Placement of Main Drain Sumps to Steel is Critical

The placement of main drain sumps in relation to the steel is critical. Placing the sumps proud of the steel by 6 to 8-inches, causes a couple of issues. The steel become “displaced” with the concrete and is no longer centered in the structure. Concrete over 8-inches total thickness, generally requires double curtains of steel.

Double curtains are required by ACI to maintain the minimum ratio of steel to concrete. The purpose of these ratios is to prevent structural cracking and to reduce shrinkage cracks. How do we do it right?There are 2 methods.

1. Stub up the pipes & box out for the drain. Install the sump and grout it in later.

2. Set the sump at the proper finish elevation over the steel (allowing for plaster thickness).Both options require that a depression be dug into the soil. A recessed “cage” for the sump follows this oversized excavated depression, maintaining the proper soil clearance.

Recently, I have seen a few pools with deep end cracks. Coring revealed these shells were 10 to 12-inches thick with a single curtain of #3 rebar 2-inches off the soil.

Swimming Pool Expert Witness