How To Fix a Hole in Polycarbonate Roofing
How do I repair a 10 mm hole in polycarbonate roofing?
For filling a small hole like this, a little silicone such as Roof & Gutter Silicone would be ideal. To get the neatest finish, cut a patch from a piece of polycarbonate roofing and bond it in place with a small amount of sealant, which both holds the patch and seals any gaps around it.
That patch-and-seal method is worth doing rather than simply filling the hole. A 10 mm hole filled with silicone alone leaves a soft plug with no mechanical support, sitting in a sheet that expands and contracts substantially with temperature; a patch spreads the load across a much larger bonded area and gives the sealant a joint to work in rather than a void to bridge.
Check compatibility before you start
This is the step to take seriously on polycarbonate. The Roof & Gutter Silicone data sheet lists the substrates it is made for — on the porous side timber and plywood, fibre reinforced cement, bricks, concrete and masonry; on the non-porous side aluminium, steel and stainless steel, mild and galvanised steel, powder-coated steel, and PVC. Polycarbonate is not on that list, and the data sheet instructs you to pre-test compatibility with substrates before use. It also states the product is not for use on polyethylene, polypropylene or PTFE.
Selleys' broader guidance is the same: users should conduct their own risk assessment before use to determine the product's suitability, and a sample should be applied to the intended area to ensure an acceptable appearance, finish and performance on the surface.
So do this first: bond a small amount to an offcut of your roofing sheet — or to an out-of-sight corner of the installed sheet — let it cure, and check both that it holds and that it has not marked or clouded the polycarbonate. Polycarbonate is also usually supplied with a UV-protective surface layer on the weather side, and that layer is what your sealant will actually be sticking to.
If your sheeting is a branded product, its manufacturer will have their own compatible-sealant guidance, and it is worth checking. There is a related question on this site about silicone compatibility with Laserlite polycarbonate.
The figures
| Property | Roof & Gutter Silicone |
|---|---|
| Technology | 100% silicone, neutral / moisture curing |
| Tooling time | 5 minutes |
| Skin time | 5–10 minutes |
| Tack-free time | 30 minutes |
| Curing rate | 2 mm / 24 hours |
| Joint movement | ±25% |
| Elongation at break | 330% (ASTM D412) |
| Shore A hardness | 32 |
| Application temperature | +5°C to +30°C |
| Service temperature | −60°C to +150°C |
| Guarantee | 25 years against crumbling, cracking or peeling* |
Figures are based on current product material data, quality test methods and testing conditions such as temperature, moisture and substrate. *When used as directed for private use and within 12 months of purchase.
What the numbers mean on a roof
±25% joint movement and 330% elongation are the reason this works. A polycarbonate roof sheet moves a great deal between a cold night and a summer afternoon. A rigid filler in a hole would crack out within a season; a silicone with this much stretch accommodates the movement around the patch indefinitely.
The service temperature range of −60°C to +150°C covers anything a roof will see, including the surface temperature of a dark sheet in full sun.
The application temperature range is the tighter constraint. Do not apply below +5°C or above +40°C ambient or substrate temperature — and a polycarbonate roof in the middle of the day easily exceeds 40°C at the surface. Do this job early in the morning or on an overcast day.
Cure runs at 2 mm per 24 hours and needs atmospheric moisture. On non-porous substrates or in low-humidity conditions, curing slows — and polycarbonate is entirely non-porous. Do not judge the repair finished at the 30-minute tack-free point.
How to do the repair
- Pre-test the silicone on an offcut or a hidden area of the sheeting, and let the test cure.
- Cut a patch from matching polycarbonate roofing, sized to overlap the hole generously on all sides — a patch three or four times the diameter of the hole gives the bond a real area to work with.
- Round the corners of the patch. Square corners are stress concentrators and are where a patch starts to lift.
- Choose the side. Patching from underneath keeps the repair out of the weather and out of the UV, but a patch on top sheds water better. On a shallow-pitch roof, patching the top face and feathering the sealant so water runs over it is usually the better outcome.
- Ensure all surfaces are clean, dry, sound and free of dust, oil and other contaminants. Clean the non-porous surfaces with a clean cloth dampened with isopropyl alcohol or white spirit, wiping in one direction only, then immediately wipe with a clean, dry cloth.
- Remove any existing adhesive or sealant from previous repairs.
- Cut the cartridge tip, screw on the nozzle and trim it to the bead size you want. Use a good-quality gun.
- Apply a continuous bead around the hole, set the patch into it, and press it down so the sealant spreads and squeezes out slightly all round.
- Tool the perimeter with a clean spatula dipped in soapy water before a skin forms — you have around 5 minutes.
