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10 Reasons Why You Must Use Primer When Antifouling A Boat

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10 Reasons Why You Must Use Primer When Antifouling A Boat

Post by Miles »

Antifoul primer.jpg
  • G.R.P. suffers from osmosis, as it is not waterproof and the gel coat/fibreglass is actually a semi-permeable membrane which needs protection from moisture.
  • Antifoul primer will help the antifoul paint make a thorough bond with the surface being painted. Regardless of the vessel's construction material (although different hull materials require different primers, such as aluminium hulls).
  • Priming a boat's hull will reduce the number of layers of antifoul paint necessary to completely cover the previous colour.
  • Underwater surfaces are exposed to the most extreme conditions including pollution and contaminants. Painting antifoul on top of a contaminated surface is in effect useless.
  • Antifouling primer also serves as a barrier between compatible and incompatible previously applied antifoul paint.
  • Soft antifoul is designed to erode at a rate depending on the level of speed the vessel travels, therefore constantly creating a surface free to release biocides which prevent hull fouling. Hard antifoul constantly release biocides and does not need to be polished by the water flowing passed it. Either type is irrelevant as the antifoul must adhere to the hull surface with effective tenacity.
  • Simply jetwashing a boat's hull and applying antifouling straight to the hull will have very poor adhesion qualities.
  • Underwater primer has excellent waterproofing properties.
  • Soft antifouling as described earlier is designed to erode so basically a fresh layer of biocides is made available to prevent growth and fouling. Excellent adhesion can not be achieved when applying fresh antifoul to a surface which is designed to erode and disconnect.
  • Antifouling any vessel is a two-tier process. Applying just one of the components is like constructing a house with a roof made out cardboard. It may look fresh, it may work for a while and even when you take the boat out of the water again, it may be free of growth. However, your boat will be far more hygroscopic. Removing old layers of antifoul and testing the hull with a moisture detector will very likely reveal higher levels of moisture and some degree of osmosis. Osmosis is often hidden from initial sight by layers of antifoul. Often only when sanded back or detected with moisture detectors is it identified.
The best method to antifoul any boat is as follows.
  • Jetwash the hull immediately when the boat is lifted out of the water.
  • Sand the hull thoroughly creating a keyed surface.
  • Jetwash the hull again to free dust and loosened materials.
  • Apply antifoul primer.
  • Leave at least 24 hours if not longer if the weather is cold and wet.
  • Apply at least 3 coats of antifoul.

Short Term Discomfort, Long Term Gain...
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