COATING THICKNESS GUIDE

HOW MUCH IS ENOUGH · HOW MUCH IS TOO MUCH

v2.3 · ISSUE 02.09.2026
REVIEW DUE 07.2028
REFERENCED BY EVERY GERMA-TECH TDS

Most of the jobs that come back are not failures of the paint. They are failures of quantity. Too many coats, too much product in each coat, and not enough time between them. This guide is the number, and the reason behind the number.

300 µm

The total film on a panel should not pass 300 microns.
That is every layer added together — epoxy, filler, primer, sealer, colour and clear. Not each one. All of them.

WHY MODERN PAINT IS DIFFERENT FROM WHAT YOU LEARNED ONOld acrylic lacquer and enamel were forgiving because they were low solids and they dried by evaporation. You could load them on and the solvent found its way out eventually. Polyurethane does not dry, it cures. It cross-links from the surface down, and once the top has gone off, anything still underneath is trapped. A heavy film skins over before its own solvent has left, and everything that goes wrong after that — pop, die-back, soft film, cracking two years later — is that trapped solvent. Modern 2K is a high-solids, low-build system. It is built to go on thin. Less is better, and less is not a compromise.

01THE STACK — WHERE EVERY MICRON GOES

Clearcoat

40-70 µm

Two coats. A third coat does not add gloss, it adds microns and takes the film past its limit.

Basecoat

15-25 µm

Colour only. Metallics over 25 µm go dark and mottle — the flake cannot orient in a thick film.

Sealer / wet-on-wet

25-35 µm

Thin by design. Over-applying a sealer is the most common hidden cause of pop under colour.

2K primer surfacer

50-80 µm

The filling layer. 80 µm is the ceiling. A third coat to chase a low spot is the wrong fix.

Body filler

SHAPED BACK — NOT FILM BUILD

Over epoxy, never bare metal, never over etch. Shape it back — the filler you sand off is not film build.

Epoxy primer

40-60 µm

Bare metal only. Thin and even — it is an adhesion and corrosion layer, not a filler.

SUBSTRATE

BARE STEEL / PREPARED PANEL — NOT FILM BUILD

Everything above is measured from here. A DFT gauge on bare steel reads zero; on e-coat, subtract the e-coat reading first.

90 µm

Built the way it should be, a full repair from bare metal lands around 170-260 µm. That leaves headroom under 300. It is only when a layer is doubled — a third primer coat, a third clear coat, colour laid on to hide instead of to cover — that the stack goes over.

02THE THREE WAYS A JOB GETS OVERLOADED

1 · ONE MORE COATAlmost always to fix something the previous coat should have fixed. A third clear coat does not add gloss — gloss comes from flow and flash, not from thickness. A third primer coat to bury a low spot adds 25-40 µm and buries nothing: the low spot is still there under more material.

2 · TOO MUCH IN THE COATGun held too close, moved too slowly, or pressure too low. A wet coat that looks beautiful going on is usually 50% over. Check the gun setup on the TDS and check it against the gun, not against memory.

3 · NOT ENOUGH FLASHThe one nobody counts as overload, and the one that does the most damage. Coat two on top of coat one before coat one has released its solvent is not two coats — it is one thick coat with solvent locked in the middle.

FLASH-OFF IS NOT A DELAY, IT IS A PROCESS STEPThe flash time on the sheet is how long that film needs to let its solvent go at 20 °C. It is not padding and it is not a suggestion. Cold weather makes it longer, not shorter. The flash before the bake is the most skipped step in the trade and the single most common cause of solvent pop — the oven drives the remaining solvent to the surface faster than the film can release it, and it blows through.

03WHAT OVERLOAD ACTUALLY DOES

WHAT YOU SEE	WHEN	WHAT HAPPENED
Solvent pop	after the bake	Solvent trapped under a skinned film boiled out and blew craters through it. Film too heavy, or flashed too short before the bake.
Die-back	hours to days after	Gloss falls away as solvent keeps leaving and the film shrinks. Almost always a heavy clear or a heavy coat underneath it.
Soft film	days to weeks	Never fully cured. Marks under a fingernail, water-spots, holds a print. A thick film cannot cross-link through its depth.
Cracking / crazing	months to years	Total build too high and too rigid over a flexible or thick substrate. The film cannot move with the panel.
Dark or mottled metallic	immediately	Basecoat over 25 µm. The flake cannot orient in a thick wet film, so it sits at random and reads dark and patchy.
Edge mapping / ringing	after the bake	Solvent from a heavy topcoat re-softened a heavy underlayer at the feather edge.
Shrinkage over filler	weeks	Sand scratches and filler edges telegraph through as the over-thick primer above them keeps shrinking.

