The cautions against thinning acrylics beyond 30% (or some similar figure) is common to run across and is something we often find ourselves having to correct, at least in regards to our own paints . We cannot, of course, comment about other manufacturers’ products, where performance can differ. So the following is really only about our brand and is not a blanket statement.The first thing to note is that our Fluids and Heavy Body acrylics can easily be thinned up to one part paint to one part water, or a 1:1 ratio, and maintain excellent adhesion onto absorbent surfaces. In fact, even when testing this on a non-absorbent material like Plexiglas, the paints still formed good films with no adhesion failures after being allowed to fully cure.To add even a little more comfort beyond that, we can share that the adhesion onto Plexiglas remained solid even when thinning with one part paint to two parts water, or a 1:2 ratio. Which would feel like a fairly fluid wash for most people.As you can see, the concerns around thinning with water can often be over stated, especially if using our Heavy Body or Fluid Acrylics and keeping the ratio to 1:1 or less.And even then, one can usually get away with going even further.However, because every application can be unique, one can always do an easy test to make sure there are no problems.To do this create a test piece with a similar surface that you want to test, then apply a few different colors both at full strength and then at 2:1, 1:1, 1:2, and 1:3 ratios of paint to water.Allow to fully dry.At this point, we typically test for adhesion at 24 hrs, 3 days, 1 week, and 2 weeks.If the paint passes the adhesion test at, say, 3 days, there is rarely a need to continue testing out further.A simpler, more down and dirty test, can be done by scoring the paint with an “X” using an X-Acto blade, then apply masking tape over the centre, burnish, then lift. In both cases you are seeing if the paint comes off. If not, then you have very good adhesion and no reason to believe that adhesion will lessen over time.You can also try rubbing the film with a wet Q-Tip to see if you get color lift, which can be another sign of an underbound film .Please note: Even though our Heavy Body and Fluid Acrylics are quite robust, when it comes to thinning, there are some products where we do recommend a lower level of water, such as our Acrylic Gesso which should not be thinned with more than 20% water, or our OPEN acrylics where we recommend a limit of two parts paint to one part water, or a 2:1 ratio. And of course we cannot comment about safe levels for thinning paints from other manufacturers.Best regards,
Sarah Sands Technical Services SupervisorGoldenPaints.com
How to Paint on Frosted Acrylic Plastic Panels
Throughout the ages, many of the greatest artists painted on unconventional surfaces. By straying from more basic materials like canvas, these artists made their pieces stand out with materials like stone, wood, and glass. Today, this same creativity persists among artists and DIY crafters with a new material – acrylic plastic, also known as plexiglass. With the right knowledge, painting on acrylic can create anything ranging from amazing three-dimensional art to eye-popping signs for an event.
However, the uninitiated sometimes dive in head-first without understanding how to paint plexiglass panels. The most common mistake is using the wrong type of paint or using a perfectly smooth sheet of acrylic. This can lead to a lot of heartbreak – an artist could spend hours painting the plexiglass sheet to then realize the paint is never going to fully adhere. To avoid these mishaps, let’s take a look at a few key recommendations for painting on acrylic panels.
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Why Paint on Frosted Plexiglass?
Frosted plexiglass and P95 acrylic are some of the most commonly used types of acrylic for painting. This isn’t just for aesthetic reasons – frosted and P95 acrylic have a light matte finish that gives paint the “tooth” that it needs to stick to acrylic. Tooth is extremely important – it’s one of the reasons why many artists reach for a bumpy canvas instead of a smooth sheet of paper. In the same way, smooth sheets of acrylic are slick, which can interfere with adherence and make the paint easier to scrape off.
P95 and frosted acrylic have a couple of important differences that painters and DIYers should consider before choosing their surface. Let’s take a closer look at what this difference means for you:
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Frosted Plexiglass – Frosted plexiglass has a matte finish on both sides of the plastic, which creates a frosted appearance. This means that paint will stick effectively to both sides of the acrylic sheet. However, its aesthetic appearance is a far cry from a smooth sheet of acrylic plastic – it is not recommended for multi-layered or reversible pieces of art.
