Sounds like your master cylinder to me. Had the same thing happen, with
same behavior as what your seeing.

You should get it fixed right away, the m/c can fail further, without
further warning.

-Arthur

North American Trade Service wrote:

> I have a 1995 EX Accord which may need a brake master cylinder. I'm
> not sure about this because just two weeks ago I had my front rotors
> and brakes replaced. Could it be that the mechanic did not bleed the
> brakes correctly, and that there is air in the system?
>
> When I press on the brake it goes to its expected place and then
> slowly goes down further, until it reaches the floor. This only
> happens sometimes, usually at long stop lignts.
>
> Can someone help me out with this.