Antifoul falling off!

[Sailfree]

On previous 2 boats I scoured antifoul and applied another coat of Internationals Micron Extra each year. I had these boats for only 3 yrs and had no problems with A/F.

I assumed it was self erroding as certainly near waterline you could see the white GRP grinning through after scouring.

Current boat is now coming up for 7 yrs and last year when I scoured it antifoul came off in patches (mostly on horizontal areas on underside) and also in places as I applied new antifoul with a roller some of these patches extended leaving white gel coat. I sanded these areas down and feathered the edges.

I suspect Bob the Builder who commissioned my boat didn't de-wax the new hull enough or is it the extra thickness of Antifoul that is now forming an independent membrane/layer causing the interface with the GRP to break down?

I would appreciate advice on :-

1. Is this a common problem after 6-7 yrs of recoating hull.

2 Is there a point when you try to scrape it all off and start again.

3. OR do you give it a harder pressure wash and scour it with the green pads and if any patches come off - rub it down locally and feather edges.

Only ever used Micron Extra A/F.

 

[G12]

Well, you're supposed to prime bare surfaces first before painting. If you're worried about the paint coming away then may I suggest you start from scratch again? Scrape it back to gel, get the surface suitably abraded and then prime followed by A/F.
It's a bit of work but at least you'd have a nice surface underwater for next season.

 

[Robin]

If it's flaking off the hull it is Bob the builder who didn't degrease or prime the moulding. If it is flaking between coats it is Sailfree the Skipper who didn't rub it down well enough OR who applied it when the surface was damp. I know they say you can just overcoat Micron after a washdown, but it is easy to miss bits and easy for there to be residual salt that attracts and holds damp.

If it is flaking off a cast iron keel BTW, moisture is a main suspect because it condenses on the cold keel in an invisible coating, just where you want to put on some expensive paint.

Oh if it is flaking, be warned that what looks OK may still flake off as you put the new coat on, often in great slabs and that can be very demoralising, sorry.

What to do depends on time and inclination, either rub down with wet and dry wet, wash off and feather in locally then patch prime and overcoat or take it all off and start again, only this time degrease and prime first. Instead of wet and dry, get a ceiling and wall plaster sander head with a universal joint to allow it to move and screw onto a pole (Decorator merchants sell them). Use the open mesh type sheets of I think carborundum grit the same folk sell in rolls, cut it into a sheet that fits like paper on an orbital sander, This used with plenty of water doesn't clog and sands very well, we could do the whole bottom of a 41 footer in 2 hours. If you are around the club I could lend you one of these gizmos, but they cost only about £10-£12 and are well worth having for future use. Good luck!

 

[Grajan]

Detachment not uncommon where there are multiple layers of A/F
interlaminar stresses build up and sheer the coating either from itself or from the hull especially if there are traces of release wax left on the hull prior to the first coat applied.

As for treatment it depends on wether you race seriously or not, if you are a cruising man feather the edges and lightly abraid bare GRP, touch up all bare areas then apply full coat(s) if it is t'other scrape back to GRP lightly abrade apply one coat of Primocon and overcoat with A/F within the reccommended overcoating time.
GRP primer was a once only use product.

 

[Sailfree]

Oh if it is flaking, be warned that what looks OK may still flake off as you put the new coat on, often in great slabs and that can be very demoralising, sorry.

Yes we had that after I had already rubbed down and feathered edges of bit becoming de-bonded.

I have never applied 1st coat of A/F is there a primer to use on GRP first?

I have a kitchen ceiling to skim/repair so I intend to get a dry linning ceiling sander on a pole. Thanks for offer. Found using battery sander was quick and fairly painless (with face mask!)

As its 43' cruising yacht and the majority has lasted OK (only small horizontal areas went last year on 7th yearly application!) I think I will pressure wash hard , scour well and sand down only any areas that become detached.

 

[Robin]

Yes we had that after I had already rubbed down and feathered edges of bit becoming de-bonded.

I have never applied 1st coat of A/F is there a primer to use on GRP first?

I have a kitchen ceiling to skim/repair so I intend to get a dry linning ceiling sander on a pole. Thanks for offer. Found using battery sander was quick and fairly painless (with face mask!)

As its 43' cruising yacht and the majority has lasted OK (only small horizontal areas went last year on 7th yearly application!) I think I will pressure wash hard , scour well and sand down only any areas that become detached.

This is what I mean by the sander and the same link shows the abrasive rolls to use. I used it every year on Micron, use with loads of water and it gives a very smooth surface, good key and yet doesn't remove too much. It is way safer than dry sanding and much more effective than wet/dry or scouring pads plus you get to stay cleaner and dryer, well a bit anyway.

http://www.screwfix.com/p/pole-sander/33586

There used to be a primer for bare grp but now International say use Primocon, which I did use on ours after having the antifoul removed by blasting. Five years on from then when we sold the boat there was not a single flake! On the previous boat having epoxied the bottom with Blakes SFE 200, we used Blakes antifoul primer to key to the epoxy within the timescale allowed, but then went to Micron as an antifoul. That also stayed flake free for years until sold. I don't know if Blakes still make their antifoul primer but if they do you could use that on the patches, otherwise scratch the bare bits up well. The real problem is if the bits around the bare patch are really stuck, or they just look like they are until you roll over some new stuff.

 

[Sailfree]

What grade Oxide paper did you use 40 , 80 or 180 please?

 

[Robin]

Pretty sure I used **80, but what I have left is not marked. It is an open mesh, sold as a roll not a solid paper and it looks like a copper screen. A cut sheet seems to last forever and I used just one sheet for each side of our boat. Do it in bands about 6ft or so wide going down from the waterline, getting it really wet with a hose first. Once you get going it creates a sort of wet slurry and it all gets easier, then wash off the first band thoroughly and wet the next one as you do it and you get into a kind of routine. I rinsed the paper off with the hose in between each band. The best was with SWMBO helping, she did the hosing and I did the sanding and that way we did both sides in about an hour and a half.

** On reflection it may have been 40, but certainly wasn't 180. I would get some of each 40 and 80.

 

[GrahamM376]

2 Is there a point when you try to scrape it all off and start again.

Ours had the same problem, years of different coloured coats and flaking more each year. As soon as the new coat solvent got to it, more would flake during rollering.

Spent last winter scraping it all off, not a nice job. Although the boat had previously been epoxied, there were numerous holes where surveyors had scraped through so took the opportunity to re-epoxy it.