One of the first points to remember with a leak in your roof is that where it manifests itself – on the ceiling or on the floor – is not necessarily where the leak actually is.

If you look at the two illustrations accompanying this feature, you will see that leak (possibly a cracked or displaced tile) on a sloped tiled roof might result in rainwater (the red dotted line) passing down a roof truss or the plastic lining many tiled roofs incorporate, and then dropping out when it meets a protuberance, or a hole in the plastic, respectively – and it is directly below that spot that the leak becomes apparent.

Also note that the lower the damaged tile or the leak is down the slope of the roof, the more severe it could be. Why? Because if at the peak or near it, there is only a small catchment area for rain above it. The further down the slope it is, the larger the rain catchment area above it – and the more water will be flowing over – and into the damaged tile.

In the case of the flat roof shown in this feature – a cast concrete double garage roof and actually mine – in this case the leak was a small crack/split in the caulking designed to seal the gap between the two sides of the garage (which is essentially two single garages with large cut-outs between them, joined side on – to form a double garage). Rainwater collecting the gully between the garage roofs flowed over the edge, but through surface tension flowed back until it reached the caulking, and then flowed down, as usual. The trouble is that with prolonged rainfall, water (shown as the blue dotted line) passed through the crack/spilt in the caulking and along any gaps it could find in the caulking between the garages – and manifested itself a full metre inside the garage. Directly above that manifestation, the sealing between the garages is perfectly fine. In this case, I used silicon bathroom sealer to cure the problem.

So… bottom line… be prepared to discover that where you think the leak is… it isn’t!


There are various leak-sealing/repair products available at Mica stores. Some are thick mastics (rather like a very thick paint), others are specialised paints, others involve bitumen-backed aluminium strips (available in a range of widths and lengths), others employ liquid rubber or products with similar sealing qualities, others use membranes applied using heat (usually you need a contractor to do this job), others employ paint-on adhesives combined with strips of nylon cloth, rather like bandages. In the latter case a first layer of the solution is applied to the leak, then the cloth is pressed into it, while it is still ‘wet’, and further coat/s of the solution are applied according to the manufacturer’s instructions to complete the seal.

Just to keep things simple, there are products specially designed for use on sloped roofs, flat roofs, tiled roofs, metal roofs and so on.

So establish exactly where the leak in your roof is, its extent, the type of roofing material you have, and then chat to the product assistant at your local Mica to get the correct product for your needs.


  1. A crack/split in the caulking, just like this, was the cause of the leak between the garages, as mentioned above.
  2. A check of the sealing between the garages revealed no problems. The water did not leak away, and a very careful examination of the whole length of the gully found it to be sound.
  3. Believe it or not, the first thing I did was to get a small container and fill it with soapy water. The second thing I did was scrub down the surfaces on which I would be working. It is absolutely essential that before you fix any leak, that you clean the surface thoroughly, removing all debris, loose or flaking paint and so on.
  4. Now I applied silicon sealant to the area and with the tip of my finger dipped in the soapy water, worked it well into the gap between the garage halves.
  5. I ensured that I worked it very well in to the underside of the lip of the gully to close any gap there – even the tiniest, so that even if surface tension resulted in rainwater flowing under the gully lip, it would not find a way into the garage. ‘OK, why the soapy water?’ I hear you ask. Simple… the sealant is sticky, naturally, but your soapy finger tip will glide over it, smoothing it and working it in where you want to – but very little if any will stick to your fingertip.
  6. As insurance I bent the lip down slightly as water doesn’t naturally flow up, and then I checked the flow with some water to check that it flowed straight off the edge of the gully and clear.
  7. A check of the rest of the roof revealed a potential area of concern, so up on the roof, I had my scraper, steel-bristled brush, flashing primer and brush to apply it, bitumen-backed aluminium flash band and a utility knife to cut it. As mentioned above, but it cannot be repeated often enough… the surface must be as clean and clear of debris, loose or flaking paint etc as possible. But I don’t use water to clean it or wash debris clear as it slows down the repair time if you then have to allow time for the roof to dry completely before completing the repair – and who knows if a bird flew overhead in the meantime?
  8. First of all, scrape off any flaking or loose paint and other debris in the area to be repaired.
  9. Follow up with a very brisk brushing to remove anything the scraper may have missed. I completed the surface cleaning by using the broom to sweep the work surface clear.
  10. Then I stirred the primer as per the manufacturer’s instructions…
  11. … And applied it with the brush, to the full width of the aluminium band I would be using.
  12. When joining two lengths like this, ensure you overlap them by about 20mm or so. Butting them edge-to-edge could mean even a small gap – and that probably means another leak.
  13. Never a borrower or lender be… I lent a friend a small roller for a paint job, but he couldn’t clean it properly, so it ended up as hard as rock. He bought me a replacement, but I kept the solid one anyway – it makes a great little roller for spreading glue – or in this case, pushing a sealing band down really well on to the surface. It works like a treat. And, courtesy my friend, I have a new roller. Sorted!
  14. In passing, another potential area for leaks in the roof is at the ends – where the tiles meet the barge boards. In this case, the wood ones with a wood capping had been replaced with the plastic version (‘No more painting, Mom’) and that left a gap between the ends of the tiles and the plastic barge board lip – and a space for rainwater to penetrate the wall, causing damp in the inside walls. It was easily sorted out with a narrower version of the flash band used above on the garage roof. Again, The Little Roller That Could, did.

Project guide

Skill level: 1

Estimated time: Depends on how serious or extensive the leak is

Cost: Depends on how serious or extensive the leak is and what products you use to fix it

Assistant: No

Tools required:

Steel bristle brush, broom (if necessary), scraper, hand brush, paint brush (if using a product to apply with a brush, such as a primer in this case, or other paint-on sealing product).


These materials are available at Selected Mica Stores. To find your closest Mica and whether or not they stock the items required, please go to, find your store and call them. If your local Mica does not stock exactly what you need they will be able to order it for you or suggest an alternative product or a reputable source.