Refacing Ugly Chimneys
Lightweight concrete "stone" upgrade
By:
Sam Crowley, Club Member
Online Rating:
   (8.5/10) Between the main house and the outbuilding that doubles as my office and woodworking shop, my home has three prominent concrete-block chimneys. Failed masonry finishes made them huge eyesores, but rather than refinish them, my wife and I upgraded the look with lightweight concrete "stone." Now the chimneys are architectural gems that suit our home's country setting beautifully and add tangibly to the property value and curb appeal. Veneer stone is made from concrete that weighs about 50 percent less than a natural stone. This makes it much easier to handle than real stone and does not require an additional structural footing that extends below the frost line. Veneer stone is molded and colored in a variety of styles that look like stone. For use indoors or out, it covers wood or masonry and is great for fireplaces, feature walls and chimneys. Giant jigsaw puzzle
We hired Dutchcraft Stone, a contractor/remodeler, to veneer the chimneys with Cultured Stone from Owens Corning. If we were doing just one chimney rather than three, I probably would have tackled the project. But with so much scaffolding to erect and surface to cover, this definitely was a project for a hardy crew. We selected the type of stone, estimated materials and priced the work. The Cultured Stone Web site explained that there are two types of components, flats and corner, L-shaped stones that wrap around outside corners. You calculate L-shaped stones based on linear feet of corners to cover. You calculate flats based on surface area minus 3/4 sf for each foot of linear corner stones. The manufacturer also recommends ordering some additional stone to ensure that you don't run out. After all, this is a giant jigsaw puzzle. While you can break or chip stones to make them fit, you don't want to get to the end of the job with 10 stones whose colors, sizes or shapes don't go together. Lath, mortar and stone cost about $5 per square foot, and labor was about $8.50 per square foot. Prices vary from region to region. Surface prep
Proper surface preparation is essential to ensure that installed stones remain secure. If veneer stone is installed over non-masonry surface, first put down a weather-resistant barrier to prevent moisture infiltration. You can use Kraft waterproof building paper or asphalt-saturated roofing felt (consult your local building inspector for specifics). For our project, stone was applied over concrete block, so a weather barrier wasn't required. The next step: Install expanded metal (diamond mesh) lath. You can use rush-inhibitive black lath on interior applications, but for exterior projects you must use 2 1/2-pound galvanized lath or 18-gauge galvanized woven wire mesh with galvanized nails or staples. The crew used galvanized masonry nails at 6-in. intervals to fasten the lath to my block-construction chimneys. Install the lath so it feels rough when you move your hand up the surface and smooth when you move your hand down. Overlap the joints by about 2 in. to create a fully integrated subsurface and to avoid cracks. The primary purpose of the lath is to create a uniform thickness of a reinforced network that holds the base coat of mortar. Screeding or troweling the mortar flush with the surface of the lath achieves the goal of creating a scratch coat. Ideally, you should spray the scratch-coat mortar with water before installing the stones. This prevents moisture from being wicked away and weakening the bond. Apply setting bed mortar to the scratch coat and butter the backs of the stones with additional mortar before pressing them into place. For the average do-it-yourselfer working alone, apply mortar to about a 5x5-ft. section of lath at a time. My experienced crew worked fast, using rectangular plasterer trowels to apply mortar to an entire chimney and then installing the stone, all in one day. Sticking stones
Intuition tells you that it is best to install stones from the bottom up, stacking one on another. But Cultured Stone recommends starting from the top to avoid wet mortar dripping on installed stones. You also can't use lower stones for support and therefore are less likely to knock off installed stones. If the stones don't stick well, the mortar isn't mixed right, the surfaces are too dry or your technique needs work. The exception would be ledge-type stones; the limited surface area might make for poor adhesion. Install ledge stones from the bottom up. You can spray the stone and/or the scratch coat lightly with water so they don't suck moisture out of the mortar. Apply the opposite L-shaped corner stones first, alternating long and short legs. Then work toward the center of the flat surface and downward. The object is to create a random pattern by mixing large stones with small stones, thick with thin and light with dark. Choose shapes that naturally fit together, and apply leaving somewhat uniform gaps for grout. With these design principles in mind, the best approach with the stone, including the Chardonnay Dressed Fieldstone we used, is to stage about a three-foot square of stones on your work platform. It's better to dry fit several stones together on a horizontal surface with the look you want than to haphazardly stick stones on the chimney and later observe that you've installed three similar stones close together with an unattractive result. The best way to install a stone is to hold it in position to verify the fit, use a pointed trowel to butter the back with a thin (about 1/2-3/4in.) layer of mortar and press the stone into place, wiggling it a bit to spread the mortar and eliminate air pockets. It's okay if the mortar starts thicker in the middle of the stone because it will spread to the sides as you wiggle and press the stone into place. Mortar should squeeze out around the sides of the stone. Just leave the excess there; you will cover later with grout. Grout - frosting on the cake Grout is a concrete-based mortar product similar to, but finer than, setting bed mortar. You can color it to match or accent the stone, and then apply it with a grout bag, similar to a pastry chef's frosting bag. A bag gets the grout into the irregular gaps between the stones without smearing the face of the stones. Don't be too fussy about how the joints look as you apply the grout mortar because you will smooth the lines with a stick or flattening tool after the grout sets but before it hardens. Depending on the style of stone, you can choose from several grout-joint options. Half-inch joints, tight-fit joints and over-grout are a few suggestions. Apply grout from the bottom up. If you get grout on the face of the stones, don't try to remove it right away because it will smear and be even harder to clean. Instead, wait until the grout has dried for at least 30 minutes, and then remove it with a stiff, dry brush. Sources:
Owens Corning Cultured Stone, Chardonnay Dressed Fieldstone (used in project) www.culturedstone.com, 800-255-1727
STEP-BY-STEP INSTRUCTIONS
Step 1: Install galvanized metal lath horizontally, rough orientation down, overlapping sheets by 2 in. Step 2: Bend lath and wrap it around corners at least 16 in. Step 3: Secure the lath with rust-resistant galvanized nails. 6-in o.c. Step 4: Fill the lath with type-N mortar to create a uniform, reinforced base. Step 5: Install L-shaped corner stones and edge stones first, starting at the top, and then fill in the area between. Step 6: Work toward the middle, alternating stone sizes, colors and shapes. Step 7: Butter the entire back of the stone with mortar before installing. Step 8: Press and wiggle the prepared stone to spread the mortar evenly and eliminate any gaps. Step 9: Transfer grout to tapered bags with a mason trowel. Step 10: Twist the open end of the bag until grout begins to flow from the tip. Step 11: Fill the gaps between the stones to within ½-in. of the stone faces Step 12: When the grout is thumbprint hard, use a joint tool or flat stick to create even grout lines. Step 13: Use a stiff dry brush to finish smoothing the joints, and bruch off mortar droppings. |