Could the room be an old laundry area? I lived on a sandy lot before and we had our laundry drain tied into the basement floor drain. It all weeped out into an 80' stone tile. The entire drainage system worked well until the weep field became plugged/collapsed. I wonder if the sand you see is washing ~into~ the tile from another area. Is it possible that some area around the house is not draining properly away at the surface? Are there puddles of surface water that are seeping their way down into the floor drain? There is a reason the tile is there. It's to provide drainage. There must also be a point that it exits to drain. I'm guessing the hole was added at some point in your homes 50 year history for some type of drainage point for something like laundry. If you have water backing up, that's a problem with; A. Drainage out or B. Water in or C. Both of the above Anyhow, that's how I look at it. I could be 100% wrong.

In the UK there's a product to go on the rafters when the roof is covered with straw. It's a firestop for 1 hour at 2000F. That's all I can help you with but it's well known and I'd say to look at the BBC show called Grand Designs .. one where a straw roof caught fire and the roof was replaced.. in about 2006. You might be able to follow up on the product name there or by looking for sites limiting to the UK for fire stop. use google this way to limit to uk. site:.co.uk fire stop roof the site:.co.uk limits to UK sites the latter words are what you're looking for. I've tried it and it works. Good luck. Andre

Basements which are mostly underground have a small heat load. In the summer the basement can actually become too cool if you leave the vents open. When I installed my new system I didn't get a separate zone for the finished part of the basement. I didn't think it was needed but now I know better. I would be concerned creating a zone for the 1500 sq ft basement with a single stage furnace. I am willing to bet the first floor system is over sized which further aggravates the problem. I suppose a contractor who is very good a zoning could do it correctly. But then again someone who understands the physics behind good zoning design would probably recommend upgrading to a variable speed 2-stage furnace.

Drill into the slab at the mid-line in half a dozen places so you can epoxy in a few short pieces of rebar. Fill the hole with sand to the bottom of the existing slab. Place concrete and level. The rebar will prevent possible movement or setting of the patch in the future.