Product Description
Crushed Surfacing Top Course (CSTC) is a crushed rock product that contains minus (also known as fines). This state-spec gravel is made up of rock pieces up to 5/8″ in diameter. The fines allow the product to pack down tightly and stay in place when compressed.

CSTC is manufactured at Kapowsin Quarry from quarried basalt rock. It is fractured and angular.

CSTC meets or exceeds WSDOT Standard Specifications 9-03.9(3) for grading:

• 99–100% passing the ¾” screen
• 80–100% passing the ½” screen
• 46–66% passing the #4 screen
• 8–24% passing the #40 screen
• up to 10% passing the #200 screen

Our CSTC also meets or exceeds all quality test requirements for fracturing, sand equivalency, abrasion, and degradation.

Product Applications
Like the name suggests, top course is typically used as a top layer on gravel driveways and parking lots. It’s often placed on top of Crushed Surfacing Base Course (CSBC).

CSTC can be used on its own to build driveways used by light cars or equipment. More often, it’s used in combination with CSBC to create sturdier roads.

Similar Products
CSBC (1¼” Minus) is often used as a base material on top of which CSTC is spread. CSBC can also be used on its own on roads used by heavy equipment.

Variations of CSTC include ¾” Shoulder Rock and Maintenance Rock.

Helpful Tips
If you’re stumped about whether to use clean or minus material, check out our “Clean v. Minus” guide.

You can also refer to our popular article and video, “Choosing the Right Rock: Comparing Crushed Rock Sizes and Types.”

About Top Course
Top Course refers to a top layer of material that works with a base course to create sturdy driving or paving surfaces. It’s also referred to as “surface course” or “keystone.” Washington Rock’s top course is a 5/8″ minus product that is made to a specification dictated by the Washington State Department of Transportation (WSDOT).

Product Description
Crushed Surfacing Base Course (CSBC) is a crushed rock product containing minus (also known as fines). It’s a state-spec gravel made up of rock pieces up to 1¼” in diameter. The fines help the product pack down tightly and stay in place when compressed. CSBC performs well in wet conditions and provides stability in muddy conditions.

CSBC is manufactured at both Kapowsin Quarry (5990-1) and King Creek Pit (5990-3). The Kapowsin Quarry version is made from quarried basalt rock while the King Creek Pit version is made by crushing streambed rock. Both products are fractured and angular.

CSBC meets WSDOT Standard Specifications 9-03.9(3) for grading:

• 99–100% passing the 1¼” screen
• 80–100% passing the 1″ screen
• 50–80% passing the 5/8″ screen
• 25–45% passing the #4 screen
• 3–18% passing the #40 screen
• up to 7.5% passing the #200 screen

Our CSBC also meets or exceeds all quality test requirements for fracturing, sand equivalency, abrasion, and degradation.

Product Applications
Like the name suggests, base course is typically used as a base layer for gravel driveways and parking lots or as a subbase for paved surfaces. It’s often topped with Crushed Surfacing Top Course (CSTC).

CSBC is an ideal gravel for roadways that are busy or are used by heavier equipment. CSBC can also be used as a structural base for retaining walls.

Similar Products
1¼” Minus Road Base (Grade 1 Tailings) (5961-1) is a more affordable, non-spec alternative to CSBC.

CSTC (5/8″ Minus) is a good choice for driveways or paths used by cars and light equipment.

We can also manufacture 1¼” Minus Shoulder Rock.

Helpful Tips
If you’re stumped about whether to use clean or minus material, check out our “Clean v. Minus” guide.

You can also refer to our popular article and video, “Choosing the Right Rock: Comparing Crushed Rock Sizes and Types.”

About Base Course
Base Course refers to a bottom layer of material that provides foundational support to driving surfaces or structures. It’s usually installed on top of a prepared subgrade (earth layer) or subbase material. It provides support to the “surface course,” which is the topmost layer of gravel and/or asphalt and concrete. Both of our base course products are 1¼” minus products. Our Crushed Surfacing Base Course (CSBC) is made to a specification dictated by the Washington State Department of Transportation (WSDOT) while our tailings are a more affordable non-spec product.