Damp proofingin Harrowour home town

In the Victorian and Edwardian terraces around Harrow town centre and Wealdstone, a genuine failed damp proof course shows as a fairly level tide mark, salt bloom on the plaster face and hollow, crumbling skirtings. Where that is confirmed at survey, treatment is an injected chemical DPC using an accredited Sovereign or Wykamol system, with the salt-contaminated plaster removed and replaced with a salt-retardant render and skim.

It is important to rule out simpler causes first. Solid floors laid without a membrane, blocked airbricks under suspended timber floors, and external ground levels built up against the wall over the years can all produce the same symptoms without a DPC ever having failed. A proper survey checks all of these before recommending an injection.

North Harrow, South Harrow, West Harrow and Rayners Lane are almost entirely built up with 1920s and 1930s bay-fronted semis and short terraces. These have cavity walls, but the cavities are narrow and were built without the debris control expected today, so mortar droppings bridging the cavity base are common.

Just as often the cause sits outside the wall altogether: a driveway widened and resurfaced above the original level, a patio built over the airbricks, or render carried down past the DPC line during a past repair. Correcting a bridge is usually a smaller and cheaper job than treating the wall, which is why diagnosis comes before any recommendation.

Harrow Weald's larger 1930s detached houses often have tile-hung upper elevations, generous plots and integral or attached garages, many of which have since been converted into playrooms, offices or extra bedrooms. These conversions were rarely built to the standard of the main house: no damp proof membrane under the floor, no DPC in the walls, and a slab set lower than the rest of the house.

Bringing a converted garage properly up to standard can mean a new damp proof course, tanking to the lower part of the walls, and a correctly insulated and membraned floor. We specify the actual scope needed after surveying it rather than treating the visible symptom.

The area around Harrow station, Harrow-on-the-Hill station and Harrow College has a concentration of flats above shops, converted houses and shared student lets. Here the most common complaint is black mould on cold corners, window reveals and behind wardrobes, which is condensation caused by high occupancy, moisture-generating activity and limited background ventilation, not a rising damp problem.

We diagnose this in writing at survey. Treating condensation with a chemical DPC achieves nothing; the fix is improving extraction where moisture is produced, maintaining background ventilation and addressing the coldest surfaces. For landlords and managing agents that written diagnosis is useful when discussing responsibility for the issue.

Harrow's Victorian terraces, interwar semis and 1930s detached houses all carry exterior finishes that fail over time, cracked or debonded render and pebbledash, spalled brick faces, eroded pointing and missing sill and drip details. Any of these will let water into the wall and are frequently the true cause behind an apparent damp problem.

We repair and renew render, repoint in a compatible mix, replace damaged brick, reinstate proper drip details, and use helical brick stitching where cracking at bay junctions or over openings needs structural repair rather than cosmetic filling. This is handled by the same team doing the damp work, so nothing is left half-finished.

From our Harrow base we cover the whole borough, Harrow town centre, Harrow on the Hill, Wealdstone, North Harrow, South Harrow, West Harrow, Rayners Lane, Harrow Weald and Kenton, and extend out into the wider Middlesex towns, Brent, West London, London, Watford, Slough, Buckinghamshire, High Wycombe and Surrey.

Calls are taken Monday to Friday 8am to 8pm and Saturday 8am to 1pm, with Sunday closed. Because we are working from home ground, surveys in Harrow itself can usually be fitted in quickly.