Does Composite Decking Warp?

Image of a composite decking material but Does Composite Decking Warp?Warping means to become twisted or bent out of shape, mostly resulting from the effects of dampness or heat. Only wood decking was available in the past, and you had to use one species of wood for a given plank of timber. With the advent of composite timber, there are lots of options for decking. Since this is a relatively new concept, you may hesitate and wonder, does composite decking warp? I will clear the air on this and enlighten you on composite decking ABCs as you read on.

Composite decking warps, but to a lesser frequency and extent than wood decking. Different types of composite decks have varying warping tendencies depending on their constitution, synthetic binders, joist spacing, composite plank density, and the engineering behind their manufacture. There are also environmental aspects such as weather that influence warping and human factors like quality of care and maintenance meted out to the deck.

It clear that warping cuts across different types of decking material and composite decking materials are not an exception, even so, the degree of warping vary depending on the specific composite decking types. Stay with me as a dig deep into some of the aspects of warping in decks.

Types of Warping in decks

Composite decking warpIf it so happens, your composite deck will warp in one or more of the following five ways:

  • Bow

The deck remains flat in the middle but bends upwards on both edges. The shape, when visualized from the side, resembles a bow.

  • Twist or Wind

The wood turns inwards at both ends, resulting in a twisted shape, which often looks like a twisted ribbon.

  • Kink

This warp happens when the composite bends upwards on one side only, producing a shape that resembles an arm bent at the elbow.

  • Crook

This defect occurs when only one end of the plank is exposed to moisture, resulting, ironically, in a shape that ironically looks like a smile or the letter C.

  • Cup

The cup is when the sides of the composite planks deeply curve inwards towards the middle of the deck. This shape looks like a piece of paper with the long edges curved towards its center.

Causes of Warping in Composite Decking

  • Improper Joist Spacing

The joists are like the entire deck’s skeleton, playing a supportive role to the whole structure. It’s vital to put in the right number of joists with the right amount of spacing for even distribution of deck board weight. The arrangement and spacing of joists affect the structural integrity of the decking. Different deck designs require different joist spacing.

For residential decks, the spacing should not exceed 16 inches between adjacent joists’ centers, decking used for commercial purposes should not exceed 12 inches of spacing, for landings and stairs, you should tightly pack the joists as they carry heavier loads. Larger spacing than is recommended leads to stress on the decking boards, which ultimately leads to warping.

  • Plank Density

This point is rather straightforward as the denser the planks, the stronger the decking, which subsequently leads to improved warp resistance. Decks made from a mixture of high-density polypropylene and recycled hardwoods are denser and better than decks made from a mixture of softwood chips and high-density polyethylene; they resist flex and sagging between the joists.

  • Weather

Image of peeling wood paint but Can I Use Concrete Paint On Wood? Weather extremes like rain, sunlight, cold, dry, and wind impact negatively on unprotected composite lumber, causing the planks to warp, discolor, and weaken. When the composite structure is exposed to excess sunlight, the UV rays degrade both the natural and synthetic binders that hold together the structure leading to splitting and bowing of your deck planks.

Continual rain on your decking makes the planks damp and initiate rotting; this leads to warping and curving of the deck. Also, sudden shifts from dry weather to cold weather cause expansion and shrinking of lumber, which is a recipe for warping.

  • Constitution and Type of Composite Deck

The main ingredients of composite/synthetic decking are wood and plastic, most of which are recycled. But they differ due to the type of wood flour and plastic they are sourced from, e.g., softwood flour, hardwood flour, bamboo flour, polypropylene plastics, polyethylene plastics, etc. As a consequence, there are several forms of synthetic decking, including products that blend plastics with natural wood or bamboo fibers, plywood, solid PVC plastic products, solid composites consisting of 100% recycled plastics, among others.

The constitution and proportions of raw materials directly influence the tensile strength of the resulting composite plank. Improper constitution leads to weaker products that are prone to warping and breaking. Well constituted decks are efficient load bearers and resistant to warping, twisting, and sagging.

  • Poor Deck maintenance Practices

These are practices that advance the warping and splitting process of your deck planks. They include improper cleaning habits, like letting spilled water soak in the lumber instead of drying it with a mop, failing to fasten loose screws to the joists on the edges of your deck, using untreated planks for deck construction, and subjecting your floor to heavy loads. All of the above cause buckling, twisting, and deformation of composite planks.

Identifying Warped Composite Decking

If you are not sure whether your composite decking is warping, all you need to do is take a look at your decking surface. A warped surface has a wavy appearance in the initial stages instead of a flat outlook; if no intervention is taken, the warping progresses. The planks ultimately end up twisted and bent out of shape. 

When inspecting your floor, check for indented or bumpy planks and timber pieces that are coming apart from each other; if it so happens, then your decking is warped.

Now, how can you fix this? Read on.

How to Fix Warped Composite Decking

  • Getting Started

After identifying the warped composite planks, you need to assemble the appropriate tools and equipment to carry out the repair. If you are a seasoned user of a power saw, you’ll have no challenges doing this. However, if you have never done this before, you can seek help from a professional or a friend who handles power saws. Still, you can watch online videos on 

how to use power saws, and then you’ll be good to go; it’s not as hard as it may sound!

