The short answer
Sometimes, but it is a stopgap, not a repair. A coating on sound asbestos cement sheets can bind the surface and slow weathering. It does not cure cracks, broken sheets or rusted fixings, and the preparation is the risk: never scrub, wire-brush, scrape or pressure wash the sheets, because that releases fibres. Find out what the roof is first, and take advice on whether coating, overlaying or careful removal suits the condition.
Why people consider sealing
Many garages built between the middle of the last century and the 1980s have corrugated sheets made of asbestos cement, a mixture of cement and asbestos fibre. They weather to a mossy grey, and once the surface has broken down they can leak and shed fine debris. A tin of masonry or bitumen paint seems a cheap answer, and some suppliers sell coatings made for the purpose. The idea is to bind the surface and keep the sheets watertight a while longer.
Before anything is done, check what the roof is made of. Our guide to whether your garage roof is asbestos lists the signs, and the page on testing a garage roof for asbestos covers how to confirm it. Do not guess from the colour.
The preparation is where the danger lies
Asbestos cement is not dangerous while it is intact and undisturbed. The risk comes when fibres are released into the air, and the usual way that happens is through the work itself. Wire brushes, scrapers, stiff brooms and pressure washers all damage the surface of the sheets and send fibres and moss debris flying. The water and slurry also run into gutters and onto the ground below, spreading contamination.
That is why cleaning a roof like this is not a job to do on a weekend with a hired jet wash. If a coating is to go on, the surface needs to be treated gently, with a method that keeps the material wet and avoids abrasion, and workers need to be trained and protected. Our page on cleaning an asbestos roof explains why scrubbing is not the answer.
What a coating can and cannot do
A coating can bind a weathered surface and colour the roof. It can slow the weathering that frees fibres. It cannot mend a cracked or broken sheet, close an open lap or replace a rusted bolt, and it will not make an old roof last as long as a new one. Any coating also needs renewing from time to time, which means more handling of an old roof in the future. If you decide to sell, a coated roof still has to be disclosed as asbestos cement, and a buyer's surveyor will look at the condition under the paint.
Sheets that are cracked, crumbling or sagging, or fixings that have failed, are signs that the roof has reached the point where coating is not enough. At that stage the choice is between overlaying and careful removal. Overlaying is sometimes an alternative to removal, depending on the frame and the condition of the sheets, and it keeps the asbestos undisturbed beneath a new covering.
Gutters, moss and the ground below
Look at what has already come off the roof. Moss and lichen growing on the sheets hold fine surface debris, and rain carries it down into the gutters, the downpipes and the ground beside the garage. Do not sweep or hose that material out of the gutter, and do not dig it into a flower bed. If the gutters are asbestos cement too, they are handled in the same careful way as the sheets. Keep children and pets away from any area where debris has built up, and have the ground checked if you are concerned. Leaving a mossy roof alone is usually safer than cleaning it without a plan.
Overlay or removal
Careful removal of asbestos cement sheets, taking them off whole without breaking them, is non-licensed work under HSE rules. It still needs a risk assessment, proper controls and trained workers. If the material will be substantially broken up, the work becomes notifiable non-licensed work. Our page on whether removal needs a licence sets this out, and the guide to asbestos garage roof removal explains how the job goes. HSE guidance is available at hse.gov.uk.
What we would do
We begin with a free survey. We look at the roof from safe positions, photograph the sheets, fixings and frame, and say plainly whether a coating is worth considering or whether the roof has gone past it. We will not sell you paint that does not solve the problem. If the roof is sound and you want to keep it a few more years, we say so, and if overlaying or removal is the right route, we give a fixed written quote for it, with a written workmanship guarantee of ten years on the new roof. The main garage roof replacement page covers the options for all types of roof.
Every roof is different. A free survey with photos settles it for yours.
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