Our Tack Coat and full wet coat process for aluminium window spraying

https://youtube.com/shorts/hQUoLkyDssk?si=klTquK38mmuSGMNG

Priming Aluminium Windows Using a 1.5 Coat System

White Primer Application with Tack Coat + One Full Wet Coat

Primer is where aluminium window painting either succeeds or fails.

Most people focus on the colour coat. That’s what photographs well. That’s what gets attention. But the coating system only performs as well as the primer underneath it.

This video shows us applying white primer to aluminium windows using a 1.5 coat system — a light tack coat followed by one controlled full wet coat.

Not two heavy coats. Not blasting primer on. Not flooding the frame.

A tack coat plus one wet coat.

That’s the system.

This article explains exactly why we use that method, what it achieves, and why over-priming is just as problematic as under-priming.

Why Aluminium Requires Proper Priming

Aluminium is smooth and non-porous. It does not absorb coatings. Paint must bond to it mechanically and chemically.

That bonding only happens if:

• The surface is cleaned

• The aluminium is properly sanded and keyed

• Contaminants are removed

• A suitable primer is applied

Primer is not decorative. It is structural within the coating system.

Its role is to:

• Bond to the keyed aluminium

• Create a stable base

• Provide consistent surface tone

• Support topcoat adhesion

• Regulate absorption and build

Without primer, topcoat adhesion relies on the old finish. That is never a professional approach.

What a 1.5 Coat System Actually Means

There’s confusion around this term, so let’s make it clear.

A 1.5 coat system consists of:

1. A light tack coat

2. One full wet coat

Total build: 1.5 coats.

The tack coat is not counted as a full coat because it is applied lightly. Its purpose is to create grip and stabilise the surface before the wet coat is applied.

The wet coat then builds the film thickness to the correct level.

There is no second full wet coat at primer stage.

Overbuilding primer creates problems. Controlled build prevents them.

Stage One: Surface Preparation Before Primer

Before primer ever enters the spray gun, preparation must be correct.

Preparation includes:

• Cleaning to remove dust and surface contaminants

• Sanding to mechanically key the aluminium

• Washing to remove sanding residue

• Degreasing to eliminate oils and handling marks

• Masking glass, rubbers, and surrounding finishes

Primer cannot compensate for poor preparation.

If sanding is uneven, primer will reveal it. If contamination remains, primer may fish-eye or separate. If masking is poor, edges will fail visually later.

Primer amplifies preparation quality.

Why We Start with a Tack Coat

The tack coat is a light, even mist layer applied across the entire aluminium surface.

It is not meant to cover completely. It is not meant to build thickness.

Its purpose is to:

• Create surface texture for the wet coat

• Reduce risk of sagging

• Allow controlled layering

• Improve adhesion between coats

• Stabilise vertical surfaces

Aluminium window frames are full of vertical faces, corners, and narrow profiles.

If you go straight to a heavy wet coat, the primer can:

• Slide

• Pool

• Build unevenly in corners

• Sag on vertical sections

The tack coat prevents that.

It gives the wet coat something to hold onto.

Flash Time Between Tack and Wet Coat

Once the tack coat is applied, it is allowed to flash properly.

Flash time is not random. It depends on:

• Temperature

• Humidity

• Air movement

• Product specification

We allow the tack coat to settle just enough that it becomes slightly matte and stable — not fully cured, but no longer liquid.

At this stage, the surface has grip.

Then the wet coat goes on.

Stage Two: One Full Wet Coat

After flash, we apply one full wet coat.

This coat is where:

• Film thickness is established

• Coverage becomes complete

• Surface evens out

• Primer becomes uniform

Because the tack coat stabilised the surface, the wet coat lays flatter and more controlled.

We focus on:

• Consistent spray distance

• Even overlap

• Controlled pass speed

• Proper trigger discipline

The goal is uniform build — not thickness for the sake of it.

Why We Don’t Apply Two Full Primer Coats

More primer is not better.

