Cumaru Decking Installation, Fastening Systems, and Expansion Gap Best Practices

 

Cumaru’s density and natural oils help it handle outdoor exposure better than many decking materials, which is why it’s a strong choice if you’re planning to build a deck that will be heavily used for many years. That said, it’s important to know that installing cumaru decking is different from working with softwood or composite boards.

One of the first things you’ll notice about cumaru is that it’s an extremely hard wood. On the Janka hardness scale, it’s rated 3,540 lbf, which makes it much harder than maple (1,450 lbf) and oak (1,360 lbf). Because it’s so dense, you’ll need to pre-drill your screw holes and use stainless steel fasteners when installing it. You’ll also want to keep in mind that the wood will naturally expand and shrink over time. 

Don’t worry, though. Once you understand a few key steps, installing cumaru decking becomes much easier. This guide will walk you through the basics so you can approach your project with confidence. 

Prepare the subfloor 

Check your subfloor and make sure it’s level and clean. With a laser level, you can spot any uneven areas so you can fix them before installing the decking. 

When you install the framing, make sure the crown faces upward. Most lumber has a slight hump, sometimes around ⅛ inch or more. If you place the framing with the hump facing down, water can sit on the surface and eventually cause the boards to warp. 

Important: Avoid installing cumaru decking directly on concrete. Concrete holds moisture, and without proper ventilation beneath the boards, trapped moisture can cause cupping or crowning over time. 

Install the decking boards 

When installing the deck boards, start at the outside edge and work your way inward using the recommended fastening system. As you go, take a moment to check each board for any damage or defects before securing it in place. 

Use the right tools 

Cumaru wood is very hard, so regular saw blades and drill bits can struggle when you try to cut or drill it. You need stronger, high-quality tools such as:

·        Carbide-tipped saw blades for cutting

·        Brad-point or Forstner drill bits for pre-drilling screw holes 

Using the right tools will make drilling easier and make the cuts cleaner. 

Seal the ends

When you cut a cumaru deck board, the freshly cut ends are vulnerable. If you leave them untreated, the wood can dry unevenly and develop cracks at the ends (called end checking). 

To prevent that, you should immediately seal the cut ends with a wax-based end-grain sealant. This slows how quickly moisture leaves the wood and helps keep the board stable so it doesn’t crack or move too much. 

·        A quart of sealant covers about 500 sq ft of decking boards.

·        You only apply it to the cut ends, not the whole board.

·        If any gets on the face of the decking, wipe it off right away so it doesn’t stain the surface.

What are the best fasteners to use? 

You should always use 305-grade or higher stainless steel screws when fastening cumaru boards. Anything less will corrode and stain the wood over time. Low-grade screws will also fail much earlier. 

Plan for natural wood movement 

The right joist spacing depends on the thickness of your cumaru decking boards. Use the guide below when planning your framing: 

Decking size	Maximum joist spacing
1x4	16″
1x6	16″
5/4x4	24″
5/4x6	24″
2x4	32″
2x6	32″

 

When installing standard or pre-grooved boards, leave the minimum recommended gap between boards to allow them to shrink slightly as they acclimate after installation. 

If you’re using tongue-and-groove boards, they can be installed tightly without leaving a visible gap. 

On average, cumaru boards may shrink about: 

·        1/8 inch on 4-inch boards

·        1/4 inch on 6-inch boards 

Actual movement can vary depending on moisture content, climate, and exposure to sun and rain.

Need materials for your cumaru deck? 

If you’re getting ready to build a cumaru deck, having the right materials and fasteners will make installation much smoother. At ABS Wood, you’ll find Grade-A cumaru decking along with reliable stainless steel fastening systems, so you can complete your project with confidence. 

You can order materials directly through our website or contact us for a custom quote at 1-877-722-7473 (1-877-7ABS-IPE) or 352-508-4990. You can also leave a message through their site if you’d like guidance for your project.

Source:https://abswood.com/cumaru-decking-installation-fastening-systems-and-expansion-gap-best-practices/