Goal: Level basement slab in our 1905 Seattle home so I can install laminate flooring.
- 21' x 25'
- unreinforced rat slab
- thickness varies from ~2" at rim to as little as 3/4" near drain towards middle top of pic
- height varies 2 1/2" from tallest points around rim to lowest point near decommissioned drain
- rat slab is patchwork of smooth and rough pours
- when i bang on floor with crowbar, most of it sounds solid, except for rectangular 5sq area that i partially dug up (see pic). Found drainage trench (now unused) underneath.
- Dark patch at foot of the near support post is base bricks of a chimney we removed.
- We had internal french drains installed around rim of basement. (we've never seen standing water; and we haven't even caught a whiff of moisture since french drains installed).
- no footers on foundation walls
- bottom of foundation walls end at base of existing slab (i.e. 2-3" below top of slab top)
- Ideal is a brand new 4" rebar reinforced slab, but can't afford loss of ceiling height and can't have slab start lower than base of foundation walls... And I'm unable to find a contractor willing to pour a new reinforced 2 1/2" slab.
- temperature averages 60-65 degrees in basement during day
- Use portland cement with aggregate to reduce height variance to 1/4" inch.
- Use self-leveling cement to finish out final 1/4"
- Is this a decent plan or should we consider alternatives?
- How do I bond new cement pour to existing floor? Do I clean and if so how? Can I add mechanical anchors (e.g. cement screws) to serve as anchors to connect the new pour to the old?
- Given the cement pour will be up to ~ 2" deep but taper out to nothing near rim, should I use aggregate and if so what size? or should i do in two steps: larger aggregate cement for deep areas in middle, smaller aggregate for areas closer to rim.
- What self-leveling compound do you recommend to go on top of the new cement pour(s) to finish leveling out the final 1/4"?
- Should we apply some kind of sealant (moisture) to any of the pours? (i.e. existing floor, new cement pour, final self-leveling pour)?