Excessive primer causes:

• Increased risk of runs

• Uneven build in corners

• Slower curing

• Solvent entrapment

• Texture inconsistencies

• Extended drying time

Primer is a bonding layer, not a filler layer.

If preparation is correct, you do not need heavy primer build.

The 1.5 coat system achieves:

• Proper adhesion

• Correct film thickness

• Controlled drying

• Stable surface for topcoat

Without overloading the frame.

Film Thickness Control

Film thickness matters.

Too thin:

• Reduced adhesion performance

• Weak base for topcoat

Too thick:

• Cracking risk

• Sagging

• Poor curing

• Texture variation

The tack + wet coat system provides controlled build without excess.

It gives enough micron build for performance without creating unnecessary thickness.

Why White Primer in This System

White primer offers advantages:

• Neutral base for final colour

• Easier defect visibility

• Even tone across aluminium

• Clear indication of coverage

In the video, you see the aluminium shift from prepared metal to uniform white.

This stage reveals:

• Missed sanding

• Surface inconsistencies

• Edge detail

If anything is imperfect, primer exposes it before topcoat.

That is exactly what we want.

Primer as a Diagnostic Stage

Primer is not just structural — it is diagnostic.

When white primer goes on, it immediately shows:

• Scratches

• Surface contamination

• Uneven abrasion

• Profile inconsistencies

This allows corrections before colour coats begin.

Skipping or rushing primer removes that diagnostic safety net.

Spray Control During Primer Stage

Primer must be applied evenly.

We avoid:

• Heavy trigger pulls

• Sudden direction changes

• Inconsistent overlap

• Uneven distance

Primer is sprayed deliberately, not aggressively.

The tack coat is light. The wet coat is controlled. That’s the balance.

Vertical Aluminium and Gravity

Windows and doors are vertical.

Gravity is always working against you.

If you apply heavy primer immediately:

• It builds in lower sections

• It thins on upper edges

• It risks sagging

The tack coat creates friction. The wet coat builds safely.

This is why the 1.5 coat system is effective on vertical aluminium.

Drying and Stability

Because we are not overbuilding primer:

• Drying is more predictable

• Curing is more consistent

• Surface remains smooth

• Recoat windows are stable

Excess primer slows the entire process unnecessarily.

Controlled build keeps the system efficient without sacrificing integrity.

How This Affects Final Topcoat

Topcoat performance depends on primer quality.

If primer is:

• Even

• Stable

• Properly flashed

• Correctly built

Then the topcoat will:

• Lay flatter

• Achieve consistent sheen

• Bond properly

• Cure evenly

Primer mistakes always show up later in gloss levels and edge detail.

Why We Don’t Rush Primer

Primer stage sets the tone for the rest of the job.

Rushing this stage leads to:

• Corrective sanding

• Uneven colour coats

• Additional labour

Doing it properly once prevents problems later.

Residential vs Commercial Context

In residential aluminium work, especially inside homes, controlled primer application is essential.

We are not in an industrial booth. We are not flooding steel beams.

We are coating precision window frames.

The 1.5 coat primer method suits this environment.

In commercial or heavily ventilated environments, systems may vary — but the principle of controlled build remains the same.

What the Video Shows Clearly

The video shows:

• White primer being applied

• Light tack coat first

• Flash

• One full wet coat

• Even coverage across frames

No excessive buildup. No double wet coats. No flooding.

Just structured, controlled application.

Why We Share This Stage

Most people only see finished black or white frames.

We show primer stage because it demonstrates process.

It shows:

• Care

• Control

• Technical understanding

• System discipline

Primer is not glamorous. But it is critical.

Final Thoughts

A 1.5 coat primer system — tack coat plus one full wet coat — is deliberate.

It is designed to:

• Build proper adhesion

• Control film thickness

• Prevent sagging

• Stabilise vertical aluminium

• Support final finish

Primer is the structural foundation of aluminium window painting.

If that foundation is correct, everything above it performs properly.

If it is rushed or overloaded, problems appear later.

This white primer application demonstrates why controlled systems matter more than heavy coats.