Study Hall: Painting

[Alan Wheeler]

Paint and Painting:
The following is a basic view and is intended to give the reader a basic understanding of the possible job ahead of them. It hopefully will answer a few questions on how to prepare and what type of paint system to go for and most importantly answer, is it within your ability, time and finance restraints.
This is not the be all and end all of painting information. Detailed info is or should be available from your paint supplier and product literature.
Make sure you read all instructions and follow them, and follow all safety advice.

Choosing Paint types:
The first question that needs to be asked is, what is already on the boat. If it is new and bare, then you have a fresh palette to make the decision for. But if you have a boat that has already been painted, then you have to first find out what is one the hull. A single component paint (oil based) will happily go onto single and two pot paints. A two pot paint (solvent based) can only be applied to a two pot paint. It must not be applied over a single pot paint. If you do wish to apply the two component paint system to the hull that has a single component system on it already, then you must strip the old system right back to the bare hull material and start afresh.
The best method to achieve a high finish standard, is to spray the paint. This is true for both types. However, someone with a good hand can achieve a very high standard of finish with roller and brush and some true professionals can achieve finishes that look as good as spray. However, if spray methods are used, then careful consideration has to be given to safety with the application of two component systems. These paints often hold some nasties that can lead to severe problems and so special breathing gear is usually required. This often takes the application beyond the ability of most back-yarders. Single component paints are much safer to apply and thus do not require as much safety/protection gear.
The main factor between the two systems is longevity. A single component paint will last 1/3rd of the time that a two component paint will. Plus two component paints can be extremely hard wearing and have high scratch resistance, making it far longer lasting than the single pot paints. Initial costs differences are very wide. Two component systems are expensive and often cost more to have applied. But in the end, the longevity of the two pot paint means that overall cost over the life of the paint is about the same and in some instances, two component systems can actually work out cheaper.

What do I have to apply:
First point is, what ever Brand paint you go with, ensure you get as much product information as you can from the manufacturer/supplier. Most all reputable brands will have a “system” to apply. A system is a series of different coatings, each having a different purpose. A “paint system” is usually superior to paints that are supposedly a one coat does it all or even a little more sophisticated undercoat/ top-coat system. Multi-layer systems have specialised coats that do a specific job and do it very well. Each layer builds up and overall high performance coating.
For single component paints, it is usually three steps. A primer coat, a high-build undercoat/surfer and a top coat.
Two component systems can have as many as 6 different layers, each having a different purpose in the system. A system is specific for the type of material you are applying it to. Steel for instance, may have a different type of primer compared to wood. Aluminium will have extra special requirements.
Above and below waterline will also have different systems, namely water proof barrier coats, which are often employed for below waterline applications.
So if you are painting below waterline, ensure you choose a paint suitable to be used below waterline.

What method of application should I use:
Brush:
This is the best method to paint small and/complex objects and shapes. It is the least wasteful of product. However, it is slow to apply the paint in this way and the appearance is not always the best, depending on ones ability.

Roller:
This can apply the paint faster than the brush and has the benefit of applying a uniform film thickness. Once again it is not wasteful. It is still slower than spray and sometimes the roller material can get stuck in the paint film. Often the roller process is used to apply the even paint film and then a brush is used to “tip off” the surface so as a nice finish is produced.

Conventional Air Spray:
This is a fast method of application and a very high finish can be achieved. Although it still requires some skill, it tends to be easier to obtain a top class finish than a novice will with Roller and Brush. Substantial quantities of product can be wasted (as much as 40%) and a high quantity of solvent is required to make the paint thin enough to spray. A high film build can be achieved, but some skill is required to obtain a high film thickness and not over doing it and creating runs and droops.
It requires good weather conditions, i.e. light to no wind, or the need to be inside a building, or otherwise application is impossible. Over-spray is a serious issue and masking and covering everything in the surrounding area is a must.
As stated before, but it is important enough to state yet again, two pot paints require special safety equipment to be worn when spraying.

