Fact & Fiction

The best way to realise the right way to restore a roof is to understand why the wrong way fails – the most common reasons for failure are as follows: 

• Inadequate cleaning of the tiles 

Pressure cleaning is important, not only to remove the dirt from a tile but also the pollution that is common to suburban roofs. Pollutants will have an adverse reaction to the acrylic paints that are applied. Loose surface sand will need to be properly removed also, so that expansion and contraction does not tear the top coats away from the tile. Professional roof restorers will use industrial machines to clean your roof with PSI pressures between 3500 and 4300. 

• Failure to replace or relocate chipped and broken tiles 

Broken tiles leak obviously, so all tiles with chips greater than 50mm should be replaced. Smaller chipped tiles are displeasing to the eye, so relocating them to the blind side of the home is desirable. 

• Over pointing the ridge caps without replacing all of the cement 

Pointing over old concrete can begin to come away as the pointing and subsequent acrylic coatings expand and contract, allowing water to find its way into your home. If your ridge caps are loose at all, they need to be removed and the old cement disposed of. A new foundation of concrete is then laid and the caps bedded onto it. The caps can then be pointed over (generally with a synthetic acrylic compound with superior flexibility an adhesive abilities) without fear of possible failure in later years (or months). 

• Bedding down the caps in weak sand/cement mix 

A good cement mix for your roof is three parts sand and one part cement. It’s very common in the roofing industry to use a sandy mix. While inexpensive, cement will dry rapidly if mixed properly. This means many trips up and down the ladder to keep mixing new cement. A sandy mix means less trips as the cement will not dry nearly as quickly.

The problem arises when the flexible pointing is applied. As this product expands and contracts on the sandy concrete, it begins to come away from the mortar mix and leave an open seam at the top. Water will then be able to get into this seam, but as the bottom of the pointing is anchored securely to your tile, it cannot drain out.

I have seen huge damage caused to a home that has never had prior problems, and all from a so-called repair! Weep holes are often used to alleviate this problem, but this allows water to get into your bedding. If your bedding is sandy it washes out anyway. If it is not sandy, you don’t need the weep holes. 

• Peeling of the coatings 

Peeling is a result of inadequate primer products being used. A common practice in this industry is to seal the tile prior to top coating it – these sealers are thick compounds that trap air in the surface of the tile. When the tile heats up, the acrylic coatings get soft and the air expands, making the top coat lift – over a period of time, this will make the paint peel off. 

To prevent this from happening, a suitable primer coat should be used. The type of primer depends on the coarseness of your tile – thinner (or even nano) primers for fine grained or newer tiles and slightly heavier primers for coarse tiles. Good restoration companies will always have a range of tile primers to recommend. 

• Patchy finish 

This is because a sealer wasn’t used. The reality is that roofs need four coats of product on them. No ifs, no buts – this is the only way to do the job properly. You need a primer to stop peeling, then a sealer to build the tile surface up to stop that thin patchy look, and then two colour coats on top. Exceptionally coarse tile may even need five coats. 

• Oxidisation of the top coats 

This is when the colour coats begin to break down and become powdery. Calcium salt is an agent used in cement to quicken the drying time – it’s also one of the main reasons that roof restorations fail no matter how good the top coats are. A special sealant is required to prevent this salt from leeching through to the top coat and doing what salt does to paint everywhere – shorten its life span. It’s unfortunate reality that he vast majority of roofing contractors are unaware of the existence of calcium salt, let alone how to prevent it. 

• Poor quality top coats 

Okay, so how do you know what is good and what is not good? I mean, it’s not like the company your dealing with will tell you their paint is rubbish, and there are hundreds of paints to choose from. Here’s a couple of facts to keep up your sleeve so you can quiz your prospective roofer on whether their paint is up to scratch:

Pure acrylic resin is the best quality you can get in a paint (then there are different types of resins, but I won’t go there and bore you to death). Resin is a liquid that has 50% solids in it. So the best types of paint would be pure acrylic resin that would only have UV stabilisers, fungicides and pigment added (the extras account for around 5% extra solids). This means that a good quality paint will have around 55% solids in it.

Be careful though, as cheaper paints will often have fillers added that will dramatically affect the longevity (but not the immediate appearance) of the coating. In order to establish the coverage of a paint and the warranty that is given, both the solids content and the percentage of resin will be known by competent companies.