How do I seal chimney brick on my roof?

depending on how bad the brick are
you could
1 temporary fix,mix 1 part building sand to 1 part cement and mix into light creamy liquid wet chimney well and apply
with roofers brush, recommend two coats
2 plaster stack with 4 parts building to 1 part cement
plaster one coat on first and scratch lines into semi dry mortar to provide key for second coat with second coat finish with ether large sponge or plastic builders float
3 have qualified builder to dismantle stack and rebuild with new brick to the same style
hope this is helpful

andy
March 2010