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Airless spray coating – Maximising your investment

The principle of an 'airless spray' is simple, consisting of a high pressure pump that atomises paint at point of discharge.

The clever part is how well the various brands and designs have refined the machinery to deliver outstanding performance, capacity and reliability.

In addition to the skills of operation of airless equipment it is essential to understand the potential of 'airless paint' applications to obtain satisfactory returns on a significant investment item that also has the potential to cost you a great deal of money!

Often the true costs are disguised by spectacular reductions in time, but at actually hugely increased material costings.

Therefore careful consideration of the potentials and comprehensive planning can ensure that all contingencies are met and the best results obtained.

Question everything to decide on a battle plan. (After repeated experiences of course this becomes a natural process).

Some of the answers are simply yes or no and you can probably add to the list. It's definitely not funny when all is ready to go but there's no power available!

However the reason to plan as best as possible is when you pull the trigger, paint comes out and lots of it. If you're not prepared you can cause some major damage, injury or waste a lot of product.

The characteristics of paint need to be understood relative to being subjected to the high pressure (and volume outputs) or airless application. Apart from the mess poor operators can make (and poor planning adds to paint problems), material overruns turn problems into disasters.

Paint manufacturers usually support their product with Product Data Sheets that describe the usage of the product and recommends Spreading Rate (expressed as Area (square metres) per litre = SR and the dry film thickness which is the thickness of the material (usually one coat) after properly drying. The thickness is usually in microns expressed as um = DFT.

Other information is often volume solids of the material, which is the amount of material in the can, excluding thinners and solvent expressed as a percentage = VS.

Because selling paint is a highly competitive industry the recommendations are the manufacturer's best average estimate considering the coverage, life expectancy, appearance and ease of application. Results wildly above and below the nominated spreading and thickness rates seldom perform with any satisfaction and generally cause a great deal of grumpiness. Because we know from the Data Sheet the spreading rate per litre, we can easily determine the cost of the material per litre for estimating work packages, and most calculations in the paint industry are based in this manner.

Because airless pumps have a high output (relative to area potentials), these sort of results occur often:

Medium sized and small airless pumps typically used in the painting trade have average outputs @ 3000 psi between 2 litres and 4 litres per minute. (The smaller capacity supporting a 17-19 thou tip).

The potential in output areas:

@ 2 litres = 20 square metres per minute
@ 4 litres = 40 square metres per minute
or 1200 to 2400 square metres per hour

Therefore proper management of the process assures some urgency, particularly when industry criticisms are:

All these are a sure sign something is very wrong and indeed it is because the costs are fantastic and you are paying!

There is a simple discipline to develop and practise to return the costs of materials to industry norms and enjoy the productivity (labour) savings and make real money.

  1. Technique - application has a set of skills.
  2. Tip and Pressure Selection - there is a balance.
  3. Materials - Paint - the sole purpose of above.

Application technique

Appreciating the paint pressure produces a fan of paint only, there are no 'soft' edges of the fan spray pattern and a system of application therefore is apparent. We need a practical plan to minimise difficulties relative to overlaying heavy coatings of the paint. Operators often attempt to compensate by adopting a 'wristy' laying off motion.

The correct attitude of the spray fan is always to maintain the fan angle at right angles to the plane of work. Any deflection, either horizontally or vertically produces at one side a thinner application, but loads the other side with an overthickness, both unsightly and likely to run.

The correct technique is with the gun at right angles and always parallel to the work face with the gun travelling at the speed that the spray fan slightly undercovers the surface. The return spray, also parallel, overlays by 50% thus, stroke by stroke, attaining full attractive coverage of the surface.

This sounds complex but is actually easy to do. However, it is not easy to correct those operators that persist spraying with a loose 'wristy' action. Short of breaking their arm and applying a plaster cast, this remains a difficult habit to correct. Left handed people rarely have this problem, possibly because they are already living in a largely right handed world and are more receptive to adaptation.

It goes without saying that all operators should be understanding of the equipment, its operation and day to day care, the safety concerns to exercise and the health contingencies.

Spray tip selection and pressure

Selection of the best size and fan width are critical to the economical function of spraying. The size is in the thousandths of an inch and is designed to produce optimum results at 300mm distance from the work.

The tip size is preceded by a number (e.g. 413, 513 etc) denoting a 13 thou tip size. The 4, 5 etc refer to the angle of spray - i.e. 40 degrees, 50 degrees and roughly double the number (4 x 2 - 8) equals the width of spray @ 300mm - similarly 5 x 2 = 10 and so on, fan widths in inches.

The tip size matches the viscosity of the material and standard matches are:

Note that the spray tip nozzle diameter is always an odd number. Fan tip sizes are always even. All spray tips must be fitted with a guard (not to protect the tip but the user). The line filter size must match the tip size (this is a common fault - mismatched filters). Usually tips are quickly changed without downtimes and are reversible for self-cleaning.

