ah no, those are just bits of white plastic people use for 'For Sale' signs etc. The are just a temporary former. Gel goes on top, when its dried lay up the GRP. When its gone off they are removed to leave a smooth section of GRP.
Any thing thin and bendy can be used, eg perspex, Formica, even thin ply, but you have to cover that with brown parcel tape to stop the gel sticking to it.
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