The Easycraft installation guide for attaching VJ paneling to masonry or Besser block walls requires you to put up timber battens and to use a finishing gun to hold the panel in place. Using a finishing gun on Besser blocks may produce undesired results and damage the VJ panel and the gun.
Using concrete nails is not ideal as it tends to shatter the surface of the Besser block. This produces an unsecured anchor and will not hold the panel in place. I suggest building a temporary timber brace to hold the panel in place while the adhesive cures.
I understand that setting battens up for this would increase the project time significantly and the cost to a smaller degree. While I would try to avoid nailing into the Besser blocks if possible, if the nailing is only intended to secure the panel while a construction adhesive cures, maybe you could instead try using screws and wall plugs to hold the sheets in place temporarily. If you leave the screw proud of the panel by a few mm, you should be able to use a hammer claw to extract the screw once the adhesive has set, and then could use a wood putty to patch the hole before painting.
I have a retaining wall made of Besser blocks and found it a real pain to attach a post to it for a gate I installed as the blocks don't have much substance for most ordinary fixings to grab into. - tom_builds
I was able to complete this successfully by using temporary screws to fix the panels to the mortar of the bricks while the construction adhesive set.
Also built a temporary brace just to help hold the boards in place and apply even pressure during the setting process.
It all worked fine and the boards set in place solid and without issue.
I simply removed the screws, puttied and painted once set. - Marshall