Slate tiles are one of the oldest types of steep-slope roof coverings in the United States. Their application dates back to colonial times. In recent decades, there has been a decrease in slate applications, due in large part to shortages in raw materials and a lack of skilled craftsman. These issues make the restoration and repair of existing slate tiles more crucial than ever.
The most important aspect of slate tile repair is to avoid damage to the existing tiles. Avoid walking on them during the repair process. The contractor should erect a scaffolding and plank system or hang a ladder from the roof peak to minimize direct foot traffic on the slate tiles.
When replacing localized slate tiles, the contractor is better served to cut the replacement tiles to exact sizes on the ground prior to application. A proper slate application uses tiles that are twice the exposure plus an additional three-inch allowance for the head lap. For example, if the exposure is 10 inches, the new slate tile should be 23 inches long. The slate tiles can be cut with a pressure cutter or a pick-like hammer. Cutting the tiles to size beforehand and in a controlled setting will eliminate field errors.
Prior to removal of the damaged tiles, insert a nail ripper at the underside of the tiles above the tile that requires replacement. This is necessary to keep the surrounding tiles in place during removal of the damaged tile. Remove the required tile and make certain that no damage occurs to tiles that are to remain in place.
Install the new fitted tile into the opening and use the gap between the sides of the course above the replacement tile to mark the location of the nails. If the new tile does not have pre-drilled nail holes, then drill them in using a 1/8-inch drill bit. The nail holes should be drilled from the backside of the tile so that the ragged part of the hole will be at the front side. This allows for the nail to sit flush in the hole.
Attachment of the tiles should be completed using 11/2 inch copper nails on new slate tiles. Old slate tiles require 11/2 inch hot-dipped galvanized nails. It is important that the nails are not overdriven or applied too tightly because this could create cracks in the tiles. If the nails are not driven in enough, the tiles will become loose. In some cases, the edges of the nail heads have to be cut off to pass between the sides of the two slates in the upper course. The head of the copper nail can be covered with a copper bib that slides up under the surrounding slates, covering the nail hole from view. The copper bib should have its edges burred or should be bent slightly so that it will not slide out after application. The top of the bib should extend well above the nail and under the slate above so that the copper is totally hidden.
Another form of attachment is the use of stainless steel slate hooks. This method is considered to be a more reliable for holding replacement slate tile in place. Using this method, the fastener end of the hook is nailed approximately three inches up from the lower edge of the replacement tile. The installer slides the tile over the hook and seats it in place.
Replacement of slate tile requires matching the slate color as closely as possible to give the roof a uniform aesthetic appearance. The replacement tile should be the same color as the one that it is replacing. If the roof has different colored slate tiles, the replacement tile should fit into the color scheme applied.