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Insulating/waterproofing Granite block foundation, Boston

Boston2022 | Posted in General Questions on

I’m looking to finish off my 1940s basement, which is a granite block foundation. Previous owners applied a black/tar waterproofing paint on it which has been starting to fail/peel off/efflorescence. Front of basement is 100% below grade which tapers to 20% in the rear as 5000sf lot is sloping to rear. Gutters have been rerouted to send to rear and side lot as dumping to the front leads to ice build up on sidewalks. That said, during heavy rain events, maybe 2-3 times per year, I get minor seepage and drips leading to maybe a 4’x4’ puddle. 

The slab will need to be excavated and repoured, and interior drain channel with dimple mat installed where it meets foundation wall. At this point no need for sump pump but the pit will be installed. 

Walls to be sprayed foamed given the irregularity shaped walls. Outside of fully removing all of the black waterproofing, my thinking is just clean off the flakes and let it be. If I mortar the damaged areas, aren’t I just going to make the water travel somewhere else? Or should I use something like radonseal in the effected areas?

Should the spray foam envelope the dimple mat? Or stop the foam before it gets to the mat?

Seen some videos of people using 1-2” of CCF on the gravel base before pouring instead of foam panels…is that common in the North East?


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