Incorrect blocks used below DPC

Harborne

Hi Everyone, hoping someone can help me with this.

Recently we have had a new extension, which involved new block work all around the building, We have completed and found the the blocked used below DPC are Fibolite 3.6N blocks, which on research can be used on the internal skin, not the external. He has used engineered bricks 2 skins below ground level and 3 skins above. The rest of the above wall we have rendered.

I have spoken to the builder who is happy to remedy the problem. Plasmor (who make Fibolite) have suggested to either chop out blocks involved, and replace or put another skin of block (fibrolite 7N) in front of the incorrect blocks below the DPC.

My first question is will doing this be sufficient for the long term?

Secondly is there another way, where by if the builder digs all around the property and maybe we can shutter around 300mm against the block and had it concreted. This was the sulphur in sold will not be in direct contact with block.

Thirdly would it be easier to render below DPC?

I appreciate anyones help, as i would rather remedy this sooner than later.