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, a wipe over with a damp cloth that has been dampened with fresh clean water. Wipe down so the surface is dust free and then allow to dry.
· If any hull damage has occurred from the scrapper, or there is damage from other means spot fill these areas with two pack Epoxy filler, allow to cure over night, then sand flush with the surrounding surface and again dust off.
· Once all of the surface preparation is complete, and the existing grey primer / undercoat has no adhesion issues, proceed with the mew paint system application. Mask along the water line with plastic masking tape if working outside.
· Then by roller apply one full coat of No 1 epoxy primer mixed 4 to 1 with its converter, once mixed up to 5 % No 12 thinner can be added to aid roller application. The practical coverage rate is approx 4.3 M 2 per mixed litre. Brush will be required to gain access in some locations, EG, skin fitting internals etc.
· As soon as you can leave a thumb print in the No 1 epoxy primer ( 1 to 2 hours ) apply the first of two coats of No 5 Ablative Copper based antifouling colour Sea Green again by roller at 4.5 M 2 per litre per coat. Up to 5 % No 12 thinner can used in hot weather.
· Allow the first coat of No 5 antifouling to dry overnight or longer, before appling the second coat at the same coverage rate. We suggest a third coat is applied to the Rudder, Keel, down the stem , around the waterline down about 350 to 400 mm and above the propeller.
· A small brush will be need to apply the antifouling inside the skin fittings and other areas where a roller is unable to be used. Continue to stir the can to keep the ingredients in suspension. 180 to 200 microns of dry antifouling film build is required.
· Once the new paint system has been applied allow at least 24 to 48 hours drying so the paint film dries hard and solvent free, this yields the best antifouling performance