Render & house washing
Render goes green on the side that never sees the sun, and it comes back within a year if the growth is only knocked off the surface. Treating it is different work from cleaning it.
Transformation
Green growth down one elevation and staining under the gutter line where a joint had been overflowing.
Soft washed at low pressure with a treatment left to work rather than blasted off, roofline cleaned at the same time.
Method
The one instruction on this page that is worth more than the rest of it put together.
Render is a coating over a substrate, and pressure separates the two. On K-Rend and other through-coloured silicone renders it also removes the surface texture, which cannot be patched because the colour runs through the material rather than sitting on it. The repair for an over-pressured elevation is re-rendering it, and that is the single most expensive mistake available in this trade.
Soft washing applies a biocide at low pressure and lets it work, from a fast acting diluted biocide which is washed off after use.
Growth establishes where a wall stays wet: the north elevation, under a gutter that overflows, below a sill with no drip, or against ground that has been built up above the damp course. Cleaning that wall without addressing why it is wet resets the clock rather than solving anything, so we say what we can see.
Masonry paint in good condition cleans well. Paint that is already flaking, chalking or blown will come off with the growth, and no method avoids that — the coating has failed and cleaning finds it. Better to know that before we start than to discover it halfway along an elevation, so a painted wall gets looked at rather than assumed.
Beds along the base of a wall get soaked before and after so anything running down is diluted immediately, and runoff is directed away from borders. Ponds get covered properly rather than rinsed. This is ten minutes of work and it is the thing people notice a week later, when the hedge has or has not gone brown.
Being straight about it
The growth is the visible part of a problem that is usually somewhere above it.
Algae needs moisture, so a wall that keeps going green is a wall that keeps getting wet. Sometimes that is simply aspect and there is nothing to fix. Often it is not: an overflowing gutter, a cracked downpipe discharging against the render, a sill without a drip groove, or ground built up above the damp course will all keep one patch of wall damp indefinitely.
We will clean the elevation either way, and we will tell you what we could see from the ground while doing it. Where the cause is a gutter or downpipe, that is the job worth doing first — otherwise the same stain returns to the same place, and the cleaning gets blamed for not lasting.
Useful to send: a photo of the worst elevation from far enough back to show the whole wall, and a close-up of the finish so we can identify the render type. K-Rend and painted render are cleaned differently, and the close-up is what tells us which.
Request a QuoteQuestions
No. K-Rend and similar silicone through-coloured renders must be soft washed, and pressure removes the surface texture permanently. Because the colour runs through the material rather than being a coat on top, a damaged area cannot be patched to match — the remedy is re-rendering the elevation. This is the most common and most expensive mistake in exterior cleaning, and it usually looks acceptable for the first couple of weeks.
Because that side never dries. A north-facing elevation gets little direct sun, holds moisture for longer after rain, and in an Irish climate that is enough for algae to establish and stay. The same happens under an overflowing gutter, below a windowsill without a working drip groove, or where ground level has been built up against the wall. The growth is following the damp, which is why it always returns to the same places.
Longer than it took the first time, if the growth was treated rather than washed off, and it depends on aspect more than on anything we do. A south-facing wall that dries by mid-morning may stay clean for years. A shaded north elevation under trees will not, and no treatment changes the conditions that made it grow. Where a gutter or a sill is keeping the wall wet, fixing that does more for longevity than cleaning it again.
Sound masonry paint is unaffected. Paint that is already failing will come away with the growth, because the bond has gone and cleaning is what finds it — that is worth establishing before starting rather than during. Windows, doors and any timber are rinsed down as the work proceeds so nothing dries on them, and uPVC is usually cleaned at the same time since the equipment is already there.
Yes, and both are soft wash work for the same reason as render. Pebbledash holds growth deep in its texture, so it takes more contact time and looks worse before it looks better. Brick is more robust than render but the mortar joints are not, and pressure erodes pointing quickly — an elevation cleaned aggressively can need repointing, which is a much larger job than the one that was booked.
It depends far more on the render type and the access than on how green the wall looks. K-Rend and painted render are priced differently, pebbledash takes longer than a flat finish of the same area, and a job needing scaffold or a tower costs more than one reachable from the ground — regardless of how much growth there is to remove.
Yes, and it is the salt in the air rather than the rainfall — salt holds moisture against a surface for longer after rain has stopped, which is exactly the condition algae and moss need. Clontarf, Howth, Sutton, Dun Laoghaire and similar coastal areas see this consistently; further inland it fades and aspect and shade take over as the main factors instead.
Send a photo of the wall and a close-up of the render, and we will tell you what it needs and what is keeping it damp.
