Hi all – I have a very old (1875) victorian with a rubble stone foundation. The poured concrete floor is thin or gone for the most part. I’m putting in a new furnace so want to replace the floor in that area now (and the rest later). My plan:
1. Remove old floor, excavate down 4″ from finish grade.
2. Trench about 8″ wide x 4″ (additional) depth around perimeter for drain.
3. Run about 12″ of dimpled sheet product against wall into gravel so it sticks up a couple inches above finish grade. This will allow any water coming through the wall to run into the drainage system. (Note: I’ve already done extensive work outside to minimize water coming in).
4. Install 4″ flexible perf pipe in gravel (with filter fabric) so that top of pipe is 4″ below finish grade.
5. Pour 4″ thick concrete slab. Note that for now this will be a pretty small area – enough for the furnace and water heater.
My questions: plastc – what thickness, where does it go, is it mandatory? Directly under the concrete, then under the gravel? Do I run it up the wall and lap the dimpled material into it? This is what makes the most sense to me.
Also, do I need the full 4″ over the drainage pipe or can I raise that a little and let the slab be a little thinner around the perimeter?
Thanks! Bill.