Expert: Dan Griffin - 3/19/2008

Question
Dan,
Just read your response on lally column replacement about removing the old at where it meets the foudation and replacing the new on top of the foudation floor. My question is, is the foundation floor strong enough? would it better to hammer away the floor to get to the footing or maybe put a large steel plate on the foundation floor to spread the load?
Thanks,
Carlosm

Answer
Carlos,  sure it would be the very best to reperform.  That installation had so much water, it had rusted the column through, my prime interest was in getting a new post that was not as subject to water.  You are so right that I should have suggested cutting out the floor and exposing the footing.  These footings are usually right at the bottom of the floor, often poured at the same time as the basement walls and set at the same elevation.  I did not verify that his lally column had been filled with concrete that would provide a direct bearing path to the original footing - I assumed.  I suspect the footings and floor were very similar in design mix and testing strength.

If you are facing the same situation, let's do this:
>>Saw cut a substantial square (24x24) around the colum - these would normally be a diamond in relation to the outside walls.  YOu might be able to work in a smaller hole, but don't skimp on working room in the hole.
>>Brace and shore as required, be sure to spread the load as best you can on the floor.
>>Remove the existing column as best you can.
>>Remove the existing concrete around the column.
>>Try to unbolt the original nuts, probably won't happen, so be prepared to saw or grind them off flush.
>>Install new column.  This will require new anchors and holes, you should probably set the column in high strength set grout to take up any voids.  You could dry pack the plates as an alternative.
>> Replace the concrete in the diamond block out.

If you are having the rust through problem also, you might pour 3000# or better concrete from the top of the existing footing to the top of the floor, this concrete will need to be doweled to the existing footing and #5 rebar providing horizontal reinforcement of the mat  You can pour new "J" bolts in this mat.  Plan on isolating the base plate away from the wet concrete floor.