How do I repair the top of my chimney?

If you use this chimney, it needs to be repaired properly.

What exactly needs repair? Not a typical homeowner DIY without significant skill. Most likely you will need a contractor to help you out.

I would have a mason with chimney experience or get a certified chimney sweep, My chimney sweep does repointing of brick and repairs chimney caps to prevent the water going down the chimney which degrades the chimney mortar. This could cause a collapse of the chimney, and a fire if you light it. Don't use it until its repaired.

If you have to ask then you don't have the skills and know-how to DIY this. Your life and family's life depend on doing it right. My Great-Aunt almost lost her home for a damaged chimney. The fire actually came through the wall because of cracks in the liner and brick-work. Some things are worth the experienced pay.

When I enlarged the picture it appears the face of several bricks are completely eroded. The only thing I know of is to replace them. Scaffolding will make the job a lot easier and safer than trying to work off a ladder. I’m trying to figure out what caused it, perhaps the mortar or grout failed allowing water in. Wow what a job, good luck!

The other option might be to cover the entire exterior fireplace if the flue is still good. I’ve seen some with horizontal wood, but I would probably use cement board, like a hardee board. Ask your building inspector if that’s legal. If you “skin” it by adding another layer, you may have to make sure the cap covers all on the very top.