Weather resistance consists of several properties

Water absorption, wet strength, swelling, drying and freeze-thaw behaviour describe different processes. A single marketing term such as "waterproof" does not answer these questions. Particularly relevant is whether the documents cover the climate and application actually intended.

The current ETA-11/0458 describes for the assessed mineral exterior board, among other things, outdoor use and durability tests including moisture and frost exposure. The scope is stated together with conditions in the assessment. It is a good basis for selecting an exterior board. [1]

On PVC-P, bitumen, PIB or TPO/FPO

A mineral board can be designed as a protective layer above these roof membrane families. This requires assessing the specific membrane, its surface and the contact. With PVC-P, material compatibility and movement play a role, among other things. With granule-surfaced bitumen, loose granules, flatness and bearing are important. With PIB and TPO/FPO, the respective system requirements govern.

For WEER, board material and roof membrane are therefore considered together. A suitable contact or separation layer must not pond water and must suit load distribution and wind restraint. Naming the membrane family alone does not replace this assignment.

Why water management matters even with a durable board

Board joints are not automatically watertight seams. Water can pass through joints to the roof waterproofing below and must drain from there unhindered. Critical points are low spots, covered outlets and board edges that sit in standing water for long periods.

Plan for inspection: keep outlets accessible, document connection zones and design the layer so that later roof repairs remain possible. A material's service life alone says little about how maintainable the whole roof is.

Distinguishing MgO boards: chloride is not phosphate

MgO is a collective term, not a complete binder specification. The Danish research project on moisture damage examined boards containing magnesium chloride in façades. There, moisture uptake and salt-laden release were described together with damage to adjacent materials and fasteners. [2]

These findings must not be transferred wholesale to magnesium phosphate-bound products, every MgO supplier or every climate. Rather, they show why binder, salt content, moisture behaviour and specific test documents are relevant. A low import price without matching documentation is not yet a sound material selection.

Moisture is also an issue beneath the roof membrane

A cover board beneath new waterproofing is protected later on, but can get wet during storage and installation. Construction moisture, condensation or later leaks add to this. Dry storage, controlled construction stages and a procedure for saturated boards therefore belong in the installation plan.

Our guide to installation position shows when SHEET beneath the membrane and when WEER on the roof surface is the right direction. For both routes: material property and water management are designed together.

A board above waterproofing needs documented exterior durability and a drainage detail. A1 alone establishes neither frost resistance nor membrane compatibility.