However, maybe you’re not keen on using a matte finish at all. If this is the case, then think ahead and pick up some fine-grit sandpaper, and plan out what you’d like to paint. Use the sandpaper to lightly scuff the area that will be painted. This will help the paint stick significantly better while keeping a rather clear appearance.
Alternatively, you can paint directly on top of a sheet of plastic, then carefully place another sheet of plastic on top of the dry painted sheet as a form of protection. If you choose this method of framing, make sure that the frame and plastic inside are well-supported, and not bending at all. For the highest level of optical clarity, we recommend using frame-grade acrylic sheets.
Prepare the Plexiglass
Once you select the right kind of plexiglass for your art piece or project, it’s time to prepare the plexiglass sheet for painting. First, clean the acrylic using either a mixture of water and dish soap or a specialty cleaning product like Novus #1. Gently wipe any excess material off the sheet using a clean, soft cloth.
For the best adhesion properties, use an acrylic-based primer – you can commonly find these as cans of spray paint at craft or home improvement stores. To avoid inhaling fumes, only spray the primer outdoors or in a very well-ventilated room. Keep in mind that acrylic primer can damage furniture, so it’s recommended to lay down newspaper or a tarp before you begin spraying. When spraying the primer, hold it about two feet away from the acrylic sheet and try to spray the surface as evenly as possible. Once the primer has dried, the sheet will be ready for painting.
Watering-Down Heavy Body Acrylics
When I’m building up an acrylic painting, I usually work from thinner diluted layers in the under-painting stages, up to more impasto thicker paint layers in the final stages of the painting.
This stems from Classical Oil Painting where you build up layers of oil paint, known as ‘fat over lean’
Fat over lean means that each succeeding layer of paint should have more ‘fat – oil’ than the preceding layer.
If you are painting in an indirect method (working in layers rather than all in one go – Alla-Prima) you need to adhere to this rule to prevent cracking and give the painting a good structure in your oil paintings.
I follow this same practise with many of my acrylic paintings.
Because the thinner watery washes at the underpainting stage create a really nice matt paint surface for the blocking-in stages. Then the subsequent layers, which are slightly thicker (less diluted) will absorb and ‘grab’ nicely into the layer below.
Don’t forget, acrylic paint is plastic-based, so if you paint the first layers too thickly, you can create a hard, shiny surface completely covering the tooth of canvas (see: What are your paints made from?)
With thin layers at the beginning of a painting, you can tweak your drawing and colours and then start painting thicker layers when you’re more confident the painting is coming together.
Absorbency
Before we go any further, I want to draw your attention to the most important factor to consider when working with watered-down Heavy Body Acrylics.
If you applied thick acrylic paint, straight from the tube to practically any surface, it would stick.
However, when acrylics are diluted with water you need to take into account the absorbency of your support to get the best results.
When I say ‘support‘, I’m talking about your canvas, paper, canvas board or even a plastic panel you intend on using. All of these surfaces have different absorbency levels which will have a direct effect on the way the paint behaves when water is added.
The most common questions I receive on this subject are from students fearful that watered-down acrylics will harm their paintings in the long run, usually thinking the painting will ‘flake and fall off’.
To be clear, watering down acrylics with water is not a problem if the surface absorbency level you choose to paint on is considered.
Think like a Watercolour Painter
If you think about Watercolourists, they sometimes dilute their paint 50:1 water to pigment, but they choose an rag watercolour paper that has been designed to absorb the watery paint effectively and hold the pigment when the water evaporates.
So if you think about how diluted you’re going to be applying the acrylics and then choose or prepare your surface sympathetically to that style of painting.
Below is a general guide to the absorbency level of a few common painting surfaces.
