Installing Tile Over a Wood Subfloor. Finished tile floor installed over a plywood and cement backer board subfloor. Installing tile over a wood subfloor is a lot easier today than it was when I started my remodeling career. The old fashioned mud method of floating a thick mortar bed in preparation for the tile has given way to using cement backer board over a plywood subfloor. Cement board is inexpensive 1. Among the trade names youll see are Durock, made by U. S. Gypsum Corp., and Perma. Base, from National Gypsum Co. Manufacturers provide clear installation instructions with cement backer board, but there are a few other important points you need to know to guarantee a long lasting installation. For example, I always like to remove the old flooring material so I can check the subfloor for any water damage. Years of water seeping along the edge of a bathtub or shower can cause areas of rot that need to be repaired. Using a cordless drill to screw cement backer board to a plywood subfloor. If everything is in good shape, use a notched trowel to apply thin set adhesive to the plywood, set the backer board in it while its still wet, and drive corrosion resistant screws made for countersinking into backer board through the plywood at the intervals recommended in the backer board instructions usually every 8 to ensure a firm foundation for the tile. If you take this kind of care with the prep work, the finished tile wont crack over time. Next, cut the cement backer board always wear an approved respirator or mask when dry cutting cement based products, and screw it down using corrosion resistant screws. Tape the joints in the backer board and apply thin set adhesive to the joints. Finally, layout the location for the tile, apply a coat of thin set to the backer board, and lay the tile. Once the tile has set, apply grout to the joints between the tile, wiping off any excess with a damp sponge. Setting tile on cement backer board with spacers used to align the tile. The proper fasteners, mortar, tile adhesive and joint tape are all specified by the manufacturer, but dont use drywall screws since they can corrode. Another mistake I often see is grout wedged between the last row of tiles and the tub, cabinets or doorsill. Grout in these transitional areas will crack as the floor expands and contracts. These areas should get a bead of acrylic or silicone caulk instead so the joint remains flexible. Im often asked by homeowners if its possible to lay down new tile over an existing tile floor. This is not my favorite way to install tile, but it can be done, as long as the existing tile and subfloor are in good condition, and the old tile is thoroughly cleaned and scuffed up with sandpaper to allow the new mortar to grip. The combination of newly applied mortar and tile will raise the level of the floor by at least 38. Trimming the bottom of the bathroom door and building up the doorsill usually hide the fact there are two layers of tile instead of one. Trimming the bottom of a door casing with a jamb saw so the tile will fit under it. The subfloor under the tile should be at least 1 18 thick, with a minimum of 58 thick exterior grade plywood topped by 12 cement backer board. Further Information. Repairing Historic Flat Plaster Walls and Ceilings. PRESERVATION BRIEFS2. Plasterers applying rough and finish coats of plaster. Drawing From the Book of Trades. Repairing Historic Flat Plaster Walls and Ceilings. Mary Lee Mac. Donald. New York importer, distributor and fabricator of natural stone products and ceramic tiles. ASK US I would like to know what paint is safe to use on a baby cot. We have bought a wooden cot would like to refurnish it. In your professional opinion. Preservation Briefs provide guidance on preserving, rehabilitating, and restoring historic buildings. Top eleven ways to repair your lath and plaster ceilings and get years more life out of them. From simple to comprehensive. Read more. Plaster in a historic building is like a family album. The handwriting of the artisans, the taste of the original occupants, and the evolving styles of decoration are embodied in the fabric of the building. From modest farmhouses to great buildings, regardless of the ethnic origins of the occupants, plaster has traditionally been used to finish interior walls. A versatile material, plaster could be applied over brick, stone, half timber, or frame construction. It provided a durable surface that was easy to clean and that could be applied to flat or curved walls and ceilings. Plaster could be treated in any number of ways it could receive stenciling, decorative painting, wallpaper, or whitewash. This variety and the adaptability of the material to nearly any building size, shape, or configuration meant that plaster was the wall surface chosen for nearly all buildings until the 1. Plaster was used as the interior surface coating of this elegant 1. Eugene, Oregon. Photo NPS files. Historic plaster may first appear so fraught with problems that its total removal seems the only alternative. But there are practical and historical reasons for saving it. First, three coat plaster is unmatched in strength and durability. It resists fire and reduces sound transmission. Next, replacing plaster is expensive. A building owner needs to think carefully about the condition of the plaster that remains plaster is often not as badly damaged as it first appears. Of more concern to preservationists, however, original lime and gypsum plaster is part of the buildings historic fabricits smooth troweled or textured surfaces and subtle contours evoke the presence of Americas earlier craftsmen. Plaster can also serve as a plain surface for irreplaceable decorative finishes. For both reasons, plaster walls and ceilings contribute to the historic character of the interior and should be left in place and repaired if at all possible. The approaches described in this Brief stress repairs using wet plaster, and traditional materials and techniques that will best assist the preservation of historic plaster walls and ceilingsand their appearance. Dry wall repairs are not