Keeping the things you work with in order costs money, and most of that cost comes off in the year you spend it. On Form T2125, it goes on line 8960, Repairs and maintenance.
What belongs here
The cost of labour and materials for any minor repairs or maintenance done to property you use to earn business income. In practice that is a tradesperson's invoice, a service call, or the parts for a fix.
What does not belong here
The value of your own labour. You cannot deduct your own time, however long the job took. Materials you bought still count — keep that receipt.
Repairs that are capital in nature. These aren't lost. Their cost comes off over several years through capital cost allowance (CCA), which spreads the cost of a lasting asset over the years you own it, rather than all at once here.
Repairs your insurance company reimbursed. You cannot deduct a cost you were paid back for, so a reimbursed repair stays off the form.
Repairs and maintenance on a workspace in your home. Those have to be claimed as business-use-of-home expenses instead.
Vehicle repairs. Servicing the vehicle you use for business is a claim within the vehicle schedule — line 9281, motor vehicle expenses, where Chart A works out the business part.
Is it a repair, or an improvement?
This is the question the line turns on. A repair restores something to the condition it was in; work that improves the property beyond its original condition is probably capital, and capital work is claimed through CCA rather than deducted here. The CRA's page on current or capital expenses sets out the tests.
Dossier flags an invoice that reads as durable or large so the question is in front of you when you file. It doesn't answer it — the answer is settled on the return, not on the receipt.
What to keep
Keep a record of all your income and expenses, with the documents behind them. For repair work the invoice matters more than the payment record: a work order that describes the job is what answers the repair-or-improvement question later.
Don't send it in with your return. Keep it in case the Canada Revenue Agency (CRA) asks to see it. Business records follow the same six-year retention rule as your personal documents.
Official CRA sources
Source: Canada Revenue Agency (canada.ca). Not tax advice.