Here's a photo of a 25-year old fireplace that I had converted to gas and now plan to update with a new surround and hearth. You can see that there are slots in the top and bottom of the face. When I first moved to this house there were pieces of rubber inserted in each of the slots but over time some fell out and others went missing so I removed them all. I wonder if these slots have any function or if I can cover the bottom row with tile. Thanks.