My paving 'grouting' is crumbling

[benjammind]

Some advice would be greatly appreciated. Over the past few months I have been laying a patio, things started off wonderfully, the slabs (600 x 600) were secure, the 'grouting' didn't crumble and life was good.

The slabs I laid most recently however I've noticed with bitter, bitter disappointment don't feel as solid, indeed a couple of them rock every so slightly now, as though the base is crumbling, and the 'grouting' between the slabs is very crumbly and comes away from the joints very easily.
These most recent slabs were lain during the very hot spell, it was probably >30c for the couple of days it took me to lay them. Whereas the first few were done in much cooler conditions.

Is the heat likely to be the cause of the crumbling? I am certain the mixtures I have been using haven't changed. For info I use sharp sand and cement for the base (on top of a sub layer) and a 3:1 ratio of sharp sand and cement (Rugby Premium Cement) + a little water for the 'grouting'.

I read somewhere that on very hot days you first should wet the slabs before laying them, and before grouting wet the joints etc. This I didn't do.

any advice is greatly appreciated.

 

[lasors]

Your mortar has dried out before the cement has had a chance to cure, because of the very hot conditions when you laid the slabs, as you have said.

No way to fix it other than to lift them up and lay again on fresh mortar, I'm afraid.

The grouting needs to be a wet mix when applied, 'a little water' may not have been enough.

 

[benjammind]

Your mortar has dried out before the cement has had a chance to cure, because of the very hot conditions when you laid the slabs, as you have said.

No way to fix it other than to lift them up and lay again on fresh mortar, I'm afraid.

Thanks Lasors, appreciate the response. Any way around it happening again? apart from not working on a hot day? Is wetting the slabs and joints prior to laying an approach I should take?

 

[lasors]

I edited my above, I'd suggest using a wet mix to lay on and your grout needs to be wet as well. If it starts to look a bit dry after laying MIST with water to keep it damp. Just a mist, don't over water it as that will weaken the mixture not to mention possibly wash it out.

Ideally, avoid laying in baking sun.

 

[Mursal]

Might help if you soak the slabs before relaying. Then let them drain before sitting into place. If in doubt use sharp sand, rather than plastering sand.

Was the cement a fresh bag, or leftover from the previous mix?

Good luck, lift them quick and just don't think about it. Then only a matter of relaying

 

[benjammind]

Might help if you soak the slabs before relaying. Then let them drain before sitting into place. If in doubt use sharp sand, rather than plastering sand.

Was the cement a fresh bag, or leftover from the previous mix?

Good luck, lift them quick and just don't think about it. Then only a matter of relaying

Thanks for the reply, it was a fresh bag and I am using sharp sand rather than plastering sand. I also enjoyed your last comment about 'just doing it' rather than thinking too much about it!

 

[wrathkeg]

relevant info here:

http://www.pavingexpert.com/faq_weather01.htm