How to Thin or Dilute Paint

Posted Oct 30, 2024 | Product Advice | 0 comments

I thought I’d write a quick guide on the riveting subject of how to dilute or thin paint. It’s something that a lot of people get confused about, particularly when it comes to trade products.

I’ll start by explaining a little bit about when you should thin paint. Then about diluting different types of paint, and what you should use as the thinner. Feel free to skip ahead and just read the information you need.

 

When You Should Dilute Paint

 

Diluting paint is something you should do in various circumstances. Let’s visit each one in turn and talk about why diluting is important.

 

Priming Bare Plaster

The first coat you apply to bare plaster is called a ‘mist coat’. You can use many different products for your mist coat, but most people use the same type of paint as the one they’re using as the finish coat. (Always check the manufacturer’s instructions).

No matter which product you use, you should always dilute it, sometimes as much as 30% (again, check the manufacturer’s instructions). This is because thinner paint is more likely to absorb into the plaster and seal it, rather than sitting on top. Failing to dilute your first coat on bare plaster will lead to adhesion issues further down the line and your paint is likely to bubble or flake.

 

Using Trade Paint

Trade paint is higher quality than retail and often comes condensed. This is so you can dilute it to suit the job you’re using it for. Most of the time, you would dilute it by 5% – 10% to help flow and reduce brush or roller marks.

However, if you are covering a deep colour with a pale one, or you’re applying an undercoat, then you may want to persevere and apply the paint neat.

 

Speeding up the Drying Process of Paint

This may sound obvious, but many people don’t consider it; a thin coat of paint doesn’t take as long to dry as a thick one. You may be painting windows and doors, and you’re worried about when you can close them. Or you might be painting outside, and you need the paint to cure before nightfall to avoid it failing.

There is an alternative to diluting oil-based paint if you want to accelerate the drying process. I’ll get into that later.

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Diluting/Thinning Water-Based Paint

 

The solvent in water-based paint is, well water, and that’s what you can use to dilute it. You should always stir paint before you apply it anyway. All you need to do is decant the paint into a larger round container, add your water, and then stir until it’s properly mixed.

I often add a little bit of water, stir, then add a bit more water, etc. until I reach the desired consistency. The reason I do this is simple; you can always add more water to make the paint thinner, but you can’t take it out again if the paint is too thin. There’s nothing worse than adding too much water!

There is an alternative to using water to dilute water-based paint. Smith & Rodger Flow & Bond is a new paint conditioner that you can add to water-based paint. It helps flow and eliminates brush marks without affecting overall opacity, so you get the benefits of diluting the paint without the negatives.

Another reason to use Smith & Rodger Flow & Bond to dilute your paint is that it helps adhesion. I use it often to dilute water-based satinwood, eggshell, and gloss. The paint is easier to apply, it prevents brush and roller marks, and the paint actually sticks better to the surface you’re applying it to.

Smith and Rodger Flow and Bond conditioner for water-based paint

Diluting/Thinning Oil-Based Paint

 

Oil-based paint can be diluted using white spirit. It’s much the same as diluting a water-based paint, in that you should decant and then mix your product before use anyway. This is when you add your white spirit.

There are three reasons you might thin oil-based paint; they are to increase flow, speed drying, and reduce brush marks.

That said, there are a couple of conditioners you can use to achieve these results without thinning the paint. I’ll go into these now. You should never use more than one of these products in the same paint.

Barrettine Terebine Driers speeds up the drying process of oil-based paint. Just add a few drops to your paint and it will act as a catalyst for the cross linking that occurs within the paint.

It’s a conditioner I use often as a Decorator, particularly when working outside in cold weather, or painting doors and windows. I often use it alongside white spirit when thinning the paint.

Terebine Driers paint conditioner to speed up the drying process of oil-based paint

The other conditioner I use is Owatrol Oil. This aids the flow of oil-based paint and reduces brush and roller marks. The other advantage of using Owatrol Oil is it reduces oxygen within the paint which helps to inhibit rust. That comes in handy when painting metal railings etc. It just means your newly painted surface is likely to last longer.

The downside of using Owatrol Oil is it extends the drying time of your paint and if you use too much, it reduces the sheen level after a period. It’s a product I do use on a regular basis, and it really does come in handy, but there are those caveats. It’s a good alternative to diluting oil-based paint providing you don’t add too much.

Owatrol Oil paint conditioner to help the performance of oil-based paint

Final Thoughts

 

Now you should understand how to dilute or thin paint when you’re decorating. Don’t be afraid to do it. After all, water is cheaper than paint, and many paints are designed to be diluted.

As a Professional Decorator, I dilute paint on almost every job. Sometimes I add just enough to loosen the paint for application. Other times, I dilute by 20% or more, especially when spraying or priming a bare surface.

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FAQs

 

Do professional Painters water down paint?

Yes, most professionals use trade paint, which comes condensed. Adding a little bit of water to water-based paint, or white spirit to oil-based paint, just helps with application and finish.

 

Does diluting paint change colour?

Diluting paint will not change its colour. However, there was one time I over-diluted an acrylic-based emulsion, and it affected the sheen level of the paint for a period. It trapped water in the paint film after it was “touch dry”, which made it more reflective. This settled down over a few days, and the paint ended up as it should have been.

 

What happens if you water down paint too much?

If you water down paint too much then you will apply thinner coats, and it won’t have the same covering power. You will need to apply additional coats.

 

What is a disadvantage of adding water to your paint?

The opacity of the paint won’t be as good, meaning you may need to apply more coats to achieve a solid colour.

 

When should you thin paint?

When priming a bare surface, when using trade paint, when you need to accelerate drying time, or to increase flow.

 

Does watering down paint change the sheen?

Watering down paint will only affect the sheen very rarely, and even then, the sheen will return to normal once the paint has fully cured.

 

What happens if you don’t water down paint?

Some paints don’t need to be diluted at all, but others do. If you don’t dilute your first coat on bare plaster, then your paint will not adhere properly and may bubble of flake off over time. If you’re not applying a priming coat and don’t dilute the paint as you should, then the paint may be thick and be difficult to apply. You may also experience brush and roller marks.

Posted Oct 30, 2024 | 0 comments

About the Author

About the Author

Mike Cupit has been in the decorating industry since 2002 and has mostly worked as a Trade Decorator in the domestic sector (peoples’ homes). Self-proclaimed “product geek”, Mike has a passion for paint and decorating tools. Mike now spends most of his time testing paint products and tools, comparing them to similar products on the market, and blogging about the industry in general.

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