Tearing the old covering off a 600 m² roof means days of work, skips full of waste and noise for the residents. So the first question we get asked is: "Can you just go over the top?" Often, yes. But not always, and the difference between the two cases only shows after opening it up.
How it is done
A repair without tear-off is a new waterproofing layer over the old one. For it we use a liquid polyurethane (or polyurethane-bitumen) membrane: applied by roller or spray, once cured it forms a seamless, flexible covering.
Sequence of work:
- Cleaning. Debris, loose granules, dust, dirt and biological growth are all removed; the surface is washed and dried.
- Local repairs. Blisters are cut open and dried out, seams that have come apart are glued back down, punctures are sealed.
- Priming. A primer matched to the type of old covering — a bitumen or mineral base.
- Reinforcing the details. Upstands, drains, penetrations and cracks are reinforced with geotextile laid into the first coat of membrane.
- Two coats of membrane over the whole area, with the consumption per m² checked.
- Top coat, UV-resistant, so the covering does not age in the sun.
There are no seams, which means the most common source of leaks is gone. The material goes around pipes, ducts and antennas without separate collars.
When it works
A repair over the top lasts for years if all of these conditions are met at once:
- The base is sound. The old covering is firmly bonded to the screed, does not peel off in sheets and does not crumble.
- The base is dry. Moisture is within the limit the membrane manufacturer requires (usually no more than 4 %). Checked with a meter or by a sample after opening up.
- The insulation is dry. This is the main one. If there is wet insulation under the covering, a new layer on top will trap the moisture inside: in summer vapour lifts the membrane into blisters, in winter ice breaks up the screed.
- The materials are compatible. According to the manufacturer, polyurethane-bitumen compounds bond to old bitumen coverings; on a PVC membrane or EPDM only after an adhesion test.
- There is a slope. If water ponds on the roof, a repair over the top will not fix the cause: the screed needs repairing.
When it doesn't
- Wet insulation — only a tear-off down to the slab, new insulation and a new roof.
- Several old layers that have separated from each other: the lower ones will not hold the upper ones, whatever is laid on top.
- Blisters over the whole area — a sign that there is moisture under the covering everywhere.
- The screed has failed: it crumbles, has sagged, or has cracks wider than a few millimetres.
- The base cannot be dried — for example, the weather has closed the season.
In these cases "over the top" is money thrown away: the leaks come back within a season, and then two coverings have to come off instead of one.
How we decide
The decision is made after an inspection and a control opening, not from a photo. The engineer checks adhesion, moisture and the condition of the insulation at one or two points and writes in the report: a repair over the top is possible — or it isn't, and why. If it is possible, the estimate gives two figures: repair over the top and full replacement, so you can see the difference.
How long it lasts
The service life is set by the material manufacturer — for polyurethane membranes it is given in the data sheet — and by how the details are made: clean drains, intact upstands, no ponding. The warranty on the work is written into the contract. We hand over after a water test, with a photo report of every layer.
Inspection — 100 ₾, deducted from the estimate if you order the work.