Red Glazed Brick & Mortar

This is my first spotting of the elusive red glazed brick. It's has a deep berry color. We've all seen stained rose color mortar (right?) but this is a red mortar. It was a very exciting morning.

The bottom row of these glazed bricks shows the surface has popped off. What's beneath was fired differently and will crumble quickly.


ty.ro said...

Hey There,

I recently learned why this happens.

When the surface "pops off" of brick it is called 'spalling'. It has to do with moisture being absorbed by the brick and then the brick expanding, and the surface being made of a different material, doesn't expand at the same rate and so it causes the surface to break off. It is especially bad in cold climates when the bricks absorb moisture, then they freeze and expand. We call this 'freeze thaw cycle failure', or something similar. You will see bricks seriously deteriorated in cold climates from this if they weren't fired to be hard enough to 'repel' the moisture or if the wall wasn't built 'to breathe' so when it gets wet from a lot of rain, that the wall can 'dry out' by ventilation. New walls have holes at the bottom of the wall for this reason, and also flashing to direct the water out of the wall at the bottom row.

Glazed brick was especially bad for this, and particularly the last/bottom row of the bricks because the moisture from all the rows above would travel down through the wall, ending at the bottom course of bricks. Today we would put 'weep holes' so the moisture could drain out, and we would separate courses with a 'flashing row' to help this water leave the wall and to help the wall dry out.

In Canada this has been a big issue because of our climate, so bricks are now fired to become harder so it doesn't happen anymore unless the walls are built really badly by people who don't know correct brick construction. Sadly, it took years for architects and people to learn why this happened, so many of the older generation won't used glazed bricks here anymore because they have seen so many deteriorate. I recently co-designed a building as a junior architect and I had to push really hard to get some black glazed brick on the building. Hopefully it will be built and we'll see what happens, my hope is that we have designed it well with weep holes and it should not spall and break off the glazed surface.

Christian Herman said...

Hi Ty.ro!
Long time.

Spalling isn't the result of firing since it also occurs to limestone.

It is indeed the result of winter rain or snow finding entry and purchase then freezing. Water expands as it freezes and yes, it blows out joints in brick or creates spalling in limestone.

There's no cure.
With these glazed bricks water finds entry behind the glaze, usually in the deteriorating mortar joint directly above the brick.

Yes, these bricks were fired differently and it has everything to do with the glaze.