concrete over concrete?

robinasqJuly 30, 2013

I have filled the space under my front door threshold with concrete. Now I want to extend the lip about 1-2" .
Can I pour new concrete over the old?
Is it too large to use concrete patch?
Do I need adhesive?
Should I mix extra cement to strengthen it?
Thanks for any guidance.

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snoonyb

You have two choices, Remove the over-pour, correctly form to the desired dimensions, install a support for the overhang portion.
Install a support for the proposed over-hang.

Adding cement to some mysterious cement product will cause it to become brittle.

    Bookmark   July 30, 2013 at 4:35PM
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klem1

That is so small amount of concrete,proper cureing is very problematic. Then you have to deal with adhearing old to new. Extra portland added to sack mix helps cure and priming old surface with portland and water slurry will handle adhesion. There are some floor underlayment products that would work but unfortanly,there are more that don't even make good underlayment. If you want to try,get a source from a floor machanic. I guess if you fail,you can always bust the old and new out as easy as the old now.

    Bookmark   July 31, 2013 at 12:06AM
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concretexpert

It sounds to me like you have made a concrete kick plate. The vertical portion that is between your threshold and step.

I would just precast the concrete slab 2" thick if possible. This way you will get a better finish and you can even round over the top edge in the formwork. After the slab is properly cured, remove from formwork, seal it on the front and sides for protection from elements, then adhere with modified mortar (like for cultured stone) or liqui nails exterior stone or landscape block adhesive.

You can add more portland to most mixes. Too much can cause cracking and weakness in concrete though. In the case of a Quickcrete or Sakrete standard bag mix you are ok to add up to ten pounds. It will make it creamier and stronger.

    Bookmark   March 2, 2015 at 1:35PM
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