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I was helping to redo the hearth on a 100 y/o fireplace, and as I pulled up the bricks and moved sand out of the way I noticed wood installed on an angle (subfloor?). The fireplace is in the middle of the room on a 100 y/o house built on stilts/pilings.

I've spoken with a few people but they don't know enough about fireplaces built this long ago.

Is the wood/subfloor suppose to be like this? It's a pretty big gap.

  • What's the question?
    – Hart CO
    Aug 24, 2017 at 21:50
  • is the wood suppose to be like this or something under the house collapse?
    – kenny
    Aug 24, 2017 at 22:14
  • Oh that's interesting, does it have same pitch on the other side?
    – Hart CO
    Aug 24, 2017 at 22:16
  • no it doesnt have the pitch on other side
    – kenny
    Aug 24, 2017 at 22:21
  • I'd think if you kept digging at the front you'd find a spot where it either cracked or just ends, but hopefully someone else is familiar with this type of setup, I'm out of my depth, just fascinated.
    – Hart CO
    Aug 24, 2017 at 22:25

1 Answer 1


The wood was used as a concrete form for that back in the day. Concrete was poured to the sub level needed top hold the finish hearth. It typically extended into the fire box, actually it was poured usually before the firebox is built and was used as a base the continue the firebox construction. It was poured after the brick is built up to the level where the concrete could be poured 4+" thick. The reason for the tapered form are such as the concrete doesn't need to be that thick at the edge. 2-3" at the thin edge works since it get another covering over it.

  • Does the lack of taper on the other side strike you as odd?
    – Hart CO
    Aug 25, 2017 at 17:55
  • 1
    Not at all, usually the taper is only on one side it does not return around the two short sides, it is only on the one long side.
    – Jack
    Aug 26, 2017 at 1:05
  • I want to add the taper is to help keep the slab balanced so to speak, since it is cantilevered.
    – Jack
    Aug 26, 2017 at 16:31

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