How to prepare the application surface
Your preparation will vary depending on the installation surface. Consult the appropriate surface prep below:
Plywood, Paneling, Wallboard, Rigid Insulation Board, Sheetrock and other Rigid Wood Related Sheathing.
Apply a weather-resistant barrier horizontally, with the upper layer lapping no less than 2 inches over the lower layer. The lap should be no less than 6 inches over vertical joints.
Figure A: Over Sheathing
- Install 2.5-lb. diamond mesh expanded metal lath. Use galvanized for exteriors, non-galvanized for interiors.
- Overlap lath sides no less than 3/8 of an inch.
- Overlap lath ends by no less than 1 inch.
- Nail or staple the lath 6 inches on center vertically and 16 inches on center horizontally, penetrating the studs a minimum of 1 inch with galvanized nails or staples.
Figure B: Rigid Insulation
- Double wrap the metal lath a minimum of 16 inches around all inside and outside corners.
- Apply a 1/2-inch thick mortar scratch coat and let set.
Metal Panels
Same as above except the metal lath should be attached with self-tapping screws that have a 3/8-inch head and that penetrate no less than 3/8 of an inch beyond the metal thickness.
Open Wood Studs
- Attach paper-backed, galvanized 3.4-lb., 3/8-inch rib-expanded metal lath using galvanized nails or staples that penetrate a minimum of 1 inch every 6 inches vertically on stud centers.
- Overlap the lath sides by no less than 1/2 of an inch.
- Overlap the lath ends by no less than 1 inch.
- Apply a half-inch thick mortar scratch coat and let set at least 48 hours.
Open Metal Studs
Same as wood studs, except use corrosion-resistant self-tapping screws with 3/8-inch heads that penetrate no less than 3/8 of an inch beyond the metal thickness.
Figure C: Open Stud Frame
Painted, Sealed or Treated Masonry Surfaces
A block or brick surface must be porous for mortar to bond to it. You can achieve this in one of two ways:
- Remove the paint or other treated coating by wire brushing, acid etching, sandblasting, or water blasting it.
- Attach metal lath with corrosion-resistant concrete nails and apply a half-inch thick mortar scratch coat and let it set.
Figure D: CMU Wall
Clean Masonry Surfaces
No preparation is necessary—the surface is ready for stone application.
How to prepare the mortar
There are several mortar preparations. The one use depends on whether the application is interior or exterior, joint-grouted or dry-stacked
Grouted-Joint Mortar Mixes
Several mixes will work for this application. Here are 4:
2 parts Type N masonry cement
3 to 5 parts masonry sand
Water to workable consistency
Or
1 part Portland cement
1 part lime
3 to 5 parts masonry sand
Water to workable consistency
Or
3 parts Type S masonry cement
5 to 7 parts masonry sand
Water to workable consistency
Or
2 parts Portland cement
1 part lime
5 to 7 parts masonry sand
Water to workable consistency
Dry-stack Mortar Mixes
Blend mortar with the stone base color for a seamless appearance. Several mixes will work for this application. Here are 3:
3 parts Portland cement
2 parts thin-set mortar
(for exterior applications use only latex modified
thin-set meeting ANSI-A118.4)
7 parts masonry sand
Water to workable consistency
Or
2 parts Portland cement
1 part lime
7 parts masonry sand
Bonding agent pre-blended 1 to 1 with water
Or
3 parts Type S masonry cement
7 parts masonry sand
Bonding agent pre-blended 1 to 1 with water
How to apply the stone.
General Preparations and Considerations
- Apply the corners first, alternating the long and short returns.
- Be sure to keep the work level as you go. Snap a chalk line every 4 to 6 inches, and use a level to check stones as you apply them.
- Use a trowel edge, nippers or other sharp, blunt tool to trim stones. For straight cuts, use a diamond or carbide saw blade.
- Conceal trimmed edges with grouting, or hide them by turning the cut side upward above eye level or downward below eye level.
- Avoid long sections of straight, unbroken grout lines in standard grout installations. Be sure to use a consistent joint width. A half-inch thickness or less is standard.
- When installing in a dry, hot climate or onto extremely dry surfaces, be sure to wet the stone and the wall first so they do not absorb moisture from the mortar. You can spray or otherwise apply water onto the back of the stone or dip it into water. Spray or brush water onto the wall as well. Allow both to dry a few minutes to remove excess water.
- If any mortar accidentally falls on the face of a stone during installation, do not wipe it off. It will smear and discolor the stone. Instead, let it set completely, then brush it away with a dry whisk broom.
- Avoid water runoff onto your installation. Divert water away with flashing, cant strips and/or gutters.
- Do not install below water level, and do not expose stone to chemicals that will stain it.
- Do not use wire brushes or acid on the stone surface.
- Do not use wet brushes or sponges to wipe mortar grouts. They will cause the mortar to smear and stain.
- Local building codes vary. Be sure to check the requirements in your area.
- Lay out the stone near your work area. As you install, choose stones that vary in color, shape and size.
- Apply stone from the top down.
- Apply a half-inch layer of mortar to the entire back of the stone.
- Press the stone into place with a gentle back-and-forth motion until the mortar squeezes out around the edges.
Standard Grout Installation
- Apply all stones to the wall, then use a grout bag to fill in the joints with mortar.
- Mortar joints take 30 to 60 minutes to firm up. When they do, use a striking tool to scrape or rake out the excess mortar at a consistent depth while smearing it along the joint seams for a good seal.
- Smooth the joints and clear loose mortar with a whisk broom. Loose mortar will clean away easily if it has set for a few hours, but not if it has set up overnight.
Dry-stack Installation
- Dry-stack stones must always be moistened before installation, as described in General Preparations and considerations above.
- Lay out the stone near your work area. As you install, choose stones that vary in color, shape and size.
- Apply stone from the bottom up.
- Use a grout bag to apply a thin bead of mortar to the edges of all adjacent stones before setting a new stone.
- Apply a generous amount of mortar around the full back edge of the stone, leaving the back center clear.
- Press the stone into place until you feel the suction pull created by the mortar vacuum on the back of the stone.
- Remove any excess mortar around the edges and pack it into gaps along the stone’s edges.
- Once you finish applying all stones, touch up the grouting as necessary to hide cuts or fill voids.
|