Alternative grouting material for copings

[steveoelliott]

Hi,

 

Earlier this year I had some porcelain copings installed by a builder on a couple of parapet walls... They were laid on top of a DPC and further down there is also a cavity tray. They were laid using a PU adhesive and pointed using this grout slated to be suitable for external work: https://www.screwfix.com/p/mapei-ultracolor-plus-wall-floor-grout-anthracite-5kg/68981?tc=AT1&ds_kid=92700058176434344&ds_rl=1249416&gclid=Cj0KCQjwu7OIBhCsARIsALxCUaM8HefqhZ2XvMMOcJ5FKFNq4X0YmiH3W2L9uTkjt9LmIvJn8v0K6AcaArp1EALw_wcB&gclsrc=aw.ds

 

I've noticed that on a couple of the coping joints hairline cracks are appearing in the grout... Now this is possibly to be expected given the massive amounts of expansion / contraction that must occur especially as being south facing these stones are very hot to touch on warm days. The question is how best to address this... The gap I am sure is too narrow for mortar and therefore grout is seemingly the best option. It looks like where it has cracked it would need raking out and redoing. Are there any better options out there for this purpose? One could seal over the top with a silicon sealer but I think that would look terrible.

 

In theory with the DPC and cavity trays any water ingress should be handled by second / third lines of defense but if I see the cracks present it makes sense in my mind to rectify them.

 

I've attached 2 pictures, one is as is and the other is zoomed right in. How much water would actually penetrate is unknown but I suspect they will get worse if not addressed.

 

 

[Mr Punter]

The water will get in through those hairline cracks.  Perhaps a low modulus sealant like https://www.screwfix.com/p/no-nonsense-builders-silicone-grey-310ml/912gr