These tampers roll gently over the material, working the polymeric sand into the joints ensuring it fills the joints fully right down to the bedding layer. This prevents the slabs or paving stones from shifting, cracking or chipping. This machine is great for larger slabs and pavers now on the market that are non-tumbled with smooth surfaces, have clean lines or have chamfered edges that can sometimes chip or crack easily if using a traditional tamper for final compaction over the pavers.