Can I just paint over weathered render?

NOT without prep. First pressure-wash, dry, apply solvent-based micro-molecular primer to stabilise, then paint.

Which render lasts longest in sun?

Silicone/siloxane texture coat (15-20+ yrs). Acrylic 12-15 yrs. Plain cement render + cheap paint just 5-7.

Degradation & Ageing: Surface Damage from UV Radiation and Rain

You look at the exterior of your house and you realise it bears no resemblance to how it looked ten years ago. The colour has faded, the textured finish has smoothed out in some areas, and if you run your hand over the wall, your fingers get covered with a fine, coloured powder.

It's not necessarily the fault of the applicator who did the work. The external render (and its paint) fights a daily battle with the elements of nature. This gradual, natural wear is called degradation (or ageing). Let's see how the sun, rain, and pollution work together to "eat" your render and how you can prolong its life.

1. The Ultraviolet (UV) Radiation and the Chalking Phenomenon

The biggest enemy of paints and modern paste renders (acrylic/silicone) is not water, but the sun. Ultraviolet (UV) radiation has the ability to break the chemical bonds of materials.

What is Chalking: The acrylic resins that act as the "glue" inside the render or paint are "baked" by the sun and over-polymerised, losing their elasticity. Gradually, these resins break down and disappear, leaving behind only the pigments (the coloured powders) and the inert aggregates, completely free on the surface.
The Signs: The wall loses its sheen (becomes completely matte), the colour fades (especially in dark reds and blues) and if you rub the surface with a black cloth, it will be covered with a chalk-like powder.

Chalking test - black cloth on faded wall

2. Rain and the "Washing" of the Wall

While the sun does the groundwork (breaking down the resins), the rain comes in to complete the work of degradation.

🌧️ Mechanical Erosion

Rainwater, hitting with force on the already weakened (by the sun) surface, carries away the free dust and sand grains. Over the years, the thickness of the render decreases.

☁️ Acid Rain

In large urban centres, the rain mixes with atmospheric pollutants and becomes slightly acidic (low pH). Traditional cement render and lime are alkaline materials (high pH). When the acid of the rain meets the alkaline cement, a chemical erosion begins that "eats" the skin of the wall.

🏙️ Pollutants and Soot (The "Greying")

If your house is on a main road, degradation is accelerated by exhaust fumes (soot). Micro-pollutants stick to the pores of the dried render. When it rains, the rain doesn't wash them away, but "soaks" them deeper into the material, giving the building that classic, dirty greyish look that cannot be cleaned with a hose.

3. Durability Comparison: Materials vs Time

How long does a render ultimately last before it starts showing the signs of ageing?

Finish Type	UV (Sun) Resistance	Rain / Pollution Resistance	Expected Time Until Maintenance
Plain Cement Render + Cheap Emulsion Paint	Low (Heavy Chalking)	Medium	5 - 7 years
100% Acrylic Exterior Paint	Good	Good	8 - 12 years
Acrylic Paste Render (ETICS)	Very Good	Excellent Waterproofing (But soils easily)	12 - 15 years
Silicone/Siloxane Paste Render	Excellent	Excellent (Self-cleaning)	15 - 20+ years

4. The Right Approach (How to Refresh the Façade)

If your wall has suffered heavy chalking and degradation, simply painting over it is money thrown away. The new paint will stick to the dust and peel off in a few months. The maintenance procedure requires proper preparation:

1️⃣ Stabilisation with Primer

Because the old render has become porous, it needs a micro-molecular solvent-based acrylic primer (or silicone primer). This liquid will penetrate deep into the pores, "re-bind" the friable particles, and create a solid base.

2️⃣ Selection of Professional Paint

Don't skimp on the final paint. Choose 100% acrylic or silicone paints, which feature built-in UV filters. If the house already has small hairline cracks, choose an elastomeric paint that acts like a flexible membrane and follows the expansions and contractions of the building.

⚠️ The Secret of Preparation: The first step is always washing. Use a pressure washer (hydroblasting) at medium pressure to wash away all the chalking dust, pollutants, and loose pieces. Let the wall dry completely.

Thermal Cracks in Render: Expansion, Contraction & Dark Colours Interior Mould on Plaster: Thermal Bridges & Ventilation Rising Damp: How Foundation Water Destroys Plaster Acrylic vs Silicone Renders: ETICS Finish Coat Guide

Plaster Pathology, Cracks & Moisture

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