== Fibreglass is not GRP, GRP is not fibreglass, GRP contains glass fibres == 

 I agree with Pschemp - by all means (in fact please do) add a paragraph and a link in the fibreglass article to highlight a common parlance, and incorrect, use of the term, but do not merge the two articles.   You might as well merge steel & concrete on the basis that the former is often used to reinforce the latter....