The Truth About Roof Coatings And Sprays

Key takeaways

• A coating sits on the surface. It does not fix fixings, battens, underlay or junctions.
• Applied to a porous tile it can trap moisture inside the material rather than keeping it out.
• The things that end a roof's life are almost all underneath the surface being coated.
• It has caused difficulties for owners at the point of sale and with lenders and surveyors.
• There are legitimate coating products for specific surfaces. The doorstep version is a different thing.

What is actually being sold

The typical offer is a cleaning of the roof followed by the application of a liquid coating, usually an acrylic or polymer based product, sprayed or rolled over the tiles. It is presented as a restoration: the roof looks uniform and coloured again, the moss has gone, and the price is a fraction of a reroof. The proposition is that this extends the life of the roof by years. The difficulty with that proposition is not the product itself but the diagnosis behind it, because it treats the visible surface as the thing that determines how long a roof lasts, and on almost every roof it is not.

What ends a roof's life, and where those things are

Roofs reach the end of their service for a short list of reasons. Fixings corrode until tiles or slates begin to slip. Battens rot until they no longer hold. The underlay perishes so the secondary barrier is gone. Mortar at ridges and verges fails. Junctions and flashings leak. Structural movement distorts the covering. Every single one of those is underneath or beside the surface that a coating is applied to, and not one of them is affected by painting the outside. A roof that is losing tiles because its nails have corroded will carry on losing them after it has been coated, only now they will be coloured.

The moisture problem

There is a specific technical objection that matters. An ageing concrete tile has become porous, which means it absorbs water and releases it again as it dries. Applying a coating that reduces the surface permeability can leave moisture that has entered the tile from other routes, from the underside, from the laps, from condensation, with a slower path out. Water held inside a tile through freezing weather is the mechanism that spalls its face. Coating manufacturers address this with breathable formulations, which is precisely why the specification matters, and why a product applied by somebody who cannot explain its vapour permeability is a risk rather than a repair.

What it genuinely achieves

In fairness, it does something. A coated roof looks better, sometimes dramatically so, and for a homeowner whose concern is the appearance of a weathered patchy covering, that is a real outcome. Cleaning off the moss as part of the process has some value in itself. And a coating may shed water slightly more readily from the surface for a period. If a coating is bought with a clear understanding that it is a cosmetic treatment with a limited life, applied to a roof that is otherwise sound, that is a legitimate transaction. The problem arises when it is sold as a structural alternative to work the roof actually needs.

The sale and survey problem

This is the consequence owners rarely anticipate. A coated roof presents a surveyor with a surface that cannot be assessed in the usual way, because the coating obscures the condition of the tiles and can look like an attempt to conceal it. Surveyors and lenders have become noticeably more cautious, and a coating applied without documentation can result in a recommendation for further investigation or a retention. That converts a cosmetic purchase into a live issue during a sale, sometimes years later, and the owner is then in the position of having to demonstrate the condition of a roof that has been painted over.

How it is usually sold

The distribution model tells you a good deal. Roof coating is heavily marketed through cold calling, doorstep approaches and unsolicited contact, frequently following a storm or during a spell of bad weather when householders are already anxious. The pattern includes an inspection offered free, a report of alarming findings, a large headline price for replacement, and then the coating presented as the affordable alternative available today. Legitimate roofing work is not generally sold this way. That does not make every coating firm dishonest, and it does mean the channel through which most of this reaches homeowners is the one associated with the least reliable practices.

The comparison that is not being made

The persuasive part of the pitch is the price comparison: a coating against a full reroof. That is rarely the real choice. The genuine options for an ageing but functional roof are usually: do nothing and monitor; carry out targeted repairs to the ridge, verges, flashings and any slipped units; strip and relay reusing sound material; or fully replace. A coating does not appear anywhere on that list because it does not do what any of them do. Presented next to the most expensive option it looks like sensible economy. Presented next to a schedule of targeted repairs it usually does not.

