Painting Garage Doors in London: Metal, Timber, GRP, Preparation & RAL Colours

Why Garage Door Painting Is Often Done Badly

The garage door is one of the most exposed surfaces on any London property, and yet it is frequently painted with inadequate preparation and inappropriate materials. The result is predictable: flaking paint within eighteen months, rust bloom on steel doors, peeling topcoat on GRP composites, and unsightly runs where paint has been applied too thickly in a single coat.

Done properly — with the right preparation, primer, and topcoat for the substrate — a repainted garage door should look excellent for seven to ten years. This guide covers how to achieve that result on the three most common door types found on London properties.

Identifying Your Garage Door Type

Metal up-and-overs are the most common type on London terraced and semi-detached houses. Most are single-skin galvanised or cold-rolled steel, spring-balanced, and operated manually. Some older examples are aluminium. The visual tell for steel is that it rusts; aluminium corrodes to a grey-white chalky surface but does not go orange.

Timber side-hinged doors are found on older properties and on some mews houses where the garage is part of an outbuilding. They're typically framed and ledged or framed, ledged, and braced in softwood, and they rot at the bottom rail and at any junction where water collects.

GRP composite doors — fibreglass-skinned, foam-filled — have become the default choice for new garage installations over the past twenty years. They are sold in a limited factory colour range, and many owners want to change colour or refresh a faded finish.

Painting Steel Up-and-Over Garage Doors

Steel doors deteriorate in a consistent pattern: paint begins to fail at the corrugated ribs and panel edges where flexing from operation causes micro-cracking, and where water sits. Rust then begins at these points and spreads under the paint film.

Preparation:

1. Open the door and set it in the horizontal (open) position. Work on the external face.
2. Degrease with a panel wipe or equivalent solvent cleaner.
3. Remove all loose paint by scraping and then sanding (80-grit on a random orbital). Do not use heat guns on steel doors — they can warp the panel.
4. Treat rust with Jenolite Rust Treatment or Hammerite Kurust (phosphoric acid gel). Apply, leave for 15 minutes, wipe off, and allow to dry. The rust turns black/grey — this is the iron phosphate conversion layer.
5. Sand the treated areas smooth.
6. Fill any deep pitting with Upol Stopper or P38 body filler, sand flush when cured.

Priming:

For steel garage doors, use a two-in-one rust-inhibiting primer or a dedicated metal primer:

• Hammerite Direct to Rust Metal Paint — can be applied directly to prepared metal as both primer and topcoat
• Zinsser Bulls Eye 1-2-3 — excellent adhesion primer suitable as a base for alkyd or water-based topcoats
• International Interprotect — a two-coat epoxy system where maximum durability is needed

Topcoat:

• Hammerite Smooth in black or a colour — durable, fast-drying, and requires no separate topcoat
• Dulux Trade Gloss over a metal primer — more colour options, excellent finish, requires longer dry time between coats
• Bedec MSP (Multi Surface Paint) in satin or gloss — water-based but extremely hard-wearing, full RAL palette available, flexible enough for a door that operates multiple times daily

For RAL colour matching on steel doors, we specify either Bedec MSP or a custom-mixed oil-based gloss. The most popular RAL colours for London garage doors are RAL 7016 (Anthracite Grey), RAL 9005 (Jet Black), RAL 6005 (Moss Green), and RAL 5011 (Steel Blue).

Painting Aluminium Garage Doors

Aluminium needs a different approach — it doesn't rust, but paint adhesion to aluminium is poor unless the surface is properly treated.

1. Degrease with acetone or panel wipe.
2. Abrade the surface with 120-grit — the surface oxide layer must be broken.
3. Apply an etch primer (Rustins Etch Primer or Zinsser Bulls Eye 1-2-3) immediately after abrading, before the oxide reforms.
4. Apply topcoat: Bedec MSP or an alkyd gloss over etch primer.

Never apply masonry paint or standard emulsion to aluminium. These will not adhere even with primer.

Painting Timber Garage Doors

Timber side-hinged doors require the same approach as any exterior timber:

1. Inspect for wet rot, particularly at the bottom rail, the hinge stiles, and any horizontal ledge. Rot less than 15mm deep can be treated with Repair Care Dry Flex consolidant and filler. Deeper rot requires timber replacement.
2. Sand back to sound-adhering paint. Where multiple paint layers have built up and are cracking, strip back to bare timber with Peel Away 1 or a heat gun.
3. Prime bare timber with Dulux Trade Quick-Dry Primer or Johnstone's Woodprimer & Undercoat.
4. Apply one undercoat and one topcoat of an exterior alkyd gloss or exterior eggshell. Farrow & Ball Exterior Eggshell or Little Greene Exterior Eggshell if the client wants a premium finish; Dulux Trade Gloss for a standard contract specification.
5. Ensure the bottom of the door has a drip groove. If rot has been recurring and no drip groove exists, routing one in is a worthwhile preventive measure.

Painting GRP Composite Garage Doors

GRP is the most demanding substrate for paint adhesion because it has very low surface energy — paint simply doesn't want to stick to it unless the surface is prepared correctly.

1. Clean thoroughly with a solvent panel wipe.
2. Abrade with 120-grit to break the gel-coat surface.
3. Apply Zinsser Bulls Eye 1-2-3 or a two-pack epoxy primer specifically formulated for GRP. Avoid basic acrylic primers, which will lift.
4. Apply topcoat: Bedec MSP is the most reliable choice here — excellent adhesion over primer, flexible, full colour range. Two-pack polyurethane coatings offer superior hardness but require specialist mixing and application.

For faded GRP that simply needs refreshing rather than a full repaint, Farecla G3 compound can restore the gel-coat gloss without any painting at all, provided the surface is not cracked or pitted.

Colour Matching to the House

A garage door colour that fights the main elevation rarely improves a property's appearance. The clearest approach is to match the garage door to one of the existing elements: if the front door is Farrow & Ball Railings, the garage door in RAL 7016 Anthracite Grey reads as a family rather than a clash. If the house render is a warm cream, RAL 9001 Cream White or RAL 1013 Oyster White on the garage door creates coherence.

For listed buildings or conservation area properties, colour changes to garage doors visible from the street may require planning consent. We advise on this during the survey visit.

Book a Garage Door Repaint

A professionally repainted garage door makes a significant difference to the streetscape of any London property. Whether your door is steel, aluminium, timber, or GRP, contact us or request a free quote and we'll specify the correct system and deliver a finish that lasts.