TO a previous generation of pen-pushers, the coalminer must have been an object of fascination. Coaldust-black apart from the whites of his eyes and the pink of his licked lips, he talked a funny, foreign language of unfathomable technicalities: in-bye, putter, hewer, marra, chummin...

To this generation - well, to me at least - the builder is just as fascinating, and in the last few days I've been privileged to have a brief insight into, to live out a tiny moment in, the builders' merchants.

I've been fascinated by this world ever since I was introduced to the fantastically-named Torus Ovolo.

He could have been a sinister James Bond villain, an Afghan warlord or a tuneless country and western singer. But, instead, he turned out to be the Victorian skirting board that runs around the foot of our walls.

This week's dip into the builders' netherworld began when the chimneysweep took one look at our fireplace and informed us that we were in need of some Vermiculite.

What a word! It could have been a Greek god, or a 1950s kitchenware plastic. It could have been a 19th century artificial rockery stone, or it could have been those strange bubbly, creasy marks that appear on your bottom as you near 40.

Enthused - but scared deep down that my ignorance would shine through - I went in search of Vermiculite at the builders' merchants. I stood apprehensively at the counter, surrounded by burly, confident men in calf-coloured boots and cement-grey jeans.

"Vermiculite?" said the man behind the counter, tearing the perforated edges off computer print-outs which are given in triplicate to anyone who even breathes in a builders' merchant.

"We don't do it any more. We do Mycafil which is even better."

I negotiated the purchase of a bag, collected my computer print-outs (edges neatly torn off) and then drove half-a-mile around the depot to get to the warehouse which I had seen from the counter was about ten yards away.

I asked the warehouseman where the Mycafil was.

"Mycafil?" he said in disbelief. "Mycafil? Never heard of it, mate."

He looked at one of my computer print-outs. "You mean Micafil," he said and wandered off into the warehouse, leaving me stupidly standing among the long lengths of Torus Ovolo which stretched as tall as trees to the ceiling.

He returned with a bag. "There you go," he said, handing it over. "Micafil."

The bag had one word in big blue letters printed on it.

"Vermiculite," it said.

I proudly took my Vermiculite home. Vermiculite turns out to be a phyllosilicate mineral which expands when heated. It is between 1.5 billion and three billion years old, deposited in the pre-Cambrian era, mined in Transvaal in South Africa and sells for £11.49-a-bag (plus, according to my computer print-outs, £2.01 VAT) in builders' merchants in Darlington.

I mixed it into a gruel with a little cement and water, and stuffed it down the gaps at the back of the fireplace. The fireplace's rough cast iron edges peeled the skin off the back of my pen-pusher's hand as if it was a potato being prepared for boiling.

Despite the blood, I didn't really care. I had dirt unshiftably packed under my fingernails and cementdust ingrained into my palm. I had bag of a Vermiculite beside me and, for an afternoon, I was a builder.