I think a note of caution is appropriate here, before rushing headlong into a Consumer Rights action, its only fair to point out there are some significant hurdles you would need to be prepared to overcome.
Firstly the CRA does allow you to claim for work done in respect of repairs which like anything must be fit for purpose and carried out competently, with teh correct materials. But it is now more than 6month since the work was carried out, so its now up to the customer to provide enough evidence that either the job was not complete, or that workmanship or materials were substandard, and I strongly suspect getting evidence to that effect will be a big up hill task. Essentially it would need a respected professional engineer to write a report that demonstrates the original repair has failed.
Bear in mind it will depend on exactly what instructions were given and accepted at the time of the repair, if anything was not properly covered in the scheme of contracted or work for the repair, teh repairers will not be responsible. But in addition it is commonly the case that when a repair is necessary for damp, the scale of works may do an good repair, but its only later that the areas adjacent to the repair that may start to leak. Again that is not the fault of the repairer, it was not part of the contract and thus they are not liable.
I strongly suspect this case would be very difficult to win.