Before 3pm on a working day, contacted the same day. After 3pm, the next working day. Contact, not a quotation. Telephone
Start a project brief
An old corrugated asbestos-cement roof on a UK industrial building seen from above at first light, weathered grey sheets, hook bolts along the crests and a pale sky.

Application

Roof coatings and waterproofing: the roof restored and sealed from above, the sheet left in place.

A liquid-applied silicone coating that follows the roof, seals every fixing and lap, stays flexible under UV and tolerates standing water. On weathered metal, aged single-ply, ponding flat roofs, and asbestos-cement roofs that are better encapsulated than removed.

Start a project brief What it costs: the cost guide
  • Nationwide coverage
  • Endorsed by architects, engineers and commercial clients
  • Expertise across thousands of projects

Is this your roof?

01The build-up

The sheet stays. The coating follows it and closes every path.

An old asbestos-cement roof does not usually fail as a sheet. It fails at the fixings, the laps and the cracks, and it grows moss in the troughs that holds water against it. Switch the drawing between the weathered roof and the coated roof.

Two states. Switch between them; the marks and the reading follow.

Swipe across to see the whole section.

WEATHERED SHEET · WATER FINDS A PATHSection, schematic, not to scale. Three marks in each state; the cards beneath read them.

Weathered sheet · water held and let throughThe threshold · water finds a pathSealed surface · water sheds

1The weathered sheet

Porous now, and brittle.

Decades of weather leave asbestos-cement porous on the surface and brittle at the edges. It holds water, dries slowly, and sheds fibres where it is worn. It is usually still sound as a sheet.

2Fixings and laps

Where the water actually gets in.

Hook bolts work loose, washers perish, and the laps open as the sheets move. Nearly every leak on a roof like this is at a fixing or a lap, not through the field of the sheet.

3Moss, cracks and ponding

Water held against the roof.

Moss in the troughs holds water against the sheet for weeks. Cracks propagate from fixing holes. On a low-slope roof, water ponds and finds the weakest point.

The short version: an ageing roof usually leaks at its fixings and laps, not through its sheets. A liquid-applied silicone coating closes those first and then seals the whole roof as one skin, without stripping anything off. The rest of this page is how it goes on properly.

02Project record

A coating going on, on a real project.

Installation footage from HOLVEM's own projects: a protective coating applied over finished spray foam. This item is a project record, played on request; nothing on this page that is not real footage carries that label.

Project recordProtective coating over foam
Protective coating applied over the finished foam. One of the coatings HOLVEM applies: here protecting an exposed foam layer from the weather.

The coating is a system in its own right.

Whether it protects a foam jacket from UV or seals an ageing roof from above, a liquid-applied coating is specified, applied to a film thickness and logged. What you see is the same care applied to a coating as to the foam beneath it.

All project records

03The order of work

Five steps, from above.

The work is done on the roof, with the building beneath it open and the sheets left in place. Each step is checked before the next begins. On an asbestos-cement roof, the condition survey gate comes first and is not skipped.

  1. Condition survey and gate

    The roof is inspected from above and, where possible, beneath: sheet condition, fixings, laps, cracks, moss and ponding. On asbestos-cement the survey establishes that the sheets are sound enough to be encapsulated rather than replaced, and the building's asbestos register is consulted.

    HOLVEM checksSound sheets; a roof that can be worked on safely.

  2. Cleaning and preparation

    Moss, lichen, dirt and loose material are removed with methods that do not damage the sheet or release fibres. Failed fixings are replaced and cracked sheets repaired. The roof is dry before coating.

    HOLVEM checksClean, dry, repaired roof; fixings sound.

  3. Fixings and laps

    Every fixing head is capped and every lap and crack is reinforced with the coating's detailing grade, so the failure points carry the thickest part of the system.

    HOLVEM checksEvery fixing and lap sealed before the field coats.

  4. Field coats

    The silicone coating is applied across the whole roof in the specified number of coats to the specified film thickness, following the profile and curing into one seamless skin. Gutters and valleys are lined in the same system where specified.

    HOLVEM checksCoverage and film thickness logged.

  5. Terminations

    Ridges, verges, eaves, rooflights, penetrations and gutter edges are detailed per project. The coating stops at a closed edge, and rooflights are either coated over or left clear, as you choose.

    HOLVEM checksEvery edge closed and detailed.

A close detail of a weathered corrugated asbestos-cement roof from above: grey porous sheet, moss in the troughs, a rusted hook bolt and a hairline crack running from it.
BeforeThe weathered sheet, from above
The substrate as it is surveyed: the sheet, the fixings that have worked loose, the moss that holds water, the crack that started at a bolt.

Every step is checked before the next. Film thickness measured, coverage logged, compiled into a QA record at completion.

04Preparation

Before the first coat: what the roof has to be.

Coating is only as good as what is under it. Three things HOLVEM establishes first, and the fourth is what this page does not do.

Sound

The sheets can carry a coating.

A coating restores a roof that is weathered but sound. It does not hold up sheets that have gone soft, delaminated or broken. The condition survey says which the roof is, and where the two meet, which sheets are replaced first.

Clean and dry

Adhesion is decided here.

