What three wet winters did to a Tigard rancher driveway

The call came from a 1970s rancher off SW Hall Boulevard in Tigard — single-story, two-car garage, standard broom-finish concrete driveway maybe 18 feet wide and 55 feet long. The homeowner had not pressure washed since moving in during 2021. Three wet winters and two dry summers had done their work.

From the street it looked gray and tired. On hands and knees it was a different surface.

What we found

Walking the slab before we pulled the rig off the trailer:

• Moss mats along both edges where the lawn creeps over the concrete lip — thickest on the north side where the house shades the slab until 11 a.m.
• Black algae in every expansion joint, especially the transverse cuts across the tire tracks
• Tire grime baked into the center run — that polished-dark strip where wheels sit every day
• Two oil spots near the garage apron — old enough that the homeowner could not remember the leak
• Rust stains below a galvanized downspout at the garage corner

No cracks worth worrying about. Just years of organic growth holding moisture against a surface that should shed water.

Why three Tigard winters matter

Tigard sits low in the Tualatin Valley — foggy mornings, slow-drying afternoons, tree cover from mature maples and firs on the lot lines. Concrete that dries by noon in Hillsboro can stay damp until 3 p.m. here.

Each winter adds a thin algae layer. Summer does not kill it — it bakes it in. By year three you are not looking at dirt. You are looking at a living film that gets slick in rain. The homeowner mentioned the slope toward the street had gotten “weirdly slippery” last November. That was the moss edge, not the concrete itself.

Our house washing vs pressure washing guide breaks down which surfaces take full pressure and which do not. Driveway broom finish is in the full-pressure category — but technique still matters.

How we cleaned it

We used a commercial surface cleaner on the flat runs — keeps the spray pattern even so you do not get those half-moon etch marks from a wand. Expansion joints got a lower-angle pass first to cut the algae without chewing the edges.

Sequence:

1. Pre-treat the moss edges and oil spots with a biodegradable degreaser — let it sit 10 minutes
2. Surface cleaner on the main slab — two slow passes, overlapping
3. Wand work on the garage apron and the tight strip along the foundation
4. Rust spot — separate mild oxalic treatment on the downspout stain only, not the whole driveway
5. Rinse toward the street — storm drain on the curb, no runoff into the planter beds

Total time on site: about two and a half hours including setup and a final walk-through with the homeowner.

What we told them about upkeep

A Tigard driveway on a shaded lot will green up again in 18–24 months without maintenance. Faster if the maple next door drops debris on the slab all fall.

We suggested:

• A light rinse every October after leaf drop
• Keeping the lawn edge trimmed back two inches from the concrete
• Re-treating the oil spots if they darken again — they were old and mostly lifted, but deep oil never disappears 100 percent

They booked gutter cleaning for October while we were there — same downspout that rust-stained the driveway was dumping fir needles onto the apron all winter.

When to call vs when to rent a machine

Home depot rental wands on broom finish often leave streaks because the angle is wrong and the pressure is inconsistent. If the slab is mostly dust and one season of grime, DIY is fine.

Call a crew when:

• Moss and algae have crossed the full width
• Oil and rust need separate chemistry
• You want even color without etch marks
• The last wash was three or more years ago

We cover Tigard, King City, and the whole Portland metro for pressure washing — driveways, patios, walkways, and house wash where the siding needs soft-wash instead of blast pressure.

Written quote by phone. Tell us approximate square footage and how long since the last wash. 503-995-1947.