Renovating a flat roof without demolition – with liquid plastic and fleece
Leaky flat roofs do not need to be removed.
Modern liquid waterproofing systems create a seamless, full-surface sealing without seams or weak points – directly on the existing roof structure.
In combination with polyester fleece, the seal is permanently reinforced and remains reliably tight even when the substrate moves.
✔ No demolition necessary
✔ Save up to 70% on % costs*
✔ Permanent crack-bridging sealant
Typical problems with old flat roofs
As flat roofs age, typical weak points develop. If these are not repaired in time, more extensive damage can result.
✔ Leaks usually occur at connections, transitions and overlaps – not on the open roof surface.
✔ Cracks enlarge over time and allow moisture to penetrate.
✔ Water penetrates the roof structure and causes consequential damage.
✔ Moisture leads to mold, frost damage and a shortened lifespan of the roof.
✔ The actual leak is often difficult to locate.
There are basically two options for the renovation:
🔴 Option 1: Complete roof demolition
- high costs
- high workload
- Large quantities of construction waste and disposal
🟢 Option 2: Renovation without demolition (recommended)
✅ Significantly cheaper
✅ Quickly implementable
✅ Existing roof structure remains intact
✅ No demolition required
What materials are needed?
To repair cracks you will need:
✔ Liquid plastic
✔ Polyester fleece for reinforcement
✔ Primer (depending on the substrate)
✔ Roller or brush
✔ Topcoat (optional)
🟢 The polyester fleece is the most important component. It prevents the tear from reopening.
Why polyester fleece is indispensable for a permanent seal
Liquid waterproofing systems can be based on different materials – e.g., bitumen, polyurethane, or acrylic.
👉 However, what is crucial for durability is not the material itself, but the reinforcement with polyester fleece.
Only by embedding the fleece does a resilient sealing system emerge that:
✔ Can permanently absorb movements of the ground
✔ Reliably prevents cracking
✔ is significantly more mechanically resistant
👉 Without this reinforcement, the seal remains susceptible to stress cracks and premature damage, especially in existing roof structures and renovations without demolition.
Note regarding roll width:
The appropriate roll width depends on the area of application and the details on site – e.g. surfaces, connections or penetrations.
Renovating a flat roof without demolition using liquid plastic
Flat roof renovation without demolition is possible in many cases. Especially with older bitumen waterproofing, cracks and transitions can be permanently repaired using liquid plastic and a reinforcing fleece.
This method saves time and money and avoids costly demolition work.
The renovation takes place in two steps: first, reinforcement of critical details, then sealing of the entire roof surface.
A [product/service] is particularly suitable for this application. polyester fleece as reinforcement in liquid waterproofing. An overview of available widths can be found here. here.
Step-by-step implementation
Step 1: Targeted reinforcement of critical connection areas
After thoroughly cleaning the roof surface of dirt, standing water residues and adhesion-reducing residues, targeted reinforcement of the particularly stressed areas began.
Transitions, connections, and penetrations are the most frequent causes of water ingress in flat roofs. To reliably accommodate movements of the substrate and permanently prevent stress cracks, these areas were specifically reinforced.
For the targeted reinforcement of cracks and transitions, a Polyester fleece 110 g/m² 0.15 x 50 m It has proven particularly effective because the 15 cm roll width allows for precise processing in detailed areas.
In addition to classic cracks, localized leaks often occur at connections and penetrations. Detailed instructions can be found in our article on localized leaks in flat roofs.
Step 2: Sealing the entire roof surface
After the targeted reinforcement of all corners, transitions and connection areas, the sealing of the entire roof surface began.
The execution was carried out using a two-layer system:
First, a layer of liquid sealant was applied to the entire surface. The polyester fleece was then laid into the still-wet coating with an overlap of at least 5 cm.
The fleece was then carefully pressed down with a roller so that it bonded completely with the sealing material and no air pockets formed.
After the first layer had cured, a second, covering sealing layer was applied, creating a seamless, permanently sealed surface.
This system ensures a permanently flexible and crack-bridging seal.
Wider rollers are also suitable for larger areas (e.g. 0.35 m or 0.50 m) available.
The result: A new flat roof without demolition
Seamless & permanently waterproof
The two-layer liquid waterproofing system forms a closed, seamless surface. This reliably protects the roof surface from penetrating moisture – even in standing water.
Connections are securely reinforced
Edge connections, roof drains, and penetrations were additionally reinforced. This permanently stabilizes typical weak points in the details and significantly reduces the risk of leaks.
Renovation without removing the old bitumen waterproofing
The existing structure could be retained. No costly demolition, less mess, and significantly less time and expense – while maintaining the same protective function.
When moisture penetrates through the flat roof
Typical warning signs
Damp spots on the ceiling or wall, water stains, peeling paint or a musty smell: In flat roofs, these are often the first signs of leaks in the detail area.
Weaknesses are usually in the details.
Transitions, connections, and penetrations are among the most common points of entry for water. It is precisely at these points that the first problems arise due to aging, movement, or cracks.
Solution: Renovate instead of demolition
If the substrate is load-bearing, a flat roof can often be renovated without complete dismantling: reinforce critical areas and then seal the roof surface with a two-layer liquid sealant.
Renovating a flat roof without demolition – with the right reinforcement
The solution shown is based on one crucial element: polyester fleece as reinforcement for the liquid waterproofing.
👉 Only in this way can a permanently tight, flexible and durable seal be created – without demolishing the existing roof structure.
Now choose the appropriate width and reinforce the seal in a targeted manner.