Situation: The 8″ wide top of an existing foundation wall needs to be recapped in order to adjust the height and to integrate it into a section of new foundation that is yet to be poured. I would like to do all of the work at the same time and with the same mix from the concrete truck in order to try to tie all parts together and to make it all one monolithic unit.
Question: How much should I chip down of the old concrete wall in order to get the desired thickness for the new cap so that it does not crack and/or “pop” over time?.
Question: Should I stop the concrete pour from the truck short and hand mix bag material if that will give a better bond and strength for the top? If so, what type of bag material is recommended?
Question: Is pinning the new top to the old material necessary or will this end up just being an extra that may actually have a negative affect.
Thank you for your input in advance.
Edited 12/19/2008 9:54 am ET by Jake0358
Replies
How much do you have to raise it?
Mike
All you have to do for chipping is expose some new surface. Brush on some bonding agent to assure a good bond. If the cap is a couple of inches thick, some pegs would not be a bad idea.
I don't see any reason not to use the ready mix from the truck.
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I second the bonding agent. I just call it concrete glue. Have someone with a broom or big brush in front of the pour laying down the glue.
If you put down the glue to early it starts to skim over. But you can freshen it up with some more on top of it.
Just make sure there is a fresh layer of it in front of the pour. you'll have to guage how fast the pour will go.
Ditto on the bonding agent. And it would not hurt to have some mechanical bond, like a couple of dowels or anchor bolts embedded in the old concrete. You generally need a minimum of 1-1/2 times the size of the aggregate, so if you have 1" stone in the mix you need 1-1/2" thickness. More is better.
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My first question would be the same as junkman's-
"How much do you have to raise it?" and also how much of the existing wall do you have to do ?
At a minium I expect to put a 3" cap on top of the old material. It is easy
enought to knock it down a bit though.