I have a 1920's foundation that was built in several 'short shots' (not a continuous pour) with many seems. I used to have regular water ingress during the rainy season (9 months of the year in Seattle), but tried to mitigate by digging a dry well far from the house at the lowest part of the lot, dug drain trenches and directed all gutter water to the drywell. Landscaped to improve things, as well. That has dramatically improved the situation. However, the basement still gets a little wet when there are 2 or 3 days of heavy rain. The walls are fine. The moisture comes in from microcracks in the slab.
I wish to finish the basement into living spaces. However, I'm on a tight budget. Options I've considered:
Option 1) Digging up outside the foundation is not an option (both financially and for technical reasons).
Option 2) Digging up the inside and putting a french drain to direct water to a sump is an option. This is very pricey. I could do it, but have a bad back.
Option 3) A third option I've seen is a perimeter gutter system (squidgee) that looks promising - you drill holes in the base of the walls to drain to the gutter system which outlets to a sump. This sounds like I could do this fairly easily.
Either option 2 or 3 would seem to help relieve hydrostatic pressure at the slab.
However, given that my floor has a bunch of seems from when the floor was poured and still has microcracks, should I seal the slab? (and if so - with what?)
My neighbor recommends doing Option 3 + pouring 2-3" of fresh concrete over the existing slab. Is this advisable or is this overkill?
If I pour a new slab - should I put a visquene vapor barrier down? or should I seal or coat the basement slab before pouring concrete? If so, what should I seal/coat it with?
Basically - I want to be 100% confident that I can go ahead and lay down carpeting and not have moisture ingress from the slab.
I plan to test the floor to ensure that I am not getting condensate from the are, as well.