Sandstone adhesive

[ellal]

I need to mend a sandstone feature.
Two chunks are loose and need putting back in place.
What sort of adhesive should I use, along with some dowels I intend to drill.
Is OB1 a good choice?

Edit: Don't need it to be visually perfect as the existing feature is painted.

 

[Wayners]

Bolt resin

 

[danfre]

Rawplug, mortar fix-pro

 

[mrrusty]

I'd use this https://www.limebase.co.uk/product/tetrion-stonefil-900ml/

It says "filler" but it's a 2 part resin and works well as both filler and adhesive