CE marking in roofing slates

PlantillamarcadoCECE marking is mandatory for all the products sold in the European Union, regardless of the country of origin of the products. In the case of roofing slate, this marking is done using the data obtained from the tests of EN 12326 (parts 1 and 2) Slate and natural stone for discontinuous roofing and cladding. The CE mark does not establish qualities, just gives information about product features. The different qualities of the slate are established by the manufacturer taking into account the market requirements and its own standards.

The results of the tests of EN have to be stated on a label attached to each pallet or slate cage. In paragraph ZA of EN 12326-1 is an example of CE label, although there are other solutions.

 

 

 

CE label as in EN 12326-1

 

CE Pizarra01

CE Pizarra00Two examples of CE marking

Together with this label must be included another document, the declaration of conformity, in which it is specified in detail the characteristics of the slate. This document must accompany each sold batch of slate; there is no need to include it to slate pallet or cage. As for the label, there is a model in Part 1 of the standard.

The CE marking is mandatory for roofing slate since 2004, so it is sufficiently well established between producers and consumers. However, there are still companies that refuse to incorporate it to their products, either by ignorance or negligence law, thereby risking a sanction by the competent authority.

Pathologies in slates, part IV

Gypsification

Gypsification is the phenomenon by which the carbonates that may be present in the slate is transformed into gypsum by contact with the sulfur (S) coming from the atmosphere or from the iron sulfides, following the reaction:

H2SO4 + CaCO3 –> CaSO4 · H2O + CO2

Fig02The transformation from carbonate to gypsum is potentially harmful, because the gypsum has a mineral size substantially larger than the carbonate, so a swelling occurs inside the slate (figure 1), affecting seriously the integrity of the tile. As oxidation, gypsification is very evident when occurs, since it develops a characteristic whitening along the surface of the slate tile (figures 2 and 3). The gypsification is closely linked to acidic environments, especially urban environments where sulfur concentrations are usually high.

Sin título-1

Figure 2 (left): Cover affected by gypsification
Figure 3 (right): Slate severely affected by gypsification after exposure to SO2 test

Gypsification prevention

The best way to know if a slate may suffer gypsification are the normative tests of exposure to SO2, as expressed in EN 12326, or to the test of weather resistance of ASTM C-217. Both tests submit the slate to acid conditions, and then quantify the alteration suffered by giving three degrees. EN 12326 provides three visual alteration levels (S1, S2 and S3), while ASTM performs a scraping of the slate surface after the acid exposure, and then makes three estimates of the service life depending on the depth of the scratch (S1:> 75 years, S2: 40-75 years, S3: 20-40 years).

The carbonate content test of EN also gives an idea of how susceptible to gypsification can be a slate. In theory, higher carbonate content will lead to a high susceptibility. However, this fact has to be taken with caution, as the carbonate may be present as well crystallized calcite, which resists very well against yesificación. Again, petrographic examination can help in this case, since it will determine the form in which is present the carbonate.

Carbonate crystal in a schist roofing slate

Carbonate crystal in a schist roofing slate, transmitted light microscopy, zoom 250, crossed polarizers

Further reading: Standard tests for the characterization of roofing slate pathologies

Different types of roofing slates

Definition of roofing slate after EN 12326

According to EN 12326-1:2005, from a commercial point of view, a roofing slate is a “rock which is easily split into thin sheets along a plane of cleavage resulting from a schistosity flux caused by very low or low grade metamorphism due to tectonic compression. It is distinguished from a sedimentary slate (shale, author´s note) which invariably splits along a bedding or sedimentation plane. Slate originates from clayey sedimentary rocks and belongs petrographically to a range which begins at the boundary between sedimentary and metamorphic formations and ends at the epizonal-metamorphic phyllite formations”.

This definition makes quite clear, from a petrological point of view, the range of rocks which can be considered slates. However, EN 12326-1:2005 continues defining roofing slate as a ”rock used for roofing and cladding, in which phyllosilicates are the predominant and most important components and exhibiting a prominent slaty cleavage”. Likewise, roofing carbonate slate is defined in the same way as above but with a minimum of 20% content of carbonate.

Metamorphic facies stability diagram. Modified from Spear, 1993.

Metamorphic facies stability diagram. Modified from Spear, 1993.

For the Subcomission on the Systematics of Metamorphic Rocks (SCMR), a part of the International Union of Geological Sciences (IUGS), a slate s.s. is “an ultrafine- or very fined-grained rock displaying slaty cleavage”. This slaty cleavage is also defined as “a type of continuos cleavage in which the individual grains are too small to be seen by the unaided eye”. The slaty cleavage is the most important characteristic of roofing slates, since it allows the rock to be split into large and thin tiles.

It is clear that there are two types of rocks, slates s.s., sometimes also called lutitic slates, which are low-grade metamorphic rocks (greenschist facies), and commercial slates or roofing slates, which are rocks composed mainly of phyllosilicates with an exfoliation which allows to produce tiles that may be used as roofing materials. This second group includes the slates s.s. together with other types of rocks, like shales, phyllites and schists.

A: Sedimentary slate (shale) with no develop of slaty cleavage. The planes correspond to sedimentation beds. Minas Gerais, Brazil.
B: Slate s.s., in which the planes correspond to slaty cleavage. Herbeumont, Belgium.
C: Phyllite, with a metamorphic grade slightly higher than the slate s.s., as the biotite crystals shows. Bernardos, Spain.
D: Schist, with a well developed schistosity. Finnmark, Norway.