DOCTOR ON THE HOUSE

Remember last week's carpet buying neighbour? It was bad, says Jeff Howell, but not as bad as the DIY brickie's back...

My neighbour had bought this carpet from a bloke at the door. Now, you know you should never, ever, buy things at the door. We all know that. But, faced with this unbelievable bargain of enough brand new carpet to do the front room for pounds 20, the neighbour's greed overcame him. To make an even better bargain, he tried to fit it himself with nails - some inch- and-a-half round heads he had in the shed. He put one through a pipe and the leak brought the ceiling down in the basement kitchen below. It cost him pounds 165 for an emergency plumber and pounds 90 for a plasterer, and about pounds 60 for takeaways while the kitchen was out of use. Oh, and there wasn't quite enough carpet either.

So there's a good example of how DIY can be a net consumer of money. And there are plenty of other stories like that. Some of the worst mistakes occur because people are scared to ask for advice; they don't like to admit they don't know.

Bricklaying is a good example. Mortar is made by mixing sand and cement, right? Wrong.

Bricklaying mortar is made by mixing sand, cement, hydrated lime, plasticiser and water. The lime makes the mortar more "fatty" and easier to handle. The plasticiser makes it flow without having to add too much water. If you just use sand and cement it won't flow unless you make it really wet, and then the mortar dribbles out of the joints and down the face of the brickwork, giving a characteristic DIY appearance.

But people don't ask. They have the idea they want sand and cement, probably from their dads, who were accountants or bus drivers or something, and so they walk into the builders' merchants on Saturday morning and ask for sand and cement. Everyone in the builders' merchants knows what's going on but doesn't say anything. And then they watch while chummy strains himself trying to put the bag of cement into the car holding it at arm's length, away from his clean jumper. Don't ever try this, by the way; it gives you a permanent lower back injury; hug that bag tight to your chest, and follow it into the car. You can hoover the car out and you can wash your jumper but you can never fix your back.

Anyway, instead of asking for sand and cement, you should stride up to the counter and say excuse me, I don't have a clue, please tell me what I need to make bricklaying mortar. Everyone in the place will immediately become your friend. The staff and other customers will vie with each other to give you the best advice. And then they will help you load the car up. Believe me, this is true. I always do it.

Not with bricklaying mortar, obviously; in that case I'm the one that's dishing out the advice. But with other things, electrics, plumbing, roofing, I go straight in and say I don't know how to do this, what's the score.

Cement, by the way, wasn't used in mortar until the 1940s. So if you want to do brickwork repairs to your Victorian house, use sand and lime. Lime mortar sets slowly and retains the ability to move without cracking, which is why some old houses look decidedly lopsided, but don't seem to have any cracks.

Cement mortar is a different proposition. It sets quickly. Rock hard. It will not accommodate any movement whatsoever. Cement mortar plus movement equals cracks. Remember that because I'll be coming back to it again.