09 November 2016

Repair and replacement of roof tiles and slates

Here we look in depth at practical steps to consider with the actual repair and replacement of individual roof tiles.

Individual tiles or slates that are damaged during or after installation should be replaced as soon as possible using a sound, matching unit fixed in accordance with the nailing and / or clipping specification. Avoid repairing damaged slates or tiles using superficial coatings, adhesives or other mechanical devices, as their performance may be limited.

In some cases, repair may not be possible without stripping back a large area of tiling / slating. If extensive repairs to the roof are required, sectional or complete re-tiling / slating should be considered; this may be the most practical and economic solution in the long term.

Replacing damaged tiles shortly after installation means additional time and expense. To minimise the risk of this, roofs and walls clad with tiles and slates should be treated as fragile and adequate precautions should be taken during installation, including:

  • use of crawling boards for roof access
  • roof ladders should be suitably packed to prevent damage to the roof covering
  • use of access platforms when accessing the roof for maintenance or repair

How to replace interlocking tiles and slates

For an unfixed tile, remove the damaged unit by first easing it up slightly, using a trowel and timber wedges, so that the tile can be slid out with the nibs clearing the top of the batten. The replacement tile can be inserted using the same procedure.

For a tile that is nailed, the neighbouring tiles should be lifted to expose the nail(s), which should be extracted carefully using a slate ripper or hacksaw blade and disposed of safely. The replacement tile can be inserted using the same procedure and re-fixed to the adjacent fixed tiles by using an epoxy resin adhesive applied to the interlock / overlock and headlap area.

Care must be taken not to bridge anti-capillary bars or interlocking water channels so that water can drain freely.

For a tile that is clipped, the clip can be prised off the interlock and the nail extracted, with the damaged tile removed as described above. The new clip and nail can then be fitted as normal (avoiding the previous nail hole), allowing the clip to rest in the clip recess of the adjacent tile. Hold up the clip, and slide the replacement tile into position, allowing the clip to be released onto the sidelock of the tile.

For a tile that is both nailed and clipped, it is necessary to establish the position of the tile nail holes in the course directly below the replacement tile. Mark out the corresponding hole positions on the top surface near the tail of the tile. Fit the replacement using the above procedure. Drill a 4mm diameter hole through the top of the replacement tile, directly above the nail hole of the tile below. Secure both courses using a stainless steel screw with cap and washer (40–120mm long dependent on tile depth) to provide a minimum 15mm penetration into the batten.

The above procedure can also be used to secure the tail of the course above the replacement tile.

If there are a number of damaged tiles that are clipped, it may be necessary to strip back the roof to the nearest verge or valley/hip in order to re-clip the replacement tiles.

It is important that both washer and cap from a waterproof seal around the hole. If necessary, a mastic sealant should be applied around the screw where it passes through the lower tile nail holes.

How to replace concrete and clay plain tiles

Plain tiles are not normally nailed in every course, and in such circumstances the following procedure applies.

Remove the damaged tile by raising up the neighbouring tiles with a timber wedge and sliding the tile out with the nibs clearing the top of the batten. Any nails should be removed and disposed of safely.

Insert the replacement tile back into position using the same technique in reverse. If required, re-nail the replacement tile using 2 No. 38mm x 2.65mm aluminium nails.

A dab of mastic can be placed on the underside to prevent movement.

How to replace Marley fibre cement slates

When using a replacement slate, first ensure that it is of the same type and size already installed. The general principle is that any damaged slates should be fixed in the same manner as they were originally installed.

The slate (or slates) due for repair should be removed using appropriate tools (e.g. a slate ripper and a hammer), usually in a triangular fashion, with the single slate at the apex up the roof slope.

To re-fix an appropriate slate in place of a damaged slate (where the two nail holes are clearly visible) use copper nails with a shank diameter of not less than 2.65 mm, of a length to give a minimum 15mm minimum penetration into the battens (excluding the point of the nail), and secure as normal.

Where only one nail hole is visible, place a stainless steel slate hook (as specified in BS 5534) to act instead of the inaccessible fixing, and nail as normal through the visible hole. Copper disc rivets should be inserted at every rivet hole position at the tail of the slate as standard practice.

The last slate in the triangle will not have nail holes accessible to fix with. In this case take a slate hook as above, and using a ‘mole grip’ and ‘pliers’, bend the ‘hook’ portion from its normal vertical position through 90°. This will allow the spike of the hook to be nailed to the batten and the replacement slate to be slipped into place without interference from the ‘hook’ end.

Once the replacement slate is in position, use ‘mole grips’ to bend the ‘hook’ portion back to its original shape, so that it grips the tail of the slate firmly in position.

It’s important to note that slate hooks are an alternative fixing for slates, as defined by BS 5534, and have known test and performance in use data. Where one or more nails cannot be used as a fixing, a hook should be substituted. The action of bending the hook for the limited distance involved does not significantly affect its durability or performance.

For further practical and onsite information about roof slating and tiling, including how to guides, you can download the Marley Sitework Guide or use our technical services resources.

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