Paso Doble, Barbican, London

Paso Doble starts with a shiny expanse of wet clay. One red slab forms the floor, a second, sprayed white, is a wall behind it. Over 50 minutes, the France-based theatre artist Josef Nadj and the Spanish painter Miquel Barcelo hack and squeeze the set around them, piling clay on to the walls or themselves, drawing pictures and squelching them out again. There are some boldly creepy moments, but Paso Doble is generally less fun than making mud pies.

It starts well. Bubbles form on the blank white wall, as Nadj and Barcelo push at it from the other side. It looks like mud near hot springs, or cooking porridge, until sticks and fingers poke through.

Emerging from behind the wall, Nadj and Barcelo get to work on the clay. They're neat figures, at least to start with: both in their early fifties, dressed in dark suits that quickly get covered in whitewash and red clay. Nadj is tall, thin, slightly hangdog. Barcelo is stockier, more emphatic.

Producing tools, they start cutting out spikes or balls, throwing them at the wall, pouring water into a hole. The process is matter-of-fact, with what looks like deadpan comedy quickly becoming dull.

Having attacked the clay, they start decorating themselves. Producing unbaked pots, they sit on them until they collapse, or mould them over their own heads. Tugging at their masks, they produce pigs, chickens, an elephant face with a long trunk. It's repetitive, but the tangled, squished faces do look sinister.

Nadj, in particular, pulls his clay masks close to his face: has he left himself room to breathe? It's more worrying when Barcelo starts sculpting the clay, with Nadj still inside it. He thrusts his fingers into the mask, making eye holes – just how close are those gouging fingers to Nadj's own eyes? At last, weighed down with several layers of clay, Nadj falls against the wall, kneeling with his face against it. Barcelo then sprays the whole wall white, making Nadj an integral part of the composition.

There are ideas here: the unnerving clay masks, the transformation or humiliation of Nadj. But they remain pedestrian, with too much repetition. The process of changing the clay isn't lively enough for performance, while the final installation isn't striking enough as sculpture. It did, however, have a hold on this audience. At the end, people crowded down to the stage, ready to take photographs of the finished, mangled wall.

Ends tomorrow (0845 120 7550)