Why they don't belong inside
Heavy elastomeric coatings form a thick film that acts as a vapour barrier (very high Sd value). The wall stops "breathing," dramatically raising the risk of mould and condensation.
Elasticity & Crack Bridging
Cracks on interior walls are one of the most common headaches in any home - from natural settling, thermal expansion, or minor earthquakes. Many homeowners' first thought: "Is there an elastic paint that will make the problem disappear?" The answer isn't a simple yes or no. Let's look at what really works, the hidden traps of using elastomeric coatings indoors, and how to deal with cracks properly.
Elastomeric Paint Indoors: Myth or Solution?
When we hear "elastomeric," we think mainly of exterior coatings - for facades and flat roofs. But can you use them in your living room?
What this means in practice
In a bedroom or living room, the elastomeric membrane traps moisture behind the wall instead of regulating it. Result: internal dampness, fungal growth and worse long-term problems.
Exterior elastomeric coatings on interior walls = bad idea. The real crack solution lies elsewhere.
The Right Solution: A 3-Step Crack Repair System
For interiors, we don't rely on the paint to bridge the crack. Instead we follow a three-step system:
① Elastic Crack Filler
Open the crack into a V-shape with a scraper, then fill it with a specialised, highly elastic acrylic or polyurethane filler. It stays flexible under the paint and absorbs vibrations.
② Fiberglass Tape
For larger cracks, apply fiberglass mesh tape over the filler. This guarantees the crack won't reopen even if the wall moves.
③ Premium Emulsion (Class 1)
Once the repair is done, paint with a top-quality acrylic/vinyl emulsion. The best paints have enough natural elasticity - thanks to high resin content - not to crack easily.
Technical Guide: What to Check in the TDS
If you're looking for a product that truly bridges cracks, marketing claims aren't enough. Open the TDS and look for three criteria:
| Criterion | What it measures | What to look for |
|---|---|---|
| EN 1062-7 - Crack Bridging | Widest crack the film can span without breaking | A1 (>0.1 mm), A2 (>0.25 mm), A3 (>0.5 mm), A4/A5 for extreme |
| Dry Film Thickness (DFT) | Minimum coat thickness for the bridging claim to hold | Standard emulsion: 30–40 µm · bridging: > 150–200 µm |
| Elongation at Break (ASTM D412) | How much the dry film stretches before tearing (%) | Quality elastomeric: 150–400 % with recovery |
If the TDS simply says "elastic" without an EN 1062-7 class, the elasticity is not officially certified. Always ask for the class number.
When an Elastomeric System Makes Sense
There are cases where an elastomeric solution is justified - but they almost always involve exterior surfaces or specialist use:
Exterior Facades
Here elastomeric coatings provide crack bridging and rain-proofing - their primary reason for existing.
Industrial / Medical Spaces
Specialised interior systems with certified crack bridging exist (hospitals, factories), but their cost is prohibitive for residential use.
Severe Structural Issues
Cracks wider than 1 mm that keep growing need a structural assessment first - no paint can substitute structural reinforcement.
Conclusion
Don't look for the solution in the paint tin alone. Avoid heavy exterior elastomeric coatings on your interior walls - they'll destroy the building's breathability.
The correct approach: open the crack → elastic filler (+ mesh) → premium emulsion. Proper surface preparation is the ultimate secret to never seeing that crack again.
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