Image of a safety google for composite decking installationBelow are the equipment needed to fix warped composite decks:

  • Power saw
  • Replacement composite plank(s)
  • Screw gun
  • PPE (Earmuffs. Safety goggles, and safety gloves)
  • Tape measure
  • Crowbar/ wrecking bar

Once you’ve assembled the materials named above, you’re ready to fix your deck; all you have to do is follow the instructions below. Before you can begin, however, you must look under the deck. Under the deck, you will see the floor joists.

Even with composite decking, floor joists are wood, so identifying them will be easy. Floor joists are the support planks that run underneath the actual decking. If your materials are gathered, and you have identified the floor joists, you are ready to start.

  • Measuring The Decking Plank

First, take the tape measure and measure the thickness of a standard plank and the warped plank; ensure the measurements are accurate. The planks’ measurement will determine the cutting depth you will make with the circular saw; composite timber is generally 1″ deep. Following the above, set the cutting depth of your power saw to match the warped plank’s thickness (s).

  • Start Cutting

After setting the cutting depth of your circular saw, wear the safety goggles, earmuffs, and safety gloves. The PPE protects you from debris, sound pollution, and blisters in the palms. Power on your saw and start cutting out the defective plank. I advise you to make cuts along the affected planks’ length because it is convenient for splitting and prying them when need be.

Be careful not to hit the joists with your circular saw as this will only lead to further damage to your deck; further damage means more repair work and higher cost. Joists are wood planks that run parallel beneath the decking surface, providing support to the floor.

  • Prying

If all goes as above, you should end up with a straight cut through the length of the warped plank; this needs a crowbar to pry. Take the crowbar and insert firmly between the split composite plank and then force them apart. Even for a cut that is not deep enough, the crowbar 

will still pry the plank for easy removal.

  • Removal of The Plank

Once you have pried the composite deck, you can now remove it. Using the screw gun, move along the plank line, removing each screw that connects it to the joist. After unfastening all of the screws, remove the plank by lifting it off entirely. If you split it cleanly, you can now measure all of its dimensions easily. It is essential to know all the dimensions of the composite plank so as to know what size is needed for replacement.

If it’s too damaged, use the measurements of one of the planks that are in good condition on the deck. For emphasis, this measurement has to be accurate so that you can get a replacement plank that perfectly fits; otherwise, you might end up with a replacement that is overlapping, too short, or too thick.

  • Cut a New Decking Board

Cut out a new piece of decking plank to fit snugly in the cut-out segment. Cutting is done after getting the correct measurement of the original deck plank. You can get a new piece of composite board from a hardware store or order online. Nick off the excess length and overlaps, and you should be careful when doing this so that your plank fits in well. After cutting, you need to finish the new plank so that it looks similar to the rest of the deck.

  • Finishing the plank

Finish or stain the new plank before installing it into position. Use the same kind of composite in the patch as is found in the rest of your decking. Unless you are replacing the entire deck, using a different type of lumber will cause the patched sections to stand out from the rest of the deck surface; So the paint or stain should match the rest of the deck’s color. After finishing, let the plank dry out before reinstalling it.

  • Installing the new board

Position the new, finished replacement composite, ensuring the gap between adjacent boards is even. Use the screw gun to secure the new board on the deck; start by drilling two pilot holes into the plank at each end, around a three-quarter inch from the edge. Also, drill pairs of pilot holes at any joist that the new plank spans. After the above, fasten the replacement composite on the deck using 3″ screws driven through the established pilot holes. 

Repeat the above instructions and steps for all the warped pieces of the composite. That’s just it! Your warped decking is now fully reconstituted for a new look.

Watch the video below on fixing some of warping decking boards:

What to Remember

It is essential to value your safety when fixing warped composite lumber. As you may have noted from the steps above, a circular saw is needed to remove warped pieces of plank. Before starting the process of repairing warped composite decks, contemplate whether you are comfortable handling power tools. If you are not, seek the services of a professional or even an experienced friend in that regard. If you are well conversant with power tools, don’t forget to put on your safety goggles, safety gloves, and earmuffs when undertaking this procedure. Fixing a warped deck is simple, so long as you follow all the discussed steps in order as they are all important.


We have looked at many aspects of decking which I hope will be beneficial to you especially if you own or looking to in stall a deck. Going back to ur subject today…

Does Composite Decking Warp?

They do! Actually, all composite decking warp, but they do so at different rates depending on numerous factors as explored in this article. The secret to making your decking last longer without warping lies in the application of the desirable maintenance practices and the prudence to install the right decking for your situation. Remember situations vary; one who lives in a predominantly sunny location requires a different composite decking from one who resides in a rainy region.

With wise and sensible choices of composite decking, coupled with good care, the structure will last a multigenerational lifetime.

Image of a woodworker wearing hearing protectors for woodworking

Tyron Otieno

Tyron is an avid woodworker and writer. He founded this website to help other woodworkers, whether hobbyists or professionals by sharing his knowledge and experiencie after a decade of woodworking.