The first major restoration work occurred during the 1890s.
This had focused upon repairs to the brickwork because engineers of the late Victorian era were concerned that the original lime mortar used in the viaduct's construction was inadequate.
It was decided that this should be replaced with cement mortar.
However, replacement facing brickwork and substandard mortar eventually caused its own failures prompting more expensive repairs later on.
This was likely due to the repair work having borne a greater share of the structure's load than intended, resulting in an accelerated failure rate; poorly bonded header bricks is another probable culprit for its ineffectiveness.
Additionally, the parapets and pavilions, although made from Caen stone (a high-quality limestone), have been subjected to heavy weathering.

By 1956, the damage to the viaduct was extensive but the cost of refurbishment work was deemed to be too high by British Rail.
The degradation was partially a consequence of the structure's long lifespan: when originally constructed, its designers had intended for the structure to have a design life of 120 years, which it had long since exceeded.
By May 1983, the viaduct had been officially recognised as a Grade II* listed structure.

By the 1980s, the eight pavilions present on the viaduct were in such a poor condition that some of their roofs had fallen in and the installation of internal props was required to stop them collapsing further.
As a consequence of its heritage status, all envisioned alterations to the viaduct need to be reviewed and agreed by English Heritage.
When British Rail proposed to dismantle the original pavilions and rebuild them using reconstituted stonework, English Heritage refused permission to do so; accordingly, there were no substantial restoration performed to the viaduct during this period, a decision  which British Rail publicly attributed to the sizeable cost of undertaking such work.
The fabric of the structure continued to deteriorate over the next decade; sections of the stonework began to fall away from the balustrades and parapets during this time.

Starting in March 1996, the viaduct underwent a £6.5 million renovation overseen by national rail infrastructure company Railtrack and partially funded by grants from West Sussex County Council, Railway Heritage Trust and English Heritage.
Harder-wearing limestone was imported from Bordeaux to ensure the closest match with the existing Caen stone in the balustrades and pavilions.
Some of the piers had to be reconstructed because of failures in the Victorian brickwork.
The new bricks were handmade in a variety of sizes to suit the existing brickwork and set in a sand, cement and lime mortar; stainless steel anchoring was used to firmly fix the new stone to the old stonework.
Throughout the work, one of the lines always remained open while restoration activity was being carried out on the other side of the viaduct.
The project, which took more than three years, was completed during September 1999.
The first major restoration work occurred during the 1890s. This had focused upon repairs to the brickwork because engineers of the late Victorian era were concerned that the original lime mortar used in the viaduct's construction was inadequate. It was decided that this should be replaced with cement mortar. However, replacement facing brickwork and substandard mortar eventually caused its own failures prompting more expensive repairs later on. This was likely due to the repair work having borne a greater share of the structure's load than intended, resulting in an accelerated failure rate; poorly bonded header bricks is another probable culprit for its ineffectiveness. Additionally, the parapets and pavilions, although made from Caen stone (a high-quality limestone), have been subjected to heavy weathering.
By 1956, the damage to the viaduct was extensive but the cost of refurbishment work was deemed to be too high by British Rail. The degradation was partially a consequence of the structure's long lifespan: when originally constructed, its designers had intended for the structure to have a design life of 120 years, which it had long since exceeded. By May 1983, the viaduct had been officially recognised as a Grade II* listed structure.
By the 1980s, the eight pavilions present on the viaduct were in such a poor condition that some of their roofs had fallen in and the installation of internal props was required to stop them collapsing further. As a consequence of its heritage status, all envisioned alterations to the viaduct need to be reviewed and agreed by English Heritage. When British Rail proposed to dismantle the original pavilions and rebuild them using reconstituted stonework, English Heritage refused permission to do so; accordingly, there were no substantial restoration performed to the viaduct during this period, a decision  which British Rail publicly attributed to the sizeable cost of undertaking such work. The fabric of the structure continued to deteriorate over the next decade; sections of the stonework began to fall away from the balustrades and parapets during this time.
Starting in March 1996, the viaduct underwent a £6.5 million renovation overseen by national rail infrastructure company Railtrack and partially funded by grants from West Sussex County Council, Railway Heritage Trust and English Heritage. Harder-wearing limestone was imported from Bordeaux to ensure the closest match with the existing Caen stone in the balustrades and pavilions. Some of the piers had to be reconstructed because of failures in the Victorian brickwork. The new bricks were handmade in a variety of sizes to suit the existing brickwork and set in a sand, cement and lime mortar; stainless steel anchoring was used to firmly fix the new stone to the old stonework. Throughout the work, one of the lines always remained open while restoration activity was being carried out on the other side of the viaduct. The project, which took more than three years, was completed during September 1999.
Ouse Valley Viaduct