In this picture from reddit, the center tiles stay wetter longer (for the most part) than their surrounding tiles. There are a variety of hypotheses there, but what do you smart Dopers think?
Well, they are end-on, so the surface porosity might be very different.
My WAG, the builder cut them on the site and if the brick maker sealed them on all six sides at the factory, that’s now lost. Now, when it rains, water gets sucked in from the cut side and takes time to evaporate back out.
ETA, if the smaller, center ones are made at the factory to that size, they’re not sealed. Factory forget, contractor ordered cheaper ones, mispicks, who knows, could be all kinds of reasons. Might even just be left over from another job.
One way or another, the long bricks have a some kind of seal on them and the short ones don’t. That’s my theory.
They could just be slightly different clay mixtures, or compacted differently, or some other manufacturing difference between the large and small tiles.
I doubt that those pavers are sealed though.
Definitely not bricks or floor tiles - these are concrete “brick” pavers, sold in both rectangles and squares and sold with and without water repelling treatments.
My guess would be they got a deal on the full bricks that included water treatment and not on the squares.
My neighbor just had his driveway done with “Pavestone” which you can see from their site, comes in similar finishes and sizes.
My guess is the squares are simply full paver bricks cut in half. Bricks typically are glazed on the outside. One side of the squares, the cut, is not sealed/glazed and absorbs water. It seems one end is still light for many of the squares, the end furthest from the cut. Quite often in these paving jobs, the edges are fit by cutting bricks to shape. Brick cutting is part of the job - someone just went overboard here.
(In the 70’s when gentrification first got into full swing, one trick in old neighbourhoods was to sandblast the old brick house to get rid of the decades of accumulated grime - resulting in the destruction of the glazed surface, at which point the bricks crumbles mercilessly and quickly due to water soaking in and the freeze-thaw cycle. Nowadays they are smarter and use chemical washes instead.)
That seems odd. Here in the UK, where most houses are brick-built, glazed brick is not that common. The vast majority of brick houses (mine included) are made of rough-textured, unglazed stock brick like this.
I’ve noticed that garden walls built of these bricks often suffer from surface spalling, but the houses don’t seem to. Whether that’s because the bricks are better quality, or simply because they are better protected by the roof, I’m not sure.
House walls are often warmer than garden walls due to waste domestic heat - so the surface moisture doesn’t always freeze. I remember this being cited as a concern when cavity wall insulation started to become popular.
Yes, I remember visiting London for the first time and being amazed that old buildings in south London appear to have been retrofitted for indoor toilets by running the waste pipes up the outside of the buildings. That couldn’t happen in at least half the USA due to temperatures.
The place where this brick cleaning was a problem IIRC was the northwest where a lot of old red brick townhouses were built in the old inner city. Places like Philly and NYC and Boston can get well below freezing multiple times a winter for extended stretches.