How to Pick Good Railing Logs: Reading a Log for Defects

You are standing in front of a stack at a small mill, or a brush pile a neighbor said you could pick through, and you have to decide which logs come home and which stay. The species is already settled. What is not settled is whether these particular sticks will make a railing that stays tight and straight, or one that twists, opens up, and fights you at every joint. Picking the wrong log is a mistake you carry through the whole build, because a flaw in a raw log does not improve once it is peeled, dried, and tenoned. This is the part that the species pages and the where to buy guide assume you already know how to do. Here is how to actually read a log before you commit to it.

A note before the pile: if your plan starts with felling trees yourself, that is dangerous chainsaw work and outside what this guide covers. Hire a qualified feller if you are not trained for it. Everything below assumes the log is already down and you are judging it as a buyer.

Straightness, Sweep, and Crook

Sight down the length of the log the way you would sight a board. A railing reads as deliberate when the structural members run reasonably true, and it reads as accidental when they wander. Two kinds of bend matter here. Sweep is a single gentle curve along the log, like a very long bow. Crook is a sharper or more local kink. A little sweep can be fine, even charming, on a top rail where character is welcome. A crook in the middle of a post is a problem, because a post has to stand plumb and carry load straight down.

Match the defect to the part. The longest, straightest stock should be set aside for posts and top rails, where the eye follows the line and the joinery has to land square. Shorter pieces with more character can become balusters, where a bit of wander is part of the look and the peeled log style actually trades on it. Rejecting a whole log for one bad section is wasteful when the clear part below the kink is exactly the baluster you need.

Taper

Every log tapers from butt to tip, narrower as it goes up the tree. That is normal, and managing it is part of log work. What you are judging is how much, and whether it is even. A steady, gentle taper is easy to plan around. A log that flares hard at one end, or that necks down sharply, gives you a short usable run and a lot of waste.

Taper also drives proportion. If you want posts and a top rail that look like they belong together, you need pieces whose diameters relate sensibly, which is the whole argument of the diameter and size guide. Pick logs at the pile with the finished assembly in mind rather than grabbing whatever is on top, because a stack of wildly mismatched tapers turns into a railing that never quite balances.

Spiral Grain

This is the defect most buyers miss, and the one that bites later. In a straight-grained log the wood fibers run roughly parallel to the length. In a spiral-grained log they wind around the trunk like the stripe on a barber pole. You can often see it on a peeled or partly peeled surface as long lines that angle steadily around the log instead of running with it, and on a checked log the checks themselves may follow that spiral.

It matters because of how wood moves as it dries. The USDA Forest Products Laboratory Wood Handbook describes spiral and other cross grain as a source of distortion: wood with grain that does not run true tends to twist and warp as moisture leaves it. A spiral-grained post can wind itself out of plumb over a couple of drying seasons, dragging its joinery with it. Some species and some individual trees are worse than others. When you find pronounced spiral grain, set that log aside for short, low-stakes pieces or pass on it, and never put it in a post.

Checks and Shake

Logs crack as they dry, and not all cracks mean the same thing. A check is a separation along the grain that opens as the outer wood shrinks faster than the core, which the Wood Handbook attributes to the uneven shrinkage of drying wood. Checks are normal and expected, and our checking versus cracking guide walks through which ones are cosmetic and which are not. A few checks on a log at the pile are not a reason to reject it. They are what wood does.

Shake is different and worth knowing by name. Shake is a separation between the growth rings, a crack that runs around the ring rather than out from the center, and the Wood Handbook lists it as a defect that is present in the standing tree rather than something that develops in seasoning. A log with ring shake can have a hidden weakness you only discover when it splits apart in handling or refuses to take a clean tenon. Look at the cut ends. A crack that follows a growth ring in a curved arc, especially near the center, is a warning. A crack that runs straight out from the middle is an ordinary radial check.

Heart Center and Ring Orientation

Look hard at the end grain, because it tells you about the log’s future. The pith, the small dark center where the tree started, is the most unstable wood in the log. A log sawn or grown so the pith sits dead center will tend to check outward in a fairly even, predictable way as it dries. That is the usual case for a round railing log, and it is fine.

What you want to notice is how far off center the pith sits and how the rings are spaced. Wood shrinks differently in different directions, roughly twice as much along the rings as across them according to the Wood Handbook, so a strongly off-center pith means one side will move more than the other and the log is more likely to bow or check unevenly. Tight, even rings generally mean slower growth and denser wood. Very wide, uneven rings can mean fast, weaker growth, though this varies a great deal by species. You are not grading lumber to a standard here. You are just stacking the odds toward logs that will dry quietly.

Sapwood, Heartwood, and Rot

On the end grain you can usually see two zones: a lighter outer band of sapwood and a darker inner core of heartwood. The distinction matters outdoors. The Wood Handbook is clear that the sapwood of essentially all species has little to no decay resistance, while what natural durability a species offers lives in its heartwood. A railing log that is mostly sapwood, with only a thin heart, is starting from a weaker position against rot no matter how good the species name on the tag. For exterior work, favor logs with a generous heartwood core, and lean on the drying and seasoning guide and a sound finish to protect what sapwood remains.

Then hunt for the rot itself. Press your thumbnail or a knife tip into the surface and the ends. Sound wood resists. Wood that feels soft, spongy, punky, or crumbles is already decaying, and decay does not stop because you brought the log home. Look for discoloration that does not match the normal heartwood color, for streaks, and for the soft, stringy or crumbly texture of advanced decay. A log that smells strongly of mildew or mushrooms when you put your nose to a fresh cut is telling you something. One soft spot can sometimes be cut away. A log that is soft through its core is firewood.

Knots and Insect Signs

Knots are where branches were, and they are not automatically bad. A scatter of tight, sound knots is part of a log’s character. What you are watching for is clusters, big knots right where a tenon or a joint has to go, and dead or loose knots that have started to separate from the surrounding wood. A knot exactly where you need to bore a mortise can wreck an otherwise good post, so picture your joinery on the log before you buy it.

Insects leave a clear signature once you know it. Small round or oval holes in the surface, fine sawdust-like frass at the base of a hole or in the bark crevices, and tunnels or galleries visible on a cut end all point to borers or other wood-boring insects. Bark left on a log shelters insects and holds moisture against the wood, which is one reason the drying and seasoning guide treats early debarking as step one. If you find active galleries or fresh frass, that log can carry the problem into your other stock. Either pass on it or plan to deal with the infestation before it sits anywhere near the rest of your wood.

None of this guarantees a perfect railing. Even a carefully chosen, well-dried log will still check and still move a little, because that is the nature of round wood. What good selection buys you is smaller, livable amounts of it: less twist, fewer surprises at the joints, and a railing whose flaws are the kind you planned for rather than the kind you find the first winter.