BASIC FAULT FINDING

This information is offered as a guide for the self diagnosis of common finishing faults.

The remedial actions assume that the compressor is working to manufactured tolerances and regularly drained. Moisture and Oil filters are fitted no more than 2-4 metres from the gun and the tip, air cap and needle combination are suitable for the intended use as recommended by the gun manufacturer.

 

Symptom

Action to take

Cissing.
Surface defects appearing as craters or fish eyes on the surface.

Cissing is often a result of contamination by Wax, Silicone or Oil. It is important to identify the source of the contamination before further work is attempted.

Check Airlines as a possible source.
Drain filters and check air quality.

Remove any aerosols from the finishing area.

Check all items that have physical contact with the surface to be coated: gloves, rags, sanding pads etc.

Items for rework will require special attention.

In extreme cases additives can be used but advice should be obtained from your lacquer supplier.

Orange peel.
Uneven surface texture like the skin of an orange.

Orange peel can be caused by a number of factors: poor atomisation of the coating, the spray gun is being held too far from the surface, inappropriate thinning or items being hot when sprayed the

Ensure the tip/pressure cap combination is appropriate for the coating and the air pressure is sufficient.

Keep the gun tips 15-20 cm from the object being sprayed. (6-8 inches)

Ensure the thinner being used is the recommended product and sufficient has been added to achieve correct spraying viscosity for the tip,air cap and needle combination.

Ensure the items to be sprayed are at room temperature.

 

Bubbling/Frying
Small bubbles on the surface or trapped in the coating.

The bubbles can be caused by solvent boiling in a forced drying environment, air introduced into the lacquer in high pressure feed systems, inappropriate shop conditions or too high a film weight.

Ensure the recommended thinners are being used at the correct level.

Check temperatures and reduce if needed.

Ensure the recommended film weight is being applied.

Air movement, humidity and temperature are at reasonable levels.

In extreme cases a retarded thinner can be used.
Seek advice from your lacquer supplier.

Chilling
The surface of the coating takes on a hazy appearance.

Chilling is a result of moisture forming on the lacquer surface.

Ensure the shop temperature and humidity are at reasonable levels (18-22’C and 55-65%RH)

Ensure the recommended thinners are used.

Prevent any drafts from entering the spray shop.

In extreme cases an anti bloom thinner can be used.
Seek advice from your lacquer supplier.

Overspray
The lacquer has a gritty texture.

 

Overspray is a result of particles of semi dried lacquer settling on the finish.
This excess can be a result of too high a pressure at the gun and or the gun being held too far from the surface being sprayed. High ambient temperatures can also be a factor.

Ensure the correct thinners and amount is being used.

Keep the gun tips 15-20 cm from the object being sprayed. (6-8 inches)

Ensure the air pressure is not excessive.

Ensure shop temperatures are not to high.

Pin Holes
Tiny holes in the surface of the coating.

Pin holes can be caused by lacquer drying too fast, incorrect overlapping spray pattern or too light a coat of sealers.

Ensure the drying conditions are not excessively hot and if required add the recommended retarder.

Overlap spray pattern correctly.

Ensure even wet coats of sealer at the recommended film weights.

Printing
The lacquer surface is figured by packing materials or surface pressure.

Printing is a result of a soft incompletely dried film.

Ensure the correct thinners and levels are being used.
(If you have used retarder thinners allow extra drying).

Ensure the correct coating weights are being applied.

Ensure that any drying systems are fully functional
and the recommended drying times are followed.

Ensure the recommended packing times are followed.

 

Sinkage
The lacquers build falls away over time.

The lacquer film contracts and the grain / surface texture of the substrate becomes apparent. Insufficient drying times between coats, unsuitable product for required build or excessive tinting with stains or over thinning can all lead to this issue. 

Ensure sufficient drying times are given to each coat.

Ensure you are using the correct product to achieve the required build on the substrate.

Use the recommended thinners at the correct amount.

When tinting the lacquers with stain ensure a compatible product is used and at the correct amounts.

 

Sagging
The lacquer begins to flow after application on non horizontal surfaces.

Sagging is a result of the product being too low in viscosity / too high an application weight.

Ensure the correct thinners are being used at the correct amount for the product.

Ensure the recommended application weight is being applied on the substrate.

Stearate Bloom
The lacquer forms an oily haze.

Some sanding agents used in traditional sanding seals are incompatible with pre-catalysed or acid catalysed products resulting in a chemical reaction.

Ensure the recommended sealer / lacquer combinations are used.
 

Patchy stain colour
The stain shows excessive tonal changes across the finish often against the grain.

Uneven colour can be caused by poor application or poor surface preparation.

Ensure the substrate has been sanded evenly to a high standard.

Ensure the stain is not applied too dry or unevenly.

With high absorbency substrates like pine it is more important to apply with the grain.

In spray wipe applications ensure the surface is wet enough to allow wiping evenly in a circular motion followed by levelling with the grain.

Poor adhesion
Surface coats of lacquer delaminating from substrate.

Poor adhesion to previous coats of lacquer can be a result of an insufficient mechanical key, excessive drying of previous coats or incompatible surface preparations/ stains or fillers.

When using higher durability coatings it is important to sand well before the application of the next coat.

Two component systems offering higher durability will require good surface preparation after extended drying periods just prior to application of a second coat.

Ensure compatible stains and fillers are used.

Discolouration on light woods.

Discolouration can be caused by action of the hardeners in some two component systems and UV light from the sun stimulating the maturing process of the wood or tinting from the actual coating.

Seek the advice of your lacquer supplier for low yellowing coatings specifically design for light coloured substrates where higher colour stability is required.

Crazing
The lacquer adopts a wrinkled appearance.

Crazing or rucking is caused by the action of the current coat of lacquer swelling the previous coat of material and can be a result of using incorrect thinners, insufficient drying time for the previous coat or incorrect hardener ratio in the previous coat.

Use the recommended thinners at the correct ratio.

Ensure previous coats have had sufficient drying.

Ensure the correct Hardener ratios are used.

If tinting the lacquer with stain ensure the correct product is used at the recommended levels.