Repost as I somehow accidentally posted in Windsurf - thanks for the heads up Subsonic!
Hi guys,
I have a little Spacesailer 24 yacht here in WA and she was due for an antifoul job (first one that I'll be doing).
I blasted off a bit of the exterior surface of the hull above the water line (the white).
I was just wondering if someone could advise what I could re-surface this with?It looks like just 1 layer of whatever it is came too. Too much pressure with the pressure gun, my mistake.My research suggests that flowcoat would be the go, but thought there might be someone on here that would already be skilled in this stuff.
Photos attached. I'm just looking to repair the white area really. The blue I will just paint with antifoul paint.
I have removed all the algae with a little bit of diluted Randex rust converter/slime remover
Subsonic suggested flowcoat was the way to go, thought I'd post here as I know there are some mad sailors here.
Cheers!
Assume these white patches are where shells were and the water blast has blasted them off plus a bit of the gelcoat? Assume they are not osmosis damage patches.
Flowcoat could be ok depending on the depth of them.
fibrefinish.com.au/products/brush-iso-npg-polyester-flowcoat-white
If they are too deep and flowcoat won't fill them even after more than 1 coat - allowing careful sand back and ideally 2 pack polyurethane paint touch up over the top - then a polyester or epoxy filler and the 2 pack poly paint would be needed.
I have done the similar job with Septone filler as below,
www.whitworths.com.au/septone-fibre-tough-polyester-filler-500g
and Resene Uracryl 402 semi gloss, colour milk white.
Select to expand quotesouthwest24kn said..
Repost as I somehow accidentally posted in Windsurf - thanks for the heads up Subsonic!
Hi guys,
I have a little Spacesailer 24 yacht here in WA and she was due for an antifoul job (first one that I'll be doing).
I blasted off a bit of the exterior surface of the hull above the water line (the white).
I was just wondering if someone could advise what I could re-surface this with?It looks like just 1 layer of whatever it is came too. Too much pressure with the pressure gun, my mistake.My research suggests that flowcoat would be the go, but thought there might be someone on here that would already be skilled in this stuff.
Photos attached. I'm just looking to repair the white area really. The blue I will just paint with antifoul paint.
I have removed all the algae with a little bit of diluted Randex rust converter/slime remover
Subsonic suggested flowcoat was the way to go, thought I'd post here as I know there are some mad sailors here.
Cheers!
Hi, a couple of questions, has the hull ever been painted or is the white original gel coat and when all the crud is removed are there indentations where the white chips are now. I ask as there is no indication that I can see that the gel coat has been removed back to the glass, so if it were me I would, after a thorough cleaning, give the damaged area a rub with 600 grit wet and dry paper on a rubber block with lots of water and see just what damage there is. If it is minimal then sand a little more, switch to 1200 paper and sand a lot more 
, buff and wax and go sailing. 
Select to expand quoter13 said..
Assume these white patches are where shells were and the water blast has blasted them off plus a bit of the gelcoat? Assume they are not osmosis damage patches.
Flowcoat could be ok depending on the depth of them.
fibrefinish.com.au/products/brush-iso-npg-polyester-flowcoat-white
If they are too deep and flowcoat won't fill them even after more than 1 coat - allowing careful sand back and ideally 2 pack polyurethane paint touch up over the top - then a polyester or epoxy filler and the 2 pack poly paint would be needed.
I have done the similar job with Septone filler as below,
www.whitworths.com.au/septone-fibre-tough-polyester-filler-500g
and Resene Uracryl 402 semi gloss, colour milk white.
G'day r13,
Yep I think it caused by shells that had previously been removed and left some weakened top layer. I applied too much pressure with the petrol pressure washer and blasted them off. I'm quite positive it's not osmosis related, judging by what is underneath.
The depth is very thin, it looks like just one layer of paint that came off, exposing what I believe is the gel coat underneath (it's a rough-ish surface).
I think one or two coats of 2 pack polyurethane paint would cover it well. That sounds like the go. I think the surface that I blasted away was indeed a poly 2 pack top layer.
Thank you for your advice!
Select to expand quoteUncleBob said..
Hi, a couple of questions, has the hull ever been painted or is the white original gel coat and when all the crud is removed are there indentations where the white chips are now. I ask as there is no indication that I can see that the gel coat has been removed back to the glass, so if it were me I would, after a thorough cleaning, give the damaged area a rub with 600 grit wet and dry paper on a rubber block with lots of water and see just what damage there is. If it is minimal then sand a little more, switch to 1200 paper and sand a lot more , buff and wax and go sailing.
Hi UncleBob,
I love your optimism.
Yep it looks like there is an exterior coat of two pack paint judging by the thin layer that came away and exposed a different surface beneath. It's about 0.5mm or less, so I presume two-pack polyurethane (based on when I think it may have been painted).
There isn't much depth but I'm thinking that some entrepreneuring sea life would see this as an opportunity to nest in there at some point down the track, so I would like to smooth it out and add that semi gloss effect back in.
Thank you!
Select to expand quotesouthwest24kn said..UncleBob said..
Hi, a couple of questions, has the hull ever been painted or is the white original gel coat and when all the crud is removed are there indentations where the white chips are now. I ask as there is no indication that I can see that the gel coat has been removed back to the glass, so if it were me I would, after a thorough cleaning, give the damaged area a rub with 600 grit wet and dry paper on a rubber block with lots of water and see just what damage there is. If it is minimal then sand a little more, switch to 1200 paper and sand a lot more , buff and wax and go sailing.