Airless pumps have a fluid pressure adjustment and the ideal situation is to have selected the best tip for the material being sprayed and adjusted the pressure to properly atomise the spray flow. Because the spray tip opening is elliptical, too little pressure prevents full atomisation and a spray pattern is produced with tails. The pressure should increase until the fan forms without any tails and thereafter increased by another 10%.

This represents ideal conditions and allows for line pressure drops, changes from climbing scaffolds and some latitude for viscosity changes mix to mix. The critical statement - 'atomise' - the lowest pressure necessary to atomise the material.

Paint needs to be properly mixed, inspected for obvious problems such as skinning. It remains good practise, because usually the volume required is high, to premix and box the paint from drum to drum ensuring colour and thickness consistency. Usually materials require between 5 and 10% by volume thinness during mixing. More than this can seriously affect the end results.

The Product Data Sheet will describe the paint material and spreading rate (SR), dry film thickness (DFT) and volume solids (VS). By applying these known factors, not only can the costs be predicted, the spray operation can be planned and executed with economy and accuracy.

The operator, having set up all the systems, including the paint and adjusting the spray properly, can apply the paint. There are two checking methods to measure the result as you work.

By matching area painted with volume used. This is simple providing the operator knows and can set the work properly. For example a material covering 8 square metres per litre will spread around 30 square metres for 4 litre and 80 square metres for 10 litres. Caution - one must allow for the volume of paint from the paint pump to the gun, which can be quite high. The advantage of this simple check system is that the spray operator can rapidly visualise areas against material volumes and form good working estimates.

The second system is to measure the wet paint thickness as work proceeds. The wet paint consists of the volume solids plus solvent spread at the correct rate. Because we need the wet paint to dry to an acceptable planned thickness, we must calculate the application thickness.

WFT (wet film thickness)
= 1000 divided by Spreading Rate (in square metres per litre)

In other words, a spreading rate of 8 square metres per litre needs a wet film thickness of 125 µ.

The measurement is taken by the painter with a calibrated hand held gauge pushed into the wet paint and the result read off. This again is simple to do and the operator soon learns the systems of setups that reliably return great results at very economical inputs.

So there it is, airless spray application can, and should, be carried out exactly in accordance with the manufacturer's recommendations. If this is done it is in harmony with all the other job inputs.

This information is drawn from the course notes provided to those who have attended Professional Painter Development Courses.

Spray painting equipmentAirless tip guide

Getting the best out your spray equipment

Manifold and gun filters

When selecting the right filter set up for your spray system there are a few basic rules that are well worth following. If your tip size is…

  1. .007 thou to .011 thou, use a 200 mesh filter (red).

  2. .012 thou to .014 thou, use a 100 mesh filter (light blue).

  3. .015 thou to .021 thou use a 60 mesh filter (black).

  4. .023 thou or more for high build coatings, use a 30 mesh filter (grey).

Using the right filter and regularly cleaning it will reduce tip clogging. Filters must be free of all material after cleaning – if they aren't then it's time to replace them.

Selecting the best diameter hose to meet your length requirements is critical to getting a good spraying pressure. The greater the hose diameter the greater the pressure at the gun. If you decrease the diameter or reduce the hose length, the pressure at the gun will reduce.

When joining hoses together, connect the largest diameter hose to the sprayer, then the smaller hose to that.

For example, unit connected to 3/8 hose connected to 1/4 inch hose will give maximum pressure when spraying.

High build coatings require a larger diameter hose (3/8) to minimise the risk of tailing.

Health and safety

At all times use and follow the manufacturer's directions and wear the appropriate gear.

Cleaning

When using waterborne coatings, it is good practice to clean your unit daily.

For best results, follow these steps:

  1. Flush your unit with water to remove paint from the unit and hose.

  2. Drop the pressure and remove all filters. Clean them and store them safely in your tool box.

  3. Put the unit back together without the filters. Clean excess paint off the pick-up shaft.

  4. Remove the dirty water and replace with a bucket of fresh water, using hot water if possible. Mix in 2 capfuls of Resene Quick2Clean Paint Equipment. Flush through the unit until clean.

  5. Mix a small amount of fresh water in a bucket with Resene Pump Protector. Run through your unit.

  6. Drop the pressure and store your unit.

Can you afford the high cost of using a worn tip?

Choosing the right spray tip is essential for a quality finish no matter what material is being sprayed, but don't forget to check and replace your tips as all tips will wear with normal use. It's impossible to say how long a tip will last, because there is a huge difference in abrasiveness from one coating to another. Waterborne coatings are usually more abrasive than lacquers or enamels and paint is sprayed at different pressures so some tips will wear faster than others. Abrasive material sprayed at too high a pressure or through too small a tip causes faster tip wear, which wastes time and paint.

Just think... A contractor spraying with a worn tip uses, on average, 20% more paint and 20% more labour. In short, while you'll pay a bit more money in tips you'll pay a lot more if you don't.

How do you determine if a tip is worn?

When a spray tip wears, the orifice gets bigger and rounder, which makes the fan pattern smaller. When the fan has lost 25% of its original size, it is time to replace the tip. When a tip with a 12 in. (305mm) fan wears down to a 9 in. (230mm) fan, it outputs 30% more paint on 25% less area. Continuing to spray with a worn tip makes the painting take longer, you use more paint and the finish may be uneven and have runs.

