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Muriatic Acid - Cleaning a hull

Old 07-13-2009, 04:49 PM
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Default Muriatic Acid - Cleaning a hull

Over the weekend, an employee at my local marina suggested to me that if I wanted to get the yellow stain off the bottom of my hull, he'd recommend using muriatic acid. He said that a lot of the big boat yards used it all the time. He did mention to use it in a well ventilated area and to use appropriate protective gear (gloves, mask, goggles, etc).

Here are my questions:

1) If I do use muriatic acid to clean the outside of my hull, how should I apply the acid to the hull? With a stiff, medium or soft brush? If not brush, what?

2) Should the solution be 50% water, 50% muriatic acid? Should I then rinse and wash with soap and water afterward?

3) After cleaning my hull, is it necessary to wax the hull? I've searched the forum and I've seen both yes and no to this question.

4) Are there better, safer, easier products to use? Apparently muriatic acid is pretty cheap stuff to buy and very easy to use?

5) Will it help remove the 'chalkiness' from my colored gelcoat (i.e., bottom of my hull is white but stained yellow; upper portion of my hull is colored but has faded. Will it help both areas?)?

Thanks n advance for your help and response.

Chris
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Old 07-13-2009, 05:38 PM
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I use SNO BOWL which is a toilet bowl cleaner whose active ingredient is acid, hydrocloric, I believe. I use one of the pads with a hande on it, not to scrub, but to keep my hands clear so I don't need gloves. The bottle has a small hole to sqirt the liquid out when the bottle is squeezed. I just go down the hull above the area to be cleaned sqirting the cleaner out sparingly while using the pad with a circular motion to spread it out evenly. By the time I get half way down one side, the area where I started is pure white so I hose it off and continue, always getting about half a boat ahead then going back to hose it off. The stuff needs a minute or two for complete cleaning. I can do my 24 1/2 ft boat in ten minutes with no scrubbing. The muriatic acid will probably be similar. Don't know about the colored gelcoat as I don't have it. USE EYE PROTECTION!!!
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Old 07-13-2009, 05:44 PM
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If you're worried about yellowing you will be in a lot of trouble if you use muriatic (hydrocloric) acid. Use a hull cleaner that already has the proper amount of muriatic acid and other chemicals. Use it sparingly because the more you use the quicker it will yellow next time.
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Old 07-13-2009, 06:38 PM
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Patrick,

I'm not sure I understand what you mean when you say that the boat will "yellow" quicker b/c of the muriatic acid. I'm assuming you aren't saying that muriatic acid promotes discoloration?
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Old 07-13-2009, 06:38 PM
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Boltune:

I just used muriatic acid to clean my hull and bottom paint before I applied new bottom paint. I applied it by using a garden bug/lawn sprayer that you can buy at Home Depot. I mixed the one part water and one part acid and sprayed it on the surfaces and allowed to soak a few minutes, then I rinsed it off. It worked well and did not disolor my hull. It cleaned the old paint real well. A boat yard suggested this technique to me. However, be careful as the acid is costic. Don't apply it on a windy day and protect your eyes and hands.
I routinely wax my boat and have not noticed any adverse affect on the finish.
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Old 07-13-2009, 06:41 PM
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Capt. Lou,

Are you suggesting that I wax the hull afterward or is that just something you do on a regular basis regardless of the acid wash?
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Old 07-13-2009, 06:44 PM
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Watch what you get it on, like your trailer... Toilet bowl cleaner works for me, another product called aluminum brite (made by snee chemical in louisiana) works well on brown hull stains.
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Old 07-13-2009, 06:45 PM
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Old 07-13-2009, 06:45 PM
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The acid strips the wax, makes the gel coat porous. Tannin will stain quicker. Wax afterwards.
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Old 07-13-2009, 07:10 PM
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Default Chemist opinion

Hi
My reccomendations is not to use something as caustic as Muratic Acid (10% hydrochloroic) on your gelcoat.There are other reasonable alternatives such as products made for boats. You have to make sure you neutralize it by thoroughly flushing with water or baking soda. It is very corrosive to any metal such , chrome, aluminum or your trailor. I am not sure what the effects of repeated applications are to gelcoat.
Kind regards
Mark
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Old 07-13-2009, 07:13 PM
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now using muriatic acid on stainless props.....amazing.......
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Old 07-14-2009, 10:07 AM
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Originally Posted by boltune View Post
Capt. Lou,

