Ensuring the quality of the products and of the project used is essential to a good roof performance, but it isn’t enough. If the composing elements of a roof are not properly applied, neither the roof tile maker nor the project designer can be said to be at fault should any problems arise.

Some of the most common and relevant anomalies resulting from incorrect application are detailed below.

Fitting of the roof tiles

A badly fitted tile might compromise the whole roof. In this manual you can find the basic rules for laying roof tiles, ridge tiles and eaves (for more details, please refer to the chapters regarding the application and laying of each tile type: Lusa, Marselha, Canudo and Milénio).

Longitudinal and transversal misalignments of the roof tile rows are some of the most common error regarding the fitting of roof tiles. Often, problems resulting from defective fitting of the roof tiles will be dealt with by applying mortar to the tiles, thus compromising the whole roof.

Roof tile overlap

Roof tile makers should declare, for each roof tile model produced, the number of roof tiles to apply per m2  and their individual dimensions.
The difference between average measured values and declared values should not exceed 2%, as was discussed in chapter 2. The number of roof tiles to apply in each row should consider the declared coverage value rather than the upper and lower limit values.

In any case, proper roof tile overlap should be ensured. Not complying with this requisite may compromise the whole roof. Insufficient overlap may result in the incorrect calculation of lath work values or its incorrect application.

Trying to reduce the number of roof tiles to apply to the roof by reducing overlap to a minimum (maximising coverage using a minimum of roof tiles) will seriously compromise the roof and its proper performance.

Misaligned rows

To correctly align roof tiles on a roof, the specifications indicated in the chapter concerning the application of each roof tile type (Lusa, Marselha, Canudo and Milénio) should be strictly followed.

Not complying with these specifications, as well as not executing lath work properly, will lead to the presence of crude faults on the roof, and seriously compromise both the aesthetical and the functional aspects of the roof.

Incorrect use of mortar

The excessive use of mortar to compensate problems related to fitting, roof tile alignment and finishing elements (such as the ridge line, for example) is a common mistake. The belief that this provides solidity to the roof is also a misconception.

Throwing mortar to a problem is not a solution. Mortar does not behave like clay materials in the presence of humidity, due to their different hygroscopic properties. Products can be classifies according to their degree of hygroscopy.

Hygroscopic Products:  when the amount of water fixated by absorption is high; cellular concrete and plaster are highly hygroscopic, for example.

Non-hygroscopic products: when mass is constant regardless of humidity levels; ceramic is a non-hygroscopic material, for example.

Mortar takes longer to dry than a clay piece. Thus, when high quantities of mortar are in contact with clay pieces, the latter will take longer to dry. This will in turn aid the appearance and development of moss and microorganisms, as well as damage from the frost-defrost cycle and will ultimately have negative effects on the roof as a whole.

The excessive use of mortar or the use of strong mortar (see section regarding the preparation of mortar in the chapter pertaining to the application of each tile type: Lusa, Marselha, Canudo and Milénio) will often result in the appearance of cracks, leading to infiltrations through the mortar itself.