Airless Spraying:
This method can apply paint very quickly and so some skill is required to set up and control the application. However, it can apply very heavy and thick or viscous paints such as Anti-fouling coatings quickly and heavily. There is little over-spray so paint loss is minimal. The equipment is expensive and for one off jobs, hiring of the equipment would be the better choice.

Air assisted Airless or HVLP (high volume low pressure):
Air assisted Airless is a bit of a contradictory of terms. But it is an old technology that was not very good in it’s day, re-invented to current day technology and is very easy to use allowing the user to obtain a very high quality finish with not a lot of skill. It uses a very low pressure but high volume of air to deliver the paint to the surface you are coating. It provides a high level of control and accuracy with very little wastage. Equipment is more expensive as you are buying a system. But much cheaper than high pressure airless and about the same as Air spraying if you had to buy all the equipment.

Painting Conditions:
Once again, read the manufacturers instructions. There are good “rules of thumb” but each manufacturer will differ in some way. You need to follow their rules, not the “thumbs” rules. However, here follows a few of those rules of thumb.
Having the luxury of being indoors is great, but sometimes even indoors can present it’s challenges. Paint does not dry in the can, because a solvent is added to keep the binders of the paint apart and allow you to get the paint from the can to the surface. Once it is on the surface, you want the paint to start drying and hardening. So the solvents must be allowed to escape and be carried away from the surface. It works much the same as boiling water. The if the steam was trapped, the water in the pot would not decrease. But allow the steam to be carried away, the water level will decrease till you burn out the bottom of the pot. Evaporation is simply the molecules of water jumping up in the air, due to the heat exciting them so much. A breeze carries the molecules away so as they can not re-enter the water.
So when painting, one of the key things is to actually have some form of air movement. It is actually not quite so good painting on a totally calm day. Plus, the humidity should be such, that the solvent molecules have “room” in the air to leap into and be carried away. The solvents must evaporate away from the paint surface, to enable the paint to dry. So a light air movement is actually good thing. Outside is not much of an issue, but it requires consideration when painting indoors. Plus if you are spray painting, you need to have a means of getting rid of the paint mist, or it will not be long before you can not see a thing.
Temperature is another major consideration. The key to getting a good paint finish with any application, is to have a balance between getting the paint to flow, maintaining a wet edge and of course, getting the paint to “set” before it sags and runs. A temperature range of 15-25deg C is usually a recommended range. Any colder, and you will have two major difficulties. The first is the paint takes a long time to set. But the more detrimental one is moisture. As the solvent evaporates, it cools the paint surface and moisture will be pulled from the air. Moisture is not good. It will ruin your gloss and it can be trapped under the film. Once the paint is dry and the sun warms up the surface, the moisture expands and lifts the film creating blisters over the lovely surface. The most infuriating point to this is, the affect may not show up for months.
The other factor is Humidity. Humidity is moisture absorbed in the surrounding air. If the air is heavily saturated with moisture, there is little room to absorb solvent as well. So a rule of thumb is a maximum of 85% humidity.
So if painting indoors, you may need some artificial heat. If painting outdoors, you may need to protect the surface from either direct sunlight or rain/snow/frost and heavy dew.
And of course light. You need good light to be able to see exactly how the paint is being laid on. Especially when painting multiple tops coats of white. It is very hard to see where you have been without good lighting to reflect the surface.
One tip I have when it comes to painting timber for the first time. The first coating of whatever, maybe primer, maybe Epoxy, should go on when the heat of the day has reached it’s peak and is falling. In other words, in the afternoon. This is so trapped air in the timber does not continue to expand and create little bubbles in the coating.

Surface Preparation:
As the saying goes, “90% of the finish is in the Preparation”. This is where the hardest work is put into the project.
Washing:
Firstly, you need to wash the surface of all dirt and remove any flaking unsound paint with a scraper, hard brush, or even high pressure water blaster. It is hard enough sanding the paint, let alone dirt as well. Plus contaminants such as salt and polishes and waxes simply get carried on through the work and will rear their ugly heads when painting is finished. So cleanliness is essential to having the finish last many years. There are cleaners available that help remove most contaminants and are helpful when used in the initial clean and also after the final sand, to ensure the surface is thoroughly clean and free from wax etc.

