Pressure Washing Guide: What to Clean and What to Leave Alone

Few tools are as satisfying as a pressure washer. One pass over a grimy driveway and you can see exactly where you've been — which is precisely why every bricolage store on the Margem Sul sells them by the pallet, and why we're regularly called in to repair the damage they cause in the wrong hands.

Living near the Atlantic makes the question more pressing than it would be inland. The maresia — the salt-laden sea air that anyone in Costa da Caparica, Fonte da Telha or Sesimbra knows well — settles on every outdoor surface, holds moisture against it, and feeds the black and green films that make terraces slippery and façades dull. Surfaces near the coast simply get dirty faster, and they corrode faster too. Regular washing isn't vanity here; it's maintenance.

But "high pressure" is a tool, not a universal answer. Here's an honest guide to what you can safely blast, what needs a gentler approach, and what you should never point a domestic pressure washer at.

Safe to pressure wash yourself

These surfaces are robust and forgiving, and a consumer machine handles them well:

• Concrete driveways and pavements — the classic job. Use a surface cleaner attachment for even results without "zebra striping".
• Calçada portuguesa and stone paving — the stones themselves are tough; just be aware you'll blast out sand between them, which needs re-brushing in afterwards.
• Rendered garden walls in sound condition — moderate pressure, fan nozzle, keep moving.
• Plastic garden furniture, bins, tools
• Terracotta and ceramic terrace tiles — common around villas in Charneca da Caparica and Quinta do Conde, and dramatically improved by an annual wash before the outdoor season.

Golden rules for all of the above: start with the widest fan nozzle, start further away than feels necessary, keep the lance moving, and never hold the jet on one spot. The turbo/rotary nozzle is for stubborn concrete stains only — it is far too aggressive for almost everything else.

Handle with care: lower the pressure

Some surfaces can be washed, but not blasted:

• Painted façades — high pressure lifts paint and drives water into hairline cracks. Low pressure plus a suitable detergent does the real work.
• Wooden decks and pergolas — softwood fibres tear at high pressure, leaving a fuzzy, splintered surface that then greys and rots faster. Maximum ~100 bar, wide fan, always along the grain, and expect to re-oil afterwards.
• Cars and outdoor blinds — foam and rinse at low pressure; direct jets destroy seals and fabric.
• Natural soft stone (limestone steps, older ornamental work) — easily etched.

As a rough guide: concrete tolerates 150–200 bar; render and terrace tiles are happier at 100–130; wood and painted surfaces below 100, with detergent doing most of the work.

Do NOT DIY: the expensive mistakes

Some jobs look like pressure-washing jobs but aren't — or are, but not for a domestic machine and a ladder.

• Roofs. This is the big one. Portuguese telha lusa clay tiles are surprisingly fragile, and a high-pressure jet strips their surface, opens micro-cracks and forces water under the overlaps — turning a cosmetic moss problem into a leak. Add the fall risk of working on a wet, sloping roof and this becomes a job strictly for professionals with soft-wash equipment and proper access. If your roof has gone dark with moss and lichen — accelerated near the coast by that same salt-humid air — book a specialist roof cleaning rather than climbing up with the Kärcher.
• Mortar joints and old pointing. A pressure jet excavates weathered mortar from brickwork, garden walls and between roof ridge tiles remarkably quickly. What looked like cleaning becomes repointing.
• Solar panels. Increasingly common on Margem Sul roofs, and increasingly a victim of enthusiastic washing. Thermal shock from cold water on hot glass, damaged seals, voided warranties — panels need deionised water and soft brushes, not pressure.
• Windows, seals and electrics. Jets defeat window seals, force water into wall vents, and should never go near exterior sockets, meters or air-conditioning units.
• Asbestos-cement roofing (fibrocimento). Still present on many older annexes and garages in the region. Pressure washing it releases fibres and is genuinely hazardous — this material should only ever be handled by licensed professionals.

Why coastal homes need it more often

Salt is hygroscopic: it pulls moisture from the air and keeps surfaces damp long after inland surfaces have dried. Damp plus organic dust equals algae, lichen and black staining — which is why a terrace in Costa da Caparica greens up in one winter while the same terrace in Pinhal Novo takes three. Salt residue also accelerates corrosion of railings, fixings and gutter brackets. For homes within a couple of kilometres of the sea, an annual wash of terraces, façades and outdoor areas isn't excessive; it's roughly the right rhythm, ideally in spring after the winter storms or in early autumn before them.

When to call in a professional

Beyond the "never DIY" list above, professional pressure washing makes sense when the area is large (full driveways, pool surrounds, whole façades), when height is involved, or when the surface needs treatment as well as cleaning — anti-moss application, re-sanding of calçada, or sealing. Professional machines also run hot water, which shifts oil stains and biological growth that cold domestic units merely redistribute. The cost depends mainly on area, surface type, access and how long it's been since the last clean.

The short version

Blast your concrete and paving with confidence, go gently on wood, render and paint — and leave roofs, mortar, solar panels and anything containing asbestos to people with the right equipment and insurance. Your surfaces will last longer, and so will you.

Got a terrace, driveway or roof on the Margem Sul that's seen better days? Send Arranja Já a photo on WhatsApp and we'll come back to you with a free quote.