Hi UncleBob,
I love your optimism.
Yep it looks like there is an exterior coat of two pack paint judging by the thin layer that came away and exposed a different surface beneath. It's about 0.5mm or less, so I presume two-pack polyurethane (based on when I think it may have been painted).
There isn't much depth but I'm thinking that some entrepreneuring sea life would see this as an opportunity to nest in there at some point down the track, so I would like to smooth it out and add that semi gloss effect back in.
Thank you!
Hi, if in fact the only damage is to the paint over the original gel coat then to repair it you need to sand the problem area and repaint, no filler, flowcoat or whatever is required, simply sand and repaint, although for a truly good finish the entire side of the hull will probably need to be redone.
Thanks southwest24kn no problem. I agree it doesn't look like osmosis.
UncleBob with always sage input has brought up the salient issue that the patches above the blue stripe look like 2 pack poly coming off and showing the original gelcoat - I should have thought of / realised this and agree.
Likewise agree that no filler should be needed for a reasonable rectification. But sanding with wet and dry starting at 600 seems like jewelers or watchmakers tolerances sorry........will take to nearly the end of time when you presumably have a slip booking for a fixed time........for sure you don't want to sand into the gelcoat but imho 240 or even 180 would be a good start - plenty of water and dust mask. For the white area finish with 400 then paint.
You have 3 different areas - the white hull topsides with original gelcoat and 2 pack applied sometime later probably ~20yrs ago, the blue boot top which you advise will be coated over with afouling, and the black afouling.
For the white topsides suggest sand the old poly paint off into the patches from all sides but don't sand the white patches. Then re-coat with the poly as relevant. As you say this is the major focus. If some local areas are still too bumpy then consider the Septone filler then the poly. The semi gloss poly recommended will assist to "hide" these but only to a certain degree - full gloss poly will make them stand out like dogs...........
For the blue - is it afouling now or something else which you are going to afoul black over along with the lower hull? If it is not the same brand and type afoul as the black you are going to use, it may need a specific primer then undercoat then the afoul.
For the black area there doesn't seem to be many white areas rather some shells and stuff - so scrape and sand back, patch prime and afoul.
Hi UncleBob and r13,
Thank you very much for your advice again. I'm new to hull materials and antifouling so it's very valuable to me to receive your advice.
r13, replying to the three areas you broke it down into:
1. White topside - as you and UncleBob suggested, it sounds like just a good sanding on the original poly two pack and re-applying some fresh stuff will do the trick just fine. I know that it's impossible to see from the photos, but the depth is very superficial. I'm positive now that it is just the old poly two pack that flaked off. One question - could I apply this with a small brush (after letting the mixture get a little more putty-like)? Or is the only method to do a nice big re-lay of the whole area? I'm only really after functionality, cosmetics aren't really a problem.
2. Yep the current blue is a blue afouling. I don't know the exact product that was used for this. I have sanded it to rough it up, and I've actually ended up priming a lot of it (because of the marks left from removed shells). I might go ahead and finish priming the whole lot before applying the black afouling like you suggest. Is the only purpose of these boot stripes just cosmetic?
3. Black has been scraped of shells and already patch primed 
Much appreciated
Hi again, just for clarification, the wet rubbing, buffing and waxing I suggested is for gel coat polishing, not for repairing a painted finish.
I would use 240 grit dry paper to prepare the painted surface, prime and roll and tip to achieve a good finish.
No problem.
For 1 I wouldn't let the mixture go off a bit and get a little more putty-like before applying - this will impact the adhesion of it. Better to do 2 or 3 coats. Note that the Resene has a "settling time" for the mix after mixing the base and hardener before using. If I recall it is around 5-10mins. By the looks of it you could have one or two largish area rectangles to brush patch the whole area, and then some outlier spots which can just be individually brush filled.
For 2 if it is uncertain if the new black afoul will be compatible with the old blue, it would be a good idea to prime the lot. Boot stripes are just to protect the area immediately above the waterline from the green scum / slime as in your photos. It is common to just raise the waterline so putting the new black over the primed blue.
@UncleBob and @r13
Thank you very much for the advice - very helpful for a first timer.
I will be starting the repairs today, will post some photos of the finished jobs :)
Select to expand quoter13 said..
Assume these white patches are where shells were and the water blast has blasted them off plus a bit of the gelcoat? Assume they are not osmosis damage patches.
Flowcoat could be ok depending on the depth of them.
fibrefinish.com.au/products/brush-iso-npg-polyester-flowcoat-white
If they are too deep and flowcoat won't fill them even after more than 1 coat - allowing careful sand back and ideally 2 pack polyurethane paint touch up over the top - then a polyester or epoxy filler and the 2 pack poly paint would be needed.
I have done the similar job with Septone filler as below,
www.whitworths.com.au/septone-fibre-tough-polyester-filler-500g
and Resene Uracryl 402 semi gloss, colour milk white.
Many great apologies this was the Septone gelcoat filler I meant to advise to use - the one above has fibres included and is not for small gelcoat repairs.
www.whitworths.com.au/septone-gelcoat-repair-putty-400g
TotalBoat is a product that is perfect not only for repairing gelcoat surfaces but also for matching different colors of the boat. All you need to do is used a tool that suits the application you are doing such as a brush, roller, or even a spray gun. What is important is to prepare the surface and make it in good condition before the application process. This is to ensure that you achieved the maximum results that you want. You can consider it.