Diagram - tip wear

Five (six) ways to extend tip life

  1. Spray at the lowest pressure that atomises the material.

  2. Strain the material before you spray it.

  3. Use the correct size filters.

  4. Clean the filters after every use.

  5. Clean the tip with a soft-bristled brush.

  6. Work less (only an option if you don't have a mortgage to pay off!)

Always make sure you have the right tip in good nick otherwise your profits will be sprayed away in excess paint and labour.

 

Size does matter

We all know that applying paint by airless spray application can be a very speedy way of getting a lot of paint on the surface very quickly, however you must make sure everything is set up just right otherwise you'll end up using up more paint and time than you planned. One of the keys to successful spray application is making sure you have the right equipment to do the job including the right tip.

Of course there are what seems like fifty thousand different options in this area so to help you wade through all the info we've picked out the important bits for you. This handy guide applies to airless spray application only, because as we all know pressure pot and HVLP are a whole different kettle of fish...

If you have always wondered what all the numbers mean in the tip descriptions here's the easy way to decipher them... Take the first digit and multiply by 2 – that gives you the width of the fan. For example, a 515 would be a 10 inch fan (i.e. 5 x 2). The second and third digits tell you the size of the hole, therefore a 515 would be a 15 hole size.

Tip 1: The orifice size alone determines flow rate of tip

If you want to cover a greater area with each pass do not try to do this by backing the gun away from the surface. The further away you are the less paint will reach the surface and the more you'll waste as overspray. Instead, use a tip with a larger fan and orifice. Remember if you use a tip with a larger fan but not a larger orifice, the build will be less and you'll have to move the gun slower.

Tip 2: Make sure tip and sprayer are rated for each other

Always make sure that the flow rate for the tip is lower than the maximum flow rate for the sprayer. If the tip flow rate is LESS than the sprayer flow rate you're all ok to go. If the tip flow rate is GREATER than the sprayer flow rate, you'll have to change either your tip or sprayer so that the sprayer flow rate is greater than the tip flow rate.

Recommended tip sizes for common coatings

Material Tip size (in.)
Stain or lacquer .011 to .013
Solventborne paint .013 to .015
Waterborne paint .015 to .019
Heavy acrylic and smooth elastomeric .021 to .025
Elastomeric and block filler .025 to 035+

Recommended tip sizes for Resene products to get you started

These are good guidelines for exterior/interior work based on the average flow of a unit. You may wish to use higher or lower tip sizes; example: for doors you may choose to use a FFLP 414 tip and a FFLP 310 tip for the frames. Please don't hesitate to contact us for further advice to suit your specific project requirements.

Power cords

Although most units are rated at 10 amps it is recommended that you use a power cord 25 metres or shorter, rated up to 25 amps. Use a ProGuard and electrical surge protection plug, especially in smaller units, such as 390, 395, 490, 495 and 595. If you need to work over a longer distance, add additional hose not cord. See hose information.

Product Data Sheet Hose
(no less than)
Filter LP tip
(yellow)
FFLP tip
(green)
Safety mask
Primers/sealers/undercoats
 
Acrylic Undercoat D404 1/4 60 mesh (black) 515 516 PV2
Broadwall 3 in 1 D810 3/8 30 mesh (grey) 523 - PV2
Broadwall Surface Prep & Seal D807 1/4 or 3/8 30 mesh (grey) 523 - PVS
Broadwall Waterborne Wallboard Sealer D403 1/4 60 mesh (black) 517 - PV2
Concrete Primer D405 1/4 60 mesh (black) 517 - PV2
Decorator First2Finish - 1/4 or 3/8 30 mesh (grey) 517 516 PV2
Enamel Undercoat D44 1/4 60 mesh (black) 515 414 Carbon filter
Galvo One D41 1/4 60 mesh (black) 515 414 Carbon filter
Galvo-Prime D402 1/4 60 mesh (black) 517 516 PV2
Laminate and Melamine Primer D414 1/4 100 mesh (blue) 411 412 Carbon filter
Limelock D809 1/4 60 mesh (black) 413 414 PV2
Quick Dry D45 1/4 60 mesh (black) 515 516 PV2
Sureseal D42 1/4 100 mesh (blue) 413 414 Carbon filter
Timber Surface Prep D814 3/8 30 mesh (grey) 523 - Carbon filter
Wood Primer D40 1/4 60 mesh (black) 515 414 Carbon filter

 

Product Data Sheet Hose
(no less than)
Filter LP tip
(yellow)
FFLP tip
(green)
Safety mask
Solventborne topcoats
 
Lusta-Glo D33 1/4 100 mesh (blue) 413 412 Carbon filter
Qristal Clear Polyurethane D52 /14 60 mesh (black) 413 412 Carbon filter
Super Gloss D32 1/4 100 mesh (blue) 413 412 Carbon filter

Download this brochure as a PDF

 

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