How I Cement Roof Tiles

Welcome to Daniel’s Roof and our guide to securing and cementing roof tiles.

The tiles which are cemented to the roof edge of many homes are often called verge or gable tiles and the condition of this cement can deteriorate over time. This is especially true if an incorrect sand/cement mixture was used during the initial construction. Driving rain will frequently splash against this cement and if the cement is too “sandy” it will simply wash out.

Replacing the cement is one option as you can see from my photos on this page but replacing the cement with a plastic dry verge system is also popular. Click here to see a plastic alternative to roof cement.

Below you can find a series of photos that show how the cement was removed and replaced on a recent project of mine that also involved replacing the timber fascia with plastic upvc boards.

Step by Step Instructions

While the photos shown above help to describe the process of renewing the cement, the following steps should help those wishing to undertake the project themselves.

  1. Remove the cemented roof tiles, starting from the top of the roof.
  2. Chisel off any cement from the tiles, replace any that break.
  3. Remove the under-boards that were used to support the underside of the cemented tiles.
  4. Replace the under-boards with either slate or cement fibre boards, fix directly to batons or timber rafter, not to the barge board.
  5. Mix sand and cement. 3 parts sand to 1 part cement, include plasticizer additives to reduce chances of cracking.
  6. Trowel cement onto under-boards (see photo 3) and press tiles down-wards, scrape off excess cement.
  7. Each tile should be screwed to the timbers underneath (if a screw hole exists) to prevent wind lift. A fixing clip may also be required depending on tile and location of property.
  8. Allow 30 minutes to pass then point in the cement face to ensure a smooth finish. If the cement starts to slump, wait another 15 minutes and then try again.
Old bargeboard and loose cement

Old bargeboard and loose cement. See more in the Photo Gallery

New Upvc bargeboard and undercloaks to support cement

New roofline board and undercloak to support new cement. See more in the Photo Gallery

Cement work in progress

Cement being laid to roof. See more in the Photo Gallery

The finished product

Cement pointed in to leave a neat finish. See more in the Photo Gallery

Hints and Tips

Never lay cement when the temperature is likely to drop below 5° in the following 36 hours. This may result in the water freezing and then expanding, thus cracks will appear.

Use a strong mix such as 3-1 sand/cement on all roof work, it prevents wash out. Cement designed for bricks (5:1 or 6:1) is not suitable on the roof where it will be laid in thicker amounts and subject to much more driving rain..

Cover cement if rain or strong direct sunlight is expected. Water will wash out the cement and sunlight may cause it to dry and shrink too quickly, again cracks may appear.

Take extra care to ensure that the sand is appropriate. Sand that is very course may not be suitable even though it easier to work with.

You can use dye in the sand/cement mix to achieve a darker colour. Black is a popular colour as a small amount will leave the cement with a grey somewhat weathered effect.

Why Cement Cracks

Here is a quick list of the various reasons why roof cement sometimes cracks:

  • Too much cement in the mix
  • Frost damage, temperature too cold
  • New Build Houses: the roof needs time to “settle”, thus there will some movement of roof rafters from the weight of the tiles, this is normal but may result in some cracks to the cement
  • Disturbance – the roof cement was laid but was disturbed, possibly by another tradesperson before it had the chance to fully dry
  • Bad sand, too course
  • Too hot, the cement dried quickly and therefore shrank too fast

How Not to Cement Roof Tiles

I have seen this a thousand times and still tradesmen do it, usually to save time and therefore money – at the customers expense of course.

The old cement must be fully removed before the new cement is applied. It may be a lot easier to paste the new cement over the old but this is called “buttering up”. You will want to avoid this at all costs, remember that from ground level it is impossible to tell the difference between a genuine and bodge job.

In effect, with this technique you are applying a very thin layer of cement over the existing mortar. It won’t last long before it peels off, usually within a couple of years and sometimes sooner.

Whether you are cementing ridge tiles, hips, valleys or verges, the tiles must be lifted up and the old cement completely removed. The tiles are then bedded down on the new cement. Once it has been allowed to dry just a little (~30 mins) you can then point in the surface to leave a smooth professional finish.

I have created a separate page with plenty of photos explaining how to replace roof cement, it also contains photos of bodge-jobs I have seen.

How Much Does it Cost to Replace Roof Cement?

This page shows example quotations detailing how much it costs to replace roof cement.

Considered Installing a Plastic Dry Verge Instead?

Some people think roof cement should be a thing of the past and there are products made from plastic that designed to replace this cement. These new products may appear to be a good idea, but remember coloured plastic has a tendency to fade when exposed to direct sunlight for prolonged periods of time. It then looks tired and in need of replacement.

These products are often referred to as “dry verge” systems.  This is because plastic is dry and requires no mixing with water unlike cement.

There is one big advantage of these plastic systems – they can be installed in any weather conditions, including rain. This is when most cement work on a building site gets postponed.

Click here to see an alternative to roof cement.

One Response to “How I Cement Roof Tiles”

  1. NORMAN BRAMMER08/10/2012 at 2:41 pm #

    Thanks Daniel, I live in France and your info has been most helpful.