Hi - we used Strata Clean on our last boat and they did a really good job. Below is the instructions I got from the Altex paint rep about the preparation after scraping back:
If the scraping method of removal is chosen and once all of the old antifouling has been removed it will leave a shiney finish on the grey primer undercoat, this must be removed , and we recommend machine sanding with 80 grit dry paper. This will remove the shine and yield a coarse surface texture for the new paint system to adhere.
· Once the sanding is complete, remove all of the sanding dust,