To repair slate roof it is first necessary to remove the nails with a slate ripper. The nails may be forced out upwards by positioning the ripper in front of the nail, downwards by positioning behind the nails or by using a combination of the two. I have marked the nail positions and the outline of the slate to be ripped out to show these positions, because, once the ripper is fed under the slate, you would not be able to see them.
There is a cool article about laying and repairing shingles at thehousingforum.com. We found out few things out of here.
The most common method of removing a slate is to get behind the nails and rip it out, especially on older roofs where the nails have corroded. First, take the slate ripper and feed it underneath the slate until you can feel the hook locate behind either nail you want to rip out. The nail can then be ripped out by hitting down on the handle of the slate ripper with a hammer or by sliding the ripper up slightly and yanking down hard and fast on the nail. Either way, it may take several strikes or yanks to get the nail out, depending on what condition the nails are in. Feel inside with your fingers to make sure that you have cleared all parts of the nail from the batten. If there is any part of a nail stuck, clear it with the ripper or a pair of pincers or pliers.
Once you are happy that the batten is clear, cut a thin strip of copper or lead to form a strap or ‘tingle’, as it is also known. Lead is perhaps the most commonly used because it is a material that most roofers routinely carry on their vans, but it is quite soft in comparison with copper and this can mean that the straps bend back over time, especially if the slates are heavy or are subjected to sliding snow and ice. The tingle should be about 20mm wide and the length should be equal to the headlap plus about 50mm. Nail the tingle between the seams of the slates and into the batten.
Sometimes, when you try to slide the replacement slate back in you may have difficulty getting the head of it on to the batten. To get round this you need to lift the head, and one way to do this is to put a nail on either side of the slate and press down on the tail while you roll the slate up into place. Once the replacement slate is installed, bend the tingle up to complete the repair.
When repairing a patch of slates try to use as few straps as possible. The recognized procedure is to strip the slates in a triangle so that, when they are replaced, they can be nailed back into place with just the last one relying on a strap. This is especially useful when stripping out and replacing long sections along the eaves. You will be able to get at only one of the nail holes of the slates at the outer edges of the triangle, so, to stop it swinging, you will need to nail it twice on the same side of the slate (‘wing’ nailing). When you do this, you must make sure that the second nail hole is at least 75mm away from the centre of the slate.
Slate ripper fed in behind nail.
Ripping out the nails.
It is also acceptable to use steel slate hooks for repairs and there are also several proprietary slate repair products on the market today. Alternatively, copper wire can be used (if you are using wire, twist a loop into one end to take the nail). Also, it is a good idea to create a ‘home’ for the wire by inserting a small nick into the bottom edge of the slate first.An alternative to wing nailing is to hang the side of the slate that you cannot get to, on a nail. This is simply a matter of forming a new hole just above the line of the batten, popping a nail in and sliding the slate into place. The exposed side of the slate is then nailed as normal.
Nailing the tingle in position.
Slide the slate into position (nails used as a pivot to lift the head).
Tingle turned up to complete the repair.
An area of slates stripped and repaired with minimal straps.