Smirke was a pioneer of using both concrete and cast iron.
A critic writing in 1828 in the Athenaeum said "Mr. Smirke, is pre-eminent in construction: in this respect he has not his superior in the United Kingdom".
James Fergusson, writing in 1849, said "He was a first class builder architect ... no building of his ever showed a flaw or failing and ... he was often called upon to remedy the defects of his brother artist."

Projects in which he used concrete foundations included the Millbank Penitentiary, the rebuilding of the London Custom House and the British Museum.
At the first two he was called in when work overseen by previous architects had proved unstable.
The prison at Millbank  (1812–21; demolished c. 1890) had been designed by an architect called William Williams but his plan was then revised by Thomas Hardwick.
The largest prison in Europe, it consisted of a hexagonal central courtyard with an elongated pentagonal courtyard on each outer wall of the central courtyard; the three outer corners of the pentagonal courtyards each had a tower one storey higher than the three floors of the rest of the building.
Work had started under Hardwick in late 1812, but when the boundary wall it reached a height of about six feet high it began to tilt and crack.
After 18 months, with £26,000 spent, Hardwick resigned.
Work continued and by February 1816 the first prisoners were admitted, but the building creaked and several windows spontaneously shattered.
Smirke and the engineer John Rennie the Elder were called in, and they recommended demolition of three of the towers and the underpinning of the entire building with concrete foundations: the first known use of this material for foundations in Britain since the Roman Empire.
The work cost £70,000, bringing the total cost of the building to £458,000.

In 1825–27 Smirke rebuilt the centre of the Custom House in the City of London, following the failure of its foundations.
The building had been erected from 1813 to the designs of David Laing.
The building is 488 feet long, the central 200 feet being Smirke's work.

He used large cast iron beams to support the floors of the upper galleries at the British Museum; these had to span 41 feet.

Another area where Smirke was an innovator was in the use of quantity surveyors to rationalise the various eighteenth-century systems of estimating and measuring building work.
Smirke was a pioneer of using both concrete and cast iron. A critic writing in 1828 in the Athenaeum said "Mr. Smirke, is pre-eminent in construction: in this respect he has not his superior in the United Kingdom". James Fergusson, writing in 1849, said "He was a first class builder architect ... no building of his ever showed a flaw or failing and ... he was often called upon to remedy the defects of his brother artist."
Projects in which he used concrete foundations included the Millbank Penitentiary, the rebuilding of the London Custom House and the British Museum. At the first two he was called in when work overseen by previous architects had proved unstable. The prison at Millbank  (1812–21; demolished c. 1890) had been designed by an architect called William Williams but his plan was then revised by Thomas Hardwick. The largest prison in Europe, it consisted of a hexagonal central courtyard with an elongated pentagonal courtyard on each outer wall of the central courtyard; the three outer corners of the pentagonal courtyards each had a tower one storey higher than the three floors of the rest of the building. Work had started under Hardwick in late 1812, but when the boundary wall it reached a height of about six feet high it began to tilt and crack. After 18 months, with £26,000 spent, Hardwick resigned. Work continued and by February 1816 the first prisoners were admitted, but the building creaked and several windows spontaneously shattered. Smirke and the engineer John Rennie the Elder were called in, and they recommended demolition of three of the towers and the underpinning of the entire building with concrete foundations: the first known use of this material for foundations in Britain since the Roman Empire. The work cost £70,000, bringing the total cost of the building to £458,000.
In 1825–27 Smirke rebuilt the centre of the Custom House in the City of London, following the failure of its foundations. The building had been erected from 1813 to the designs of David Laing. The building is 488 feet long, the central 200 feet being Smirke's work.
He used large cast iron beams to support the floors of the upper galleries at the British Museum; these had to span 41 feet.
Another area where Smirke was an innovator was in the use of quantity surveyors to rationalise the various eighteenth-century systems of estimating and measuring building work.
Robert Smirke (architect)