FAQs

Most slates were deposited over 400 million years ago in layers of different quality under a sea bed then the earth moved and split into different parts and later divided by political borders. There have been various colour and quality slates in the market. The good quality slates to be determined by testing the material under EN12326 to achieve T1, S1, W1 and A1. The Spanish slates have very neat and uniform edges. The Madog Grey and Conwy Blue have the Welsh traditional deckle edges.

Our slates are tested to T1 in EN12326 report and free of damaging pyrite. They will not rust. We do not sell T2 slates that may rust or stain. 

Rosettas looks like bird droppings on the slate surface, normally round or oval. These are naturally occurring formation of calcium or Magnesium carbonate, formed during the development of the slate layers and are then exposed when the slates are split. Rosettas will not affect the performance of the slate. It will not be visible on roof if the rosettas are at the underside or inside the overlap part of the slate.

Our slates are tested to EN 12326-2 (T1 and S1) they will not change colour or weather rapidly.

Slates that change colour were not T1 slates, they would go rusty or have a higher calcium content, they would react to rain and sunlight and would weather quicker.

When we test and have slates that produce a slightly higher calcium carbonate content but pass the acid test, we would mark these as weathering slates.

We do not sell T2 slates that could go rusty.

A slate and half slate is used on the verge on alternate courses to create the horizontal lap. A slate and half may also be required on areas of the roof where slates need to be cut, for example around roof lights, chimney stacks etc. The use of slate and half slates ensures the width of any slate on the roof is more than the minimum width allowed in British Standards BS5534 which is 150mm.

Copper or Aluminium nails should be used to British Standard BS 1202 3.3 mm diameter.

Slate battens should be 50 x 25 mm should be used in accordance with British Standards BS 5534 Part 1 2003.

The portion of the slate which can be seen is known as the Margin and is dependent on the head-lap and calculated as (length of slate – head-lap / 2). This is also called gauge.

The Head-lap is the measurement of the slate that is covered by two layers of slate from the two courses above.

The Head-lap is what makes the roof watertight from Wind Driven rain, the Head-lap is increased on shallower pitched roofs and roofs with greater site exposure. If not sure please get advice.