Help Me Solve Water Behind Liner on Pool Remodel


New member
Apr 3, 2021
20 year old 18 x 40 x16 vinyl liner pool, galvanized steel side walls with concrete bottom. Salt Generator.

We have had our 4th liner installed on this pool for this remodel.
The concrete coping edge was cut off flush with the wall of the pool in order to install new composite decking coping. (We installed the new composite decking on top of the existing concrete pool deck). To construct new coping 2 x 6 composite decking joist were installed flush into the existing concrete pool deck. This was done in order to replace the old concrete coping( that was saw cut off) so that the new composite coping could be screwed into the composite joists and square up the edge of the pool.
Currently water is getting between our new vinyl liner and the galvanized side walls. We are not sure how it is getting there. We know we have groundwater issues and are putting in a new french drain system to alleviate water leaching into the side walls from underneath the old concrete pool deck. However, we are wondering if water could be getting behind the liner track because of installation of the composite coping. We suspect water is leaking through the coping and getting behind the track of the pool liner. Do we need to cover the composite joist area with a waterproof membrane (such as a roofing ice and water shield) before installing the surface coping made from composite decking? We have water tested the new coping and determined that water is coming from the old concrete coping area going down the surface of the liner but cannot determine if it is going behind the liner track? Has anyone experienced water getting behind the liner from leaking behind the liner track?


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Well-known member
Jun 18, 2014
Hauppauge, NY
Pool Size
Liquid Chlorine
Get a hose out and start putting water down a two or three feet from the pool and see what direction the water runs. I would guess if the water was coming from the pool the level would drop.


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Have you always had this problem of water getting behind the liner or did it only start after the deck remodel?

If you had a solid concrete deck before and now have a composite deck with lots of opening for water to get into the ground then you have a basic ground water management problem.

Let's try and get @jimmythegreek thoughts.


Mod Squad
Gold Supporter
TFP Guide
Jun 16, 2019
I'd be looking more towards the pitch of the decking. You have entirely changed how much water goes where. The new deck boards are likely carrying rainwater from areas that drained a different way, and bringing it to a spot that gets overwhelmed, which then doesn't drain like it used to.


TFP Expert
Bronze Supporter
In The Industry
Aug 10, 2017
Morris Cnty NJ
If this problem is new it's due to surface water. Previously the deck was pitched away from the pool. With the coping gone and open, water can get in and have no where to go. Have to figure many factors into custom stuff like this, aesthetics are a small part of the plan
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Mod Squad
Gold Supporter
TFP Guide
Jun 16, 2019
Late last night when the real good thoughts awake you from a slumber, another idea hit. Your 'deck joists' are are likely touching the patio in many places and daming runoff in those spots. Or there was a tiny gap which got plugged with sand/pollen/etc and now funnels the water a different way. If it redirects it towards the pool, there ya go.


Silver Supporter
Jun 23, 2021
Suburb of Atlanta, GA
What I believe to be happening is certainly water going thru the composite coping, down thru the two 2x6 composite rim boards and down behind the liner and or wall. There is no easy way that setup will become watertight like the concrete coping was. With the concrete coping, if installed correctly - the water would flow away from the pool, over the sealed joint (that should have existed) to the concrete decking. Now a lot of the water will go down thru the coping to the rim boards where before it would not have.

You *might* be able to add a rubber membrane under the composite coping to keep water flowing away from the pool and the rim boards.
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