Replies

1. 
   Chipper | Oct 06, 2006 09:06pm | #1

   A cedar wood pergola will hardly have enough weight to be concerned with. You are apt to do as much harm as good with this. Are you planning to cut THROUGH the slab or place the crete under it? The new crete will likely shrink down as it cures, creating trouble for you if you don'
   t cut through.

   OTOH, the existing cslab is thin and we don't know if it has steel within and what the soils are under it. What are the climate conditions and has this slab moved in the past.

    

    

   i will cut through slab approx 2'x2' sections, & use 16"diameter sono-tubes for c-form.

   there is no rebar or wire reinforcement in existing slab. I will use wire reinforcement to tie in old & new concrete. the soil below slab appears to be compacted fill, it appears that patio area was filled as to create a walkout from back doors onto patio versus - utilizing steps down to patio.  The slab has visible signs of stress fractures, the plane of the concrete slab tends to waver. thickness of slab varies  in various spots. Soils in area tend to be sandy & clayish. Climate is typical 4season relative to northeast (new jersey - shore area)
1. 
   pickings | Oct 06, 2006 09:22pm | #2

   Howdy,

   You should do the new conc footings independently of the exist slab....no real need/benefit to tie them together. Let the slab "float" between the four cols.

   That way, down the road, you can replace the cracked slab w/ bricks, pavers, white gravle, shells etc, and not bother the column footings.

2. 
   Piffin | Oct 06, 2006 09:41pm | #3

   great thorough answers to the point. Thank you.I would then do as you plan, cutting out slab to pour piers. do compact thoroughly as you refill. The friction should be plenty to support the pergola.if the slab were 4" with steel, free of movement with good subsoils, and in the dry SW, I would take a chance on perching the cedar posts right above it, but it sounds like this patio is in the beginning stages of faailure already. Therefore, be sure to take photos before and after to documemnt in case you get blamed for its coming apart later on 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

1. 
   Chipper | Oct 06, 2006 11:54pm | #4

   thanks for the advice of taking before & after pictures!  Gret idea.  the slab looks like a soggy wilted lasagna noodle - but nicely hidden by pretty brick pavers atop.