Acrylic-bound paints can significantly harm historic building fabric, mainly because they trap moisture in porous masonry and renders, disrupting the wall's natural ability to "breathe." This trapped moisture triggers a cascade of deterioration, from paint failure to structural damage.

Historic masonry (brick, stone, lime render) is porous and designed to absorb and release moisture vapour. Acrylic paints form a relatively impermeable film that blocks this natural process. While acrylics are not completely vapour-tight, their resistance to water vapour is significantly higher than traditional finishes like limewash, and this is enough to cause problems in old walls.

Because water inevitably finds its way into masonry (via rising damp, leaks, or condensation), an acrylic coating prevents it from escaping. This causes moisture to build up behind the paint film. The damage manifests in several interconnected ways:

Paint Failure and Surface Damage: Moisture pressure from behind causes the acrylic film to blister, crack, and flake off. This is often the first visible sign of a problem.
Freeze-Thaw Destruction: In colder climates, trapped water freezes and expands. The ice exerts immense pressure within the masonry pores, causing the brick, stone, or render itself to crack, spall, and disintegrate.

Salt Damage (Efflorescence and Subflorescence): Moisture in masonry often carries dissolved salts. When an acrylic coating restricts surface evaporation, these salts can concentrate and crystallise. They may appear as unsightly white deposits on the surface (efflorescence) or, more damagingly, crystallise inside the pores (subflorescence), creating internal stresses that pulverise the material.

Mould and Biological Growth: A persistently damp wall creates an ideal environment for mould and algae, particularly on interior surfaces or exterior walls where moisture is retained.
Substrate Decay: The constant presence of moisture behind an impermeable film can eventually soften and weaken the underlying render or masonry, compromising its structural integrity.
 

We carry out simple tests to identify acrylics and plastics in paints.

The "Span" (Knife) Test: We look at the elasticity of the samples. Acrylic- and plastic-based dispersion paints often produce a slightly elastic shaving, whereas traditional oil or alkyd paints tend to be brittle.

Solvent Swelling/Dissolution: We apply a solvent with a cotton swab. Including: Alcohol (Ethanol/Spirit) (Pure acrylic dispersion films often soften or swell when rubbed with alcohol); White Spirit (Mineral Turpentine) (Many dispersion paints (including acrylics) will swell, while solvent-based acrylics may dissolve); and Xylene or Nitro Thinner (Pure acrylic facade paints and plastoelastic systems often show strong swelling or solubility in stronger solvents like xylene or nitro thinner; alkyd paints may only soften or blister with paint stripper)

To positively identify the polymer type (e.g., acrylic vs styrene-acrylic vs vinyl acetate), you need instrumental methods. Infrared Spectroscopy (FTIR): This is a primary method. By analysing the infrared spectrum of a paint film (often using a diamond cell), you can identify the specific functional groups. Pure acrylics, styrene-acrylics, and vinyl acetate polymers produce distinct, identifiable spectra. Or Pyrolysis Gas-Liquid Chromatography: According to standard practice (like ASTM D3168), this is particularly useful when acrylics are used as a minor comonomer or blended with other resins (like alkyds). Heating the paint film to decomposition and analysing the resulting "pyrogram" identifies specific acrylic components that FTIR alone might miss.