Here is my problem: Our fireplace is a 1" stone veneer and is at a 45 degree angle from either of the the adjoining walls. There is a gap around the fireplace up to an inch wide in some places that we've sealed with spray insulation. The stone itself is not mitered to a 45 degree, so the gap is quite noticeable.

Solution #1: Miter a piece of wood so it is parallel with the stone (miter sits against the wall) and we can then either have it flush with the stones and contour the edge against the stone so it's a tight fit or can have it overlay the stones. This solution could either have the wood painted the same colour as the wall or black to match the mantle.

Solution #2: Miter a piece of wood so it's perpendicular to the wall (miter sits against the stone and contour the edge so it's a tight fit.This solution could either have the wood painted the same colour as the wall or black to match the mantle.

Solution #3: Use concrete or grout to fill in the gap. This is risky because of the size of the gap and that it's completely vertical. I'd likely have to put in some kind of metal support structure.

I don't know which of the top would be the best solution or if there is something I haven't thought about. Input and ideas are welcome! (As you can see, we've recently painted from a dark orange (which I tried to hide the spray insulation by painting over it) to a light blue.....LOL VERY NOTICEABLE now