blueman wrote:

One of the 12" wide treads on our main staircase has an ~18"
longitudinal
crack in it. As per an earlier thread, the consensus seems to be that
these treads are 150 yr old heart pine.

Here is a link to a pic:
http://96.252.37.8:8080/public/1stFlrTread.jpg

I am not concerned about the visual look of the crack (if anyting it
adds "character") but the area under the crack is not well supported
and
gives a bit when you put weight on it -- in fact, the absence of such
support may be the proximate cause of the crack. The crack has
probably
been there for many years.

Since replacing the tread is not easily feasible given the old wood,
I
would like to repair the tread.
snip

If you truly mean, "I am not concerned about the visual look of the
crack", then the repair is fairly straight forward.

Using a Fein MultiMaster with a straight blade, plunge completely thru
the tread in the crack, then clean out the crack at least 1/8" wide or
what ever is necessary to remove all damaged tread material.

The width of the cut is not important as long as it is wide enough to
allow the thickened epoxy to freely flow and fill the cut.

On the bottom side of the tread, cover the saw cut with some duct tape
which gets removed later.

Mix up some SLOW epoxy, thickened slightly with micro-balloons, and
pour into crack about 1/4" deep. (Just enough to seal the cut
completely against the duct tape.

Wait 24 hours, then mix up more thickened epoxy and complete filling
the cut proud.

Wait 48 hours, then sand smooth and remove duct tape from bottom.

When the tread returns to compost, the epoxy repair will still be in
service.

If color is important, you can play around with some artists dry
pigments to try and match tread color.

Have fun.

Lew