included here, but have been written about extensively in other contexts. Finally, this Brief describes a replacement option when historic plaster cannot be repaired. Thus, a veneer plaster system is discussed rather than dry wall. Veneer systems include a coat or coats of wet plasteralthough thinly appliedwhich can, to a greater extent, simulate traditional hand troweled or textured finish coats. This system is generally better suited to historic preservation projects than dry wall. To repair plaster, a building owner must often enlist the help of a plasterer. Plastering is a skilled craft, requiring years of training and special tools. While minor repairs can be undertaken by building owners, most repairs will require the assistance of a plasterer. Plasterers in North America have relied on two materials to create their handiworklime and gypsum. Until the end of the 1. Lime plaster was made from four ingredients lime, aggregate, fiber, and water. The lime came from ground and heated limestone or oyster shells the aggregate from sand and the fiber from cattle or hog hair. Manufacturing changes at the end of the 1. Gypsum and lime plasters were used in combination for the base and finish coats during the early part of the 2. The builders of this mid 1. Lime was used for the finish plaster. Photo NPS files. Not only did the basic plastering material change, but the method of application changed also. In early America, the windows, doors, and all other trim were installed before the plaster was applied to the wall. Generally the woodwork was prime painted before plastering. Obtaining a plumb, level wall, while working against built up moldings, must have been difficult. But sometime in the first half of the 1. Installing these grounds so that they were level and plumb made the job much easier because the plasterer could work from a level, plumb, straight surface. Woodwork was then nailed to the grounds after the walls were plastered. Evidence of plaster behind trim is often an aid to dating historic houses, or to discerning their physical evolution. Lime Plaster. When building a house, plasterers traditionally mixed bags of quick lime with water to hydrate or slake the lime. As the lime absorbed the water, heat was given off. When the heat diminished, and the lime and water were thoroughly mixed, the lime putty that resulted was used to make plaster. When lime putty, sand, water, and animal hair were mixed, the mixture provided the plasterer with coarse stuff. This mixture was applied in one or two layers to build up the wall thickness. But the best plaster was done with three coats. The first two coats made up the coarse stuff they were the scratch coat and the brown coat. The finish plaster, called setting stuff, contained a much higher proportion of lime putty, little aggregate, and no fiber, and gave the wall a smooth white surface finish. Schifferstadt, a simple house of German origin that dates to 1. The building is located in Frederick, Maryland Photo NPS files. Compared to the 38 inch thick layers of the scratch and brown coats, the finish coat was a mere 18 inch thick. Additives were used for various finish qualities. For example, fine white sand was mixed in for a float finish. This finish was popular in the early 1. If the plasterer raked the sand with a broom, the plaster wall would retain swirl marks or stipples. Or marble dust was added to create a hard finish white coat which could be smoothed and polished with a steel trowel. Finally, a little plaster of Paris, or gauged stuff, was often added to the finish plaster to accelerate the setting time. Although lime plaster was used in this country until the early 1. A plastered wall could take more than a year to dry this delayed painting or papering. In addition, bagged quick lime had to be carefully protected from contact with air, or it became inert because it reacted with ambient moisture and carbon dioxide. Around 1. 90. 0, gypsum began to be used as a plastering material. Gypsum Plaster. Gypsum begins to cure as soon as it is mixed with water. It sets in minutes and completely dries in two to three weeks. Historically, gypsum made a more rigid plaster and did not require a fibrous binder. However it is difficult to tell the difference between lime and gypsum plaster once the plaster has cured. Many of these traditional plastering tools are still used today. Drawing NPS files. Despite these desirable working characteristics, gypsum plaster was more vulnerable to water damage than lime. Lime plasters had often been applied directly to masonry walls without lathing, forming a suction bond. They could survive occasional wind driven moisture or water winking up from the ground. Gypsum plaster needed protection from water. Furring strips had to be used against masonry walls to create a dead air space. This prevented moisture transfer. In rehabilitation and restoration projects, one should rely on the plasterers judgment about whether to use lime or gypsum plaster. In general, gypsum plaster is the material plasterers use today. Different types of aggregate may be specified by the architect such as clean river sand, perlite, pumice, or vermiculite however, if historic finishes and textures are being replicated, sand should be used as the base coat aggregate. Today, if fiber is required in a base coat, a special gypsum is available which includes wood fibers. Lime putty, mixed with about 3. Lath. Lath provided a means of holding the plaster in place. Wooden lath was nailed at right angles directly to the structural members of the buildings the joists and studs, or it was fastened to nonstructural spaced strips known as furring strips. Three types of lath can be found on historic buildings. Wood Lath. Wood lath is usually made up of narrow, thin strips of wood with spaces in between. The plasterer applies a slight pressure to push the wet plaster through the spaces. The plaster slumps down on the inside of the wall, forming plaster keys. These keys hold the plaster in place. Metal Lath. Metal lath, patented in England in 1.
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