Scorching heat didn't keep Mike Holmes from rallying his staff to finish a rebuild of a beloved Toronto playground, but record-breaking temperatures did slow the process.

As the mercury climbed above 35 on Friday in Toronto, the celebrity contractor said about half of his 50-person crew was sidelined from working on the Jamie Bell Adventure Playground in High Park, which was destroyed by arson in March. One worker was hospitalized for a heat-related illness.

"I'm telling everyone to pay attention and to look at the other guys around you, make sure they stop after 20 minutes and get some water," said Mr. Holmes, the host of HGTV's Holmes Makes It Right. "If we don't do that, I'm going to be losing more guys."

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Toronto smashed its July 6, 1988, record temperature of 34.7 by midday Friday, but the humidex made it feel more like a scorching 42.

"We've had in Toronto, counting today, 12 days where the temperature has been above 30. Normally for an entire year you'd get 14 of those," said Environment Canada senior climatologist Dave Phillips, who said the past year has been the city's warmest on record.

Toronto EMS received six heat-related calls on Friday, two of which came from construction sites. However, a chance of thunderstorms this weekend could bring some relief: Environment Canada is forecasting sunny skies and temperatures in the high-20s for next week.

The stifling heat also caused two separate blackouts in Scarborough's Guildwood neighbourhood, leaving roughly 3,400 homes without electricity for a few hours on Friday afternoon.

As Toronto baked under an extreme heat alert between Wednesday and Friday, Mr. Holmes and his crew worked upward of 14 hours a day to complete the castle's reconstruction by the July 7 deadline.

After the fire, community members offered to contribute free labour and volunteer to rebuild. As well, more than $100,000 has been donated. When local councillor Sarah Doucette sent Mr. Holmes a video asking for his help, he immediately said yes.

A community rebuild and ribbon-cutting ceremony is scheduled for Saturday, but Ms. Doucette said the playground cannot be officially opened until it's been examined and deemed safe.

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Most likely, the construction site around the new castle structure will be contained, while the old playground area will be opened up for the community to repaint. But it won't be all work and no play – a barbecue, bouncy castle and water activities are also on tap for the day-long event.

"We had obviously wanted to be completely open and approved and everything by the end of [Saturday], and we definitely need the community here to help us do what we can do," Ms. Doucette said. "But if we need Holmes's group to come in next week to finish off the castle, they're not going to leave us half-finished."

By Friday afternoon, the castle's wooden shell was erected. About a dozen off-duty firefighters were cutting out shield-shaped wooden panels for children to decorate and place on the new castle.

More than 300 people are expected to turn up for Saturday's event.

Area resident Pierre Perron said his family will be among the first to arrive. When he first laid eyes on the burned-out castle, Mr. Perron said he choked up.

"All the time that I spent here with my kids was just running through my head," he said. "I felt really sad. We spent countless hours here."

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Mr. Perron said he was impressed with the progress at the park.

"They've done an amazing job."