New Capped Composite Decking Advances Again

What Do You Need To Know About Capped Composite Decking Boards?

The new capped stock composite is designed last longer and hold color better.

The latest advancement in the composite deck category is the concept of capped boards. Its also called capstock decking.

These are essentially composite boards with the wood plastic core but have an impervious layer of textured plastic around the board.

This skin now covers just the top or three sides with the bottom side uncovered and free to breathe.

The Advantages

The concept of encasing the more vulnerable wood fiber plastic core makes good sense.

These durable skins can really be made to stand up to sun, staining, mold, bacteria and all kinds of other environmental predators.

They can also be textured and colored for quite stunning visual effect. All of this is good and are things consumers have always wanted. They are more expensive though and some of the higher end capped composite decking gets into the $4.50+ per foot range.

Some of the hardwoods can be purchased for this range and they are the real thing and almost indestructible. And there is one I really like.

The Disadvantages

Ends of boards could expand and mushroom.

This is what many builders unfortunately found out in the very early days of this new material. It seemed that the more the board was encapsulated, the less it could expand if water was absorbed at the exposed ends.

With the older style boards, water could be absorbed all over and the board would expand widthwise and lengthwise freely and then shrink when dried out.

But especially with boards that were covered on all four sides, the ends of the boards were mushrooming when they got wet.

Imagine the wood core is like a straw and sucks in the moisture if the end gets wet but there is no where for the expansion pressure to escape, except out the ends of the boards. Consequently, there were some horror stories of boards expanding sideways at the ends. And worse yet, they never went back to normal.

Now it is quite possible that the phenomenom is greatly reduced if the board is only covered on the top surface and/or the sides.

But certainly this is why you will see now that the capped composite decking always has an unsealed bottom and usually partially unsealed sides as well.

Clearly, the attempt is to stop this from ever happening again and allowing the board to breathe and expand when wet.

Still A Big Improvement

The open bottom that lets the board breathe and move seems to be working.

Despite these early issues, I think as long as you are aware of what caused the original problem and can satisfy yourself that the open bottomed boards are able to allow for explansion in the event the ends get wet, you will be fine.


There you have it. A nutshell on the good and what was not so good on capped composite decking. If a composite board is not your preference there are many other materials to choose from.

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