Silicone? Like in computers? Not quite! Silicone polymers or polysiloxane, are compound mixtures of long polymer strands. These strands contain silicone, and usually some organic compound (such as rubber). These can then be used in a variety of applications. This can include medicine, adhesives, lubricants, oils, cooking utensils, electrical, thermal, sealants, and insulation. Some common ways silicon products tend to manifest are silicone oils, greases, silicone rubbers, resins, and silicone caulk. Today’s focus is on the caulking application.
Silicone-Based caulking products are normally used in bathrooms and outdoors to seal and waterproof surfaces, corners, and crevices. This is, in part, due to its superb ability to bead and resist infiltration by water. That is to say, silicone caulking is very hydrophobic. This makes it great for places like tubs and sinks, or even uses in sealing decks and waterproofing your insulation. It’s also used in joint compound, as well as adhesive weatherproofing for things like retaining walls, to help resist erosion moving the features. These are all well and good, but this also means something else: silicone becomes a nightmare to paint.
Painting Silicone 101 – Drawbacks and Headaches:
Paint won’t stick to caulk for the same reason mildew won’t stick to it: it’s not very porous. Add to that, silicone actually cures by absorbing ambient moisture, meaning that it’s always saturated at its base level. In addition, the nature of the polymerization process makes polysiloxane very, very tight, in terms of actual bonding. This creates that smooth, almost laminated feel. This slippery, tightly woven, and saturated polymer is paint’s worst nightmare.
Paint simply will not stick to it. The paint will bead on the surface, and be washed off with the next shower, or simply fall away once dry. Though you wouldn’t be using water-based paints in a shower, this is also true for oil-based as well. For that reason, most professional painters usually elect to paint before applying the caulking to said surface. Most will also warn of these pitfalls when being requested to paint over caulk.
How to get it done: Tips and Tricks
- Denatured Alcohol: This will actually help break up some of those long polymers that have oxidized on the surface, This will allow you the ability to treat the silicone with primers. You might need several passes. Also, be aware that this will degrade the caulking, but that’s what this next step is for.
- Siliconized Acrylic Latex Caulk: A thin layer over that caulk you just denatured will allow you the surface you need to paint, without losing the benefits of the properties contained within your 100% silicone underneath! for best results, a nice bead, immediately passed over with a masonry brick joiner will do wonders.
- Oil-Based Primers (Two Coats): Usual rule of thumb with primer is you wanna lay it on as little as possible to allow the paint the best chance of sticking. The same is true here: use multiple coats and slowly build up on the caulking to allow that paint-able surface. Transparent primer’s gonna work best here, for sure. You don’t want to use an opaque colored primer or even an all in one, as the coat’s probably going to look really caked on.
- Oil-Based paints (Two coats): Light and slow. make sure the paint has time to absorb into the only real foothold it has. Observe the directions on the paint can very carefully, and take extra time to allow curing to begin. Working in this way, you can ensure that the caulking and the paint layers don’t simply slide off of each other.
I would avoid using the shower, or anywhere water would pool for that matter, before testing a small area with some running water. That way, you can see if you need to start over. Some people also suggest removing the original caulking all together if you’re having too many issues. Applying alcohol before the curing process is complete actually interrupts it and creates a very “pockmarked” effect. However, this might also not be aesthetically pleasing, unless you wanted to also use the siliconized acrylic. Good luck with your caulking and painting! I’m sure it will look gorgeous.