The legitimate uses

It is worth being fair, because coatings are not inherently worthless. Liquid applied systems are a genuine and established technology on flat roofs, where a properly specified liquid membrane is a recognised covering in its own right rather than a decoration. Protective treatments and biocides applied to masonry and to some roof surfaces have real applications when correctly specified. What differs is the context: a designed system applied by somebody who can explain what it is for, against a doorstep offer to spray a pitched tiled roof that is losing its fixings. The word coating covers both, which is part of why the confusion persists.

Questions that settle it quickly

If a coating is being proposed, a few questions resolve the situation. What is the condition of the underlay, and how was that established? What state are the fixings and battens in? Which junctions were inspected and what was found? How does the coating address any of those? Is the product vapour permeable, and what is the manufacturer's specification? What happens at a sale when a surveyor sees a coated roof? A supplier with a genuine product and a sound diagnosis can answer all of them. One who cannot is selling appearance and describing it as longevity.

What to do instead

If the roof looks tired and you want to know where it stands, commission an assessment that includes the loft, the underlay, the fixings and the junctions, and ask for photographs and findings rather than a price. That will tell you whether you are looking at years of remaining life with some targeted repairs, or a roof approaching replacement. Either answer is more useful than a coating, and the assessment costs a fraction of it. If the concern is genuinely appearance rather than performance, that is a legitimate thing to spend money on, and it should be decided with the condition of the roof known rather than instead of knowing it.

The honest summary

A coating changes how a roof looks and does not change how long it lasts, because the things that determine that are underneath it. On a sound roof it is a cosmetic purchase with a limited life and some risk attached at the point of sale. On a failing roof it is money spent on the one part of the problem that was not the problem. And the fact that it is predominantly sold through unsolicited approaches to worried householders, at a price positioned against the most expensive alternative, is the clearest signal available about the proposition being made.

Your rights if you have already agreed to one

Where an agreement is made at your home following an unsolicited visit, consumer protection legislation generally provides a cancellation period, and traders are usually obliged to give written notice of that right. Failing to provide it can extend the period considerably and can be an offence. If work has been agreed on the doorstep and second thoughts have set in, that position is worth establishing rather than assuming the contract is binding. Citizens Advice publishes guidance on cancellation rights for contracts made at home, and it is the appropriate starting point before paying a deposit or allowing work to begin.

Frequently Asked Questions

Does roof coating extend the life of a roof?

Not meaningfully, because the things that end a roof's life are underneath the surface being coated: corroded fixings, rotted battens, perished underlay, failed mortar and leaking junctions. A coating changes the appearance of the tiles and does not affect any of those.

Can a coating cause harm?

It can. On an ageing porous tile, a coating that reduces surface permeability may slow the route by which absorbed moisture escapes, and water held inside a tile through freezing weather is what spalls its face. This is why vapour permeability is a specification question worth asking about directly.

Why do surveyors dislike coated roofs?

Because the coating obscures the condition of the covering, so it cannot be assessed in the usual way, and it can read as an attempt to conceal deterioration. Surveyors and lenders have become more cautious, and it can lead to a recommendation for further investigation during a sale.

Are all roof coatings a bad idea?

No. Liquid applied systems are an established and legitimate technology on flat roofs, where a properly specified membrane is a covering in its own right. The concern is with unsolicited offers to spray a pitched tiled roof as an alternative to work that roof actually needs.

It is much cheaper than a new roof. Is that not worth it?

That comparison is usually the wrong one. The real options for an ageing roof are monitoring, targeted repairs to ridges, verges and flashings, a strip and relay reusing sound material, or replacement. A coating sits alongside none of those, and next to a schedule of targeted repairs it compares far less favourably.

What should I ask if somebody offers this?

What condition the underlay, fixings and battens are in and how that was established, which junctions were inspected, how the coating addresses any of it, whether the product is vapour permeable, and what happens when a surveyor sees a coated roof at sale. Those questions settle it quickly.