Paver block defects: causes, fixes and how to cure blocks properly

Most paver block defects trace back to one of four things: the mix, the mixing, the compaction or the curing. Here are the common ones and where to look first.

Common defects and their causes

DefectLikely causesWhat to try

Porous or rough surface

Mix too dry, too few fines, not enough vibration

Adjust water and fines; check vibration time and the vibrator motors

Blocks stick to the mould or slump

Mix too wet, dirty moulds, poor release oil

Reduce water; clean and oil moulds every shift

Chipped edges and corners

Handled too early, worn moulds, weak mix

Move green blocks gently on pallets; replace worn moulds

Hairline cracks

Drying too fast in sun or wind, too much water

Shade and cover fresh blocks; start curing promptly

Uneven colour

Pigment not fully mixed, varying water or cement

Mix longer in a pan or colour mixer; batch by weight

White patches (efflorescence)

Salts carried to the surface by water

Use clean water and aggregates; avoid excess water

Low strength in tests

Low cement, poor aggregates, high water, poor compaction or curing

Review the mix design; weigh batches; extend curing

Uneven heights

Uneven mould filling, worn moulds, pallets not flat

Check the feed, moulds and pallets

Curing: where strength is made or lost

Cement needs water to keep hardening. A block that dries out in its first days stops gaining strength, and later watering does not fully recover it.

1. Protect fresh blocks. Keep them out of direct sun and wind on the day they are made. Plastic sheeting holds the moisture in.
2. Start curing the next day. Once blocks have set, keep them continuously moist by sprinkling or by stacking under wet cover.
3. Keep it going. Cure for at least the first week, and longer in hot, dry weather. Strength keeps growing up to 28 days, which is the age at which grade is tested.