New cement onto extg

[Newapprentice]

Last year I cemented a few vertical sleepers into the ground (quite deep), it will be a long wall when it's done.

I couldn't finish the job in one go so I used some timber shuttering to stop the cement pouring out.

I'm about to carry on with the job, so I'll be removing the shuttering and throwing new cement next to the cement that has already cured.

Do I need some sort of agent/fluid to paint on the extg cement so the new cement bonds with the old?

Many thanks.

 

[r896neo]

Not sure what you are doing as concrete around a sleeper would obviously be in a hole so not sure what you have shuttered? Obviously posts holes should be into solid ground and should never be shuttered so maybe you did a level base/foundation for them?

Concrete doesn't bond particularly well to itself but make sure its very clean and that will probably be ok. If you were catching existing concrete in a critical situation where you want to reduce movement than drilling and fixing some rebar into the old will do that.

We could give clearly more appropriate advice if you describe a little more what you have got and what your next move is?