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Brick Chimney Arches with Steel Bars and Self Corbeling Brick

Self Corbeling brick over arch

  1. Self-corbeling of the Bricks above the arch means the arch does not have to hold much weight.

  2. The steel bar is often seen in Victorian fireplaces.  Particularly in openings for ranges. It allows for quick construction as it is used as a “left in place” former. It also allows a much shallower, wide arch to be reliably constructed. 

  3. How the bar works: As well as being a former it also acts as a reinforcing bar in a similar way that steel is added to concrete beams. Bricks are great in compression ie. the top of the arch but hopeless in tension ie. if the base of an arch spreads .  The steel ties the bottom of the arch together so the joints between the bricks don’t pull apart. This effect relies on the adhesion of the bricks to the bar, in particular where the bar goes through the columns.

  4. Problems with working fireplaces: When the fireplace is in use the bar will heat up and expand at a greater rate than the surrounding brick work and mortar.  This expansion and contraction, overtime, causes the bar to de-bond from the brickwork and can cause cracks to form in the mortar joints.  This is the cause of many chimney breast arch problems.

Implications for our particular fireplace: 

See our fireplace re-building here

This differential  between the steel expansion and the relative stability of the brickwork could cause future problems when the Stove is fitted and working.  I’ll report back on any problems.  If we hadn’t got a desire to recreate the former arch shape I would have built a much deeper arch and not used the Victorian steel bar.  It’s a compromise we have had to come to, balancing our efforts to retain evidence of the past with the need to rebuild a reliable structure.  Hopefully as the steel is exposed with an airflow around it the temperature and related expansion will be minimal. The worst that can happen is a few mortar cracks and possible loosening of bricks, the structure itself will remain intact.

Rebuilt arch with steel bar support
Rebuilding the fireplace in our Whitby cottage

More about the Whitby Cottage Renovation/Restoration start here.

For more information about stove fitting and running cost have a look at our Experience and analysis of running a wood burning stove.

Any Comments or Questions about the fireplace are most welcome over on the Blog.