Inspection chamber cover

[alphazulu]

Hi,

I had an inspection chamber (precast concrete) in my garden covered with a piece of ply. I decided to fit a proper cover on it a couple of weeks ago, rectangular galvanised cover with a metal frame. I mixed up some 3:1 mortar using building sand, sprayed the precast concrete with water (been dry for a long time and it was a warm day), laid a bed of mortar and put the frame on this. Left it to go off for a couple of hours and then put the cover on. Then again using 3:1 mortar I haunched around the frame.

The next morning I noticed some cracks in the mortar but didn't worry about it too much. The last few days I have noticed more cracks and I was thinking about redoing the haunch. Today, I noticed the whole thing (frame and cover) will move if I kick the edge of the haunch.

I need to redo it and I was hoping one of you could tell me where I went wrong. Did I use the wrong mortar mix? Or is it because the precast concrete has a smooth surface so there is no key for the mortar? How should I do it so it is solid and doesn't move?

Thanks for your help.

 

[noseall]

You need to use sharp sand AKA screed sand, concrete sand etc. Mix it 3:1 and not too much water.

Wet the recipient area prior to applying. Allow the water to dry slightly you don't want it ponding - just damp. Cover it with polythene after you have trowelled it smooth to protect it from drying out too quickly.

 

[alphazulu]

Thanks! I know how I'll be spending Saturday morning.

When I was thinking about just redoing the haunch I was planning to use sharp sand. I've spent a lot of time looking at them lately when I'm out and about! The same day I fitted the cover I filled some gaps in crazy paving using a 3:1 sharp sand mix and that mortar is rock hard with no cracks at all.

At which point would you put the cover in the frame?

 

[noseall]

At which point would you put the cover in the frame?

Leave it as long as you can without leaving a danger. If you could pop some ply over it even better. However, haunch in the morning and it should be ok by lunchtime for the lid.

 

[noseall]

P.S. 'morning' to us is 7:45 a.m.