In the first part of this article we looked at capillary action and solutions for pitched roofs, (you can access part 1 via the IT website if you missed it). In addition to water driving up under tiles, the roof junction areas are a common point of water ingress on both new build and older properties.

Flashing (What flashing?)

Unlike the UK where lead flashing is common, the traditional flashing methods used in Spain are far less reliable. Normally the upper course of tiles is chased into the wall slightly while the junction is ‘flashed’ with a cement sand mortar fillet. Over time the mortar often cracks allowing water to penetrate. In most cases (except where a waterproof additive has been used in the mortar mix) the junction is also dependant on a good surface paint finish over the mortar fillet. A lack of regular maintenance (common at roof level due to difficult access), will result in paint breakdown and hence failure of this critical barrier against damp ingress. It is important to note that in Spain, the combination of UV related damage and temperature extremes play havoc with fragile building elements and a mortar flashing may crack through within days (even hours) of installation during hot weather.

So what is the solution?

As a bare minimum, the cement sand mortar mix for any roof details should include a latex additive e.g. ‘Sika Latex’. This will help adherence and help to waterproof the mortar as well as reducing the risk of cracking. The additive must be well mixed with the water first (according to manufacturer’s instructions) before making up the mortar.