Northern Light
Superstar
I would think it is harder - tiles (except grout) and panels are smooth and can be treated to reduce grime adherence. Not so sure about regular concrete (I mean, just how many cases of good concrete cleaning have we seen - particularly in the context of the TTC?)
re: terrazzo - labour intense to set up - probably even more so than tiling.
AoD
I believe the rationale, other than simply saving the cost of tiling was that the bare concrete 'hides' the brake dust better, and therefore reduces the need for cleaning.
The TTC has multiple excuses....(ahem, reasons) for not wanting power-wash trackside walls.
First, they claim they have to shut the power down so that cleaners can operate from track level; and that this is a logistical hurdle.
Then, they note that 'track time' must be booked.
They won't let non-TTC staff do the cleaning, and have various claimed that this is too labour-intensive and expensive.
I've also heard the excuse (ahem reason) trotted out that they the MOE gave them trouble at some point due to the chemical soup going into the track-level storm drains and thereby the storm sewer system.
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Considering that they did carry out a trial run of cleaning the trackside walls from the Island platform ( @ St. George, I believe) .......the storm drain issues seems false.
It would also establish the feasibility of not booking track time or having to turn off the the third rail, and/or isolating the turn off to only the affected section of track.
Personally, I always thought they should just have a work train that was set up like a carwash, with big brushes, water tanks w/hot water w/soap and a rinse treatment, and you could, if so desired, set up a suction system under the car that would take most of the dirty water back and allow it to be treated off-site.
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The trackside walls need proper finishes.