When choosing a silicone roof coating, one of the most important factors to understand is solids content. While both high-solids and low-solids 100% silicone roof coatings provide excellent waterproofing and UV protection, they perform differently during application and over the long term.

In this article, we’ll break down the key differences, advantages, and disadvantages of high-solids silicone (GacoFlex S4200) versus low-solids silicone (GacoRoof GR1600) so you can choose the best option for your roof.

What Does “Solids Content” Mean in Silicone Roof Coatings?

Solids content refers to the percentage of coating material that remains on the roof after curing.

• High-solids silicone leaves more material behind, creating a thicker membrane in fewer passes.

• Low-solids silicone contains more solvent, so the cured membrane is thinner per coat and may require additional material to reach the desired thickness.

Both types are still 100% silicone, but their application characteristics and performance differ.

High-Solids 100% Silicone: GacoFlex S4200

Pros of GacoFlex S4200

Thicker Coverage per Coat

High-solids silicone builds film thickness quickly, allowing contractors to achieve required mil thickness with fewer coats.

Excellent Ponding Water Resistance

Like all silicone coatings, S4200 is unaffected by standing water, making it ideal for flat and low-slope roofs.

Long-Term Durability

The thicker cured membrane provides enhanced resistance to weathering, UV exposure, and foot traffic.

Reduced Material Shrinkage

Since more solids remain after curing, there is less volume loss compared to low-solids coatings.

Cons of GacoFlex S4200

More Difficult to Apply

High-solids silicone is thicker and can be harder to spray or roll, especially in cooler temperatures.

Higher Initial Cost

The upfront cost per gallon is typically higher than low-solids silicone.

Requires Experienced Applicators

Because of its viscosity, proper equipment and experience are important for consistent application.

Low-Solids 100% Silicone: GacoRoof GR1600

Pros of GacoRoof GR1600

Easier Application

GR1600 flows more easily, making it simpler to spray, roll, or brush—especially for smaller projects or less experienced installers.

Smoother Finish

The thinner consistency allows for easier leveling and a more uniform appearance.

Lower Initial Cost

Low-solids silicone coatings generally have a lower cost per gallon.

Excellent Waterproofing

Despite lower solids, GR1600 still provides outstanding waterproofing and UV resistance once proper thickness is achieved.

Cons of GacoRoof GR1600

Requires More Material

Because of solvent evaporation, more product is needed to achieve the same dry film thickness as a high-solids coating.

Longer Application Time

Multiple passes may be required to reach manufacturer-recommended mil thickness.

More Shrinkage During Cure

Higher solvent content means more volume loss as the coating cures.

Side-by-Side Comparison

Feature	GacoFlex S4200 (High-Solids)	GacoRoof GR1600 (Low-Solids)
Solids Content	High	Lower
Film Build	Thick per coat	Thinner per coat
Application	More difficult	Easier
Material Usage	Less overall	More overall
Cost per Gallon	Higher	Lower
Ponding Water Resistance	Excellent	Excellent
Ideal For	Large commercial roofs, experienced crews	Smaller projects, ease of application

Which Silicone Roof Coating Is Right for You?

Choose GacoFlex S4200 if:

• You want maximum durability and thickness

• You’re working on large commercial or industrial roofs

• You have professional application equipment and experience

Choose GacoRoof GR1600 if:

• Ease of application is a priority

• You’re working on smaller projects or maintenance coatings

• Lower upfront material cost is important

Both products deliver the core benefits of 100% silicone roofing—including waterproofing, UV resistance, and long service life. The right choice depends on your roof size, application method, and performance expectations.