Why a diamond dowel is diamond shaped, and what that means for a slab joint that has to move
A dowel at a slab joint has one job: carry load across the joint while letting the two slabs move. A round dowel does the first part well and the second part in one direction only.
What the shape is for
A Diamond Dowel Plate sits in a sleeve cast into the first pour, with its points facing the directions the slab will move. As the slab shrinks, the plate has clearance on both sides. A round bar in a round sleeve has clearance along its length and none across it, so the joint quietly restrains the movement it was detailed to allow.
- Cast the Diamond Dowel Sleeve into the first pour, square to the joint
- Check the sleeves are in line before the pour, not after
- Set the plate once the form is struck
- Keep the second pour clear of the sleeve mouth
The failure this prevents is not a dramatic one. It is a joint that holds instead of moving, and a crack that turns up somewhere the drawing never put one.
Where a speed dowel fits
A Speed Dowel Sleeve does the same job for a round bar where the joint only has to move in one direction. It is the simpler component and there is nothing wrong with it, provided the movement really is one directional.