Moss, lichen, chalking and dirt come off, with methods suited to the substrate. The roof is dry at the time of coating. A coating over a dirty or wet roof peels, and a peeling coating is worse than none.

Understood

Asbestos-cement, in particular.

Encapsulating an asbestos-cement roof in place is a recognised way of managing it, and it avoids stripping and disposal. HOLVEM coats and encapsulates; it does not remove asbestos or advise on its legal management, and the roof's asbestos register is consulted first.

Survey, or photographs?How HOLVEM works: we understand your project before we price it

05What the coating achieves

What the coating does, and what it does not.

A roof coating is a waterproofing and restoration system. Three things it achieves on an ageing roof, and the one thing it is not. What it costs is priced per project and explained on the cost guide, not here.

WaterproofRestoration

One seamless skin over the whole roof.

Fixings and laps sealed, cracks reinforced, the field coated, gutters lined where specified: the roof is waterproofed as one skin, and an asbestos-cement roof is encapsulated in place with its fibres bound.

FlexibleDurability

Stays elastic under UV; tolerates standing water.

Silicone stays flexible as the roof moves with temperature and does not break down in sunlight. On low-slope roofs where water ponds, it does not soften or swell, which is where acrylic coatings fail.

ReflectiveSummer comfort

A pale roof reflects heat.

The pale finish reflects a large share of summer sun, so the building beneath runs cooler. The coating is not insulation: for winter heat loss and condensation, the roof underside pages carry the thermal case.

A corrugated asbestos-cement roof from above finished in a smooth, pale silicone coating, every fixing capped and every lap sealed, rainwater beading and running off under a bright sky.
AfterThe coated roof, from above
The finished surface: one pale seamless skin over the profile, the fixings capped, the laps sealed, the sheet still in place beneath it.

Thickness and objectiveWhat it costs: the cost guide

06Where it suits

The roofs that are better coated than replaced.

Asbestos-cement and weathered metal roofs cover a large part of Britain's older industrial and agricultural estate. Three building pages where this application is common.

Building

Agricultural buildings

Asbestos-cement and corrugated steel roofs on barns and stores, restored from above without stripping and without stopping the farm.

Read the building page

Building

Industrial units and factories

Ageing roofs over working production, waterproofed in place with the line running beneath.

Read the building page

Building

Warehouse and distribution

Large low-slope roofs with ponding and failing laps, sealed as one skin while the racking stays where it is.

Read the building page

Every building type HOLVEM works on

07What HOLVEM checks

Three things checked before anyone talks about coats.

HOLVEM does not specify a coating from a photograph. The roof is understood first: whether it can be coated, what the coating has to withstand, and what the building needs from the roof beyond keeping the rain out.

Condition survey

Can this roof carry a coating?

Sheet condition, fixings, laps, cracks and ponding, from above and where possible from below. On asbestos-cement, whether the sheets are sound enough to encapsulate. Where they are not, HOLVEM says so; a coating over a failed roof is not offered.

The exposure

What the roof has to withstand.

UV, ponding, temperature movement, foot traffic and anything the site adds: the coating system, its detailing grade and its film thickness are specified for them.

The building beneath

Waterproofing is not insulation.

If the roof also runs with condensation or loses heat, that is a separate case for the underside: closed-cell foam beneath the same sheet, with a condensation risk analysis and U-value calculation. The two are often done together, from above and from below.

Condensation risk analysisU-values and Approved Document LFire performance and coatings

08Straight answers

Ask us the hard ones.

The questions people with an ageing or asbestos-cement roof actually ask on the call, answered the way the specialist answers them.

Can you coat an asbestos-cement roof without removing it?
Yes. Encapsulating sound asbestos-cement in place is a recognised way of managing it, and the coating seals the surface and binds the fibres while waterproofing the roof. HOLVEM coats and encapsulates; it does not remove asbestos or advise on its legal management, and the building's asbestos register is consulted first.
Will the coating stop my roof leaking?
If the leaks are at fixings, laps and cracks, which on an old roof they almost always are, yes: those are sealed first, then the whole roof is coated as one skin. If sheets have failed, they are replaced before coating. The condition survey tells the two apart.
Does a coating insulate the roof?
No. A roof coating waterproofs and restores; its pale colour reflects summer heat, but it does not stop winter heat loss or condensation. For those, the roof is insulated from beneath with closed-cell foam, and the two are often done together.
Why silicone rather than an acrylic or bitumen coating?
Silicone stays flexible under UV and tolerates standing water without softening or swelling, which is where acrylic coatings fail on low-slope roofs. It also bonds to metal, aged membranes and foam without a primer on most substrates.
How do you prove it was done properly?
Film thickness is measured and recorded, coverage is logged coat by coat, and the evidence is compiled into a QA record handed over at completion.

Project records

Where we have done this before.

All project records
Project recordGlobal House, Surbiton1575 m² of asbestos-cement roof sealed from above, with neighbours within 30 m.Read the record

The next step

Your roof.
Your brief.
A specialist.

You do not need to know the system to start. Tell us what the roof is made of, where it leaks and how old it is. Photographs from above and from inside are the most useful thing you can send.

Start a project brief Send photographs first

Or call . Enquiries received before 3pm on a working day are contacted the same day. After 3pm, the next working day. We understand your project before we price it.