Workshop Notes
Moisture, Sealing and Edge-Banding in Coastal and Highveld Conditions
Why the same board behaves differently in Durban and Johannesburg
Plywood reacts to where it lives. A sheet that stays flat through a dry Highveld winter can cup within a week on the KZN coast, and the difference usually shows up at the edges first. The core soaks up ambient moisture faster than the faces, so the board swells along its exposed perimeter while the middle stays put. That is why a stack that looked fine in a Gauteng yard can twist once it reaches a Durban workshop.
Before machining, check moisture content with a pin meter in a few spots across the sheet. Readings above 12% on interior-grade board are a warning sign. Let the sheet acclimatise to the workshop for a few days, stickered and off the floor, before you cut anything that needs to stay flat.
Sealing exposed edges
Cut edges are the weak point. A brush-on sealer or thinned wood glue works for interior work, but on coastal jobs or anything near a wet area, a proper edge sealer or exterior-grade paint is worth the extra pass. Two thin coats beat one thick one. Let the first dry before the second goes on, otherwise the film skins over and traps moisture underneath.
Edge-banding choices
Edge-banding is not just cosmetic. A well-glued ABS or melamine band slows moisture movement at the edge and helps the panel hold its shape. On shelving and carcasses that live in humid rooms, iron-on banding with a decent adhesive is a reasonable middle ground. For van fit-outs and anything that sees temperature swings, glue and pin the banding rather than relying on heat activation alone.
Storage in small workshops
Most small shops do not have a climate-controlled rack, so airflow matters more than anything else. Keep sheets flat on a level surface, stickered with thin offcuts every 400 mm or so, and leave a gap against the wall. Stacking boards directly on a concrete floor is the fastest way to pull moisture up through the bottom sheet. If space is tight, rotate the stack every few weeks so the same sheet is not always on the bottom.
None of this is complicated, but it does need to be consistent. The boards that fail are usually the ones that were stored badly, cut wet, and sealed in a hurry.
