How to Measure the Gloss of the Textured Gelcoat Surface

[roggy]

one of our customer ask us to meet the requirement for the gloss of textured gelcoat .I want to know which is standard for this issue?
thanks a lots!

[Alan Wheeler]

I don't quite follow what you mean by "textured" gelcoat. Can you explain further please.
To measure gloss level on any surface a special meter is used. Not cheap by the way.

[roggy]

Hello Alans:
the textured means the gelcoat surface is not smooth ,the surface is textured (structured),now for us it is so hard to meet the requirement ,can you tell me whether we can measure the gloss level for the textured surface,or are there any standards for this issue?
thanks!

[Alan Wheeler]

I am not aware that there are any "standards" as such. There is a "percentage of gloss" measured by a meter. A gloss meter measures this with a great deal of accuracy, although a proffesional can guess it by experiance. The meters are very expensive., being in the range of perhaps US$800-1000 perhaps.
A poorly chalked up gelcoat surface will be giving a reading of aprox. 30-35% and a really good shine will read around 80%. The only advantage the meter will give you is a Number. Just quite how you can shine a textured surface beats me and why you would want a shiney textured surface is even further from my reasoning. Surely this is for anti-skid and shiney would render the anti-skid rather useless.

[Pelagic]

Alan, I think the purpose of a textured finish is usually when the fairing is not quite perfect on a large surface and they texture or flatten it out to hide the ripples.

“Depth of Gloss” is really the warrantable issue when someone is concerned about gloss retention (read protection and longevity) and is still a factor in a textured finish.

A meter does not work so the only way to measure the depth of the clear coat is to also spray a sample board during the shoot and have it analysed.

Tends to get a bit anal!

Roggy the paint manufactuer's technical data sheet will tell you wet and dry film thickness of his paint to meet warrantable coverage (ie depth of gloss)

[Alan Wheeler]

I am not following Roggy then. Is he asking for gelcoat gloss after polishing? or is he asking for paint film thickness?. The two are chalk and cheese

[seafox]

Stand back and smile. If you can count your teeth it is a good gloss. If you cant you either need false teeth or a new painter

[Pelagic]

On a cross thatched polyurethane like Awlgrip it should never be polished until such times as the gloss has diminished. The value of this kind of paint is that, properly applied it can have gloss retention for 5 to 6 years provided you use proper cleaners that don’t allow a wax build up. Basically an aircraft coating where in that market they can expect gloss retention for up to 10 years because of better QA in application.
When this paint tacks off a chemical reaction takes place separating the color pigment from the hardening clear coat (Gloss) so a measure of film thickness is also a measure of gloss assuming that the correct mix of convertor and thinners have been used for the ambient conditions. Therefore, in the absence of orange peel or sags a measure of film thickness can be used to measure the gloss thickness

[Nordic cat]

check this out for a better description:

PRA Optical Properties > Gloss Measurement

Regards

Alan

[CKDK08]

Having spent 20+ years in automotive painting I have some experience with this.
Gloss is measured as DOI (distinctness of image) on a scale of 1 to 20.
1 being very low ( think non-skid ) and 20 being very high. As an example, BMW had Project 18 for many years that aimed at producing vehicles with a paint job that measure 18 or above. The meter to measure this is very expensive. The main variables are how smooth the substrate is and how smooth the paint lays out. The end result is gloss or the absence of Orangepeel. If you are starting out with a realitvely rough surface you will never get a high DOI.
A cheap way to compare golss is to print up an index card with several sentences in different size fonts. Hold it at a 45 to the surface and see which line you can read. This can be used to compare one surface with another. So if the customer wants his wrinkled old hull to shine like his new Beemer. It ain't gonna happen.
Without getting to technical, most of us just want it to look pretty and shiny and chasing a number will drive ya batty.
Let me know if there are any more technical questions.
Craig

[CKDK08]

Second Lesson....
The gloss of the surface does not indicate a good OR bad paint job.
Think of the GM and Chrysler vehicles that the paint fell off in sheets. These all started out as shiny with a DOI of 12 or better. But a glitch in the technology caused failures.
I would rather have a quality finish that lasted.
Measuring the thickness of the paint is not an indicator of weather or not it will be shiny when dry. In fact it is possible to lay on a very thin shiny coat that won't last. Did it on vehicles for car shows. Didn't need it to last.
Again, I'm open to questions.
Craig

[capt_douglas]

Gloss has been defined as the attribute of a surfaces that causes it to have a shiny or lustrous, metallic appearance.

The gloss of a surface can be greatly influenced by a number of factors, for example the smoothness achieved during polishing, the amount and type of coating applied or the quality of the substrate. Manufacturers design their products to have maximum appeal. Such examples are; highly reflective car body panels, glossy magazine covers or satin black designer furniture. Now what happens when products all of a sudden look different? Customers see this as a defect, or poor quality. Using a glossmeter and having good quality control practices eliminates this variable as a problem.

It is important therefore that gloss levels be consistent on every product or across different batches of products. Gloss can also be a measure of the quality of a surface, for instance a drop in the gloss of a coated surface may indicate problems with its cure- leading to other failures such as poor adhesion or lack of protection for the coated surface.

Gloss measurements depend on the gloss level. Gloss meters are either specific for the paint or multilevel ones.

If Semi Gloss - 10 to 70 GU Measurement Angle: 60 °
If High Gloss > 70 GU Measurement Angle: 20 °
If Low Gloss < 10 GU Measurement Angle: 85 °

The gloss value is determined by directing a light, which has a similar wavelength to the human eye, at the test surface and measuring the amount of specular reflection. Gloss is measured with angles of 60° and 20°. The 60° angle is universal for all applications. The 20° angle gives improved differentiation of measurement on high-gloss coatings above 70 gloss units.