The Alhambra, which towers over the city of Granada in Andalucía, Spain, contains many buildings. For most of these one visits for the architecture and the decoration, but there is one where the building stone  makes itself very evident.

The Palacio de Carlos V (or the Palace of Charles the Fifth) is odd for many reasons. It was built after the defeat of the Moors in 1492. Work started in 1527 and was finished only 50 years ago. It took so long for several reasons. One was that Carlos’s wife said she could not stand Granada. Another was that the peasants, many of Moorish origin, whose taxes were paying for it, were revolting. It may be that the former reason was a cover for the latter.

The front of the Palace of Charles the Fifth

It was built to underline the defeat of the Moslems. It is a defiantly Western building planted on top of a Moorish Palace.

And it looks as if it should be in the middle of Florence. The architect, Pedro Machuca, a pupil of Michaelangelo, was in love with the Renaissance and used his opportunity to the full.

It is a geometric building, square with a circular patio in the centre. The outside is of sandstone and typically Florentine - two giant stories, big blocks, rusticated in the ground floor, fancy bronze decorations and with columns on the higher part of the frontage and lots of fun with pediments.

The interior patio also follows all the Renaissance rules. The columns are Ionic on the lower floor and Corinthian in the upper. The proportions look right so Machuca was following the best precedents.

The interior courtyard of the palace

But the interior patio is built of a coarse conglomerate! It is difficult to think of a more unsuitable rock for renaissance building. One should be looking at the purity of form as created by the hand of man. The stone should complement the skills of the architect and artisan. It should be a blank canvas on which their skills are displayed; or a carefully selected, polished marble, displaying nature as the refined handmaiden of the artist.

A panel unsuited to fine carving

This conglomerate is anything but blank! And it is exceedingly coarse! The interior structure of the rock overwhelms any surface shaping and nullifies it. It is like a delicate painting on a rough sack. You know the painting is there but all you can see is the sack.

The carving has been done on finer grained rock, but the conglomerate dominates

And it must have been the devil to work. I suspect that when the rock was fresh the matrix was of  the same strength and hardness as the clasts. So when the drums of the columns were turned and polished the matrix would be removed and polished at the same rate as the clasts. Otherwise getting a smooth surface would have been impossible

Detail of the carving. The Spaniards have a thing about bulls!

But with the advancing years the matrix, being finer grained, has weathered more quickly and has tended to fall out. Once the matrix is compromised the clasts tend to fall out, and as they are very large, great holes appear.

A Conglomerate Column

Attempts have been made to patch the columns but they are unsuccessful - they only succeed in showing the deficiencies of the conglomerate.

Cobbles fall out of the finished stonework

One wonders why this stone was selected. Throughout Andalucia decorative columns with large irregular clasts are common. But they are usually of limestone or serpentinite breccia. And many of them are of Roman origin, reused in later buildings both Christian and Moorish.

A Conglomerate Column

Perhaps the architect insisted on exotic columns and there was a shortage of  more suitable ones. And so they used what was to hand

An attempt to repair a column without the benefit of a sedimentologist.

I have tried to discover the age of the conglomerate but without success. I suspect it is of Tertiary or younger as we are in the Sierra Nevada which is of Alpine age and this conglomerate is the product of rapid erosion in a mountain environment. And building stones, especially bad ones, are not transported far.