Basement Damp Proofing and Utility Room Refit – Putney, London SW15

Basement Damp Proofing and Utility Room Refit – Putney, London SW15

Fawe Park Road is a street of large Edwardian houses in Putney, SW15. This one runs to three storeys with a small cellar underneath. The cellar was earning its keep — boiler, consumer unit, washing machine, dryer — but it was damp, and you could smell it before you reached the bottom of the stairs.

That smell is usually what prompts the phone call. It is also the part that paint will never fix.

What we found

Solid brick walls, painted white at some point decades ago. Along the base of every wall ran a dark tide mark about half a metre high, with black mould pushing through the paint. In places the paint had blown off and taken the face of the brick with it.

Houses of this age were built with a damp proof course, usually slate or bitumen. After a century it is often bridged, cracked, or simply no longer there. Ground moisture then travels up through the brickwork until it can evaporate, carrying ground salts with it. Those salts stay behind in the wall face and pull moisture out of the air on their own. That is why a wall can still read damp long after the original source has been stopped, and why treating the cause without dealing with the wall face gets you nowhere.

The floor was the original black and white chequerboard. Filthy, but flat and sound. Worth keeping.

Clearing the room

The utility room came out first. Washing machine, dryer and the units around them were disconnected and taken out, so we had a clean run at the full length of every wall.

The boiler and the consumer unit stayed where they were. Both were bagged in plastic and taped. Cables were unclipped from the walls and hung from a timber batten fixed across the ceiling, clear of wet render and clear of a trowel.

None of this shows in the finished room. But if you cannot reach the bottom metre of a wall, you cannot treat it — and a treated wall with a missed section is not a treated wall.

Damp proof injection

We drilled a line of holes into a mortar bed low down on each affected wall and injected damp proof cream into them. The cream spreads into the mortar and the surrounding brick and cures into a water repellent band — a new damp proof course formed inside the wall that is already standing, without taking anything down.

You can see it in the photographs: a row of drilled holes with white cream standing proud of each one, at an even height and spacing. The spacing is the whole job, because a gap in the line of injection is a gap in the barrier and water will find it.

Waterproof render

Injection stops the water rising. It does nothing about the salt-contaminated finish already on the wall, so that came off back to bare brick across the damp zone.

The walls were then rendered in cement gauged with Sika waterproof liquid. The additive goes into the mixing water, so the whole coat resists moisture rather than relying on something brushed over the top afterwards. Expanded metal lath went in at the corners and at the junctions between new render and existing wall — the lines where cracks otherwise turn up a year or two later.

Where the damp had only ever reached a metre or so, the render stops at that height and the sound painted brick above it was left alone. There is no point hacking off a wall that is dry; it costs the client money and gains nothing.

Pipework running along the walls was cut in around rather than boxed over, so the runs stay accessible.

Painting and refitting

Once the render had dried out we painted the ceiling, the walls and the woodwork.

Then the utility room went back — same appliances, same positions, reconnected, standing on the original chequerboard floor, which was cleaned rather than replaced. The cupboard under the stairs carries pipework and had the same problem as the rest of the cellar, so it was treated and finished at the same time.

The room now does what a cellar in a house this size should do: takes the laundry, houses the plant, and does not announce itself from the top of the stairs.

Working in an occupied house

This was not an empty building site. The house was lived in, the boiler had to keep running, and the consumer unit could not sit dead for days at a time. Stairs and floors were sheeted, the dust was kept to the cellar, and the appliances were out of use for as short a stretch as we could manage.

Putney and the streets around it are full of houses of this period and this construction. The cellars vary. The problem rarely does.

Frequently Asked Questions

What causes damp in an old London basement?

Most often the original damp proof course has failed or been bridged and ground moisture is rising through solid brick walls. It shows as a tide mark low on the wall, blown paint or plaster, black mould and a musty smell. Damp can also come from a leaking pipe or from external ground levels sitting higher than the internal floor, so it is worth establishing which one you have before spending money on a fix.

How does damp proof injection work?

A line of holes is drilled into a mortar bed near the base of the wall and damp proof cream is injected into them. The cream spreads into the mortar and brick and cures into a water repellent band running through the thickness of the wall, which stops moisture travelling up past that line. It forms a new damp proof course inside the existing wall, so nothing has to be taken down.

Why does the old wall finish have to come off?

Rising damp carries ground salts into the wall face and leaves them there. Those salts attract moisture from the air, so a contaminated finish stays damp even after the rising damp itself has been stopped. Leaving it on is the most common reason a damp job comes back. On this project the old finish was taken off back to bare brick across the affected zone before rendering.

Why cement render with a waterproof additive rather than ordinary plaster?

The additive — Sika waterproof liquid on this job — goes into the mixing water, so resistance to moisture runs through the whole coat instead of sitting on the surface. Ordinary gypsum plaster applied straight onto a wall with a damp history will draw moisture and break down. Render is also a more sensible base in a cellar that has to take knocks from appliances and storage.

Can an original floor be kept?

Often, yes. The black and white chequerboard floor in this cellar was dirty but flat and sound, so it was protected during the works, cleaned and kept. Floors of this type are hard to match and worth saving wherever the condition allows.

Do you carry out basement damp proofing in Putney and South West London?

Yes. Putney, Wandsworth, Southfields, Barnes and the surrounding South West London streets are regular working ground for us, and the housing stock there is largely Victorian and Edwardian with exactly this kind of cellar. This project on Fawe Park Road, SW15 was carried out by our own team, from stripping the utility room out to putting it back. Call Force Builders Ltd on 020 8578 6285 to talk yours through.