Are you suggesting that I wax the hull afterward or is that just something you do on a regular basis regardless of the acid wash?
I regularly wax my boat irrespective of the acid wash. I live in an area along the NJ shore where you get a lot of brown crud on the waterline. It is caused by the run off of fresh water from the NJ Pine Barrens into salt water that brings cedar tar from the Barrens and it looks brown. This brown stain is a common occurrence amongst all boats in my area. In the spring, I wash down the hull and old bottom paint with 50/50 water/acid and then rinse it thoroughly. Baking soda/water application is a good idea as it will neutralize the acid. After that I wax the entire hull, then, paint the bottom.
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Old 07-14-2009, 01:45 PM
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What do you think Mary Kate On/Off is? Muratic acid is 1/4 the price for a gallon.

I use it all the time and pour it in a plastic paint roller pan and use a soft bristle brush to apply on one side of the hull at a time. Let sit for 2 minutes and rinse will plenty of water.

Works great.
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Old 07-14-2009, 01:46 PM
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Originally Posted by UnclebobJHC View Post
The acid strips the wax, makes the gel coat porous. Tannin will stain quicker. Wax afterwards.
I'm not so sure about making the gelcoat porous.

Starbrite Hull Cleaner works very well for removing the brown or yellow waterline stain. It contains oxalic acid and some other ingredients. You can use Dekswood deck cleaner as a substitute. It also contains oxalic acid and is listed on the label as safe for fiberglass.

Either one can be sprayed, mopped, or brushed onto a damp surface. Let it sit a few minutes, then brush or wipe some more, then rinse. A soft brush is appropriate. Protect your skin and eyes.

Any of the acid products may discolor a galvanized trailer. Other than this discoloring, the trailer will not be harmed. Or, you can cover the trailer.
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Old 07-14-2009, 01:59 PM
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I just did my Aquasport hull that was a bit messy. Now I can use it to shave it's so shiny. Here is what I did. It's my typical spring ritual. The compounding is not always necessary.

- Quick soap and water wash to removed the easy dirt.
- Cover alum trailer parts with plastic. Cover metal through hulls with masking tape.
- Apply On & Off with soft bristle brush (long handle) and lightly scrub where necessary. Avoid the nasty fumes.
- Rinse thoroughly, remove plastic & tape.
- Lightly compound the whole hull. Pay special attention to those black marks that somehow get there when someone else is piloting :-)
- Wax entire hull and buff it till your arms are about to fall off. Then pass the buffer to someone else and he/she buff until arms are about to fall off. Repeat twice.
- Then go get your razor and make sure you can use your hull as a mirror :-)

That should do it...
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Old 07-14-2009, 04:36 PM
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I recently tried the toilet bowl cleaner "The Works".
I believe Dunk recommended it.
And guess what?
It friggin works. Like magic.
Brush on and rinse off. It removed years of tannic acid stains in a matter of minutes.
You can find it in an Ace Hardware store. I believe it contains hydrochloric acid. Ace has their own brand but it cost more. Go figure.
I applied wax afterwards.
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Old 07-14-2009, 05:51 PM
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Muratic acid is by far the fastest way to remove the yellow water stains. All other products have some sort of acid in them but just diluted. Just dont get the acid on your tralier or any galvonized metals. Stainless Steel is the only metal it will polish. Rinse with lots of water then wash with soap, then wax.
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Old 07-14-2009, 08:26 PM
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Great feedback. I appreciate your comments.
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Old 07-14-2009, 08:36 PM
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As 24/7 says.

If you feel better paying $$$$$ more just cause it says 'marine' on the label, do it.

I've been using muriatic acid, like the boatyards, for years now. 50/50 with water. Apply with paint roller or paint pad. Rinse off. Wash with soap & water. Wax.

No ill effects whatsoever. Had 1 boat 13 years. Gel coat waxed up almost like new.

Muriatic acid is a 'must have' in boat maintenance weaponry.
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Old 07-14-2009, 08:39 PM
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Get oxalic acid(wood bleach) and spray on, will remove yellow in a few minutes, as safe as oxyclean(Billy Mays). I remove concrete rust marks every day with it.
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