Tom and Alan, thank you both very much for your replies and advice.
i have been trying to do the 600 topper followed by the 600 Nubond. . it seems to be taking forever for the nubond 600 to get rid of the pits – in fact i am still trying.
i have been wondering if i should obtain a nubond 325 and use that instead of the topper 600…… but for now i will persevere. if i continue to struggle then i may have to change to another approach like batt lapp with loose grit as suggested by Alan