National Museum & Library

I’ve been rooting around for some info about the stonework of these two buildings in light of the Museum’s recent restoration, and have found some interesting stuff.

I think most people know about how the original sandstone dressings of the two buildings weathered very badly and very quickly, and this is always claimed to be as a result of the stone being of poor quality.
However it was in fact the result of a major (but common) flaw in the construction of the buildings that caused the problem.

The sandstone was face-bedded onto the buildings, which means the natural grain of the stone which runs horizontally in the ground, was positioned vertically on the structures, causing very severe weathering effects, very quickly. The vertical positioning was used for asthetic reasons as most of the dressings are vertical, from the window surrounds to the many columns.
It is unclear whether the architects TND & Son, or the contractor William Beckett were responsible.
As there was great competition for the the contractors job after the architectural competition of 1883, Becketts’ rivals took great pleasure in seeing the stone eroding away barely 10 years after completion.
The most common form of damage to face-bedded stone is whole sheets of it peeling and flaking off, as a result of water penetration and freeze-thaw action.

As a result, the Ntl Library’s sandstone ornamentation was replaced with the usual Ardbraccan limestone (which the Custom Houses’ drum was rebuilt with), but I cannot find out when this was done, a guess is the 1920s. T
The columns surrounding the rotunda were not replaced, presumably on cost grounds.

The Ntl Museum must have fared a little better as its sandstone was not replaced, maybe as it wasn’t exposed as much to the south-westerly winds and rain blowing up Molesworth St.

What the OPW have just finished is the restoration and cleaning of the building.
The sandstone had to be repaired, but naturally couldn’t all be replaced on cost and conservaion grounds, so a special hard mortar was developed, which contains ground sandstone to match the original colouring and texture.
I don’t know if this has been used to literally plaster over all the sandstone, or just to repair patches.
Work began in May of 1995 and took a whopping 8 years to move around the whole building, for it to be largely completed by May of 2003.
The part now behind the wall of Govt Bldgs is now the last part to be finished.

The rotunda of the Ntl Library now has to be cleaned. It’s street facade was however cleaned first around 1994/5.

The sandstone of the two buildings is Mountcharles sandstone, or rather Drumkeelan stone a couple of miles away, in south Donegal.
Unusually, this stone was originally mined underground here, although these two buildings’ stone was quarried in a newly opened quarry.
It comes from a band of sandstone 2 metres deep and over 50 metres wide, and is no less than 300 million years old!