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  • Posted February 28th, 2016

    It’s time to repair greenhouses and cold frames: glass cutting advice

    It’s time to repair greenhouses and cold frames: glass cutting advice

    It’s that time of year when thoughts have already turned to the vegetable patch and raising seedlings. This is where the glasshouse and cold frame make a huge difference to getting those plants going. With these thoughts also come the reminder of all those little jobs that needed doing, but the weather was terrible and they never happened.

    The glasshouse should have been cleaned, maybe a jet washer was used and maybe some panes were cracked or broken.

    This is the time to visit that part of the property where all the second-hand glass is stored. Beware toughened glass as you cannot cut this and it ruins your cutter, some of this is marked (see photo) but as the building regulations now insist on toughened glass in and around doors, or below 1 metre in height then some of it is no longer easily identified.


    The saved glass is never the right size and so it will need to be cut, and there are a set of skills required to cut second-hand glass that are easy to acquire, and some knowledge that although intuitive is not immediately obvious.

    Many people through bitter experience will tell you that it is not possible to cut reclaimed glass, but believe me it is. This is not armchair theorist opinion but based on years of doing it. All the glass in our house renovation was re-cut reclaimed material, and it is being used in our home-made storm-window-type double glazing.

    The cheap glass cutters have 6 hardened steel cutting rollers mounted in the adjustable head. Only one roller is used at a time and the pin that the cutter rolls on should be lubricated with something like white spirit or paraffin.


    The first important thing is to make sure the glass is clean so that the glass cutter wheel will roll freely, because bits of muck will make it skid and not score the glass cleanly.

    Following this is the all important-issue – the glass must be warm. I don’t mean hot but it should not be cold. Half an hour in a warm room, or use a heat gun to warm it up (not too rapidly). If you do not attend to this then the likelihood that the cut will wander off line is greatly increased.


    I mark the glass with a permanent marker making sure the marks are on the waste side of the line. Using a straight edge of your choice, but make sure it is wide so it does not move sideways on the clean glass surface. If you have trouble, a few bits of duct tape should sort the problem out.

    Hold the cutter upright and firmly run it along the edge of the straight edge to score the glass. Only once! As repeating this operation on the same line blunts the cutter immediately.

    Here’s a video I have uploaded to show all this in action:

    Remove the straight edge and turn the glass over. With the metal head of the cutter lightly tap along the back of the score line and you will see a silver reflective break move upwards through the glass from the score line. Do this all the way along the proposed cut line and you will then have two pieces of glass.

    A bit of practice on waste glass will improve confidence.

    Here’s a related video – the first in a series of videos on repairing the windows in your home

    Andy Reynolds

    Author of Timber for Building

    The views expressed in our blog are those of the author and not necessarily lowimpact.org's


    • 1ethicalinternet March 1st, 2016

      Thanks, Andy, really useful advice. There must be thousands of people around the country who are about to go and get some replacement glass for their greenhouse this month. You’ve inspired me to try to cut my own reclaimed glass next time I need a piece for a greenhouse.

    • 2Rob Coles February 15th, 2021

      Hi Andy, my success rate of cutting greenhouse glass was 1 pane cut to size, 5 panes shattered. I was using language my wife had never heard before and stomping around like a bear with a sore head. Watched your video and tried again – new rate… 6 panels cut, 5 perfectly and one with too steep an angle (My fault). What’s really made a difference for me is turning the sheet over and tapping the back – never seen that before but it works every time. My wife’s ears and me, both thank you – you’ve lowered my blood pressure ?

    • 3Claire Peterson May 20th, 2024

      Thanks for this. Just repaired my shed window with an old piece of glass. Complete novice but it worked!

    • 4Ciara June 17th, 2024

      Hi there, will this work on toughened greenhouse glass? Thanks.

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