Sanding:
Paint is not a miracle glue that sticks to anything. It works by being able to lock itself to a surface. This is called “Keying”. We have to create the “lock” as it were, to allow the paint to key to the surface. This is done by cutting the surface with Sandpaper and a lot of elbow work.
The first step will be filling and fairing the surface. Fairing compounds can be shaped and surfaced with 40-60grit dry paper. The final finish surface of fairing should be done with an 80grit dry paper.
High build epoxy surfacer type paints are often used at this point and the use of 80-150grit dry papers to smooth the surface off would be used.
Once the filling and fairing is complete, it is into the sanding prep for painting. We use finer grades of paper at this point. Paint films are thin and very soft, so using coarse grades will cut away the film too much and too fast. The final coat of highbuild surfacer, would require a grade of 120-150dry paper. The subsequent coats of primers, undercoats require grades of 320-400grit dry paper. These require very light sands between coats and the sanding is to remove surface imperfections and dust. If you do not do this, it is striking as to how the smallest spec of imperfection will stand out so glaringly in the final gloss coats. The final coats may need very light rubbing. Only if the surface has been contaminated by some dust. This requires very light grades of 400 and above to simply knock off the imperfections. I suggest you find the source of the dust before the final coat application, as you need to stop applying layers of paint at some point and live with the finish.

Applying the Paint:
If you are using spray guns to apply, I will assume you know how. If you don’t know how, I suggest you get someone to show you before trying to apply paint to your prized hull. There is more to it than just squeezing the trigger and waaay more than I could discuss here. So we will discuss Brush/roller application here only.
There is a difference between water based paints and solvent based paints when it comes to the brush and roller department. Plus you want to obtain a high quality finish. So go for the equipment that is of good quality and designed for solvent/oil based paints. If you don’t, Solvents will dissolve the glues that the roller sleeves are held together with and will allow “fluff” to mix into the lovely gloss surface you are applying. Synthetic bristle brushes may dissolve in some solvents, nor do they produce a nice flat finish. You really do get what you pay for when it comes to a brush and so buy a good one, look after it well and treat it like a special tool.
The way to obtain a good finish is to maintain a “wet edge”. This is the edge of the paint you have applied and the subsequent application of the next line of paint beside it. If the “edge” is allowed to skin, it can “tear” the surface and become lumpy. If allowed to dry too much, it will build up a layer and show through, resulting in the surface looking patchy. Very large hulls can sometimes have gangplank walkways around and a team of painters all working at different levels, to cover the surface and maintain that wet edge. We will assume you are working solo here, so you want to divide the surface up into segments and plan the way you are going to apply the paint as easy as you can. Any edges that you can not control, need to stop at points that will hide them. This maybe the waterline for instance. Edges you can control, will then be the vertical edges as you work along the hull.
The next important aspect to obtaining a good finish is maintaining a uniform film thickness
You can apply paint using just a Brush. The technique normally used is, brush out the paint over the surface in a cross hatch figure. This covers an area fast and helps to keep that uniform thickness. The next step is to “layoff” the surface. Experts use two brushes. One to brush on the paint, the other to lay off the paint. To layoff the paint, you are using just the tip of the brush and a very light hand so as the fine bristle tips flow the paint film smooth. The brush should be kept empty of paint. It is to only smooth the surface, not build up the paint thickness.
The use of a roller means you can quickly apply paint uniformly over a large area at a time. You then simply layoff the surface with the tip of your brush. Don’t get to far ahead of yourself however. Keep the area workable.

Finally:
There are many additives available to combat many isues that can arise when painting. Some additives will cslow the drying of paint for especialy hot days. These are called retarders. Some speed up the paint for especially cold days. These are called acclerators. There are additives for waxes and silicon contaminations. There are additives to make the paint surface ruff for non-slip applications. Whatever you need, there is most likely a product available. Ask your supplier. He/She should have the expertese to direct you.