ᐅ Why is Malm so sensitive to moisture?

I have a specific question regarding the material properties of marlstone, particularly why this rock is so sensitive to moisture. I have noticed that marlstone building elements or natural formations tend to erode faster or appear more porous under high humidity compared to other types of limestone. This seems to be related to the mineral composition and porosity, but also to the interaction between water and certain components. Could someone explain in detail the exact reasons for this high sensitivity to moisture? Are there typical physical or chemical processes that make marlstone especially vulnerable? And how can these characteristics be best taken into account in construction projects or in the preservation of historic buildings?

Malm is particularly porous and has many fine capillaries that absorb water quickly. This leads to increased sensitivity to moisture. Simply put: water penetrates easily, and damage occurs more rapidly.

The chemical composition of Malm, especially its high calcium carbonate content, reacts with CO2 in water when moisture is present, causing it to slowly dissolve. This makes the rock more susceptible to erosion.

To better understand the moisture sensitivity of Malm, let's examine the interaction of physical and chemical factors:

1. Porosity and capillarity: Malm has a very fine-grained structure with many pores and capillaries. These absorb moisture quickly and retain it for extended periods.

2. Calcium carbonate dissolution: The calcium carbonate contained in Malm chemically reacts in the presence of water and carbon dioxide to form calcium bicarbonate, which is water-soluble. This causes the rock to dissolve slowly.

3. Freeze-thaw cycles: When moisture penetrates the pores and freezes during cold weather, the water expands. This mechanical stress creates microcracks that make Malm more porous.

Summary: The combination of fine-grained porosity, chemical reactivity, and freeze-thaw effects makes Malm highly sensitive to moisture. For construction and heritage conservation, this means careful moisture control and protective measures such as impregnations or roofing.

Tofra45 schrieb:
Malm is particularly porous and has many fine capillaries that absorb water quickly.

Exactly, that’s why Malm building components should always be well protected against direct moisture, otherwise water can quickly penetrate and damage the material.

I believe we should also consider the variability within Malm itself. Malm is not a uniform rock; its composition and structure vary significantly depending on the deposit.

Therefore, the question of why Malm is so sensitive to moisture needs to be specified as: Which exact type of Malm?

There are Malm formations with rather dense sections and others with higher porosities. Without precise identification, any answer will be too general. Additionally, it is important to examine whether atmospheric conditions or microclimatic factors amplify or reduce the effects of moisture.

Could someone provide more detailed comparative data on this?