Maintenance-Free Exteriors: Installing Composite Deck Boards

By Bruce W. Maki, Editor

Introduction:

A lot of treated-wood decks have been built in the last couple of decades, and many people have become fed-up with the need to frequently seal their wood deck surfaces. Many people don't bother to seal their decks at all, and after a few years they begin to wonder why their deck surfaces look so dreary, tired and weathered. I've seen pressure-treated deck boards begin to rot after a decade of rain washing off a nearby roof, perhaps because the frequent water-torture dissolved some of the preservative chemicals.

There is a big movement towards alternatives to treated wood for deck surfaces. There are many brands of synthetic or composite decking available. This list of web links shows some.

The 6' x 24' deck extension after the framing had been completed and some of the handrail posts had been installed.

The older part of the deck has already had its deck boards replaced, by other people.

This is a TrapEase™ brand of screw that is meant for fastening composite decking material. The package claims that there is no need for pre-drilling and there will be no "mushrooming" around the screw head. That was not my experience.

I used a big, low RPM drill to drive these screws. My impact driver did the job but was getting rather warm from all the activity, so I decided to try a regular corded drill.

Mushrooms On Deck:

At first I just drove in the screws without pre-drilling. It seemed that the screw heads would stick up slightly and leave a small mound around the head. This mound is called a "mushroom" So I pre-drilled some holes with a drill-countersink combination bit.

When I pre-drilled the holes the screws sank in just fine, perhaps a little too deep.

By placing a straight-edge over the screw head you can see the difference. The pre-drilled screw heads were sunk fine with barely any visible mushrooming.

But without pre-drilling it was another story. You can see the mushrooming, because there is a gap under the straight-edge. But even worse, these screws just spun once they got this deep, as though they had stripped out the wood underneath. That did not give me a feeling of confidence, though they seemed to hold okay.

After trying a few screws without pre-drilling, I decided to pre-drill all the remaining screws. This added to the installation time, perhaps doubling the time needed to fasten the boards.

Obstructions:

Where the deck boards met a handrail post I laid the board next to the post and marked the notch. I also marked the end cut so the board would overhang the end by one inch after a facing was installed on the stair riser. The home owner wants skirting installed around the deck to conceal the space underneath, and the plan is to use this same material for skirting.

Like treated Southern Yellow Pine deck boards, these composite boards have quite a curvature. Unlike yellow pine, this material is very easy to straighten as it's being fastened. I just pushed on the board with my knee.

I used nails to give me the required space between boards. The instructions call for a 1/8 inch gap at the sides and ends. I used thin siding nails most of the time, but also some thicker 12d nails to provide a greater space to correct the curvature problem that was started by the guys that installed the first batch of deck boards.

To straighten out the curvature, I placed a scrap of deck boards at each end, separated by a thin nail from the previous board, and snapped a chalk line (red arrow) between the edges of the boards.

In the middle of the deck, there was an obvious gap between the chalk line and the edge of the new board. Consequently, I used larger nails for spacers in the middle of the deck. By doing this over several rows of deck boards I was able to correct most of this curved deck board problem without creating gaps that were obviously uneven.

More Gap Issues:

Since the deck was almost 24 feet long, and the boards were 16 feet long, I had to pay attention to the way the boards "broke", that is, the pattern of end gaps between boards. It looks stupid if all the end gaps line up in a row.

There are many ways to handle this problem. You can use random lengths of decking to create a random patterns of end gaps, but with manufactured decking that is impractical. I alternated the gaps (red arrows) by starting one row with the long board on the left edge, then the next row would have the long board against the right edge of the deck.

Break Down:

It would be entirely possible (and logical) to use a full 16' board to extend from the edge of the deck to the exact center of a joist, since 16 feet would land right on a joist center. BUT... not my luck.

After framing this deck extension the homeowner told me about wanting to use this same decking for a skirting material to conceal the space below the deck, and he also decided to relocate the stairs to a different side of the deck. Suddenly if I allowed a full deck board to break on a joist I would not have enough overhang at the edge to cover the skirting (one inch thick) and provide the desired one inch nosing overhang that is normally used on stair treads.

So the logical solution is to let the deck board break one joist closer to the edge, and cutting each board shorter by about 14 inches. But the 14 inch scrap would be wasted. So I decided to let the deck boards break two joists closer to the edge, thus cutting each board shorter by about 30 inches. Since this deck is about 20 to 24 inches above the ground, these off-cuts could be used for the skirting material with only a few inches of wasted material.

If I could've used exact 16 foot boards, I could also use a board that was just less than 8 feet for the remainder of the row, which meant that a full board would give me two short pieces. This was the plan... use 3 boards for two rows of decking. We had not ordered much extra decking. It's common to buy about 10 percent extra material for a job like this, but with expensive composite decking that becomes undesirable. Besides, you don't need to discard any bad boards, right?.

But when I cut the long boards shorter, the next board in the row needed to be about 10 feet long, leaving a 6 foot off-cut. Knowing that I would be using this deck material for the stairs, I set these 6-footers aside. It's amazing how a small oversight can cause complications later, unless you have money to burn and don't mind wasting expensive decking material.

At this point I was down to the last two rows of decking, and I had one full-length board remaining and numerous pieces around 6 feet long. There are five handrail posts to notch around, and both rows of decking need to be notched.

I cut a deck board to length and laid it against the posts, then I marked the edges of the post on the deck board.

I measured the distance from the previous board to the deck post, in each location.

Then I measured across the deck board to mark this dimension. It's easy to get turned around here and draw this mark measured from the wrong edge, resulting in a notch that's way too deep, so stop and think about things before you plunge into cutting notches.

I cut the notches with a jig saw. This material cuts just like wood, with some minor differences.

The instructions say to leave a small gap around posts.

The decking after completion. The outer edge (far left) was made from 4 boards ranging in length from about 6 to 8 feet.

I was lucky that the final row of decking did not need to be ripped narrower. The homeowner measured the width of the deck extension, and pointed out that with small gaps between boards we should be able to get the desired overhang (about 1˝ inches) at the final board by using only full-width boards.

If I had needed to rip the final board, it would have been necessary to round-over the cut edge with a router or router table.

I understand that some people start installing deck boards at the outer edge of the deck and work inwards, towards the house. If the final board needs to be ripped narrower, then the cut can be concealed next to the house (under the edge of the siding) or perhaps it just won't be very noticeable.

Trimming The Ends Of The Boards:

Sometimes the best way to install decking is to simply let the boards run a bit too long, then cut the ragged ends later.

I marked the ends for an overhang of just over one inch (I would prefer more, but the other guys didn't leave enough) then snapped a chalk line and cut the boards with a circular saw. After trimming the ends of the composite deck boards I used a belt sander to round over the sharp corners.

Later we'll install this same composite material for skirting to conceal the area below the deck. Read about installing deck skirting.

The completed project, after the stairs, skirting and handrails had been installed. This is such an improvement over pressure treated lumber.

Copyright © 2005  HammerZone.com

Written May 12, 2005
Revised June 3, 2005