 parts lime

       8-12 parts sand (To match existing mortar as

       closely as possible.)

 

NOTE: The exact mix required will relate to the

grain size and sharpness of the sand and will vary

depending on the supply.

 

-OR-

 

For historic masonry set in standard mortar, use

the following mortar mix (ASTM C270 Type "0") as a

starting point:

 

       1 part portland cement

       2 parts lime or lime putty

       6 to 9 parts sand and stone dust (To match existing

       mortar as closely as possible.)

 

-OR-

 

For Limestone (ASTM C270 Type "N"):

 

       1 part portland cement

       1 parts lime

       4-6 parts aggregate

       Enough water to form a workable consistency

 

   4. Mix a final "job-size" batch once the correct sand

       color, cement content, etc. have been determined

       through small tests to ensure the on-site mixing

       conditions will result in the same final product.

PART 3---EXECUTION

3.01 ERECTION, INSTALLATION, APPLICATION

 

A. Carefully remove shifted and loose stone panels. Clean

   of dirt, mortar, and loose debris. Retain for re-use.

   Re-build support masonry and lay new bedding material.

B. Clean any exposed metal anchors of all corrosion by

   scraping and brushing with stiff wire brushes. Replace

   any unsound anchors as necessary with new stainless steel

   anchors of same approximate size and shape. Bed new

   anchors in epoxy grout.

C. Re-set limestone, maximum tolerances from plumb and level

   of new work not to exceed variation from plumb and level

   of adjacent existing work.

D. Wet masonry and lay in full bed of mortar. See 04100-03-

   S for mortar mixing procedures. Construct uniform

   joints. Shove vertical joints tight. Adjust stone units

   to final position while mortar is soft and plastic. Set

   stone with joints tooled back one inch. Point remaining

   depth as the rest of the stone is pointed. For pointing

   procedures, see 04520-02-R.

E. Keep mortar and stone damp (80-90% RH) for 72 hours or

   until mortar is cured.

 

3.02 ADJUSTING/CLEANING

A. Immediately after repairing, patching, pointing and re-

   setting the stone, 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. After all work is complete, clean stone only with fiber

   bristle brushes and water. Use no acids, detergents, or

   other cleaning agents.

END OF SECTION

 

Last Reviewed 2017-03-03