04MEASURE IT

Use an electronic film thickness gauge. On steel a magnetic gauge is enough; on aluminium and over filler you need an eddy-current or a dual gauge, or it will read nonsense.
Zero it on the bare substrate before you start, not on a painted panel.
Take the reading in the middle of the panel and again 100 mm in from each edge — edges are where the build runs away.
Read the existing paint before you start. On a repair you are adding to whatever is already there, and a car that has been done before may already be at 200 µm.
Write it on the job card. A recorded number is what settles a warranty question.

IF THE PANEL IS ALREADY OVERDo not put more on top hoping to level it. Sand the build back into range before you go further. If the existing finish is already at or past 300 µm before you have added anything, that panel needs stripping, not another system over the top. Nothing you spray will fix a film that cannot get its solvent out.

05EVERY GERMA-TECH PRODUCT — BUILD, MAXIMUM, FLASH

Taken straight from the current technical data sheets. Where a sheet has no maximum stated, treat the top of the build range as the maximum.

PRIMERS & UNDERCOATS

CODE	PRODUCT	COATS	FILM BUILD	MAXIMUM	FLASH BETWEEN COATS
GP1390	1K PLASTIC PRIMER (GREY) GP1390	Wet Spray 2.5 coats MAX (1 light tack coat + 2 solid coats)	1-2 µm	2 µm (2.5 coats (1 light tack coat + 2 solid coats) at 1-2 µm is maximum)	10 min at 20 °C between coats (allow extra time in colder conditions)
GP3501	1K PRIMER SURFACER	2.5 coats (1 light tack coat + 2 solid coats)	40-60 µm total	—	At 20 °C, 5-10 minutes
GP3401	2K EPOXY PRIMER	2.5 coats (1 light tack coat + 2 solid coats)	40-60 µm total	—	At 20 °C 5-10 minutes between coats
GP3325	2K PLASTIC PRIMER (GREY) GP3325	Wet Spray 2.5 coats MAX (1 light tack coat + 2 solid coats)	10-20 µm	20 µm (2.5 coats (1 light tack coat + 2 solid coats) at 10-20 µm is maximum)	—
GP4648	2K PRIMER HI-FILL SURFACER - NO REDUCER	2.5 coats (1 light tack coat + 2 solid coats). First coat - 1/2 coat…	50 - 80 µm total	80 µm	At 23 °C 3-6 minutes between coats (adjust flash off longer or shorter based on climate conditions)
GP3101	2K PRIMER SURFACER - HI FILL	2.5 coats (1 light tack coat + 2 solid coats)	50 - 80 µm total	80 µm	At 23 °C 5-7 minutes between coats (flash off longer in cold climate)
GP-AI-301	AUTO INDUSTRIAL 2K PRIMER HI FILL SURFACER	Apply two even coats (2.5 coats (1 light tack coat + 2 solid coats)…	40-80 µm (2 coats preferred at build 40-80UM)	Standard 80 µm, can build to 150 µm	10 minutes flash off between coats, apply second coat once touch dry but still tacky
GP-AI-201	AUTO INDUSTRIAL EPOXY PRIMER / EPOXY HIGH…	2.5 coats (1 light tack coat + 2 solid coats) (GP-AI-201 TDS);…	Wet-on-wet 1-2 coats, 40-80 µm · sanding build 2 coats, 40-100 µm	100 µm of this product	At 20 °C 15-20 minutes between coats (GP-AI-201 TDS); Allow 5-20 minutes flash off between coats at 25 °C,…
GP3401F	FAST DRY EPOXY PRIMER	2.5 coats (1 light tack coat + 2 solid coats)	40-60 µm total	60 µm of this product	At 20 °C 5-10 minutes between coats
GP3201	MULTI 2K PRIMER PLUS (3:1) - SPEED PRIMER…	HI FILL: 2.5 coats maximum (tack coat followed by 2 solid coats) \|…	HI FILL 50-80 µm \| WET ON WET 25-35 µm	80 µm (Hi Fill)	Speed Spot Repairs: 1 minute or no flash time \| Standard Repair: 2 - 3 minutes (adjust up in cooler…
GP3301	PLASTIC PRIMER (1K, TRANSPARENT)	1 coat	1 - 2 µm	2 µm	At 20 °C 5-10 minutes between coats

