Digging into semi set concrete

[macadonald]

I will be having foundations poured this week. Although a will need to shutter ina drain on one side, I also want to have a gully pot and another drain pipe. We are head of run, so these will be nearish to the top of the foundations.

Rather than shuttering these in, is it feasible to simply dig out the concrete when it hasn't fully set. Perhaps pushing play side into the concrete on either side while wet and then remove what's in between.

 

[^woody^]

Why would you want to break out concrete?

Shutter it or use polystyrene and save time and effort

 

[Norcon]

Yes. Concrete is like placticine when setting and you can sculpt it, shape it and dig out lumps whilst setting is taking place.
Do that all the time.

 

[macadonald]

Wasn't planning to have to break out set concrete, just thought it might have been easy whe still wet, but hard enough not to collapse.

Polystyrene? Tell me more. Would I need a large cube the dimensions of the void I'm trying to create? Wouldn't know where to get something like that. I guess the other option is polystyrene sheets cut in stuck together. Never priced polystyrene, is it much more than shuttering with ply?

Thanks

 

[JohnD]

if you put a block of polystyrene in, you can burn it away with a blowlamp once the concrete is fully cured (after a couple of weeks) to leave a block-shaped void with a sticky black residue.

 

[^woody^]

A solvent to dissolve it is better. Petrol may be too expensive nowadays, but probably white spirit or something