Auto body repair & detailing: Car roof restoration, full respray, duraglass

Question
G'day William  I've recently had a sunroof removed from my classic car & a metal plate welded in to restore the roof to original. 6 months later & after a full respray, the center of my car roof has cracked (approx 3mm gap, 45cm long). Whilst the panel beater/tradesman has said he will repair it, I wanted to be sure he was following the correct process. Any tips on best way to ensure this doesn't happen again, or repair methods to avoid. Cheers

Answer
The roof needs a new support welded underneath the area where the roof patch was welded in. There should be a layer of foam between the new support and the roof skin to give it a little flex without denting the roof from underneath. I also suspect that filler was over applied, and this is also leading to cracking. If he used fiberglass over the roof patch it will make for a fast failure. Fiberglass has no place on a steel bodied car. A coat of quality waterproof filler like evercoat or duraglass is the way to go, followed by a quality smoothing filler. This is a tough repair under the best circumstances, and heat build up in the car will lead to a fast failure. If you're in a hot climate, the repair needs to be a perfect one, with a bare minimum of filler. This is tough for even a seasoned professional- roof skins are flat, and welding warps steel. What would be a perfect (but expensive) repair would be to remove the roof skin and replace it with a skin from a donor car. This is a huge undertaking, requiring the removal of the front and rear windscreens- which are easily broken. Weigh your options carefully. Bill