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Why do brick spall?


mgbinspect
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Brick spall when they are too soft and porous. This permits the brick to absorb and retain too much water which then can freeze and expand breaking away the brick surface.

While this is merely a general rule and not an absolute, there are two typical times when brick spalling occurs. The first is when brick have been reclaimed and re-layed as "used brick". The second is a manufactured brick that was simply substandard.

The interesting thing about the first reason is that early American masons actually did understand brick density and vulnerability issues. They culled and set aside the soft brick for the interior withes of solid masonry construction.

Unfortunately, masons in the 60's and 70's weren't as thoughtful and installed them as exterior brick. It didn't take long for them to fail.

Occasionally an inspector may notice spalled brick on the side of an old row house and assume this is an exception. But, typically, upon closer examination it will become obvious that even these exposed soft brick were not originally exterior brick. Another building which has been torn down once adjoined this building. The silhouette of the previous building will be apparent (outlined) through a change in brick appearance and quality of workmanship.

The second common circumstance under which an inspector will see spalled brick is in houses built in the 60's and 70's. Some brick manufacturers during that period of time were using inferior materials. When that fact became apparent, the ASTM devised absorption standards that some pits and manufacturers could not meet. They were forced to close down or bring in the needed supplementary material to meet the standard.

For these reasons, an inspector should not expect to see much brick spalling in homes built in the recent past or future.

As a side note, on occasion we may see brick that have come apart near the top of a chimney, but this is not typically spalling. When the crown or top courses and joints fail on a chimney and permit water to enter and freeze in the cores, bricks can literally spit apart.

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Originally posted by mgbinspect

The first is when brick have been reclaimed and re-layed as "used brick".

I've read that used brick aren't as strong in a wall as new brick. The reason given was that the pores in the brick are where the chemical bonding between brick and mortar occur, with the mortar/chemicals filling the pores. Therefore when the brick was used again there were far less open pores for the bonding process to take advantage of. Any thoughts on that?

Brian G.

Bonding...James Bonding [:-tophat]

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Brian,

I suppose that is possiible and reasonable. Used brick are usualy hand cleaned at the yard by super cheap labor, washed and then palletized (I've actually watched it all happening).

But what you are talking about would affect the masonry system at large. In most cases used brick is not installed as a structural component so it isn't significant. It would niether be a factor in brick spalling.

From now on, mentally note the color of the bricks that spall. They will always be salmon to bright red brick and so soft throughout that you can scrape material away with a pocket knife.

An old ceramics engineer and brick plant owner/operator explained that they were on the outer rows of the kiln and under fired. They were never suitable for exterior use. In sharp contrast the very deep dark red or even approaching even black bricks (ironite) are very fired and hard as nails. They rarely if ever spall.

Finally, notice on an old row house how different the general color of the exterior brick is from the interior brick. Most of the lighter red to orange bricks will be inside and the darker better fired bricks will be outside.

The old ceramics engineer explained that these soft inside brick even behaved a bit like wood in that they would actually receive a nail.

At any rate, as always, old school architects and tradesman, were so much more knowledgable and deliberate about all they did.

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That is absolutely true. I see reclaimed brick all the time. When it's "bad", someone that didn't know brick was using a softie in the outer wall, instead of burying it in the inner wythe.

The old time masons would cull through all the brick before a job & allocate the softies to the inner wall & the hard stuff for the upper parapets most exposed to weather. If it's done right, the wall(s) will last >100 years w/no visible deterioration.

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Thanks for the authoritative confirmation, Kurt. :-)

The old mason's were actually intelligent professionals. They knew their trade in and out, up and down.

Unfortunately, the scarcity of masons and the need for them has eliminated the time and need for education. It's mostly monkey see monkey do anymore.

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  • 4 years later...

I also see brick faces spalling-off when mortar was retro-fit that was 'too hard' (too much Portland cement in the mortar.... ). The brick 'gives' instead of the mortar flexing.. I see this every day in Boston.. Tons of 'bad work' going on up here... TONS of 1870's brick piled up here in the City..

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Read the thread "Re-inventing the Wheel" which speaks of the woes of Portland cement and masonry unit compatibility.

https://inspectorsjournal.com/forum/top ... C_ID=10921

Re-pointing old brickwork is both an art and science that, when not done correctly permanently destroys old historical buildings every day.

Every time I go into downtown Richmond and see someone repointing masonry incorrectly it just kills me. I want to stop and give them a lecture, but it's obvious that most of them simply wouldn't really grasp it or care just so long as the check's good.

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  • 4 weeks later...

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