Building Deck on Top of a Raised Slab That is Warped

by Kevin
(Signal Mtn., Tennessee)

Patio - North Wall Crumbled Concrete Slab

Patio - North Wall Crumbled Concrete Slab

I have a 19 by 34 foot raised patio (about 2 foot tall back filled with a concrete slab on top) at the back of my house.

It had flagstone covering the slab but the roots of a very large oak tree within 2 feet of it has bowed the slab up visibly over the years and the flagstone had broken and come loose.

I removed the flagstone and when I did that I found that the concrete blocks holding the north wall had crumbled making the slab suspended on the back fill.

I'm now trying to decide whether to

(a) cut down the tree and have the slab leveled (pour a new one on top of the old one) and the wall rebuilt; or

(b) level concrete block supports across it, put posts in the ground on the north side (with the crumbled wall) and build a deck on top.

Budget is very tight since my teaching income is the only income in our family right now while my wife raises our children. Are any of these realistic ideas?

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Jan 03, 2010
Removing or Building over a Concrete Slab Patio
by: Editor - Rich Bergman

It certainly looks like this concrete patio slab has seen its best days.

With a large tree root underneath I think your best option is just to rent a jack hammer and break the hole thing up, throw the pieces into a dumpster and have them haul it away.

Mind you that is a lot of work. But that is probably your best long term solution.

I just think that the roots from the oak tree will always be near the surface and problematic. Unless you want to get rid of the tree and then chip away the roots near the surface. Again, more work.

If the root and tree are to stay, then I think you consider removing the slab and building a low level deck that approximates the look and feel of a slab on grade patio. Although it will not be quite as low as a concrete slab you will avoid some of the problems of trying to reuse what you have.

Pouring a new slab properly means excavating and back filling with say 3/4" minus granular stone and doing it right with re-bar. The whole nine yards.

Option B of just building on top of what is left I think is fraught with potential problems and would be a very short term solution at best - and not a wise one.

You have posed a great question about what to do with an old concrete slab and I think we should put this one out to the tens of thousands of folks who subscribe to my RSS feed.

With so many people reading this we are likely to be able to tap into the power of the collective wisdom of many, many years of experience.

So any of you expert contractors or builders out there who have dealt with this kind of a problem, please chime in and help Kevin out.

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