"Ben" wrote

Ben, you say under the bottom brick, IE not between bricks? At the base
of
the floor?

That's right.

Good and i see from the later parts, well away from any spot that gets hot.

We'd need to know what the floor is of there to answer. I't certain you
It is on a wooded base.

In this case, check with the guys when they inspect and clean but i believe
there are simple
caulks which will be better this time than re-mortaring it. Certainly
easier.

If i get to my local hardware store soon, I will look about but this one
isnt going to be hard to
find as long as you tell them the right information. What you want is heat
resistant but you do not need
'fireproof' as your dimsions show you are well from any flame danger and
caulking to a wooded base.

The hearth comes out about 13" from the fireplace and has a concrete
top that is about 14" off the floor. It sticks out about 19" from the
side of the fireplace. The front and sides of the hearth are 4 bricks
tall. The mortar under the bottom brick is what's worn way. I can't
see anything other than the wood floorboards in the space. I assume
that the floorboards sit on top of floor joists, since this is the
upper floor of a 70s raised ranch.

Hehehe I think it's funny the only other responder didnt think to ask if it
was upstairs. Not bad, he just
didnt think of it.

What you likely have is slow settling, normal to a house of that age. It's
created mild gaps so you do need to fill
with something that will help vapor and water barrier. If looks matter much
depending on the dimensions, backfill
with a heat and water resistant cault then you can thinly cover the
outermost with some mortar.

Lived in a house like that with a double fireplace (one very small on the
floor above, same chimney and some odd older design so one didnt smoke out
the other). The upper one had
a problem a bit like what you say and was caulked then a thin layer of
gritty sandy stuff was in the outermost caulk so except at close inspection,
it looked like
mortar.

What I'd do is see if you can get a free inspection along with paying for
a
cleaning (tell them upfront of the problem and ask if they can check for
safety and write an estimate if needed). They did that for me in my area
without a problem. Alternative was pay for the inspection with no
cleaning
(slightly cheaper). It turned out i didnt need cleaning so they charged
me
for the inspection which was quite reasonable on their part since it was
a
package deal. In my case, the damage was significant and we knew that
but
we were unaware the water pouring in had been enough to make the thing so
clean you could almost 'eat off the walls'!

I would like to get a cleaning, so I'll look into an inspection as
well.

No problem! I dislike 'home cleaning' unless it's an occasional extra
between one or a frankin type stove pipe where you just dismount it then
take
it outside and run a brush through it.

I insist on annual professional cleanings here. Worth their weight in gold.
If you have a downstairs fireplace below it, they package deal the price. I
call my single fireplace
cleaning 70$ *well spent* as we use the thing almost daily in winter.

Oh on inspections, you do not need the fancy camera ones that cost 150$ or
more unless theres something about your particular configuration and a
normal one shows more
indepth is needed. See if you have 'ww.chimneycleaners.com' in your area.
They did well by me. (no affiliation other than happy customer)