Repointing: reasons for failure?

[mike004]

I have been repointing some patio slabs using Wickes pre-mixed repointing mortar. (A small bag of ready-mixed sand/cement for DIYers).

Two weeks after I did the job, about half of the repointing has failed. The mortar is brittle, cracks easily and has a grey ash appearance.

What's gone wrong?

* It was a hot day when did the job. Has the mortar dried out too quickly -- I seem to recall that slabs which I repointed using a fairly "wet" mix seem to have survived better.

* Wrong mix? The Wickes bag reckons it is OK for repointing...

I'd like to get to the bottom of this. I've just repointed some verge tiles in cooler weather and am hoping it survives better.

Thanks
Mike

 

[Thermo]

two things really
1:- wickes ready mixed mortar, pile of poo and the only useful thing is the bag it comes in
2:- in hot weather it will dry out very quickly and crumble. if you use decent cement sand mix, you need to keep it covered, to stop it drying quickly or mist it with a hose constantly