- Leave it undisturbed to cure. Excess on tools cleans off with turps; cured sealant needs mechanical removal or Selleys Sealant Remover — and note that sealant remover is itself not suitable for use on polycarbonate, so keep it off the sheet.
Limitations
- Pre-test compatibility with substrates before use. Polycarbonate is not among the listed substrates.
- Not for use on polyethylene, polypropylene or PTFE.
- Not paintable. Allow paint to dry for at least 7 days before applying the sealant on top. Choose your colour — translucent is the obvious choice on a clear or tinted sheet.
- Do not apply if the ambient or substrate temperature is below +5°C or above +40°C.
- Not recommended for continuous submersion or below-waterline use. A ponding low spot on a flat roof is worth fixing rather than sealing over.
- Avoid contact with materials containing high levels of plasticisers, such as rubber and bituminous substrates.
- The sealant requires atmospheric moisture to cure, and cures more slowly on non-porous substrates or in low humidity.
- Do not use for structural glazing. A roof sheet is not glazing, but a large hole in a sheet that has become structurally compromised is a sheet replacement, not a patch.
Common questions about patching polycarbonate roofing
Can I just fill the hole with silicone?
You can for a very small hole, but a patch bonded with a small amount of sealant gives the neatest finish and a much stronger repair.
Is Roof & Gutter Silicone safe on polycarbonate?
Polycarbonate is not among the substrates listed on the data sheet, and the instruction is to pre-test compatibility before use. Test on an offcut and let it cure before you rely on it.
Where do I get a patch?
A piece of the same polycarbonate roofing. Matching material means matching movement, colour and light transmission.
Top or underside?
On a shallow pitch, the top face usually sheds water better. Underneath keeps the repair out of the UV. Either works if the bond is sound.
What temperature should I work at?
Between +5°C and +40°C ambient and substrate. A sunlit polycarbonate roof exceeds that easily, so work early or on an overcast day.
How long before it is watertight?
Cure runs at 2 mm per 24 hours and slows further on non-porous surfaces. Tack-free at 30 minutes is not cured — allow at least a full day.
Which colour should I use?
Translucent on a clear or tinted sheet. Roof & Gutter comes in a wide colour range including Colorbond-matched colours, and it is not paintable.
Will it last?
Roof & Gutter Silicone carries a 25-year guarantee against crumbling, cracking or peeling when used as directed for private use and within 12 months of purchase, and is UV and weather resistant.
What if the hole is much bigger than 10 mm?
A patch scales up to a point, but a sheet with a large hole or a crack running from it is compromised. Replacing the sheet is the durable answer.
How do I remove old sealant from a previous repair?
Remove all existing adhesives or sealants before resealing. Note that Selleys Sealant Remover is not suitable for use on polycarbonate, so remove it mechanically and carefully.
How do I fix a small hole (around 10 mm) in polycarbonate roofing?
To fix a small hole in polycarbonate roofing, first clean the surface thoroughly to remove dirt, grease, oil, and debris around the hole, and lightly sand the area to improve adhesion. Then apply Selleys Marine Flex, which can be used directly on polycarbonate without a primer and provides a waterproof seal with excellent weather and UV resistance.
Do I need to prime polycarbonate before applying Selleys Marine Flex?
No, Selleys Marine Flex can be applied directly to polycarbonate surfaces without requiring a primer.
Why is light sanding recommended before repairing polycarbonate roofing?
Light sanding is recommended prior to applying an adhesive like Selleys Marine Flex because it improves surface adhesion and enhances bonding strength on polycarbonate.
What are the benefits of using Selleys Marine Flex on polycarbonate roofing?
Selleys Marine Flex provides waterproof sealing capabilities, offers excellent weather and UV resistance, can be applied to wet or dry surfaces, and delivers superior performance in demanding situations, making it suitable for roofing repairs.
Can Selleys Marine Flex be applied to a wet surface?
Yes, Selleys Marine Flex can be applied to wet or dry surfaces.
Which products should I avoid using on polycarbonate roofing?
You should avoid Selleys Sealant Remover, as it is not suitable for polycarbonate, and All Clear sealant, which may cause damage to polycarbonate. Certain sealants are also not recommended for polycarbonate, particularly in underwater or submerged applications.
Is there a quick temporary fix for a leaking polycarbonate roof?
For temporary or emergency repairs to stop leaks quickly, Selleys Storm sealant is suitable for most plastics and can deliver an immediate waterproof seal on building materials, whether wet or dry.
What should I do to prepare the surface before repairing polycarbonate roofing?
Before applying any adhesive or sealant, clean the surface thoroughly to remove dirt, grease, oil, and debris around the hole, lightly sand the area to improve adhesion, and ensure the surface is completely dry before proceeding.