Does a silicone water-repellent treatment stop a wall from breathing?

No. Proper silicone (silane/siloxane) impregnation bonds to the pore walls and keeps the capillaries open, so water vapour can still diffuse through the substrate.

How can the surface repel rain if the pores stay open?

The treatment increases the water contact angle on the pore walls. Liquid water beads up and cannot wet the surface effectively, so capillary uptake drops dramatically while vapour diffusion remains largely unchanged.

What is the limitation of breathable hydrophobisation?

It is not a waterproofing system against hydrostatic pressure (for example, basements or pools). It is designed for driving rain, splash water and reduced capillary absorption.

Silicone water-repellent treatment can remain effective for many years and, in documented cases, for decades. Durability depends on surface type, exposure and correct application: clean and dry substrate, sufficient uptake, and wiping off any excess product.

FREQUENTLY ASKED QUESTION – HOW SILICONE HYDROPHOBISATION WORKS

How can a silicone‑treated wall repel water and still breathe?

Vapour diffusion remains Pores stay open Real video demonstrations

Silicone impregnation – illustrative image

Short answer: yes – a properly silicone‑treated mineral wall remains breathable. The treatment does not “seal” the pores; it lines their walls with a water‑repellent chemistry.

1) Why the wall still “breathes”

Mineral substrates (brick, plaster, concrete, natural stone) have an interconnected pore system. Water vapour moves through these pores by diffusion. Silicone impregnation (silane / siloxane) reacts with the mineral pore walls and becomes part of the surface chemistry, without forming a continuous film across the pore openings.

Think of it like this: the pores stay open, but the “walls” of the pores become water‑repellent. Vapour can pass; liquid water is strongly discouraged.

2) Why it repels rain even with open pores

Liquid water normally wets mineral surfaces easily, so capillary suction pulls it into the substrate. Silicone treatment increases the water contact angle (wetting angle) on the pore walls. The result is beading and dramatically reduced capillary uptake. This is why façades can be both water‑repellent and vapour‑permeable at the same time.

Important limitation: breathable hydrophobisation is not a waterproofing system against hydrostatic pressure (for example, basements or pools). It is intended for driving rain, splash water and reduced capillary absorption.

3) Real demonstrations (videos & images)

Demonstration A – air passes through an impregnated porous material

In this glass funnel we use an impregnated porous stone, pour water on top and blow air from below. The bubbles rise freely – a simple visual demonstration that the pore network is not “blocked”.

Narration (EN): “The porous sample is silicone‑impregnated. Water sits above it, but when we blow air from below, bubbles pass through the material and reach the surface. This shows the pores remain open – the treatment does not create a sealed film.”

Demonstration B – microscope image: pores open vs. film‑forming coatings

Click to enlarge. The treated side shows open capillaries, while film‑forming polymer coatings can partially close or block the pore structure.

Demonstration C – why the surface stays clean(er)

The diagram below illustrates a typical effect: an untreated mineral paint surface wets easily and holds dirt; a silicone‑modified surface sheds water, which helps reduce long‑term staining.

Demonstration D – “the writing stays dry” test

When the wall is wetted, the untreated area darkens (it takes up water). The silicone‑treated lettering stays noticeably lighter – because it remains dry.

Narration (EN): “We pour water over the wall. The untreated surface darkens immediately, showing water uptake. The silicone‑treated text remains light and dry, demonstrating the strong reduction of capillary absorption.”

Demonstration E – wetting angle (contact angle)

Wetting angle is the angle between a liquid droplet and the solid surface. The closer it is to 180°, the less the liquid wets the surface. Silicone treatment increases this angle, forcing water into a beading droplet shape.

(click to enlarge)

Demonstration F – bridging small cracks & depth of protection

Because impregnation penetrates into the pore system (typically a few millimetres, depending on the substrate), minor surface abrasion does not immediately remove the protective zone. On very porous materials you can even observe a “bridging” effect across small cracks.

Demonstration G – double aerated concrete droplet test

This video shows the difference between treated and untreated aerated concrete (YTONG) with water droplets side‑by‑side.

Narration (EN): “On the untreated YTONG, the droplet spreads and is absorbed. On the silicone‑treated side, the droplet beads and stays on the surface. This visual difference comes from the increased contact angle after impregnation.”

Demonstration H – resistance against staining liquids (example: cola)

In practice, reduced wetting also helps against common staining liquids. This example compares an untreated aerated concrete block with Coca‑Cola (contains acids and colouring agents) versus a treated surface.

Narration (EN): “Cola contains acids and dyes. On the untreated block it wets and penetrates quickly; on the treated surface wetting is reduced, helping to limit deep staining. Always test first on sensitive surfaces.”

Bottom line: silicone impregnation combines two advantages: mineral‑like breathability and strong water repellency. If you need help choosing the right product for your substrate (brick, plaster, concrete, stone), write to us and we will recommend a safe procedure.

In brief: the key idea

Breathability stays: pores remain open, so vapour diffusion continues.

Water is repelled: contact angle increases, water beads and capillary uptake drops.

Fast drying: after wetting, treated areas typically dry quicker and more evenly.

Know the limit: not for water pressure (basements / pools) – for rain & splash water protection.

Common mistakes

applying on a damp substrate → patchiness / weak performance
leaving excess on the surface → streaks / glossy patches
impregnating over dirt or algae → contamination gets “sealed in” visually
expecting waterproofing under pressure → wrong system for the job