There's a crack in your chair. Maybe you've been watching it for three summers. Maybe it went from hairline to visible gap over the last two winters. Either way, you've been meaning to do something about it.
Here's where to start: not with the glue. With the humidity in your shop.
The Winter Humidifier Trap
Most woodworkers in coastal climates run a humidifier all winter. Interior RH stays at 40–45% instead of crashing to 20–25% when the heat runs nonstop. The humidifier feels like the fix.
It is half a fix.
Here is the math. At 45% RH in winter and 75% in summer — a normal coastal home without any active summer dehumidification — cherry equilibrium moisture content swings from 8.7% to 14.0%. That 5.3% movement puts you in the marginal zone. One dry winter with the humidifier struggling, and that swing pushes further. That is where checks happen.
The intervention that crosses the boundary is not better humidification in February. It is active dehumidification in July and August.
Get summer RH down to 60% or below, and the total swing from winter to summer drops to 3.5%. Same shop. Same wood. Same chair. That 1.8 percentage points of moisture content is the difference between a piece that lasts decades and one that lasts generations. Most woodworkers in wet climates have the winter half. Almost none have the summer half.
When You Find a Check
The depth of the check tells you what to do.
Under 0.5 mm: Watch it. Record the date and the depth. Check it again next spring. Don't inject it with CA — CA is brittle enough to fail under seasonal stress, and it may concentrate stress at the film edge and make the next crack worse.
0.5 to 1.5 mm: This is the action threshold. Re-glue with hide glue in late winter or early spring, when the wood is at its driest and the check is slightly open. Then get the summer dehumidifier running. A 1 mm check, hide-glued at the right moment and held in a 40–60% RH band through the following summer, buys 4–10 more years before you need to look at it again. The glue resets the clock. The climate control is why the clock doesn't run as fast the second time.
1.5 to 3 mm: Climate control first. Re-gluing at this depth is less reliable. Past 1.5 mm the fracture mechanics start working against the hide glue, and at 2 mm you are already at the edge of what it will hold across a full seasonal cycle. Glue to buy one season while you get the dehumidifier sorted. The priority has shifted from repair to prevention.
Over 3 mm: Disassemble and remanufacture. Knock the joint apart with heat and steam — hide glue allows this, which is part of why it belongs in chairs — re-machine the mortise to get past the checked wood, cut a new tenon, and reassemble. On a dining chair, that is 4–6 hours per joint. Significant. Not a replacement.
Joint play — rocking, rattle, audible creak: Full disassembly regardless of what the check looks like. Structural play means the joint has already moved past the point where surface repair matters. The visible check depth doesn't tell you anything useful at this stage.
The One Thing Missing From Your Shop
A hygrometer near the floor. Specifically near the lowest rungs of the chair.
Read it between 6 and 8 in the morning, before the household wakes up. That is the overnight equilibrium reading. It represents the moisture condition the wood has been sitting in for the past 30 days. If the summer reading is above 60%, you know what the problem is.
If it is consistently below 60%, you have one fewer thing to worry about.