New Guy...

[CaptNemo]

MY 24 X 24 shop is a total after Hurricane Katrina. I have a huge sycamore tree through the roof of the shop and it's begun to collapse the structure. The insurance adjuster has been here and I'm waiting for a settlement check, so i'ts not all out of pocket. The vast majority of the contents of the shop ( tig, mig, plasma cutter, tool boxes, fab tools, etc. )are OK and in storage for now
One of the things I hated about this shop was that it flooded pretty regularly, it was built too close to ground level and after a good rainstorm, there would be an 1/8th inch of water over most of the floor. Since the structure has to be taken down to the slab, I'd like to pour an additional 4 inches of concrete over the existing slab to get the floor above grade & keep it dry. I understand that will have to prep the existing slab to get good adhesion.

Are there any problems that I may have overlooked ?

Also, I am looking to add onto the shop for more square footage within the Set Back ordinances so it may get a clean room / engine assembly area on one side and may get an extra 2 to 3 feet each way to get the most of the available area. Bigger is better !

The really bad news: my 1940 Plymouth Pick-up truck is crushed by the tree and was not covered by insurance because it was not inside the shop.

 

[dink]

Welcome to the board

I would look into under the concrete and make sure the ground under there is secure....meaning no sink holes have started that sort of thing....thoroughly check the whole area for safety concerns above and below ground

 

[trovato]

My sympathies, captain. I don't know much about concrete work, but that won't stop me from giving advice anyway! I don't understand why you would care about adhesion between the two slabs. If the top slab were to float independent of the bottom slab, what would be the problem? As the original slab may or may not have a vapor barrier underneath, maybe you should put one down on top of the slab before pouring the new one. Then the new slab would definitely not be adhering to the old. Anyway, these are just some random thoughts. I really don't know what I'm talking about, so perhaps someone who knows more will comment on these ideas.

 

[dink]

But actually wouldnt it be better just start completely over...make it exactly how you want it....as high as you want...instead of trying to figure out how to law a new slab over a new one....yes it will probably cost more but in the long run it could be alot safer for you and your cars

 

[MacTexas]

I had the same problem with my garage. Real heavy rain would flood into the garage. I tore my old garage down and built a new one two feet higher. Left the old floor and made up the difference with fill sand. put down vapor barrier and poured new floor on same foot print. No problem with water now.
Bottom line is my suggestion is to raise the floor higher than just pouring on top of the old floor.

 

[CaptNemo]

I don't want to raise the deck that much, I need to be able to roll equipment ( engine hoists, engine stands, TIG welding Machine, etc. ) in and out of the main doors without too much incline. I figured the 4" dimension would be a good compromise between flooding resistance and workability.

If I expand the dimensions of the shop, the "Overlap" would provide a footing for the new slab, so there is an additional plus to going bigger.

 

[trovato]

If I expand the dimensions of the shop, the "Overlap" would provide a footing for the new slab, so there is an additional plus to going bigger.

I don't know what you mean by this. The way things are built around here, footings are placed below the frost line, as per building code. Walls are built on top of the footings. The floor is just poured inside the walls, not really connected to the structure at all. Of course, there are lots of regional differences, and I know there are building "on a slab" systems. Is that what you have?

 

[dink]

I had the same problem with my garage. Real heavy rain would flood into the garage. I tore my old garage down and built a new one two feet higher. Left the old floor and made up the difference with fill sand. put down vapor barrier and poured new floor on same foot print. No problem with water now.
Bottom line is my suggestion is to raise the floor higher than just pouring on top of the old floor.

Did you have one of those garages that actually is below the ground were the driveway slopes down and collects all that water right there at the base of the garage door??

 

[CaptNemo]

What's "Frost" ??? I live in Mobile, Alabama, on the Gulf Coast.

The original slab is about even with the natural ground elevation. There is maybe +1/4" of elevation from the shop floor elevation to the driveway elevation. Pretty close, and no accounting for drainage. It was a bady designed system when it was originally built. I'm trying to correct some shortcomings of the meatheads that built this the first time.

 

[MacTexas]

Did you have one of those garages that actually is below the ground were the driveway slopes down and collects all that water right there at the base of the garage door??

Yes

 

[dink]

Ah okay....yea that is mandatory I told my wife that we not get a house were the garage sits lower then the street for that one reason