Primer for GRP hull

William_H

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I have a very old GRP trailer sailer. I have applied A/f for 36 years. However recent years antifoul paint seems to have a habit of disappearing exposing patches of gel coat after a few months. Using a fairly cheap A/F made I think in Malaysia. I wonder if I should prime the affected areas. So I looked at Primacon and found it recommended for all surfaces but not GRP. Am I missing something. Any ideas. yes I do in water scrub fairly vigorously and frequently but I don't think that is the cause of paint loss. ol'will
 

VicS

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I have a very old GRP trailer sailer. I have applied A/f for 36 years. However recent years antifoul paint seems to have a habit of disappearing exposing patches of gel coat after a few months. Using a fairly cheap A/F made I think in Malaysia. I wonder if I should prime the affected areas. So I looked at Primacon and found it recommended for all surfaces but not GRP. Am I missing something. Any ideas. yes I do in water scrub fairly vigorously and frequently but I don't think that is the cause of paint loss. ol'will
The Tech data sheets for international antifoulings on the UK (GBR) website says "BARE GRP: Prime with Gelshield 200 for osmosis protection, or Primocon or Interprotect. "

The description for Primocon says
Substrates:
Aluminium / Zinc-Galvanised Steel
Epoxy Composite / Carbon Fibre
GRP / FRP
Lead
Steel
Wood

And the Tech data sheet says
Preparation
Wash all surfaces except STEEL with Super Cleaner.
BARE GRP Sand using 180/220 grade (grit) paper.


If you have been applying new antifouling on top of old every year for 36 years you are finding the same as I am . The old stuff falling off and leaving bare patches. If that the case I think the real solution is to strip it all off (
Then
Abrade as above , apply Primocon followed by new antifouling
( according to the UK site its Interprotect thats not suitable for GRP)

But I just apply the new antifouling sticking any flaky bits down with the new)
 

dankilb

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Primocon (or something like Jotun’s Vinyguard - other brands are available!) do claim to work as a tie coat too. If you’re disinclined towards a full scrape-back-to-gelcoat job, you could try a very aggressive pressure washing to remove any flaky bits and then a ‘tie coat’ of one of the vinyl primers, before new AF.

At £30 per 5l for the cheaper stuff, it might be worth a try, as scraping is grim - even on a smaller boat!
 

Caer Urfa

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If the existing antifoul is to thick it will continue to just crack a peel so hate to tell you 'get it all off',
If its peeling at the waterline or you have a boot topping use International Toplac, you can scrub it easy without it coming off

I have used Jotun Silver Vinyguard for years and no problem and is far cheaper than International Primocon, and easy to apply

SML Marine Paints - Jotun Vinyguard
 

Rhylsailer99

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Screenshot_20210220-205027.jpgim about 75% done scraping i got vinguard silver primer for the bottom once all done , I do about 1 sq metre a day as time is on my side during lockdown. I plan to do a coat of West epoxy on the keels as they need a lot of work filling all the gouges and nicks
 

William_H

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Thanks all for the advice. I am aware of the flaking problem with build up of a/f. I tend to use minimum layers and scrub with sand paper at the end of each season in water.
No the problem is not flaking as such no step edges etc. I will try a primer probably primacon and see how it goes. ol'will
 

MADRIGAL

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I have used Interprotect with great success. I see from International’s literature that both Primocon and Interprotect are recommended for use under antifoul. Primocon can be used as “a barrier coat over unknown or incompatible antifoulings”, so that may be your best choice.
 
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