The very short answer is, “No, you cannot paint over silicone”. However, there are so many variables, and the less short answer should perhaps be “No, but you shouldn’t need to paint over silicone.”
You may have found yourself in a situation where you need to apply a sealant. But you will need to paint over that sealant, and you have heard an answer like the one we gave above; “No, you cannot paint silicone.”
Sound familiar? That’s because it is a widely-known statement.
As adhesive specialists here at Forgeway, we know that you cannot paint over silicone. However, we believe you shouldn’t need to paint over your sealant in the first place.
But you may have already applied the silicone. Now, you want to know how to ensure the paint will stick to the silicone.
This article will discuss the cause of this issue and ways you might be able to paint over silicone. We’ll then describe alternative methods of ensuring your sealant is the correct colour in the first place so you won’t need to paint over it.
We understand that this topic can get quite complicated and confusing. So, we aren’t promising to provide the most technical answer and the scientific cause. Instead, we promise to describe it in a simple way for you to understand. Once you have this base-knowledge, you’ll be able to assess your options.
The sealant you’re using will determine how difficult painting over will be
You won’t find it difficult to paint over all sealants. You may be thinking sealant and silicone are the same things. They aren’t.
There are several different types of sealants. As the name suggests, a sealant is any type of adhesive that is used to ‘seal’ a gap or void.
Silicone is one type of adhesive. When people say to use a ‘silicone’, they likely mean to use a sealant. Sealants can be made up of one of several chemistries; Silicone, hybrid polymers (like MS polymers) and polyurethanes to name a few.
You will not find it difficult to paint over sealants with a base chemistry of hybrid (MS) polymer or polyurethane.
On the other hand, you will find it very difficult (pretty much impossible) to paint over silicone. So for the purpose of this article, we will explain why you cannot paint over silicone.
Why is painting over silicone so difficult?
This section is where we could get technical. But, I tried to simplify the answer as much as possible so here goes.
To begin with, we should explain that silicone and emulsion paints aren’t compatible. If you paint over the top of silicone with emulsion paint, the silicone will repel the paint.
The main reason for this is the hydrophobic nature of silicones. As Emulsion paint is water-based, the silicone will repel the paint.
The ability of silicone to repel water & form watertight seals is the main reason it such an effective sealant and is why it is so popular.
As mentioned already, this is a very top line demonstration of why water and silicone don’t bond. But hopefully, it makes it a little clearer.
How can you paint over silicone?
Now that you have an idea behind the reason why you will struggle to paint over silicone, we will discuss some options that could help you paint over it. We aren’t saying they will work though.
The first option you can try is to use oil-based paint. These use solvents which take the place of the water in emulsion paints. This means the silicone will not repel the paint – but it doesn’t necessarily mean that it will attach to it.
You have to bear in mind that some paints and silicones will contain budget-grade raw materials. These low-quality materials could be in place of other additives that improve adherence. Yet we know that oil-based paints are not always a viable option.
If you have tried oil-based paint and it doesn’t work or you can’t use oil-based paint, there is still one other solution you can consider:
Try etching the silicone with sand paper to give more surface area for the paint to stick.
This method is commonly used when trying to find a way around the problem.
Here at Forgeway, whenever we get asked for methods to paint over silicone we always say that you shouldn’t be in this situation in the first place. You shouldn’t need to worry about paint cracking or flaking off after it has covered the sealant.
Several options are available to eliminate the need to paint over silicone, but you will need to plan ahead to ensure they work.
Why using a colour-matched sealant could be the best option for you
As mentioned, we believe the best way to eliminate the risk of paint flaking or cracking after it has covered the sealant is to plan for the situation in advance. As the saying goes, “prevention is better than cure”.
You are probably wondering how this is possible. It’s quite simple.
Silicone is one type of sealant, so you can use another type of sealant (like MS polymer) in its place. I can imagine you’re thinking “but I’ll still need to paint over the other sealant?”
This isn’t necessarily the case. Some adhesive manufacturers can offer colour-matching of sealants (you can colour-match silicone too). This colour-matching can be fine-tuned to the exact colour you require for your substrate. This, in turn, eliminates the need to paint over it.
Once you have determined the colour you need and you have purchased the product, you apply the sealant and there are no further steps required. You will not need to go over the sealant to ensure it is the correct colour.
The benefit of colour-matching using a non-silicone sealant comes if you need to paint over it (such as spray-painting the side of a bus). A non-silicone sealant will not repel the paint meaning it will not flake off and crack.
This may not seem like an issue, but imperfections (like cracks) in the paint are the primary cause of filiform corrosion.
How do I know which is the best solution for me?
Without understanding your exact situation it is difficult to say which solution will work best for you.
You can try the mitigation methods we mentioned above (such as etching the silicone). Although, we know that it is a lengthy and difficult process to try and find ways to make the paint stick to silicone.
Purchasing a colour-matched sealant is significantly easier. It will also reduce the risk of the paint flaking off and ensure filiform doesn’t creep in.
The colour-matched sealant will be more expensive though. An unpigmented (white/black) sealant will cost between £5 and £10 for a tube. Silicone was once the cheapest sealant, but that has changed. Silicones will likely be around the same price – if not more – than other sealant types.
A colour-matched sealant will cost between £15 and £20 per tube. If the colour you require is in-stock or has already been produced, the supplier might not need to charge a set-up fee (usually around £100).
We believe the best option is to use a colour-matched sealant so that you don’t need to paint over it at all.
But, you still may want to try some of the methods we discussed above. They are difficult and time-consuming, but they may provide the solution and allow you to paint over silicone.
However, if you are fed up with trying to paint over silicone, you can read about the silicone sealant alternatives below. Click on the banner to read more.