By Eng. Carlos F Molina
As any person in a project knows, consumables control is difficult, and critical. And while there are some calculators and guides in the internet and literature for things like control of welding and safety consumables, there is not much for painting consumables. In fact, a google search for “abrasive performance” has little results, and a search for “paint control” yields almost no result. For people in charge of paint control, this can be a nightmare.
I haven´t found any paint control strategy on the web. I am sharing one I have used before with success. It is mainly useful in large surfaces that are going to be painted by the airless spraying method.
I am aware this might not be the only nor the best approach there is to the subject. But maybe it will serve as a catalyst for debate in the subject. I am open to criticism. I know there are many experts in the field already. And finally, this is not my creation only, but the work of others put together as an overall strategy.
NOTE 1: In this article, I use the word paint for a) the liquid in the buckets before applied b) the act of painting, and I use the word coating when referring to the product applied and already dry over the substrate.
NOTE 2: In this article, I use the example of a project where you have to paint the inside of tank with a single coating and the exterior with a 2-coat arrangement.
NOTE 3: In this article, I assume all paints are 2-part (a resin and a hardener). However, it serves with single component paints.
NOTE 4. In this article, I talk about the possibility of being untrue to specifications of a paint job in very small areas. Take the advice at your own risk. (Remember: any standard is a form of risk reduction, so your professional criteria should always be used.)
NOTE 5. Finally, none of this information can be used to blame me later about anything. This is not a contractual document anyways, but only an strategy.
THE IDEAL SCENARIO
We mechanical blokes must face it. I think in terms of welding, of static equipment standards, etc. I don´t think in terms of paint. Paint is more unpredictable, more uncontrollable, potentially more damaging than mechanical work, which leads to stress and doubts.
So.. how can we record and control paint consumables?
An ideal scenario for paint control would be the following.
1. You estimate the area to be cleaned.
2. You calculate the amount of abrasive to be used.
3. You choose the correct set up for abrasive cleaning (not the subject of this article)
4. You estimate the area to be painted.
5. You calculate the amount of paint needed based on the technical data sheet.
6. You choose the correct setup for paint application. (not the subject of this article)
7. You record every piece of info of the coating application.
8. You measure your DFT first thing the following morning
9. If you are over the specified thickness, set an strategy for paint conservation.
If you can record all of the information in these stages, then you can calculate consumables performances and tackle other similar paint projects.
The problem with recording begins when days pass by. You go to work and record today, but tomorrow you do have an obligation and no one records anything. That can happen to you or your collaborators. Or your collaborator doesn´t understand or is not able to comply with your instructions. That´s why you need an strategy for the following:
• Record every important generated data.
• Put that information into a tool that calculates performances for you
Mark the paint buckets of the same kind of paint in consecutive order and keep a record of the bucket number vs the batch. Just after creating the record, you can ask for the certificates of the material.
The idea behind marking the buckets is that they should be used in the same order as your record document states. So ideally you will begin painting with buckets marked #1, number #2, etc. If a batch is defective, maybe you can still detect which batch was it. Make sure to communicate this order to the staff.
For the control of the consumables, the most important thing is securing the information on site. You can do that with a form that will remain on site. In the form, you will record every piece of important data. I use the following array of data. Pay attention to it because later on we are going to be talking again about it.
Print one form for every blasting or painting day you will have (If you prefer, you can print one form for every painting day, meaning you will only record data of “already painted surface”). Make a notebook composed of these forms and let it in the project´s location.
PREPARE A DRAFT OF YOUR SURFACE
With the intention of recording which area you paint day by day, draw an schematic of the area to be painted. It is not necessary to make it true to dimensions, but only as a guide. You can even go as far as creating a draft of the area to be painted over graph paper so you can count squares to calculate areas.
You will draw a draft for every type of coating. Every day, you will have to draw in the draft the areas that were painted in the workday, using a different color for very day. At the end of the job, your draft may look like this
Using this draft technique and matching with the buckets used for the day, you will know exactly where every bucket went. If you finish the job and later you detect that a batch is defective, then you can isolate that batch number and ask the manufacturer for a guarantee.
ASSIGN YOUR PEOPLE DATA COLLECTION DUTIES.
The amount of data generated day by day can be big, and if you have little time, collecting data can be difficult. That´s why you have to rely on the numbers. I mean, you will have to assign your people data collection duties.
Make your people sign instructions about what they need to record. The blasting pot operator needs to record the weight of the abrasive used. The mixer of the paint (or the painter) needs to tell you how many gallons of paint were used at the end of the workday. The person in charge of the air compressors must report the hour count at the start and at the end of each shift. The abrasive operators can record each their starting and ending time.
AFTER YOU HAVE ALL THE DATA, FEED IT TO A SOFTWARE
The recorded data of the table 1 can be then used to feed any software to calculate efficiencies. I use an excel spreadsheet that you can see here.
The most important thing is make it work. People sometimes work so hard in their shift that they forget about taking notes. They try to remember. People will change roles and they will feel not responsible for taking numbers, people will not know how to record data. I think it is bad that paint companies don´t receive buckets back. Safety first.
PAINT CONSERVATION STRATEGY.
If you are over the specified thickness, then you need to take measures to stop spending too much paint.
I use the following. (This strategy relies mainly upon the brute force of your DFT measuring device. You will need a good, fully charged ultrasonic meter to accomplish this task.) The main principle in mind is this: while you don´t want to be stingy with the amount of paint, you also don´t want to spend one more mil than needed. One mil of paint in such a large area means a lot in money terms. Therefore, you will aim at the specified DFT, not more, not less.
For example, let´s consider the coating of the internal surface of a tank that needs to be at least 16mils thick according to the specifications. However, some areas have too thin a coating. What can you do to reduce the paint expenses?
You will need to measure a lot of spots and enclose the thin areas inside lines made with permanent markers. Some client inspectors allow an 80% of the specified thickness as acceptable (SSPC PA-2). You can take advantage of that, but do it at your own risk. With thin areas, you can make an estimate of the amount of paint lacking and mark the value inside that zone. If the thin zone is big, paint it to specifications.
When paint is scarce, we take our risks. If an area with thin paint is small, say 0,3m2, don´t paint it, but do that at your risk: the risk that the client inspector will notice.
And that´s how you will conserve your employer´s paint and record all the data and give meaningful significance to your work.