The short answer: Softwash cleans and protects. Coating restores appearance and adds water repellency — but it's always applied after a softwash, not instead of one. Whether you need coating depends on your tile type and how much cosmetic restoration you want.
What this guide covers
1. What each treatment actually does
Softwash biocide treatment
A professional softwash applies sodium hypochlorite-based biocide at low pressure to the roof surface. The chemistry penetrates the tile and kills moss, algae and lichen at the spore level. The visible result appears over 4–8 weeks as rainfall washes the dead biological matter off the roof. A professional softwash keeps a roof biologically clean for 4–5 years and comes with a written regrowth guarantee.
Softwash treats the cause of the problem — embedded biological growth — but does not change the underlying tile surface, its colour, or its water absorption properties.
Roof coating
A roof coating is an elastomeric or acrylic coating sprayed onto the tile surface after a softwash clean. It does two things: it restores faded tile colour to a consistent, vibrant finish; and it reduces tile porosity, slowing water absorption and future biological colonisation.
A coating addresses the appearance of the roof and its long-term surface properties — but it must be applied to a clean roof. Coating on top of biological matter traps the growth beneath and causes the coating to fail within 2–3 years.
2. Side-by-side comparison
| Softwash only | Softwash + Coating | |
|---|---|---|
| Kills moss & algae | Yes | Yes (softwash included) |
| Prevents regrowth | 4–5 years | 10+ years |
| Restores tile colour | No | Yes |
| Reduces tile porosity | No | Yes |
| Suitable for all tiles | Yes | Concrete only |
| Typical cost (semi) | £350–£450 | £1,100–£1,400 |
| Guarantee | 5-year regrowth | 10-year coating + 5-year regrowth |
| Visible result timing | 4–8 weeks | Immediately (colour) + 4–8 weeks (full clean) |
3. Which tile types can be coated
This is the most important filter. Roof coatings are designed exclusively for concrete tiles.
- Concrete tiles ✓ — Elastomeric and acrylic coatings bond correctly to concrete's porous surface. Coating is most valuable here because concrete tiles fade significantly over 15–20 years.
- Clay tiles ✗ — Clay tiles have different thermal expansion rates and surface properties. Coating is not appropriate and may cause adhesion failure or moisture trapping.
- Natural slate ✗ — Slate is a natural stone with a layered structure. Coating traps moisture in the laminate layers and accelerates delamination (splitting). Never coat slate.
- Fibre cement slates ○ — Occasionally suitable for specialist coatings designed for that substrate. Not a standard application — assess at survey.
Not sure if you have concrete or clay tiles?
Concrete tiles are heavier, more uniform in size, and show more colour fade over time. Clay tiles have a natural variation in tone and tend to hold their colour better. If in doubt, we'll identify tile type at survey and advise accordingly.
4. When coating is worth it
Coating adds genuine value when:
- Your concrete tiles have faded noticeably from their original colour — patchy, washed-out or bleached appearance even after cleaning
- The roof is structurally sound — no cracked, slipped or seriously damaged tiles (coating is cosmetic; it doesn't fix structural problems)
- You want to extend the roof's life without replacement — the reduced porosity measurably slows future degradation
- You're selling the property within 5 years — a coated roof looks like new tiles at a fraction of replacement cost
- You want the longer guarantee — 10-year coating manufacturer warranty vs 5-year softwash guarantee
5. When softwash alone is enough
Coating is not always the right choice. Softwash alone is appropriate when:
- You have clay or slate tiles — coating is not suitable; softwash is the only correct treatment
- Your concrete tiles are relatively recent (under 15 years) and the colour is still good — cleaning will restore the appearance without needing coating
- You want the lowest cost treatment — softwash at £350–£450 is the most cost-effective route to a clean, biologically protected roof
- Some tiles are cracked or damaged — those need replacing before any coating; sometimes softwash first while you arrange repairs is the pragmatic sequence
6. Costs compared
| Treatment | Semi-detached | Detached |
|---|---|---|
| Softwash only | From £350 | From £450 |
| Clean + coat (combined) | From £1,100 | From £1,400 |
| Coat only (post-recent clean) | From £800 | From £1,000 |
All quoted as fixed price. Survey required before final quote — tile type, condition and coverage area determine the final figure.
The cost-per-year calculation often favours coating for older concrete tile roofs:
- Softwash alone: £400 every 5 years = £80/year
- Clean + coat: £1,200 every 10–12 years = £100–120/year
Add the cosmetic and kerb-appeal value of a freshly coated roof, and for the right property, the premium is easy to justify.
Not sure which is right for your roof?
We assess tile type, condition and coverage at survey and give you an honest recommendation — not just the higher-margin option.
Get my free survey & quote7. Frequently asked questions
What is the difference between a softwash and a roof coating?
A softwash is a biocide cleaning treatment that kills moss, algae and lichen and keeps the roof clean for 4–5 years. A roof coating is an elastomeric or acrylic coating applied after cleaning to restore tile colour and add water repellency. Softwash treats biological growth; coating changes the tile's surface properties. The two are complementary, not alternatives — a coating is always applied after a softwash clean.
Is roof coating better than softwash?
They serve different purposes, so "better" depends on what your roof needs. If you have moss and want it killed and prevented from returning, softwash is the answer. If you also have faded concrete tiles you want to restore cosmetically, coating adds that dimension. There's no scenario where coating replaces softwash — coating without cleaning first traps biological matter under the coating.
What types of tiles can be coated?
Concrete tiles only. Elastomeric and acrylic coatings are designed for the porous, pigmented surface of concrete tiles. They are not suitable for clay or natural slate. If your roof is clay or slate, softwash cleaning is the correct treatment — no coating.
How much does roof coating cost vs softwash alone?
For a standard semi-detached, a softwash alone costs £350–£450. Adding a coating (clean + coat combined) costs £1,100–£1,400. Coating alone (where the roof was recently cleaned) starts from £800. The coating adds meaningful cost but also meaningful longevity — the coating itself carries a 10-year manufacturer guarantee.
Does a coated roof still need softwash treatment?
A properly coated roof reduces biological growth significantly because the surface is less porous and more water-repellent. Most homeowners find the coating lasts the full 10-year manufacturer period without requiring a repeat softwash. When the coating eventually thins, a softwash and re-coat is the recommended cycle.
What happens if I coat a roof without cleaning it first?
The biological matter (moss, algae, lichen) is sealed under the coating. It continues to grow underneath, eventually lifting and cracking the coating from below. The result is a flaking, blotchy coating within 2–3 years, and the underlying tile is harder to clean because you now have to remove the failed coating as well. Cleaning first is non-negotiable.
This guide is updated periodically. Last updated: 27 May 2026.