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duncan (the other one)

yellow coating on gelcoat - how to clean?

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I'm in the middle of cleaning up a ~15yo dinghy. Small dings, scratches and chips in the hull, that sort of thing.

It has been kept fairly well - probably garaged - so the rest of the gelcoat is generally in nice shiny condition; no oxidation to speak of.

The repairs obviously need the usual sanding back,  wet and dry and compound polish. 

I plan to finish off the whole hull with something like starbrite when I'm done.

 

My problem is that the gelcoat (white) seems to have a glaze of wax or similar that has yellowed.  The only non-abrasive I've found (in my box of cleaning chemicals) which removes it is acetone with some vigorous rubbing.

I've tried detergent, simple green, automotive wax and grease remover, and other kitchen-type general cleaners with no success.

 

Am I doomed to rubbing the hull down by hand with acetone-soaked rags before I put my finish on, or is there something else which will work?.. and what is it? Old car wax? 

 

note: boat is a well built racing dinghy.. gelcoat is minimal (you can see the glass weave through it), so I do not want to compound the whole boat.

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an electric polisher w/bonnet and some polishing (not rubbing) compound won't do the job?

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14 minutes ago, hobot said:

an electric polisher w/bonnet and some polishing (not rubbing) compound won't do the job?

yeh - it would .. but again, why polish if it can be removed with a solvent?

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Try Clorox Cleanup or CRC On & Off.

If they don't do it then you'll have to do it the hard way.

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Try On and Off hull cleaner.  Its an acid wash for gelcoat. 

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Oxalic acid solution will take it right off. Mix your own or buy Starbrite hull cleaner or similar. Be sure to polish&wax well afterwards.

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9 hours ago, duncan (the other one) said:

yeh - it would .. but again, why polish if it can be removed with a solvent?

Because you're going to have to polish afterwards anyway. If you use want a shortcut, polish with 3M Cleaner+Wax and get a two-fer.

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On & Off contains oxalic, phosphoric, and hydrochloric acids.  So you probably have most bases covered with that sort of mix. 

I tried about 4 or 5 different cleaners to get some stubborn stains off the deck.  On & Off was the only one that worked.

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Depends on what the stain is.  On and Off is great for waterline stains, tannins, rust, organics etc.

Sounds like you could have some previous owner shit on there if it looks like a coating, a different job all together.  Some industrial strength floor wax remover is where I'd start if acetone works and others don't.  It seems to work well on a lot of the wipe on crap coatings like poli-glo etc. 

 

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Diggers oxalic acid from Bunnings.

Cheap miracle product.

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I use oxalic as seldom as possible. They say that acid takes the yellowing off, but also makes it come back easier, if not polished and waxed properly.

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Poli Glow I think it was called, was a miracle gelcoat fixer that didn't last.  I heard it's a pain to get off once applied.  Any history of that? If on and off won't get it off your screwed.

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1 hour ago, Blitz said:

Poli Glow I think it was called, was a miracle gelcoat fixer that didn't last.  I heard it's a pain to get off once applied.  Any history of that? If on and off won't get it off your screwed.

Not true. On and off is an acid cleaner for organics, doesn't help on coatings much.  Floor stripper is the tool for the job on that one.  Or 3m Safe-T-Strip, but that's expensive, and slow.  Both work on varnish when you leave an employee unsupervised around non-skid...

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Reporting back:

Oxalic acid did the trick. Concrete Rust and Stain remover from the local hardware store, per harryg above.  Mixed with a bit of detergent to help it foam and stick, wash off after 5min.

Then a polish of the wet-sanded parts, followed by starbrite on hull.

It should fill the most important requirement - a psychological blow to my opponents before we even start a race.

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On 10/18/2018 at 12:56 AM, duncan (the other one) said:

yeh - it would .. but again, why polish if it can be removed with a solvent?

Actually, it won't remove it completely.  It will grind small particles of wax into the gel coat and leave it there.  It way get the yellow gone, but don't fool yourself.  If you were painting afterwards you'd be very sorry that you didn't degrease. 

As a solvent, acetone sucks. It evaporates too quickly and leaves deposites behind.  Mineral spirits works much better, and is cheap from big box stores rather than marine stores. 

 

Cool that you got the acid to work. Go scare your competitors off the course,. 

