To screw down Durock cement board effectively, you must use specific fasteners—either specialized wood screws or hot-dipped galvanized roofing nails—driven through the panels into the subfloor while the underlying adhesive (thin-set mortar) is still wet. This ensures a strong, durable bond crucial for tiling and other finishes.
How to Properly Fasten Durock Cement Board
Properly fastening Durock cement board is a critical step in preparing surfaces for tile installation in bathrooms, kitchens, and other moisture-prone areas. This process involves more than just driving screws; it requires careful preparation, the right materials, and adherence to specific spacing guidelines.
Choosing the Right Fasteners
The durability and stability of your Durock installation heavily rely on the correct fasteners. According to manufacturer guidelines, two primary options are recommended:
- CGC Durock Wood Screws: These are specially designed screws with corrosion resistance, often featuring a drill point and counter-sinking head for flush installation.
- Size: 32 mm (1-1/4 inches)
- Hot-Dipped Galvanized Roofing Nails: These nails are coated with a thick layer of zinc for superior corrosion resistance, essential in wet environments.
- Size: 38 mm (1-1/2 inches)
Both options provide the necessary holding power and resistance to moisture for a long-lasting installation. Using standard drywall screws or common nails is not recommended as they can corrode and fail over time, compromising the integrity of your surface.
Preparation Before Fastening
Before you begin fastening, proper preparation ensures optimal adhesion and a stable base:
- Prepare the Subfloor: Ensure your subfloor is clean, dry, and structurally sound. Remove any debris, dust, or loose materials. For wood subfloors, make sure they are flat and free of significant deflection.
- Apply Adhesive (Thin-set Mortar): Spread a layer of unmodified thin-set mortar onto the subfloor using a notched trowel. The thin-set serves as both an adhesive and a gap-filler, creating a solid bond between the Durock and the subfloor. This step is crucial for distributing load and preventing cracking in the tile above. For best results, use a high-quality thin-set recommended for cement board applications. Learn more about choosing the right thin-set at Tile Council of North America.
- Position Durock Panels: Carefully place the Durock panels onto the wet thin-set mortar. It's essential to:
- Stagger Joints: Offset the Durock panel joints from the subfloor joints to create a stronger, more stable surface.
- Fit Closely: Position the ends and edges of the Durock panels closely together, but do not force them. A slight gap (e.g., 3mm or 1/8 inch) is acceptable between panels to accommodate expansion, which will later be filled with thin-set and tape.
The Fastening Procedure
Once the Durock panels are positioned on the wet adhesive, proceed with fastening immediately to ensure the best bond:
- Fasten While Adhesive is Wet: It is critical to fasten the panels to the subfloor while the thin-set adhesive is still wet. This allows the fasteners to draw the Durock firmly into the thin-set, creating a strong mechanical and chemical bond as the thin-set cures.
- Spacing Guidelines: Fasteners must be strategically spaced for maximum hold:
- General Spacing: Place screws or nails every 203 mm (8 inches) "on center" (o.c.) in both directions across the entire panel. This means you will create a grid pattern of fasteners.
- Edge Spacing: Ensure fasteners are placed along the perimeter of each panel, typically 25 mm (1 inch) from the edges.
- Driving Fasteners:
- Screws: Use a drill with an appropriate driver bit. Drive the screws until the head is flush with the surface of the Durock, but avoid over-tightening, which can strip the screw hole or damage the board.
- Nails: Use a hammer to drive nails until their heads are flush with the surface.
- Check for Flatness: After fastening, run a straightedge over the surface to ensure the panels are flat and securely attached. Any proud fasteners should be driven flush.
Essential Tips for Durable Durock Installation
- Cutting Durock: Score the panel with a utility knife and a straightedge, then snap it along the score line. You may need to cut through the mesh on the back.
- Seam Treatment: Once all panels are fastened, apply fiberglass mesh tape over all seams between the Durock panels. Embed this tape in a layer of unmodified thin-set mortar, ensuring a smooth, continuous surface. This helps prevent cracks from forming in the finished tile work.
- Work Safely: Always wear appropriate personal protective equipment, including safety glasses and gloves, when cutting and installing cement board.
- Consult Manufacturer Guidelines: Always refer to the specific installation instructions provided by the Durock manufacturer (USG Durock) for the most accurate and up-to-date recommendations.
By following these detailed steps, you can effectively screw down Durock cement board, creating a strong, stable, and long-lasting base for your tile or other finishes.
