Section_04_20_01_Masonry_Repointing.doc

SECTION 04 20 01

MASONRY REPOINTING (NON-HISTORIC STRUCTURES)

02/11

PART 1 GENERAL

1.1 REFERENCES

The publications listed below form a part of this specification to the extent referenced. The publications are referred to within the text by the basic designation only.

ASTM INTERNATIONAL (ASTM)

· ASTM C 73 (2010) Calcium Silicate Brick (Sand-Lime Brick)

· ASTM C 91 (2012) Standard Specification for Masonry Cement

· ASTM C 94/C 94M (2012) Standard Specification for Ready-Mixed Concrete

· ASTM C 144 (2011) Standard Specification for Aggregate for Masonry Mortar

· ASTM C 150 (2011) Standard Specification for Portland Cement

· ASTM C 476 (2010) Standard Specification for Grout for Masonry

· ASTM C 593 (2006; R 2011) Fly Ash and Other Pozzolans for Use with Lime for Soil Stabilization

· ASTM C 780 (2011) Preconstruction and Construction Evaluation of Mortars for Plain and Reinforced Unit Masonry

· ASTM C 1019 (2011) Standard Test Method for Sampling and Testing Grout

1.2 SUBMITTALS

Submit the following in accordance with Section 01 33 00 SUBMITTAL PROCEDURES:

SD-03 Product Data

Mortar Mix & Color(s)

Masonry Cement

Water-Repellant Admixture

SD-07 Certificates

Installer qualifications

Mason qualifications

1.4 QUALITY ASSURANCE

1.4.1 Installer

Work must be performed by a firm having not less than 5 years successful experience in comparable masonry restoration projects and employing personnel skilled in the restoration process and operations indicated.

1.4.2 Masons

Only skilled journeymen masons who are familiar and experienced with the materials and methods specified and are familiar with the design requirements shall be used for masonry restoration.

1.5 DELIVERY, STORAGE, AND HANDLING

1.5.1 Cementitious Materials, Sand and Aggregates

Cementitious and other packaged materials shall be delivered in unopened containers, plainly marked and labeled with manufacturers' names and brands. Cementitious material shall be stored in dry, weathertight enclosures or be completely covered. Cement shall be handled in a manner that will prevent the inclusion of foreign materials and damage by water or dampness. Store sand and aggregates in a manner to prevent contamination or segregation.

PART 2 PRODUCTS

2.1 GENERAL REQUIREMENTS

The source of materials which will affect the appearance of the finished work shall not be changed after the work has started except with Contracting Officer's approval. Submit certificates of compliance stating that the materials meet the specified requirements.

2.2 CONCRETE MASONRY UNITS (CMU)

Failed or masory units damaged during work shall be replaced in kind and grouted in place.

2.3 MORTAR

ASTM C 270, Type S with min f'm of 1,800 psi at 28 days. Type N with min f'm of 750 psi at 28 days may be used for parapets. Use type M with min f'm of 2,500 psi at 28 days where in contact with earth or where structural loads are present. Test in accordance with ASTM C 780. Use ASTM C 150 Type I or II Portland Cement or Masonry Cement. Do not use admixtures containing chlorides. Use up to 40 percent Class F fly ash with type IP cement in cement-lime mortar. Fly ash shall comply with ASTM C 593.

2.3.1 Colored Mortar

Mortar coloring shall be added to the mortar used for exposed masonry surfaces to produce a uniform color matching the adjacent masonry units. Mortar coloring shall be chemically inert, of finely ground limeproof pigment, and furnished in accurately pre-measured and packaged units that can be added to a measured amount of cement.

2.3.2 Sand and Water

Sand shall conform to ASTM C 144. Water shall be clean, potable, and free from substances which could adversely affect the mortar.

2.4 WATER-REPELLANT ADMIXTURE

Use on single-wythe walls or where indicated. Polymeric type formulated to reduce porosity and water penetration and water absorption of the mortar and masonry units.

2.5 GROUT AND READY-MIXED GROUT

Grout shall conform to ASTM C 476. Cement used in grout shall have a low alkali content. Grout slump shall be between 8 and 11 inches. Minimum grout strength shall be 2000 psi in 28 days, as tested by ASTM C 1019. Do not change proportions and do not use materials with different physical or chemical characteristics in grout for the work unless additional evidence is furnished that the grout meets the specified requirements. Ready-Mixed grout shall conform to ASTM C 94.

2.12.2 Grout Barriers

Grout barriers for vertical cores shall consist of fine mesh wire, fiberglass, or expanded metal.

2.18 EXPANSION-JOINT MATERIALS

Backer rod and sealant shall be adequate to accommodate joint compression equal to 50 percent of the width of the joint. The backer rod shall be compressible rod stock of polyethylene foam, polyurethane foam, butyl rubber foam, or other flexible, nonabsorptive material as recommended by the sealant manufacturer. Sealant shall conform to Section 07 92 00 JOINT SEALANTS. Submit one piece of each type of material used.

PART 3 EXECUTION

3.1 EXAMINATION AND IDENTIFICATION OF JOINTS TO BE REPOINTED

Examine conditions, bonding pattern, levels and lateral reinforcement locations. Identify and projected problem areas to the Contracting Officer before initiating work.

