Sealer for flagstone spillway

[fyton2v]

I have a flagstone spillway from the spa to the pool. When running the filter pump on a low speed it's not really enough flow to get the water going (there is a separate booster pump for this). Since it's all flagstone and grout, including flagstone around the waterline on the inside of the spa, I'm getting some seepage. Water trickles through the grout, under the flagstone ledge then down the spillway. And since it's a slow I'm seeing some calcium buildup.

So... I'm looking for a sealant product that I can apply along the spa's inside edge to prevent leaking through the grout. Any idea what would hold up in this environment?

Here is an image of what I'm trying to describe...

 

[maxepr1]

I use I think it is Deck-O-Seal. Comes in a gallon jug, looks like milk. I apply with a roller to my flagstone coping. It cuts down on the erosion and also water proofs the flagstone without changing the color at all. Has to be reapplied couple times a year.

 

[fyton2v]

Think it'll make grout waterproof? I was thinking that there might be something that would prevent the inevitable cracks, or minor gap, that'll appear between the bottom of the flagstone coping and the grout.