A house that looks dirty a few days after a soft wash has not always been washed badly. Here are the usual causes, from rain splash and fading shadows to mineral salts and missed patches, plus a plan for what to try yourself and when to call the crew back.
In This Article
First decide: left over, revealed or new
Every after-wash complaint falls into one of three groups, and the group decides the fix.
- Left over. Growth that was treated but has not fully gone, or a spot that was missed.
- Revealed. Something the growth was hiding, or something the water brought to the surface: rust, faded paint, mineral salts, old stains.
- New. Fresh dirt that landed after the rinse: soil splash, pollen, sap, bird droppings, overflow from a gutter.
One rule of thumb helps. New algae needs moisture, shade and time, and in most conditions that takes weeks, not days. A wall that looks grubby three days later is rarely regrowth. Look for another cause first.
Match what you see to the likely cause
| What you see | Likely cause | What to do |
|---|---|---|
| Grey or greenish shadows where growth used to sit | Dead algae or mould that has not weathered off yet | Wait for a couple of rains, then look again |
| Dark flecks along the bottom of the wall | Rain splashing soil or mulch onto clean siding | Rinse with a hose and keep soil below the siding edge |
| Vertical stripes under the roof edge or a downspout | Dirty runoff from a full or overflowing eavestrough | Clear the trough, then wipe or rinse the stripes |
| White powder on brick as the wall dries | Mineral salts (efflorescence) drawn out by the moisture | Let it dry and dry-brush it. It is not growth |
| Orange or brown trails | Rust from a fastener, a fixture or a metal edge | Find the metal source. A wash will not fix it |
| Yellow-green dust on ledges and sills | Pollen or maple seed debris, mostly in spring | Rinse with a hose |
| Clean patches beside dull or streaky ones, sometimes in straight lines | Uneven application, or a section missed or left to dry | Photograph it and ask the crew to look |
| Cloudy spots on the glass | Hard water from rinse water drying on the window | Squeegee it, or book a window visit |
| Green or black patch back in the same place | A thick colony or lichen that needed a second pass | Tell the crew and let them re-inspect |
Waterloo Region and Guelph have hard groundwater, which is why glass is the first place mineral spotting shows.
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Give it a rain or two, then look again
Killing growth and removing every trace of it are two different steps. The cleaning mix kills the colony, and the dead film then breaks down and washes off over the next few rains. On a north wall or a shaded roof slope, a faint shadow can hang around for a week or two.
Judge the wall properly before deciding anything.
- Wait until it is completely dry. Damp siding looks darker and blotchy.
- Look in the same light as your before photos, ideally low morning or evening sun.
- Rub a damp white cloth on a shadow. If it comes off on the cloth, it is loose film that rain will finish. If nothing shifts, it is a stain in the material.
- Photograph it with the date, then check again after the second rain.
What you can safely do yourself
- Rinse from the top down with a garden hose on a wide, gentle spray.
- Use a long-handled soft brush, plain water and a little mild dish soap on one stubborn streak, testing a small spot first.
- Clear eavestroughs and downspouts so dirty runoff stops striping the wall.
- Pull mulch and soil down below the bottom edge of the siding.
Leave two things alone. Do not spray household bleach on the wall to finish the job, because uneven strength leaves blotches and it is hard on plants and metal. And do not rent a pressure washer to correct it. A jet on siding can crack panels and drive water behind the wall, which is a far bigger problem than a shadow.
How to take it back to the crew
If the problem is a missed patch, a streak or a stubborn colony inside the agreed scope, a reputable crew will want to hear about it. Do it in this order.
- Note the date of the wash and today's date.
- Take close and wide photos of each problem, matched to your before shots.
- Say which cause from the table you think it is, and point to the line in the written scope.
- Send it in writing, with a request to re-inspect and a date to hear back.
Be ready for an honest answer. Rust, efflorescence and failing paint sit outside what a wash can do, and a fair crew will explain that instead of re-spraying the wall. D&D confirms every quote in writing before work starts, so there is a document to point to, and that makes the conversation easier for both sides.
For the method itself, see soft washing, and for how treated growth breaks down, read about removing green algae and mould from siding. If glass is the complaint, window cleaning fixes hard-water spots.
Key Takeaways
- Sort the problem as left over, revealed or new: dead growth, hidden stains and fresh dirt each need a different fix.
- Real regrowth usually takes weeks, so a wall that looks dirty within days points to shadows, splash, runoff, pollen or salts.
- Judge a dry wall in the same light as your before photos, and check again after two rains before deciding it failed.
- Rinse gently and fix the water source yourself, then send dated photos to the crew for missed patches or streaks inside the written scope.
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