There are basically two types of caulk polyurethane and silicone. The basic difference is rather obvious. Polyurethane is based on organic materials while silicone is inorganic. But there is more to the differences than that.
What follows is the definition of both types, which one is better for your specific needs, and when to use either type of sealant for the situation at hand.
What is Polyurethane Sealant?
The reaction of glycol with an isocyanate creates the organic compound known as polyurethane. It is highly resilient in terms of corrosion and moisture. This makes it the perfect type of caulk for many surfaces and substances.
The main advantage is its flexibility, which allows it to successfully resist chemicals, corrosion, and moisture. Plus, its flexible nature means that it can expand and contract with the materials over time.
Polyurethane sealant will adhere to most surfaces including wood and plywood.
You can purchase polyurethane caulk that can be mixed and applied to most surfaces. Also, you can purchase the product in ready-mix form, but that is somewhat less flexible.
What is Silicone Sealant or Hybrid Caulk?
Silicone is created from inorganic compounds, so it does not have the inherent flexibility of polyurethane. However, it is far more resilient to ultraviolet or UV rays and can withstand more extreme changes in temperature.
Silicone is Durable
Another advantage is that silicone does not break down as quickly as polyurethane. This means that you can expect the caulk to last for up to 20 years while the polyurethane will only last for about 5 years under normal conditions.
Water-Resistance
As water-resistant as polyurethane is, silicone is better. Plus, you can purchase silicone caulk with fungicide that is perfect for bathrooms where mold or mildew might form.
Disadvantages of Silicone Sealant
Silicone will not adhere to wood properly and is not recommended. It works on most other surfaces including tiles, bricks, plumbing work, etc.
However, any areas used for food preparation is not recommended for silicone caulk.
Silicone is also expensive when compared to polyurethane sealant.
Silicone vs. Polyurethane Caulk: Which is Better for Your Job?
In terms of overall quality and flexibility of uses, silicone caulk is superior. Because you can use silicone caulk both outdoors and indoors as it resists UV rays. It also lasts at least four times as long as polyurethane caulk.
However, one substantial drawback is that silicone caulk cannot be painted. If you are going to repaint the surface, then polyurethane caulk is the one to choose. Even for outdoor jobs, the paint should provide the UV protection for the polyurethane so that it will last.
But what type of specific jobs should you use each type of caulk? The answer will depend on the circumstances and environment that the caulk will be placed.
When to Use Polyurethane Sealant?
You should choose polyurethane sealant in the following situations.
- For sealing wood: If the surface is wood, then you should use polyurethane caulk because it adheres to that material far better compared to silicone. And since most wood surfaces will be painted afterwards, it is a natural choice.
- Paint the sealant: If the surface is going to be painted over, then use polyurethane caulk. This means wood and most other materials are perfectly suitable to polyurethane as it will adhere to the paint.
- Fast curing: Another use is when you need to caulk something fast and UV rays or outdoor exposure is not occurring. Polyurethane caulk will dry in 24 hours. It’s also easier to clean up compared to silicone caulk. And when properly protected, you may get up to a decade’s worth of use out the polyurethane.
- Food Safety: Polyurethane sealant is not-toxic. Once cured, it does not react to oil, hydrocarbons, etc. and is food safe.
- Cost Effective: Polyurethane caulking is inexpensive. While it may not make a difference for small repair work, it maybe worth considering when constructing a new house or doing a large remodeling project.
Use polyurethane on wooden surfaces, surfaces that will be painted, and indoor areas where moisture is not that big an issue. While moisture-resistant, silicone is far superior in that regard.
When to Go for Silicone Caulk?
Silicone is generally superior to polyurethane in many different applications. Apart from wood, silicone adheres to most surfaces as well as polyurethane. And while you cannot paint over it, if the caulk is to be exposed, silicone is generally better.
Use silicone caulking,
- Outdoor Use: If the area is exposed to sunlight, the elements, or water, then silicone is far superior. It is more expensive compared to polyurethane, but it also lasts up to four times as long. And the silicone may last even longer if no sunlight is present.
- Better water resistance: Use silicone in areas where moisture is present. This includes the bathroom, shower, toilet, sinks, and plumbing. In addition, silicone is perfect for outdoor use as well. Windows, doors, cable openings from the outside, and the like.
- Cold Weather: Silicone caulk is also better in colder conditions when applying. While polyurethane tends to harden and become harder to apply, silicone tends to remain more flexible.
- Long-lasting: And if you are looking for caulk that lasts for a long time, silicone is the one to choose.
Choosing between silicone and polyurethane can be difficult depending on the circumstances, but in general silicone is better if the surface is not wood or will be painted over.
Dan Miller is a professional toolmaker with extensive experience in the metalworking and tooling industry.
An avid DIY enthusiast and passionate hobbyist woodworker, Dan shares his expert knowledge here.