COLOUR & TOPCOATS

CODE	PRODUCT	COATS	FILM BUILD	MAXIMUM	FLASH BETWEEN COATS
GPFEXC100	ACRYLIC BINDER	2.5 coats (1 light tack coat + 2 solid coats)	40 µm total	—	At 20 °C, 2-3 minutes between coats
	GP AUTO 2K COLOUR	2.5 coats (1 light tack coat + 2 solid coats)	40-60 µm total	60 µm of this product	At 20 °C, 5-10 minutes between coats
	GP-1K BASECOAT COLORS (SOLVENT)	2.5 coats (1 light tack coat + 2 solid coats)	15-25 µm total	the metallic paint film should not be thicker than 25 µm	At 23 °C, 5-10 minutes between coats
	NT FLEET LINE 2K COLOUR	2 Coats	40-60 µm total	60 µm of this product	At 20 °C, 5-10 minutes between coats
	SHOWELL SH 1K WATERBORNE BASECOAT	SOLID: 1. Apply one wet coat firstly at a gun distance of 10-15 cm.…	15 +/- µm	—	Solid: blow off or bake till the surface is dry between coats (no time stated). Metallic: 2-3 minutes after…

CLEARCOATS

CODE	PRODUCT	COATS	FILM BUILD	MAXIMUM	FLASH BETWEEN COATS
GP4301	FAST DRYING CLEAR COAT (AIR DRY CLEAR) 4:1	2.5 coats (1 light tack coat + 2 solid coats)	40-60 µm total	60 µm of this product	Continuous wet-spray without flash off time between coats is better for paint leveling
GP899K	GP899 SUPER HS GLAMOUR CLEAR	2.5 coats (1 light tack coat + 2 solid coats) — or 2 solid coats	40-60 µm total	60 µm of this product	5-10 minutes at 20 °C
GP4410	HIGH VELOCITY CLEAR COAT	2 Coats	40 µm total	—	At 20 °C, NO FLASH OFF TIME between coats
GP4101	HS HIGH SOLID CLEAR COAT	2.5 coats (1 light tack coat + 2 solid coats)	50-70 µm total	70 µm of this product	5-10 minutes at 20 °C
GP4411	MIRROR EFFECT CLEAR COAT	2.5 coats (1 light tack coat + 2 solid coats)	40-60 µm total	60 µm of this product	5-10 minutes at 20 °C
GP4201	MS MEDIUM SOLID CLEAR COAT - SUPER HIGH…	2.5 coats (1 light tack coat + 2 solid coats)	40-60 µm total	60 µm of this product	5-10 minutes at 20 °C
	SNAP CLEAR COAT	2 Wet Coats (max 2 coats)	40-60 µm total	—	At 20 °C, 2-3 minutes between two wet coats (max 2 coats)
GP4403	SUPER HS PREMIUM CLEAR COAT	2.5 coats (1 light tack coat + 2 solid coats)	50-70 µm total	70 µm of this product	5-10 minutes at 20 °C

ANCILLARY

CODE	PRODUCT	COATS	FILM BUILD	MAXIMUM	FLASH BETWEEN COATS
GPFUNC10	2K TEXTURE COAT	1-3 Coats	total 150-450 µm	—	60 minutes at 20 ˚C
GA117	RUBBERISED UNDERCOATING	1LT sheet: spray a thin layer, repeat this process 3 times at an…	1LT sheet: When the undercoating thickness reaches 2mm, better noise deadening effect…	—	1LT sheet: at least 10 minutes between sprays at normal temperature

Issued by Terry Livingstone Trading Pty Ltd as trustee for the Terry Livingstone Trading Trust, trading as Ampro Australia. This guide is the document referenced as the "Germatech Coating Thickness Guide" on Germa-Tech technical data sheets. Figures are taken from the current TDS for each product and change with them. All times and film builds are quoted at 20 °C and 50% relative humidity unless stated otherwise. Read the Safety Data Sheet before use.