# Wood movement damage: read the failure, check the cause, then repair it Hewn Shop Notes · https://hewn.build/shop-notes/the-movement-209 AI-drafted, not yet checked: Drafted by Chip, the writing system Hewn runs on Claude, from Hewn's craft corpus. Jonathan Salomons has not read this note yet, and no outside reader has checked it. Read it as a shop note: check a number before you cut to it. Cite as: "Wood movement damage: read the failure, check the cause, then repair it." Hewn Shop Notes, hewn.build/shop-notes/the-movement-209. Drafted 2026-03-16; AI-drafted, not yet checked. --- Before repairing wood movement damage, determine whether the movement is still happening. A crack that opens every winter and closes every summer is ongoing seasonal movement, and a crack that has stayed the same since one dry season may be a one-time event. The two can look identical and need different repairs [1]. ## Ongoing or one-time A panel that split once in a dry winter, or after a move to a drier room, and has been stable since may be a one-time event [1]. A panel crack that opens and closes with the seasons is ongoing movement. A repair that addresses only the visible crack, and not the movement, fails again [1]. ## Reading a split panel Where a split runs is a clue to its cause, not proof of it. Check the piece before you name the cause, because the repair depends on what you find. A split along the grain through the wood itself can be a constrained-movement failure: a panel fixed rigidly, or glued into a frame without float clearance, tears along its own grain when it cannot move [1]. It can also be a drying check made when the board was dried. A drying check can stay hidden until the board is surfaced and open later, in a panel that is free to move [5]. So before you call it restraint, check how the panel is held: pull or look behind the fasteners, see whether the panel slides in its groove, and measure the float left at each edge. Ask where the board came from and how it was dried, if anyone knows. A split at a glue line usually means the adhesive failed rather than the wood. Common causes are a cold glue-up, a starved joint, a contaminated surface or adhesive that has degraded with age [1]. Look at the glue line itself before you settle on one. A split that follows figure may be a stress concentration at interlocked grain, where moisture cycling builds internal tension at the grain reversals. This is common in bigleaf maple and in heavily curly or quilted wood [1]. A drying check can follow figure too [5]. ## Reading a racking case To check a case that feels loose or leans, measure its diagonals [1]. If a case is out of square by the same amount all year, a failed joint is the likely cause; find it before you repair it [1]. If a case goes out of square and back with the seasons while its joints are intact, the case lacks diagonal resistance, usually because the back panel is missing, thin or poorly fastened [1]. ## Reading a breadboard end gap A breadboard end that pulls away from the panel at its ends usually has one of two causes: the slots are too short for the actual moisture swing, or the center fastener is slotted like the others [1]. Check the fasteners and slots before you choose a repair. On a breadboard end, the center fastener is fixed and every other fastener rides in a slot. When the center fastener also moves, the whole panel drags the breadboard and the gap opens at the ends [1][2]. A breadboard gap that closes in summer means the breadboard end is working [1]. ## Repairing a split panel For a clean split in a panel that still moves seasonally, once you have checked that the panel is free to move, wait until the panel is at its widest, in peak summer humidity, then run thin cyanoacrylate into the crack. This holds the closed position. It is a cosmetic repair, not a structural one, and it holds only if the cause of the split is gone [1]. For a split that has stopped moving and will not close on its own, cut butterfly splines across the crack, with their grain perpendicular to the crack, to keep it from reopening [1]. For a panel you have found was wrongly built for its environment, such as a wide flat-sawn white oak panel glued solid into a frame with no float clearance, break the panel apart, remill the edges and reglue it with float clearance. There is no small fix for a fundamentally wrong construction [1]. ## Repairing a racking case A properly attached plywood back is the most effective single fix for a racking case. Add a back if it is missing, or replace or refasten a back that is thin or loosely attached [1]. A plywood back at least 1/4 inch thick, fastened at 8-inch spacing, gives a case real diagonal resistance [1]. Repair any failed joints in a racking case, then address the back panel. The failed joints were likely the first to take racking stress, and an adequate back prevents the next failure [1]. ## Repairing a breadboard end gap A breadboard gap that closes in summer needs no repair. Document it and disclose it to the owner [1]. If the center fastener of a breadboard end is fixed and the outer fastener holes are round, slot the outer holes [1][2]. Size breadboard slots for the moisture swing of the room where the piece actually lives, not for a reference-table assumption [1]. The seasonal travel at a breadboard fastener = its distance from the center fastener × the species' dimensional change coefficient per 1% moisture content × the moisture content swing in percentage points. Use the tangential coefficient for a flat-sawn panel and the radial coefficient for a quartersawn panel [3]. A breadboard slot is long enough for the fastener's travel in both directions from its fitted position, plus the diameter of the pin or screw [2]. Never fill a breadboard end gap with wood filler, putty or any rigid material. When the panel swells in summer, it blows out whatever fills the gap. Filling the gap has the same effect as gluing the breadboard end along its full width [1][4]. ## The cause underneath Much wood movement damage is an accommodation failure: the wood moved as wood always does, and the construction did not leave room for it [1]. Not all of it is. A drying check can open in a piece built correctly [5], which is why the cause is checked on the piece before the repair is chosen. ## Sources 1. Hewn heuristic entry HEU-R988, wood movement damage diagnosis, Reed Run 131, 2026-03-16, Hewn internal, unreviewed. The verification log marks the entry confirmed for crack diagnostics, butterfly splines and the plywood back fix, with the cyanoacrylate step only partly confirmed; the 8-inch fastener spacing is not separately confirmed (Hewn's notes, R988). 2. Hewn deep-research note DR#34, Breadboard End Construction, as summarised in heuristic entries HEU-R354, HEU-R355 and HEU-R740, Hewn internal, unreviewed. 3. USDA Forest Products Laboratory, *Wood Handbook* (FPL-GTR-282), Chapter 13, Equation 13-3 and Table 13-5, dimensional change coefficients, valid 6 to 14% moisture content (as listed in Hewn's notes, entry HEU-R735). 4. Woodworkingtalk.com "What to do with this gap between breadboard and panel?", LumberJocks "breadboard ends lessons learned", blog.woodworkingforamateurs.com "Breadboard Ends Done Right" (as listed in Hewn's notes, R988). 5. USDA Forest Products Laboratory, *Drying Hardwood Lumber* (FPL-GTR-118), Chapter 9, printed pages 103-104: drying checks can be hidden until the lumber is surfaced, and can reopen later. Read by Cal (Codex) at research.fs.usda.gov/download/treesearch/5710.pdf on 2026-10-23; this seat cannot reach that host.