i found bricks at my local lawn and garden store that were made for a kiln able to take high heat for extended periods of time...not sure what they were called they were only a few cents more per brick but the guy said they would not crumble over time...i laid them on the bottom as a patio with no hole dug at all so i could just shovel out the ashes as needed and not keep making the hole deep..plus this helps keep the ground dry so u can have a fire anytime. i did not uses mortar i thought that may break down over time i just stacked them in a circle...if they fall down i just put em back up.