You may think that painting over existing silicone sealant would be a quick way of tidying sealed joints around windows, skirtings etc. However, you will quickly discover that this is not such a good idea.
Should you attempt to paint over silicone, you will come across two main issues:
The paint will have a thin, streaky finish, no matter how many coats you apply.
The paint will eventually flake, leaving a patchy mess. This is especially common in areas that are regularly cleaned, such as interior window frames etc.
So now you know that paint will not stick to silicone, let’s take a look at why .
Why does paint not stick to silicone sealant?
This may sound like a simplistic answer, but silicone is designed so that nothing will stick to it. With its waterproof characteristics and extremely smooth finish, the paint will not adhere well enough for it to last. This is especially true in areas that are cleaned or wiped down on a regular basis.
Lightly wiping a painted silicone bead with a damp cloth will only remove the paint.
Silicone will also stretch and contract, sometimes up to 25% of its original size. As paint does not share the same flexible characteristics, it is sure to crack and flake in areas of relatively high movement.
Can you make silicone paintable?
Many DIY bloggers will try to give away “trade secrets” and claim there are ways you can make paint stick to silicone. But unfortunately, for reasons mentioned previously, these simple tricks and hacks do not work in the long term.
Can you caulk over silicone sealant?
Decorators caulk is a great substitute for silicone in areas where waterproofing and excessive movement is not an issue (ceiling perimeters, skirtings, architraves etc). Applying caulk in these areas is a great way of filling gaps and taking your eye away from insightly joints, plus you can paint over it.
So can’t you just caulk over silicone?
Well yes and no!
It’s a trick that many handymen and decorators use to get the job done quickly, get paid, and get the hell out of there.
However, this is not advisable.
As mentioned before, nothing will bond to silicone. Not even caulk. And while the painted surface may look great, the caulk can easily peel away from the silicone overtime.
The only possible way to get around this, is if the bead of silicone underneath is very thin. The caulk over the top needs to be wider than the silicone so that it sticks to the wall and the substrate next to it (i.e window frame, skirting etc).
While this works in some cases, most of the time, the caulk will eventually crack, leading to fractures in the paint work.
Can you prime silicone before painting?
A popular method mentioned by a lot of so-called professionals is to apply a shellac primer over the top of the silicone before painting.
What is Shellac Primer?
Shellac, in its original form is a resin secreted by lac bugs in the forests of India and Thailand. When dissolved in alcohol, it becomes the perfect primer to prepare problem surfaces for painting (i.e. existing oil painted surfaces, timber, old varnish, metal etc).
It’s also used as an effective stain block in areas where water marks, grease or nicotine stains are present.
Zinsser’s B-I-N shellac based primer is a popular choice used by many painters and decorators, and comes in either a spray form, or in a tin.
Can you apply Shellac Primer over silicone before painting?
Unfortunately no. As with the caulk, the painted finish may look good. But with a light wipe, the shellac primer will easily come away from the silicone.
This video on the painting and decorating Youtube Channel demonstrates perfectly why priming or caulking silicone before painting is a terrible idea.
So if there is no effective way to paint over silicone, what’s the solution if you want a perfectly painted joint?
The answer is to remove the silicone altogether, caulk the joint, then paint it.
Yes it’s more work and will take a lot longer, but the finish and long term results will be worth it.
If you want to find out the best way to remove silicone, read our article “How To Completely Remove Old Silicone - The Pro 4 Step Method.”
Summary
You cannot paint over silicone.
Caulking or priming the sealant with shellac is not advisable. Even if at first the finish is flawless, it will fail over time.
If you have a sealed joint that you want to paint (for example, along the top of skirting or around a window frame), you are always best to remove the existing silicone first, caulk the joint, then paint. This will give a longer lasting, superior finish.
Remember, if a jobs worth doing, it’s worth doing properly!