Replies

1. 
   Guest_ | Nov 09, 1999 09:46pm | #1

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   GJR

   Before any qualified answers are given, more information is needed. * How big is the old slab? * What is the thickness of it? * How big of a new slab do you want to build? * Are you going to build a one story garage or put an apartment above it? * What is your frost line? * How deep do your footings go now or do you have any footings? If it is a small slab and there are no footins, I'd recommend that you start new and tear the whole thing up, bring in your fill dirt, compact it and start from scratch. You have to remember that if the foundation is not good from the start, you are asking for trouble later. If you are going to build a bigger garage and the slab is quite thick, I'd put in a foundation around the outside of the old slab (going below the frost line), build up a stem wall to at least 8" above the height of the new slab, bring in fill dirt for the outside of the stem walls, gravel or sand (compacted) for between the stem walls and then pour my slab. If you are only going to raise the floor 5", you might just want to go with concrete.

   Vince

2. 
   Gary_R | Nov 10, 1999 01:36am | #2

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   Vince,
   The size of the old slab is 10x20 and apporx. 4 inches thick. I'm planning to build a one story workshop a few feet larger in both directions. There are no existing footings and I live in the northeast (LongIsland) so I believe the frost line is about 4 feet. Anyway, I think I know what needs to be done by your first reply, and that's tear out the old and start new. Thank you for your reply, and any other comments will be greatly appreciated. Thanks again Vince.
   Gary (GJR)

1. 
   Ralph_Wicklund | Nov 10, 1999 12:25pm | #3

   *Maybe there is someone out there who can explain why one would have to remove an old slab, then fill and compact. After 70 years you would think that the earth is plenty compacted and rather stable, especially with 4 inches of unmoving concrete on top of it. Is there an over riding reason not to just put down your footers outside the current slab footprint, raise a stem wall above the current slab and pour within that boundary? Ralph

1. 
   Gary_R | Nov 10, 1999 07:53pm | #4

   *Ralph, Your comment was my original thought. Although I can handle the framing part of this project, I'm not experienced in foundation work. I thought any settling has taken place along time ago, and I need to raise the floor above the old slab approx. 5 inches. So why not construct footings around the old slab and go from there. Thanks for your comment. Gary (GJR)

3. 
   Guest_ | Nov 10, 1999 08:32pm | #5

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   GJR you're right in your guess. The problem is with concrete people have taken to many short cuts and blame the product and not the steps to get there. With 5" of concrete over your old slab I'ld go ahead and pour over it. Now I'm assuming that the old slab is soild and that you're planing to add footers at the edge for your new slab. Sounds like you got a plan going. Don't cheat on the footers and you'll be ok.

4. 
   Gary_R | Jan 04, 2000 11:30pm | #6

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   I am planning to demo an old dilapidated garage and rebuild over the existing slab foundation. The existing slab is cracked and has settled in some spots over the years (70). I need to raise the floor approximately 5 inches above the existing grade in order to avoid flooding during a heavy rain. I would like to set up the framework around the existing slab and pour over the old slab. Is this acceptable or will I need to demo the old slab and start from groun zero?