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1 minute ago, Grrr... said:

Actually, it won't remove it completely.  It will grind small particles of wax into the gel coat and leave it there.  It way get the yellow gone, but don't fool yourself.  If you were painting afterwards you'd be very sorry that you didn't degrease. 

As a solvent, acetone sucks. It evaporates too quickly and leaves deposites behind.  Mineral spirits works much better, and is cheap from big box stores rather than marine stores. 

mineral spirits - aka Turps here in Oz - didn't work.

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4 hours ago, duncan (the other one) said:

mineral spirits - aka Turps here in Oz - didn't work.

Mineral spirits is great, when dealing with what it works well(oil products for wood, un-cured oil based paints, grease and oil on engine parts, thinning oil paints and varnish).  Not much good for anything else.  Good on you for finding something that worked(acid cleaner!).  Test patches and getting to the right chemical is always a satisfying feeling. 

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I have the same task coming up: waterline is yellowed by the exhaust and under the transom, some yellowing on the bow. will be using some oxalic, probably starbrite, on as needed basis, not the whole topsides for example.

I took extra care to polish and wax well in the spring, extra coats by the waterline,  and it seems to have helped a lot. Almost no yellowing this season (6 months in the water)

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8 hours ago, Itsabimmerthing said:

I have the same task coming up: waterline is yellowed by the exhaust and under the transom, some yellowing on the bow. will be using some oxalic, probably starbrite, on as needed basis, not the whole topsides for example.

I took extra care to polish and wax well in the spring, extra coats by the waterline,  and it seems to have helped a lot. Almost no yellowing this season (6 months in the water)

Yours sounds like the exact situation that On & Off is for - waterline mustache.

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I've found Mr Clean Magic Erasers (or the generic equivalent) work great on gelcoat. You can get a box of 100 for $5 on eBay. Look for melamine sponges.

  

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I have had good luck with CLR, especially on white gel coat. I keep it wet for about 10 minutes then wipe off followed with an all purpose cleaner like 409 to remove any CLR residue. It also works well removing rust stains if kept wet ( I use paper towel like shop rags soaked with CLR over the stain) for as long as necessary, sometimes overnight.

CLR worked into non skid areas with a medium stiff brush really cleans them up.

 

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+1 on toilet bowl cleaner. Sponge it on and leave for 5 minutes. Rinse well. 

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6 hours ago, Vin said:

+1 on toilet bowl cleaner. Sponge it on and leave for 5 minutes. Rinse well. 

Or for the really in a hurry, a bottle of "blue stuff" aluminium brightener from Lordco.  Works great on teak too, beats the piss out of teak brightener.  Dilute 1:5 with water.   :P  Done in 10 seconds.  Will melt your face too though and acid gas cartridges are a must.   Not that I'd ever do such a thing or recommend it, even if you have run out of regular acid. 

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WTF are " acid gas cartridges" and why would I need them?

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1 hour ago, SloopJonB said:

WTF are " acid gas cartridges" and why would I need them?

A type of respirator cartridge, you should be using them to avoid screwing up your lungs with any hull cleaner, or at least use a OV cartridge if you're doing it as a once off job and are too cheap to protect yourself properly.

When dealing with aluminium brighteners(Hydrofluoric acid) they are absolutely a bare minimum along with good ventilation, disposable chemical resistant suit, chemical resistant gloves, proper goggles and half face or better a full face respirator.   Looks like Lordco discontinued Blue stuff, Trotac etc still sell it as Alumabrite+ and neither have any sort of warning label that make clear how much more dangerous they are to work with than your regular hull cleaner which I always thought strange.    I have done it myself a pinch when stores were closed, it worked better than the usual products at a higher dilution ratio and far lower cost(about 1/4 the cost of on and off after dilution) but I would never allow anyone working for me use something off label like that, or recommend anyone doing it despite it's effectiveness.  

If someone decides to do so anyways, that's their business and they need to take precautions.

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Iron Out or Rust Out are cheap from a hardware store or Home Depot. Both are mild oxylic acid. Just spray a little on and yellow disappears immediately. Get the liquid not the powder. Put some RejeX  on the area afterwards.

 

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On 10/18/2018 at 10:36 AM, IStream said:

Because you're going to have to polish afterwards anyway. If you use want a shortcut, polish with 3M Cleaner+Wax and get a two-fer.

I like this product, it cleans streaks and so on and waxes in a single use.  

 

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