Some Roof Restoration companies make claims that their work will be good for 20-25 years. This is simply not true! A “good job” using a quality coating, enough coating and done with the right preparation by a quality tradesperson will last approximately 15 years*. This figure is based on both data collected and simple observation.

*Disclaimer: Subject to sunlight (UV) conditions, coating colour choice and mould growth.

Why Roof Restorations Projects Fail

The next time you go for a drive, if you take notice, you’ll see roofs with peeling paint. There was a time when this was the excepted norm, especially with metal roofs. Times have changed, though. Roof coatings have improved, as have application methods.

These days the only reasons a roof coating will blister, peel, or flake off, is if the roof wasn’t prepared properly, insufficient primer or no primer was used, or the surface wasn’t completely dry when the paint was applied.

This sounds really simple but there is much you need to know, especially in regards to the preparation.

Preparation for tiled roofs:

The roof must be pressure cleaned at a minimum of 3000 p.s.i. Most domestic water blasters don’t even come close to that (the average household Gurni puts out 1000 – 1500 p.s.i), which is why most DIY roof restorations fail. Most credible roof restoration companies will use machines that put out at least 3000 p.s.i, but normally upwards of 3500 p.s.i.

The power of the water blaster is paramount because roof tiles, by the time they are 10 years old, have lost their glaze. Once the glaze has eroded, the coating underneath oxidises and becomes very chalky. This chalkiness must be removed, along with the dirt and grit that’s on the surface and in the craters and pores of the tiles.

Where most people come unstuck in cleaning a tiled roof, however, is in cleaning the tile noses (the ends of the tiles). If you ever see a bad roof restoration job, the first thing that stands out is how the ends of the tiles are black. This is simply because they weren’t sufficiently cleaned.

An inexperienced cleaner will avoid cleaning the noses, though, through fear of flooding the ceiling cavity. You see, done the wrong way, cleaning the tile noses will push water up under the tiles and into the roof. It’s catch 22. You have to get them spotless, but you don’t want to flood the ceiling!

An experienced cleaner, however, knows the exact angle to hold the lance at to get the noses spotless, yet avoid flooding the roof. Speed is also a factor. You must move fast to avoid putting too much water in one place. Only a skilled and experienced operator has enough practice to be able to move fast enough to avoid pushing water inside, while still doing a thorough job. This is vital.

Preparation for Metal Roofs:

Preparing a metal roof is similar to preparing a tiled roof, especially if the roof is pre-painted. If it’s not pre-painted, then the critical factor is removing all of the dirt and grit. We still recommend a water blaster capable of putting out 3000 p.s.i for a metal roof too, even though you’re not removing oxidised coating.

You need to get every centimetre of the roof spotless. There should be no streaks left by the water blaster.

Preparing Pre-painted Roofs:

Whether tiled or metal, if the roof is pre-painted, then the preparation will likely involve stripping the old coating. And this is not easily done.

If the old coating is peeling or flaking off, then you know straight away that you’ll need to strip it. If it’s not peeling or flaking, then you’ll find out when you start cleaning.

When you hit the roof with 3500 p.s.i, if the coating that’s on there is even a little loose, it will start to come off. Then you need to try and strip as much off as possible. This can often involve two cleans. You see, as mentioned above, speed is a critical factor, yet moving fast means that you won’t get enough off. In that case, you need to go back for a second go at it. The second clean, however, is best done a couple of days later, when the edges of the remaining paint have curled up, allowing you to get more off on your next clean.

Now here’s the key to making it work…..

After your second clean, you need to get the primer on the roof as soon as it’s dry. If you wait until next day, any paint that you couldn’t get off on your second clean will curl up on the edges. And you can’t paint over curled edges – it looks terrible!
Now, if you’ve cleaned it at 3500 p.s.i twice and there is still paint on the roof, it’s safe to assume that it’s well adhered and it will stay there. So it’s okay to coat over this left-over paint. But you must get the primer on before the edges curl.

There’s another key…..

You need to use a lot more primer when coating a pre-painted roof. Flood the surface with primer in this case. Really flood it on to the point that it’s literally running off the roof into the gutters. This further helps lock down the edges. If time permits, it’s a good idea to get a top coat on same day as well. The weight of the top coat does more to weigh down the edges and keep them locked down. A word of warning, though…..

You must use a water based primer to make this work. Solvent based primers cannot be over-coated same day, whereas water based ones can.

Primer:

In avoiding roof coating failures, the type of primer used, the amount of primer are also critical factors. Firstly, for a tiled roof you should use a concrete tile primer or sealer. For a metal roof, you need a “Gal” primer.

The amount depends on whether or not the roof is pre-painted. For a non pre-painted roof, you’ll need approximately 15 litres per 100m2 for a tiled roof, and approximately 10 litres per 100m2 for a metal roof. With a pre-painted roof you’ll use more. How much more will depend on the thickness of the previous coating (if you couldn’t get it all off). The thicker the previous coating and therefore the more pronounced the edges are, the more primer you’ll need. It’s difficult to give exact coverage rates in these situations but it can be up to 50% more than is required on a non pre-painted roof.

If you get the above (proper cleaning/preparation and correct amount of primer), and you’re using a quality roof coating system, then the roof should never flake or peel. But it’s easier said than done. That’s why you should only ever engage an experienced company or operator to restore your roof.