What mix to use for concrete slab repair/fill (with ufh)

[oranjeboom]

Okay, having dug up those areas of my slab that needed ufh loops to be pushed down from the surface (see below) , I am now ready to fill the voids.

 

 

 

 

 

Depth wise it needs to be about 100mm and I'll put in some new mesh on top of the ufh pipe. Any bits of pipe that had the concrete grinder skim a bit of plastic from the pipe, I will PVC tape prior to concreting. The rooms to be poured have had their loops pressure tested and all seems okay (slight drop in pressure, but I think that is down to some connections on the manifold).

 

This time round I will be doing the concreting which means no 'professionals' are involved and therefore it's actually going to be done properly for a change.  All voids have been cleaned of debris etc so ready to pour. My only question:

 

is a 4:2:1 mix okay? or in reverse: 1 part cement : 2 parts sand : 4 parts coarse aggregate (20mm)

[Mr Punter]

The mix sounds fine.  You could use ballast instead.  You may want to PVA the adjacent bits of slab. I would sort out any iffy connections and thoroughly re-test before concreting.

[PeterW]

May also be worth using rapid set so you don’t have to wait as long for it to go off and hold the pipes down. 

[oranjeboom]

6 hours ago, PeterW said:

May also be worth using rapid set so you don’t have to wait as long for it to go off and hold the pipes down. 

 

Shouldn't be a problem this time as the pipes won't flex up to the surface as no gorilla's will be standing on the mesh. But I've also tied it down to make it foolproof.

 

 

6 hours ago, Mr Punter said:

The mix sounds fine.  You could use ballast instead.  You may want to PVA the adjacent bits of slab. I would sort out any iffy connections and thoroughly re-test before concreting.

 

PVA would be to help bond the two concretes together and getting rid of any dust? Neat PVA or watered down?