Deck-O Seal or Mastic is essentially the caulking between your pool decking and the coping (brick or stone) around the perimeter of your pool. The sealant acts as the expansion joint that expands and contracts during warm and cold weather.

Do you need mastic around a pool?

The mastic acts like a seal between pool coping and deck to keep your deck dry. If the pool caulking around coping wears down, then you could experience cracks in the concrete or rotted wood decking from spilled-over or leaking pool water, which can cause some severe damage over time.

What is the caulking around the pool called?

A ‘Proper’ Expansion Joint, is a gap between the pool wall and pool deck that goes clear to the earth beneath the pool deck. Without caulking in the gap, the gap or space soon fills with sand, pebbles, seeds, dirt, etc.