Patio joints: repointing, sanding and sealing explained

Why joints fail

Cement pointing is rigid and the patio underneath is not, so seasonal movement, frost and the odd heavy planter crack it. Once cracked, water gets underneath and freezing pushes it out. Sand-filled joints simply wash out over the years, especially where water runs across the surface. In both cases the void fills with organic silt, and that silt is what weeds and moss root in.

This guide sits under our Patios & Driveways work, covering 20-mile radius of Plymouth.

Cement pointing: traditional and unforgiving

A properly mixed and well-compacted cement mortar joint is durable and looks right on older stone. It has to be worked into a clean, damp joint of adequate depth, and it will fail if it is buttered thinly over the top of loose material. It also cracks where there is any movement. If half your existing pointing is loose, patching is a short-term measure; the honest answer is raking out and repointing the lot.

Jointing compounds: convenient and flexible

Brush-in resin or polymeric compounds are swept into the joints and set with water or air. They flex slightly, resist washout and slow weed growth. They need joints of the right width and depth to work, they need the surface genuinely clean beforehand, and they must be applied within their temperature and moisture window. Applied badly they haze the stone, which is why preparation matters.

Kiln-dried sand: for block paving, not slabs

Kiln-dried sand belongs in block paving, where the tight joints and the interlock of the blocks hold it. On wide slab joints it washes straight out and gives you a weedy patio within a season. If someone proposes sanding a flag patio with wide joints, that is a sign they are treating it like a driveway.

Clean first, always

Every jointing method needs a clean joint to bond or key to. That means the growth killed and the old material raked out, not just the top brushed off. This is why jointing normally follows a proper clean rather than being done as a standalone job, and why a patio project is usually clean, dry, joint, then optionally seal.

Where sealing fits

Sealing goes last, onto a fully dry, fully cured surface. It reduces staining, slows the return of black spot on porous stone, and makes subsequent cleaning easier. It changes the appearance, usually enriching the colour, so test an offcut or a discreet corner first. It is a maintenance product with a life of a few years, not a permanent treatment.

Drainage matters more than any product

If a patio holds water against the house or ponds in the middle, no jointing will keep looking good. Falls should take water away from the building, channels and gullies need to be clear, and the surface should sit well below the damp course. Where those things are wrong, fixing them is worth more than any amount of cosmetic work.

Realistic expectations

Good jointing hugely reduces weeding, it does not abolish it, because seeds also germinate in surface debris regardless of what is underneath. Sweeping regularly and clearing leaves in autumn does as much as the product choice. Plan on refreshing joints every several years and treating the surface annually if it is shaded.