Section 620 — Stone Masonry

Description

620.01This work consists of constructing or rehabilitating stone masonry structures and the stone masonry portions of composite structures.

620.02Definitions.

(a)Dimensioned masonry. Stones are cut in two or more dimensions and laid in a broken-course pattern in mortar.

(b)Class A masonry. Stones are shaped, dressed to within ¼ inch of true line, and laid in mortar.

(c)Class B masonry. Stones are shaped, dressed to within ¾ inch of true line, and laid in mortar.

(d)Rubble masonry. Stones vary in size and shape, are roughly dressed, and laid in random courses in mortar.

Material

620.03Conform to the following Subsections: General mortar 701.05(a) Neat hydraulic cement grout 701.04(a) (2) Preformed expansion joint fillers 712.01(b) Reinforcing steel 709.01 Rock for masonry structures 705.03

Construction Requirements

620.04General. Submit stone samples for approval representing the range of colors and sizes to be used 14 days before starting work. When no dimensions are shown in the plans, provide the rocks in the sizes and face areas necessary to produce the general characteristics and appearance shown in the plans. Keep an adequate inventory of stone on the site to provide a variety of stones. Mix new stone with existing stone to produce a uniform pattern and color. Do not use rock with depressions or projections that might weaken it or prevent it from being properly bedded. Excavate and backfill according to Section 209. Construct minor concrete according to Section 601.

620.05Dressing Rock. Remove thin or weak portions of rock. Dress face rock bed and joint lines to a maximum variation from true line as shown in Table 620-1. Table 620-1

Maximum Variation from True Line

Class Distance

Dimensioned Reasonably true

Class A ¼ in Class B ¾ in Rubble 1½ in

(a)Bed surfaces. Dress face rock bed surfaces normal to the face to a depth of 3 inches. Beyond that point, do not exceed 1 inch departure from normal per 12 inches for dimensioned masonry or 2 inches departure from normal per 12 inches for other classes.

(b)Joint surfaces. For dimensioned masonry, dress face rock joint surfaces normal to the bed surface. For other cl asses of masonry, dress face rock joint surfaces to form an angle with the bed surface of at least 45 degrees. Dress face rock joint surfaces normal to the face to a depth of 2 inches. Beyond that point, do not exceed 1 inch departure from normal per 12 inches. Do not round corners at the meeting of the bed and joint lines more than the radii shown in Table 620-2. Table 620-2

Masonry Rock Rounding

Class Radius

Dimensioned No rounding

Class A No rounding

Class B 1 in maximum Rubble 1½ in maximum

(c)Arch ring rock joint surfaces. Dress ring rock joint surfaces radial to the arch or normal to the front face to a depth of 3 inches. Beyond that point, do not exceed ¾ inch departure from the radial or normal per 12 inches. Dress the back surface adjacent to the arch barrel concrete par allel to the front face and normal to the intrados to a depth of 6 inches. If concrete is placed after the masonry is constructed, vary adjacent ring stones at least 6 inches in depth.

(d)Finish for exposed faces. Remove drill or quarry marks from exposed fac es. Pitch face stones to the line along beds and joints. Finish the exposed faces as shown in the plans.

(1)Fine pointed. Make point depressions approximately ⅜ inch apart. Limit surface variations to no more than ⅛ inch from the pitch line.

(2)Medium pointed. Make point depressions approximately ⅝ inch apart. Limit surface variations to no more than ¼ inch from the pitch line.

(3)Coarse pointed. Make point depressions approximately 1⅛ inches apart. Limit surface variations to no more than ⅜ inch from the pitch line .

(4)Split or seam face. Provide a smooth appearance, without tool marks, depressions below the pitch line, or projections exceeding ¾ inch beyond the pitch line.

(5)Rock faced. Provide an irregular projecting surface without tool marks, concave surfaces below the pitch line, and projections beyond the specified pitch line. For example, the specification "1.50 R.F." means no projections 1½ inches beyond the pitch line. Where a variable rock face is specified, uniformly distribute stones of the same height of projection.

