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During the last five years or so I have seen a distinct increase in the number of companies offering to colour, seal, coat or paint old roof tiles. You may well have noticed this surge too?
Perhaps like me, you have also been bothered by pesky door-to-door canvassers or seen eye catching leaflets put through your door?
There is one question I really wanted to address:
Do concrete tiles actually need to be re-sealed?
Re-sealing is the process of applying a waterproof coating to the surface of the tile in an effort to keep rainwater off the tile.
Let’s Dispel a Myth
One common myth, often used by salesmen is that old concrete tiles will become porous and water will seep through them and into the property.
Actually this doesn’t happen at all.
Old tiles that have had decades of weathering will keep rainwater out of the house regardless of whether they have a waterproof seal on the surface or not.
Because tiles are laid on a pitched roof (a sloped roof) water runs off the tile and onto the next tile below. The water continues like this until it enters the gutter.
The way tiles are laid (i.e not flat) means that even a porous material like concrete wont leak. Gravity pulls the water not into the roof but down onto the tile beneath – don’t forget that all tiles are overlapped.
That is how a porous material like clay or concrete can be used on roofs. In fact most roofs in the United Kingdom are made from materials that could be considered porous. They normally only leak if the roof pitch (slope) is too shallow or if a tile breaks.
So Why Seal Roof Tiles?
There are a couple of advantages to sealing roof tiles but in my opinion they certainly do not outweigh the disadvantages.
I will leave it to you to decide for yourself:
Advantages of sealing tiles:
Stops water from entering hairline cracks where it could freeze and potentially crack the tile or roof cement (water expands when it freezes)
Stops rainwater from weathering the surface of the tiles – possibly extending the life of the roof by a few years (please see the disadvantages below)
To apply the sealant one must first thoroughly clean the tiles, i.e with a pressure washer. This actually strips the surface off many types of tiles and shortens the life expectancy of the tile. There is also a flood risk involved with pressure washer use (see this BBC Rogue Traders episode as a good example) and of course the tradesman will need to walk all over the tiles, at least several times, this increases the chances of breaking tiles. I have already covered this on another page titled is it safe to use a pressure washer on a roof?
Roof sealants also tend to wear off after a few years, all that rainwater flowing down the pitched roof, it shouldn’t be a surprise that a lick of paint or sealant won’t last long here. You may want to think about what a roof looks like when sealant starts to peel off. Here are some photos you may want to explore.
It’s an expensive exercise, all the preparation work for a short term product. If the process needs to repeated every 3-8 years then it just isn’t cost effective at all. It would be much cheaper to have the roof checked every few years and any cracked tiles replaced.
So to Answer the Question…
No, concrete tiles do not need to be re-sealed, the process is entirely optional. I have seen concrete porous tiles on very old roofs and not one drop of water has entered the property. The pitch of the roof and the way tiles overlap means water cannot seep through them directly.
Most salesmen who sell roof coatings won’t tell you that though. ( Here are some tips on what to expect from dodgy roof coating salesmen)
If you decide that you still want to go ahead with tile re-sealing then that’s fine but hopefully you won’t be doing so because some door canvasser has told you your tiles are becoming porous and you need this “miracle” sealant.
If you really have been hoodwinked into sealing or coating the exterior of the tiles, then you could consider using a clear/translucent sealant. At least when it starts to wash off/peel/crack etc you won’t be able to see it! And of course your roof won’t look like this:
Ever wondered what your local Trading Standards Office has to say about roof coatings? Did you know that the BBC Rogue Traders programme has featured several of these coating companies. Find out more here.
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