Broken pointing with deep gaps between patio slabs

[elmag28]

Hi,
The pointing in our patio had cracked & weeds were growing. So, I have been clearing the pointing & have found that there are very deep gaps especially towards the centre of the slabs. It looks like the slabs have been laid dot & dab with sand filling the gaps. The pointing was about only 10 mm deep.
A lot of central areas have deep gaps going under the slabs.
The slabs are not loose & don't really want to take them off to re lay them.
I was planning to use a 1cement:1:lime:1sharp sand:4 building sand semi-dry mix to fill the gaps.
I am not sure that will get under the deep gaps.
Can I use something like expanding foam first to fill the gaps & then fill with pointing mix or can I use wettish mortar through a mortar gun to fill the gaps.
Many thanks.

 

[aveatry]

Cannot talk about the depth of the gap issue but I use 50/50 sand and sharp sand mixed to 1-3 with some fibreglass reinforcing mixed in as well as a waterproof additive mixed as a mortar - so not dry. I then go over it when its dry with a sealer/ waterproofer.
An OTT method I use is to use gaffer tape and mask off the gaps so I can slap it down there without the need to try not to get it on the slab face. Saves time in the long run. The cloth backed tape easily rips down the middle to get 25mm from a 50mm wide roll.

 

[elmag28]

Adding fiberglass seems a good idea. Hadn't thought of using tape on the edges. Thanks

 

[aveatry]

Its the very fine chopped stuff a little goes a long way and makes a big difference. The tape is the best way I have found - it looks a little nuts and takes time to do but you can then get the cement down there much quicker. I have tried putting the mix down dry but it never lasts as long as doing it wet.