620.06Placing Stone. Do not place stone masonry when the ambient temperature is below 32 °F. Clean stones and moisten before placing. Use hand tools to clean the exposed faces of the stones of mortar if removing and resetting stone masonry. Clean and moisten the bed. Clean the bearing surface and moisten before spreading the mortar bed on footings. Level the cross beds for vertical walls. Lay beds for battered walls from level to normal to the batter line of the face of the wall. Place stone to pr ovide a consistent pattern and color. Lay stones with the longest face horizontal and the exposed face parallel to the masonry face. Construct masonry joints to the thicknesses shown in Table 620-3 for face stones. Construct arch ring stone joints on the faces and soffits between ¼ inch and 1½ inches thick, but make the bed of each course of a uniform thickness throughout. Construct head joints vertically in dimensioned masonry. Construct head joints in other masonry classes at ang les with the vertical from 0 to 45 degrees. Maintain completed masonry at a temperature above 40 °F for 24 hours after construction. Remove stones loosened after the mortar has taken initial set, clean off the mortar, and relay the stone with fresh mortar. Table 620-3

Masonry Joint Thicknesses

Class Bed Joint , inch Head Joints , inch Dimensioned ⅜ to 1 ¾ to 1 Class A ½ to 2 ½ to 1½ Class B ½ to 2 ½ to 2 Rubble ½ to 2½ ½ to 2½

620.07Pointing.

(a)Pointing new joints. Crown the joint mortar slightly on top surfaces to provide drainage. If raked joints are required, squarely rake mortar in exposed face joints and beds to the required depth. Slightly rake the mortar where weather joints are required. Do not leave the mortar flush with the stone faces. Clean stone faces of mortar stains while the mortar is fresh. After the mortar sets, clean stone faces again using wire brushes and acid. Protect masonry during hot or dry weather by keeping it moist for at least 3 days after the work is completed.

(b)Repointing joints. Remove loose mortar from joints using a small mason’s chisel, small pneumatically- power chisel, or other approved raking tool. Do not use power saws or grinders. I f power equipment is used, demonstrate proficiency to the CO before removing mortar from the structure. Remove mortar to a depth of two and one -half times the width of the joint. Remove dirt or vegetation with a wire brush or other approved tools. Clean joint of loose fragments and dust with pressurized air or water. Construct a 36- inch te st section of joint along the structure for approval before continuing with work. Approved test section may be incorporated in the work. Moisten adjacent stone before filling the joint. Do not place mortar to a depth greater than two and one -half times the joint width. Place mortar in layers of approximately ¼ inch for joints deeper than ⅛ inch. Add successive layers once mortar has attain ed thumb -print hardness. Tool the final layer to match the approved joint appearance. Clean excess mortar and stain from stone masonry using a bristle brush after the mortar has dried, but before the initial set. Do not use chemicals for cleaning. Protect masonry during hot or dry weather by keeping it moist for at least 3 days after the work is completed.

620.08Constructing Walls. Construct an L -shaped test section of wall at least 5 feet high and 8 feet long; showing examples of face wall, top wall, method of turning corners, and method of forming joints. Do not construct masonry other than the foundation masonry before the test section is approved. Set face stones to produce the effect demonstrated in the approved test section. Do not extend bed joints in an unbroken line through more than five stones and head joints through more than two stones. Bond each face stone with contiguous face stones at least 6 inches longitudinally and 2 inches vertically. Do not allow the corners of four stones to be adjacent to each other. Do not bunch small stones or stones of the same size, color, or texture. Construct walls using stones decreasing in size from the bottom to the top. Use large stones in corners.

(a)Headers. Distribute headers uniformly throughout the walls of structures to form at least 20 percent of the faces.

(b)Backing. Construct the backing out of large stones. Bond the individual stones composing the backing and heart with the stones in the face wall and with each other. Fill openings and interstices in the backing with mortar or with spalls surrounded by mortar.

(c)Coping. Finish with coping if shown in the plans. If copings are not required, finish the top of the wall with stones wide enough to cover the top of the wall from 1.5 to 5 feet in length, and of random heights, with a minimum height of 6 inches. Lay stones so that the cap course is an integral part of the wall. Pitch the top of the capstones to align in both vertical and horizontal planes. (d) Parapet walls. Use stones squared and pitched to line and with heads dressed in the ends of parapet walls and in exposed a ngles and corners. Interlock spreaders with as many headers as possible. Extend headers through the entire wall thickness. Interlock both the headers and stretchers in the two faces of the wall. Use headers and stretchers to comprise a majority of the wall volume. Fill openings and interstices with mortar or with spalls surrounded by mortar.

