shell harling

Can I ask for some assistance please.
Recently I had in some tradesmen to replace the wood facing of a garage door. In knocking out the old wood they dislodged some pieces of the harling of the wall. The harling is composed of broken shells. They said they would come back at the next weekend and put it back .............
This was about October but I guess they 'took the money and run'. Anyway, question - I used to be OK at jigsaw puzzles.
What kind of 'stuff' should I get to get these bits of harling back?
I have never posted to this group before. My son always tells me to think of the protocol. Apologies if I have offended.
Doreen Paterson -
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