How to Detect Poor Powder Coating: Key Indicators and Solutions
October 21, 2024How to choose the right color for your next powder coating project?
November 20, 2024Introduction
As powder coaters, we often work hard to distinguish ourselves from the world of liquid coatings of which we have evolved. We know the advantages that powder has over liquid. Our environmentally-sustainable-lower-applied-cost-more-durable coating system works well when applied properly and will outlast most commonly used liquid systems.
Until it gets damaged in the field. Then we have a problem.
This is where we need to develop an understanding and appreciation for how liquid coatings can bring benefit to powder coating.
“There is no way to touch up powder coating in the field”
When out working to build up our client base, we often hear the above statement as a complaint and reason not to use powder coating on a project. While it is true that you cannot bring an IR or convection oven to the affected site and reapply powder, you can still touch up a damaged coating with a liquid system. This is an opportunity for us to educate a a concerned customer.
In the photo below you can see a fusion bonded epoxy panel (powder coated) that has been primed with self-etching liquid epoxy primer, and top coated in a liquid two-part urethane.
After allowing the proper time for the two coat system to cure, a pull off adhesion test was done demonstrating that the liquid coat held to the powder up to 938 PSI. For most applications, this is more than sufficient.
Furthermore, the failure that resulted was not between the FBE basecoat, but instead was between the self-etching epoxy primer and two-part urethane top coat.
Therefore, you can touch up powder coating with liquid.
The success of the touch up will depend on the following:
Quality of liquid touch up used
Quality of surface preparation prior to coating application
Ability of person doing the touch up in the field
Quality of Liquid System
The most immediately important attribute of the touch up paint is going to be the colour. This is also typically the easiest obstacle to overcome. Most liquid paint suppliers are able to provide a custom colour match when you supply them with a panel. I recommend doing this every time instead of submitting a RAL colour code or a email with a photo. In both cases there will likely be colour variation between what you have sprayed and what is on a sample chart or computer screen (It is a very bad idea to match to a computer screen for the following reasons: ambient lighting when photo was taken; quality of camera; representation of colour on customer computer screen; representation of colour on your computer screen. And don’t even get me started on printing colour samples on your InkJet).
Depending on what requires touch up you should specify whether you want it in an aerosol can or in a quart canister.
Successfull match
Chemistry of liquid coatings
The chemistry of the liquid coating will have a bearing on the price and method of application. In our company there are four different chemistries that we commonly use.
Quality of Surface Preparation
While there shouldn’t be any mystery with how to properly prepare the surface for application, it can easily be overlooked when doing repairs in the field. Generally this is due to the ability and understanding of the person who is tasked with taking on the job. Depending on the type of damage will determine the best method for touch up.
With so many different scenarios where touch up may be required, the following points are offered as suggestions and not the rule:
Considerations prior to surface prep
Masking
Protection
Application Equipment
Timing
Equipment
- To what points should you mask off? Look for natural breaks in the surface that will hide the area that you have to mask to. When doing major repairs it is likely you will need to coat more surface area than just the damage.
- Is temporary cover required to protect from the elements? Should drop cloths be used to prevent overspray in the area?
- Is it safe to use application equipment or should brush application be used? (Some areas may not permit the use of electrical or aerosol equipment due to fears of explosion, fire, etc.)
- Does time allow for this repair to be done start to finish?
- Do I have all the equipment I need at hand?
General Guideline for Touch Up
Degrease
Hand Sand
Solvent Wipe
Tack Cloth
Apply coating
Other considerations
Ability and understanding of Applicator
Even if the above mentioned steps are observed, the person who will perform the touch up should have the following attributes: patient, detail oriented, and skilled with the mode of application (brush, aerosol can, spray gun). Whether you have to touch something up in your shop or if it is in the field, the person responsible should excel in these areas. Liquid application is a different beast compared to powder application and consideration must be given to the quality of the coating and surface prep as well as the following:
- What is the relative humidity of the environment the coating is to take place in?
- If there is wind, is there danger of overspray landing on other surfaces which could result in expensive insurance claims?
- What is the temperature of the substrate that is to be coated? Does it need to be preheated?
- What is the correct application technique that should be used for the repair?
- Are all the tools required available: brush, tape, sandpaper, tack cloth, solvent, paint, masking paper, application equipment, respirator, safety glasses, gloves
The Finish
While a repaired surface will never perform as well as the area would have prior to the damage, when done correctly a field repair will perform as well as the combined coating system, surface preparation, and applicators ability allow. The liquid coating will adhere to a powder coated surface, and a color match to a coated sample plate is possible. When considering the options, be sure to demonstrate the ability of the coating to adhere to powder with a sample plate by performing a cross-hatch adhesion test. And if you are not going to be the one responsible for administering the touch up on site, at least provide the person responsible with the recommended guidelines for doing so. Rest assured, you can touch up powder coating in the field.
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