Battgirl 23 Posted March 2, 2015 Share Posted March 2, 2015 Am removing all the antifoul off my boat so i can check the condition of the fibreglass hull. I can confirm that caustic soda - 250gms mixed in a litre of water -thickened with a premix of cornflour and water does work. I am wearing full battle kit of disposable overalls with hood, boots, gloves and a powertool helmet with the visor covered in gladwrap (not affected by the caustic soda and it doesn't fog up) while mixing and using. I put the stuff on with a 4 inch nylon brush then spray it with water to keep it wet and after half an hour to an hour i use a plastic scraper to slide it off straight into a bucket lined with a grocery bag. It comes off easily. A litre of mix covers about 3 square metres. Link to post Share on other sites
rossd 16 Posted March 3, 2015 Share Posted March 3, 2015 That sounds easy. I have spent 3 afternoons hand scraping off antifoul from a 28fter and one more to go. Hand scraper with vacuum attached to the handle and face shield. 150mm orbital sander wouldnt do it. Would not the caustic affect coats underneath? Link to post Share on other sites
grantmc 59 Posted March 3, 2015 Share Posted March 3, 2015 I put the stuff on with a 4 inch nylon brush then spray it with water to keep it wet and after half an hour to an hour i use a plastic scraper to slide it off straight into a bucket lined with a grocery bag. It comes off easily. A litre of mix covers about 3 square metres. Brilliant suggestion and very grateful for the advice. It should be on the notice board at every marine yard around the country. Would you be able to post a before/after photo? Does your mixture have any effect on the hull itself? Link to post Share on other sites
Battgirl 23 Posted March 4, 2015 Author Share Posted March 4, 2015 Credit for the idea goes to the UK ybw forum. I am removing several layers of antifoul and what i am finding is that the top layers slide off leaving underlying layers soft and easy to remove with a scraper. It doesn't seem to affect the fibreglass hull Link to post Share on other sites
rossd 16 Posted March 4, 2015 Share Posted March 4, 2015 You say: "Underlying layers soft and easy to remove with a scraper" So are you infact going right back to clean fibreglass? I dont think that would be wise on a wooden hull as mine is? I am dry scraping back to what looks like sound, hard primer and fillers. A moulded glass hull is smooth and fair, where as an older wooden hull has fillers, bog, glue, putty, high build primers, you name it. Link to post Share on other sites
Island Time 1,225 Posted March 4, 2015 Share Posted March 4, 2015 Rossd, no idea of your experience, so I presume none! Disregard this if you know more than I! You'd be normally looking to remove all the old anti-fouling only, then have the hull back to a sound surface (smooth, no flaking etc) surface for your new anti-fouling. I've never used this method, but I'd be surprised if it softened anything but the anti-fouling?? Battgirl might answer that. To go back to bare timber in your case would create more work than normally required, unless there is a good reason to do so (Timber to replace etc). Link to post Share on other sites
Battgirl 23 Posted March 4, 2015 Author Share Posted March 4, 2015 I agree with IT on the timber hull. On my fibreglass boat which i have owned for a few months i am doing a one-off strip back to the gelcoat, checking for osmosis then epoxying the hull and applying new antifoul. It takes 45 minutes to an hour to remove all but the last half to 1mm layer of coating after applying gooy caustic soda to about 3 square metres of hull and leaving it for half an hour to an hour. Link to post Share on other sites
Battgirl 23 Posted March 4, 2015 Author Share Posted March 4, 2015 I have also used caustic soda to remove varnish from timber in the same way. I found the timber was only affected in small patches if the caustic soda was left on too long. Link to post Share on other sites
rigger 47 Posted March 4, 2015 Share Posted March 4, 2015 Have posted this before - only for use on wooden / timber hulls - DO NOT USE on Fibreglass Two people - one uses the I-Strip device (Resene used to rent them out) the other follows with a scraper or putty knife - whatever works the best for the individual. If you want to remove fibreglass from timber it works well leaving a surface that needs a light sanding depending upon how good you are with the blade or putty knife. Link to post Share on other sites
rossd 16 Posted March 5, 2015 Share Posted March 5, 2015 This is really confusing now!! I have no belief in taking off good paint layers on anything Island Time, without good reason. Thats why I am scraping off old antifoul and have a good primed base showing now. I can see rigger it might be worthwhile on a wooden hull where you need to go back to bare wood for some reason, but thats not me at the moment.and besides if its no good on fibreglass its no good on a glass sheathed wooden hull as mine is. Link to post Share on other sites
Battgirl 23 Posted March 8, 2015 Author Share Posted March 8, 2015 Job done. I gave the hull a good scotchbrite clean and rinse and am pleased with the results. The fibreglass hull has not been affected and looks to be free of osmosis as well. Link to post Share on other sites
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