Patio Cleaning, Repointing & Repair Questions

Algae, lichen and moss regrow fast on porous surfaces, especially in shaded or damp spots. Without a post-clean biocide treatment, spores left in the surface can recolonise within weeks. Repointing open joints also helps, as crumbling mortar traps moisture and organic debris that feeds regrowth.

Yes, if the pressure is too high or the lance held too close. Soft stone such as sandstone can be etched or pitted, and high-pressure water blasts out existing joint mortar, leaving gaps that let weeds in. The correct approach uses controlled pressure matched to the slab material.

Open joints let water penetrate the sub-base, which softens and shifts, causing more slabs to rock or sink. Loose slabs are also a trip hazard. Over winter, water in the joints freezes and expands, widening gaps further and accelerating the rate of deterioration.

Yes. Freeze-thaw damage opens joints by forcing mortar out as water expands on freezing. Raking out the failed material and refilling with a flexible, frost-resistant jointing compound restores the joint and reduces the risk of the same cycle repeating the following winter.

Most patio cleaning jobs in Cambridge come in at £150-£400, depending on the area in square metres, the surface material and how heavily soiled it is. Repointing or slab repairs added to the same visit will increase the total.

The main factors are the total joint length to be raked and refilled, the jointing product specified, the number of slabs to be relaid, and access to the site. Heavily degraded mortar that needs deeper raking takes longer and adds to the overall cost.

The patio is surveyed and the work is quoted before anything starts. If the survey reveals more extensive sub-base movement or slab damage than was visible initially, the additional scope and cost are explained before proceeding.

Not necessarily. If the joints are solid and intact, a thorough clean may be all that is needed. Check by pressing the mortar with a key, if it crumbles or feels hollow, repointing is worth doing at the same time rather than returning to the job later.

Look for mortar that is crumbling, recessed more than 5 mm below the slab edge, or missing entirely. Weeds growing in joints and slabs that rock underfoot are also clear signs. If the joints are firm and flush after cleaning, repointing can wait.

Only the affected area needs attention. Isolated slab relay and localised repointing are standard practice, there is no need to lift the whole patio. A site survey will confirm whether the problem is contained or whether the sub-base has shifted more widely.

Someone experienced with paved surfaces is the better choice. Correct mortar mix ratios, jointing compound selection, raking depth and pressure-wash settings all vary by slab material. Getting these wrong can damage the slabs or cause the new mortar to fail within a season.

Not on its own. Clay shrinks and swells with moisture, causing ongoing movement that will keep lifting or cracking slabs. Surface repairs help short-term, but a lasting fix usually requires addressing the sub-base, either improving drainage or laying a more stable base layer. A site survey will confirm the extent of the problem.

Clean first, then repoint. Removing algae, moss and debris gives a clear view of which joints genuinely need attention, and fresh mortar bonds better to a clean slab edge. Repointing onto a dirty surface risks poor adhesion and premature failure.

For heavy algae or lichen, a professional-grade sodium hypochlorite or quaternary ammonium biocide applied after pressure washing outperforms slow-acting no-rinse products. Wet and forget works as a maintenance treatment on lightly soiled surfaces, but it will not shift established growth quickly.

They solve different problems. A deep clean removes surface contamination; repointing restores structural integrity to the joints. If the joints are crumbling, cleaning alone leaves the underlying weakness in place. Most patios in poor condition benefit from both carried out together.

It will shift light surface grime but has no effect on algae, lichen or deep staining. Detergent residue can also make wet slabs slippery. For anything beyond a light dust, a purpose-made patio cleaner or pressure washing gives a far more thorough result.

Yes, in most cases. Lifted slabs are relaid on a fresh mortar bed once the sub-base is checked and levelled. Replacement is only necessary if the slabs themselves are cracked beyond use or if the sub-base has failed across a wide area. Patio drainage issues often underlie repeated lifting.

Usually yes, for a standard-sized patio. The sequence is clean, inspect, rake out failed joints, relay any lifted slabs, then repoint. Larger areas or extensive slab relay may need a second visit, confirmed after the site is assessed.

Old mortar is raked out using an angle grinder with a mortar-raking disc or a manual plugging chisel, clearing to a depth of at least 20 mm. The joints are then blown or brushed clean before new jointing compound is packed in and finished flush.

Yes. Debris from raking and cleaning is cleared as the job progresses, and the finished surface is brushed down before the installer leaves. Any mortar smears on slab faces are cleaned off once the jointing compound has reached the right cure stage.

Late spring to early autumn is ideal. Dry, mild conditions help biocide treatments work effectively and allow repointing mortar to cure properly. Avoid working in frost or heavy rain, as both compromise mortar adhesion and slow the drying of any applied treatments.

Not during the work itself, and not immediately after repointing. Most jointing compounds need 24 to 48 hours before foot traffic, and longer before heavy loads. The specific curing time for the product used is confirmed before the job finishes.

Cleaning comes first. Joints need to be clear of moss, weeds and loose material before new compound goes in. A thorough clean also helps the repointing bond properly and last longer.

Old or damaged joint material is raked out to a consistent depth, then new jointing compound is applied. If slabs have moved, they are lifted and reset before the joints are finished.

Yes, if the angle or pressure is wrong. High pressure aimed directly at joints strips mortar and loosens slabs. The angle and pressure are adjusted to the slab material before washing starts.

Water gets under the slabs, the bedding mortar fails, and the sub-base can settle unevenly. What starts as a joint repair becomes a full lift-and-relay job, significantly more disruptive and costly.

It may shift light surface dirt, but it will not remove moss, algae or deep staining, and it does nothing for crumbling joints or loose slabs. It is not a substitute for pressure washing and repointing.

Repointing with a flexible, polymer-modified mortar significantly slows joint breakdown compared with standard sand and cement. It will not last indefinitely, foot traffic, freeze-thaw cycles and tree roots all cause wear over time, but correctly done joints should remain sound for several years.