poolgirl1,
All concrete expands and contracts. The deck-O-seal is used to mitigate the pressure that the concrete exerts on the coping. The deck-O-seal is used in conjunction with a foam expansion joint that is placed between the coping and the concrete.
Lacking this joint can cause the concrete to apply enough pressure to loosen the coping after a period of time. This could be accelerated if the deck is poured against a patio or foundation. It may take several years for this to occur. Long after your warranty has expired!
Also, if the concrete shrinks you will have a joint that will allow water to penetrate and will cause the deck to settle or heave depending on the type of soil (sandy, clay, etc.) under the deck.
This may not seem important but it is. This is pretty basic pool 101 stuff. Good luck.

I agree with golfgeek. It is a bad idea not to seal that joint.

Hello Pool girl,

It is unfortunate that your builder did not stress the importance of this option. Golfgeek is right on. This will be an expensive problem down the line when you have to fix loose coping, cracked tile and lifting or sagging of the decking, and even possibly cracked gunite and plaster. I would do some preventative maintenance and have an experienced contractor build an expansion joint($10-$15/ linear foot) and put in the mastic ($5-$6/linear foot). You are looking at thousands of dollars in repairs down the line if you don't take care of this sooner than later. As Benjamin Franklin said âÂÂAn ounce of prevention is worth a pound of cure.âÂÂ

Here is a link that might be useful: Pool Plastering Contractor