Joints to be repointed include: (1) mortar erosion to a depth more than ½ inch, (2) crumbling mortar, (3) cracks between the block and mortar and (4) missing mortar. Visual observation in combination with light scraping with a metal tool can detect cracked, spalled and crumbly mortar joints.

3.2 PREPARATION

3.2.1 Protection

Prevent repointing mortar from staining the face of masonry or other surfaces to be left exposed. Remove repointing mortar that comes in contact with such surfaces. Protect sills, ledges and projections from droppings. Cover partially completed work when work is not in progress.

3.2.2 Temporary Support and Staging

Provide temporary support where necessary to prevent displacement of masonry units during repointing and until mortar has achieved sufficient strength.

Where required to maintain support of units, rake out and repoint each unit in stages, allowing freshly repointed portions to cure sufficiently before raking out and repointing remaining portion of joints supporting the unit.

Remove temporary shims and supports when no longer necessary, and repoint voids left by temporary shims and supports.

3.2.3 Removing Anchors

Remove any exposed or unused anchors, nails, pins, and similar devices and point hole with mortar.

3.2.4 Removing Joint Sealant from Joints

Cut out failing joint sealant with a caulking cutter (Fein tool) assisted by hand tools and trim or lightly grind joint sealant from joint faces. Vigorously scrub joint faces with a stiff brush to remove embedded dust and debris from joint faces, followed by vacuuming, working from top to bottom of wall.

Remove existing underlying mortar to the depth specified prior to repointing.

3.2.5 Removing Existing Mortar

All joints with failing mortar shall be raked back to sound, solid, back up material. Raking out shall leave a clean, square face at the back of the joint to provide for maximum contact of pointing mortar with the masonry back up mortar. Shallow or feather edging will not be permitted.

Do not widen the existing masonry joints. Do not spall or chip the surrounding masonry edges in the process of mortar removal. Damage to surrounding brick or stone resulting from rotary blade over running shall not be permitted. Contractor shall replace brick or stone damaged during mortar removal with replacement units that match the original as determined by the Architect.

Brush joint faces and vacuum debris from joint to remove dirt and loose debris, working from top to bottom of wall.

3.2.6 Mortar Removal Depth

Existing mortar joints shall be raked out to whichever depth is greatest:

· 5/8 inch.

· 2-1/2 times the width of the existing mortar joint.

· Until bonded, cohesive existing lime mortar is encountered.

3.2.7 Prewetting

Brush joint faces and flush out joints with water to remove dirt and loose debris, working from top to bottom of wall. Rinse stone joints with water to remove dust and mortar particles. Thoroughly wet wall below to avoid soiling. Joint surfaces should be damp but free from standing water.

Prior wetting is necessary to achieve the proper absorption rate before masonry repair commences and is essential to good masonry practice. Presoak walls and joints with water as required by project and weather conditions. During hot or windy weather, wet walls and joints several times in advance of pointing. Re-wet walls and joints yet to be pointed if masonry dries out before pointing. Masonry units shall be damp but without standing water at the time of pointing.

Maintain hand mister bottles or a garden sprayer with clean, clear, potable water immediately available to masons at all times during the repointing process. A very low pressure spray (garden hose with nozzle adjusted to a fine, low-volume mist) may be used over large areas providing erosion of joints is prevented.

Exposed surface of masonry adjacent to joint shall be wet prior to repointing.

3.3 REPOINTING

Where joints are greater than 3/4 inches deep, joints shall be pointed in layers or "lifts" leaving the last lift to a uniform joint depth of 3/4 inches deep. Compact each layer at the time it is placed in the joint by applying firm pressure with the pointing tool. Allow each lift to become thumbprint hard before applying the next lift. Joints shall be tooled until the mortar is thumbprint hard. Horizontal joints shall be tooled last.

Tool joints in exposed exterior and interior masonry surfaces to be slightly concave. Joints shall be tooled with a jointer slightly larger than the joint width so that complete contact is made along the edges of the unit. Provide mortar and tooled joints between flutes of fluted masonry units (cover full profile). Tooling shall be performed so that the mortar is compressed and the joint surface is sealed.

Finish joints uniformly. Do not overwork. Leave the surface of the masonry clean.

3.4 CLEANING

Maintain clean surfaces on the face, sills, ledges, and projections of masonry on a daily basis. With a trowel, strike off minor dabs of adherent mortar from face of masonry. Masonry surfaces shall not be further cleaned until mortar in joints has hardened.

Remove minor mortar marks from masonry by misting with water and brushing with a small, stiff-bristle brush or high-pressure stream as required. Metal tools and metal brushes shall not be used for cleaning.

Masonry surfaces shall be left clean, free of mortar daubs, dirt, stain, and discoloration, including scum from cleaning operations, and with tight mortar joints throughout.

3.5 CURING

Keep mortar from drying out too quickly. Mist walls with water as required by project and weather conditions to insure slow curing of the lime mortar. Shield from direct sun and drying winds for the first 48 hours after installation using plastic tarps and tie downs.