Gutters and fascias take a lot of water, and small leaks are common. Some are simple to fix with the right sealant. Others need parts replaced, or point to a problem sealant can’t solve. This guide explains how to tell the difference from the ground, what sealing involves and when to call someone else.
Leaks sealant can often fix
- Joint drips. Water dripping from the joint between two lengths of gutter, or at a union, often means the seal there has failed.
- End cap leaks. Water running out of the end of the gutter where the cap meets it.
- Outlet leaks. Drips where the gutter meets the downpipe outlet.
- Fascia and soffit joints. Gaps between boards or trims that let water or draughts in.
- Garage door frames and roofline trims where the joint has opened.
Our gutter and fascia sealing service covers these joints.
Problems sealant can’t fix
- Sagging gutters. If a section droops between brackets, the brackets have failed or are too far apart. Water pools and overflows. That needs refixing, not sealing.
- Cracked or split gutters. A crack along a length of plastic gutter usually means the length needs replacing.
- Overflowing gutters. If water pours over the front edge, the gutter is likely blocked or doesn’t fall to the outlet properly.
- Rotten fascia boards. Sealant won’t hold onto rotten timber. The board needs repairing or replacing.
- Roof problems. Water coming from under slipped tiles or failed felt is roofing work. We don’t do roofing.
Need it done properly? Mr Mastic covers the South East, London and Scotland, with a one-year guarantee on every job. Call or email for a quick quote.
Telling the difference from the ground
Watch the gutter during or just after heavy rain. A steady drip from one point, often a joint, suggests a failed seal. Water spilling over a long length suggests a blockage or poor fall. A visible dip in the gutter line suggests failed brackets.
Look for staining too. Dark streaks down a wall below a joint are a common sign. Green moss or algae on the wall can mean water has been running down it for some time. Use binoculars rather than a ladder if you just want to look.
Older gutters and safety
Older homes may have cast iron gutters, whose joints are traditionally sealed with a gutter sealant or mastic. They can often be resealed once the old material is removed and the joint cleaned.
Some older buildings also have asbestos cement gutters or downpipes. HSE says buildings built or refurbished before 2000 may contain asbestos, and its asbestos essentials task sheets include one on removing asbestos cement gutters (HSE task sheet A14). If you think your gutters could be asbestos cement, don’t drill, cut or scrape them. Read our asbestos guide first.
Any work at height should be done by someone with the right equipment and training.
Sealing a gutter joint properly
The joint must be cleaned of dirt, moss and old sealant, then dried. Gutters in use are rarely dry, so this needs a dry spell. A sealant suited to the gutter material is applied to the joint and tooled so water runs over it, not against it. Sealing is a good moment to clear the gutter too, so the repair isn’t sitting under standing water.
Quick answers
Can sealant fix a sagging gutter?
No. Sagging means the brackets have failed or are too far apart. The gutter needs refixing before any joint is sealed.
Why does my gutter drip only in heavy rain?
Often a joint that is just failing. In light rain, the water passes it. In heavy rain, it overflows the weak seal.
Do you replace gutters?
No. We seal leaking joints, end caps and fascia joints. Broken or sagging gutters need a gutter fitter or roofer.
Related services
More advice
- Conservatory Leaks and Glazing Silicone
- Scotland’s Weather and External Mastic
- Could Old Mastic Contain Asbestos?
- All advice
This guide is general information about sealant work. It isn’t legal, fire-safety or structural advice; for those, speak to a qualified professional.