Block Paving Driveway Restoration: Soil Removal, Deep Clean and Re-Sanding

There is a line in every guide to having your driveway pressure washed about brushing off the loose leaves and twigs beforehand. It is sound advice and it was no use whatsoever here, because the first tool this job needed was a shovel. What was sitting on these blocks was not dirt. It was soil — the composted end product of years of leaf fall, deep enough to plant in, with grass rooted into it and growing happily. You cannot wash that off. You have to dig it off.

Which means the honest way to describe the first half of the day is excavation. The spoil came off by hand, piled into one corner, and sat in the May sun for a few hours to dry, because wet soil is roughly twice the job that dry soil is and half of what you are lifting is water. Then it went into bags and off the property. Nothing about that appears on any checklist of what a driveway clean involves, and it was most of the work.

A word on where it went, because it is the part nobody thinks to ask about until afterwards. Spoil like this is not garden waste and it is not the council's to take away. Once it had dried it was handballed into rubble sacks, loaded, and taken to the local waste yard — which is a slower and dearer way to finish a day than the alternatives, and the only one that leaves nothing behind for somebody else to deal with. Removal is part of the job, not something that happens to the job.

Then the edges, which turned out to be the transformation nobody was expecting. Cutting the turf back to the true line of the blocks gave the drive its shape back — the curve on both flanks, the proper width, the actual footprint somebody laid. The owner had been living with a vaguely defined rectangle for years. What came out from under the grass was a metre wider on each side and had a deliberate form to it. He had not lost a driveway. He had lost the outline of one.

Only after all that did a pressure washer earn its place, and then it was a full day of it. Rotary cleaner across the entire surface, lance held well back for the edges and the returns against the garage. No chemical treatment at any point on this drive, because none was needed — the problem was mineral and physical, not biological, and once the soil was off there was nothing living for a biocide to kill. Selling a treatment would have been selling something that did nothing.

Block paving is also the surface that tolerates this best. Concrete pavers are cast and cured under pressure, dense and hard-wearing by design, and they take a firmer hand than most patio slabs will — which is exactly why the same setting that is fine here would be wrong on a softer flag. Where you can see the difference is what comes off: work a tarmac drive and you will sweep up grit, a real pile of it by the end. Block paving does not shed like that, and knowing which surface is losing material as you go is most of what separates a clean from a wearing-down.

Now the part that had nothing to do with cleaning. Before starting I asked what was in the garage, because the whole drive falls towards it. He declined to tell me — his business entirely — and said the garage was off limits. Fine. So I explained I would want to lay waterproof blockades at the thresholds regardless, because water was going to try to get under those doors and I would rather it did not.

He already had sandbags, as it turned out, for exactly that reason. And then, having decided I was not a threat to whatever was behind the doors, he opened them and showed me — which was a real treat — and the floor was covered in the parts and materials he used working on it all himself. Water did come under those doors that day. It hit sandbags.

I mention it because it is the part of this trade that never makes it into a quote. Nobody prices in the ten minutes spent working out which way the ground falls and what is sitting at the low end of it. But the difference between a good day and a very expensive one was a conversation that took two minutes and a customer who happened to have the right thing in his shed.

The last step was not on the same day and could not have been. The joints were re-sanded on the seventeenth, four days after the wash and also cleaning the patio behind the property, because kiln-dried sand put into a damp joint clumps at the top and never beds down. One or two days of May weather is what it takes for blocks that have carried an inch of wet soil to dry all the way through. That return visit is the step that gets quietly dropped from a cheap quote, and it is the one that decides whether the drive holds together.

BS 8221-1:2012

Most exterior cleaning is sold on results. Very little of it is sold on method, and almost none of it references the published guidance that already exists on how masonry and concrete should be cleaned. We think that's backwards, so here is the standard we work to and what it will tell you — whether you hire us or not.

What the standard is

BS 8221-1:2012 — Code of practice for cleaning and surface repair of buildings: cleaning of natural stone, brick, terracotta and concrete. It came into effect on 31 July 2012 and incorporates Corrigendum No. 1.

It sets out recommendations for removing surface deposits from a building's substrate without damaging the fabric underneath, along with the principal cleaning methods available and the characteristics of the deposits themselves. It is written for building owners, surveyors, architects and contractors.

Its scope covers natural stones, clay brick, calcium silicate brick, glazed and unglazed terracotta and faience, and cast concrete products including cast stone, concrete brick and concrete blockwork.

The document is structured around considerations affecting cleaning decisions, then separate treatment of stonework, brickwork, terracotta and concrete, followed by removal of specific deposits, the cleaning methods themselves, and health and safety. Its annexes deal with precautions for hand cleaning, water cleaning and abrasive cleaning, plus further detail on chemical cleaning.

Being straight about scope

BS 8221-1 is a standard for buildings — walls, elevations, masonry. "Concrete blockwork" in its scope means walling blocks, not the block paving on your drive.

So we don't claim it governs a driveway. What it governs is the reasoning: identify the deposit, match the method to the substrate, prove it on a small area first, and accept that some things should be left alone. That reasoning doesn't stop applying because a surface happens to be horizontal. We use it everywhere, and we tell you where it formally applies and where we're simply borrowing good sense.

The three principles worth knowing

Identify the deposit before choosing the method. Atmospheric soiling, biological growth and chemically altered crusts are three different problems that happen to look similar at a distance. A treatment that lifts algae does nothing to a sulfate crust, and a method that removes a crust may take stone with it.

Gentlest effective method, always. Established conservation practice — and the reason water and soft brushes are the default starting point for historic masonry — is to begin with the least aggressive approach that works and escalate only when it demonstrably doesn't. Pressure is not a setting you choose in the morning. It's a decision you make in front of each surface.

Prove it on a test patch. Conventional practice is a small trial area, roughly six inches square, somewhere inconspicuous, with more than one method tried side by side. It costs ten minutes. It's the difference between knowing what a surface will do and finding out across the whole of it.

What that black staining actually is

The dark crust on a sheltered elevation usually isn't dirt sitting on the surface. Sulfation is the process: sulphur dioxide in the air reacts with the calcium carbonate in limestone to form gypsum, and that gypsum traps airborne carbon as it forms. The result is a black crust that is chemically part of the stone rather than deposited on it.

Which leads to the least commercial sentence on this page: sometimes the right answer is not to clean. Where a sulfate crust has become integral with the stone, removing it removes the surface beneath. A contractor who will quote to clean anything has not asked that question.

Where to get it

BS 8221-1:2012 is published by BSI and must be purchased — it isn't a free document. BS 8221-2 covers surface repair and repointing.