(e)Weep holes. Place weep holes at the lowest points where free outlets can be obtained. Space holes no more than 10 feet apart.

620.09Facing for Concrete.

(a)Stone placed before concrete. Make the back of the masonry uneven. Pack voids in the back of the masonry with grout. Use No. 4 reinforcing steel bent into an elongated letter " S" to anchor the stone. Embed each anchor in a mortar bed to within 2 inches from the face of the stones. Project the other end about 10 inches into the concrete backing. Space the anchors 18 inches apart both horizontally and vertically. Clean the back masonry surface of dirt, loose material, and mortar drippings after the mortar has attained suff icient strength. Wash surfaces with pressurized water before placing concrete.

(b)Concrete placed before stone. Set galvanized metal anchor slots flush with the projected face of concrete. Set the slots vertically at maximum horizontal spacings of 24 inches. Use foam filled slots to prevent filling with concrete. Fit the metal anchors in the slots at a maximum vertical spacing of 24 inches. Extend the anchors to within 2 inches of the face of the stones. If the shape of the concrete face is unsuitable for the use of metal slots, use 9-gauge galvanized iron wire ties at a rate of 6 ties per square yard of exposed surface. Keep the concrete face continuously wet for 2 hours preceding the placing of the stone and fill interstices with mortar or with spalls surroun ded by mortar.

620.10Constructing Arches. Submit drawings for falsework according to Section 562. Stratify arch ring stones parallel to the radial joint and stratify other stones parallel to the beds. Lay out a full -size template of the arch ring showing face dimensions of each ring stone and thickness of joints. Do not shape or dress ring stones until falsework drawings have been approved. Do not place ring stones until all ring stones have been shaped and dressed. Construct arch centering according to the drawings. Provide suitable wedges for adjusting the elevation of the forms. Set arch ring stones and hold in place with wedges until the joints are packed with mortar. If required, support centering with jacks to prevent settlement during masonry placement. Lower the centering gradually and symmetrically to avoid overstresses in the arch. Ensure the arch is self -supporting before installing coping or other features. Strike the centers of filled spandrel arches before constructing the spandrel walls to avoid jamming of the expansion joints. Place the backfill so the ring is uniformly and symmetrically loaded.

620.11Guardwall. Use rubble masonry. Construct cast -in-place concrete corewalls according to Section 601 and precast concrete corewalls according to Section 578. Construct a 25- foot test section of guardwall. Do not construct additional guardwall until the test section is approved. Construct the guardwall true and uniform along its length with no stone projecting more than 1½ inches beyond the face of the guardwall. Construct masonry beds and joints for face stones to the thicknesses shown in Table 620-1. Rake the joints and beds to a depth of 2 inches on the front and top sides and to a depth of 1½ inches on the back. Use a one- piece capstone for the full width of the guardwall for at least 25 percent of the total length. Use a two -piece capstone with the joint within 4 inches of the guardwall center for the remaining length. Place stones (including the capstones) randomly to avoid a pattern. Lay stones to reflect the width of the expansion joints. Do not leave a gap or a mortar edge at the expansion joint . Use various size stones to coin or key the corners of the guardwall.

620.12Acceptance. Rock for masonry structures will be evaluated under Subsections 106.02 and 106.04. Material for mortar will be evaluated under Subsections 106.02 and 106.03. Mortar placement will be evaluated under Subsection 106.02 . Construction or rehabilitation of sto ne masonry will be evaluated under Subsections 106.02 and 106.04. Excavation and backfill will be evaluated under Section 209. Minor concrete will be evaluated under Section 601. Precast elements will be evaluated under Section 578.

Measurement

620.13Measure the Section 620 pay items listed in the bid schedule according to Subsection 109.02 and the following as applicable: When measuring stone masonry by the cubic yard, measure in the structure. When measuring stone masonry guardwall by the l inear foot, measure along the gutter line including terminal sections. When measuring remove and reset stone masonry by the cubic yard, measure in the structure after resetting. When measuring repointing of stone masonry by the linear foot, measure along the centerline of joint. Do not measure test wall sections not incorporated in the work.

Payment

620.14The accepted quantities will be paid at the contract price per unit of measurement for the Section 620 pay items listed in the bid schedule. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05 . Progress p ayments for lump sum pay items will be prorated based on total work completed under this Section.