Not sure if this is the best forum, but I noticed on my fireplace that there is a gap between the brick and the firebox of my fireplace. It looks like there was mortar there but it appears to have loosened and fallen out over time. I figured I could remortar it, but am wondering if there could be a better solution? I was thinking I could stuff the gap with that fireproof cord you see on wood burning stoves, or something similar. Any advice?