Re: aluminum boat cleaning
Cleaning Aluminum boat hulls
This should only be done outdoors!
1st step is to power wash the hull, if you don?t have a washer go to a car wash, this can save you some scrubbing.
When Grumman was making aluminum canoes and boats they dipped the metal into a vat of phosphoric acid with an electrical charge applied the resulting product had a bluish tinge to it. This is an oxide on the surface that provides a long lasting protection and leaves a smooth hull. Most manufacturers don?t do this any more, when I bought my Bass Tracker I don?t believe it had anymore than a wax applied to the aluminum. If you decide to act preemptively you will have to remove any wax or oils on the hull before using a conversion coating. Both Navel Jelly and chromate are conversion coatings. If using a chromate conversion coating you must prep the hull with hydrofluoric acid or a product sold as a pre-wash for chromate conversion coatings.
Cleaning with Navel Jelly:
Navel Jelly is a good product for cleaning the hull, however it is slow working and takes a lot of scrubbing but does a good job and if done correctly leaves a protective film on the hull. It will have a slight bluish tinge. Its active ingredient is Phosphoric acid, if you buy the acid alone it will work quicker and give some protection also but not as good as if an electrical charge was applied. The key to getting a protective film is the length of time the chemical is on the hull, on a humid day it will stay wet longer with out being refreshed.
Use Navel Jelly straight from the bottle. Keep dipping the pad in the gel, remember each time you go over an area it brings fresh acid to it and it?s the acid that does the work. Do an area about 2?x2 ? and don?t let it dry before rinsing. If the hull is badly stained you may have to repeat the process more than once. You do not have to apply a protective coating if you use Navel Jelly and it is done properly.
Hydrochloric acid (Muratic acid) can also be used but does not work all that fast and leaves no protective coating, and produces noxious fumes.
Cleaning with Hydrofluoric acid:
Hydrofluoric acid can also be used; it is the fastest of all the cleaners and the easiest to use but also the most dangerous. It also produces noxious fumes. It will turn the hull a silvery white. It will also etch glass and stainless steel but is harmless to plastic and most paints used on boats. Test a small area if there is any question. Be very careful using this product and wear protective clothing.
Hydrofluoric acid can be purchased at some air conditioning supply stores under the brand name ?Con-Coil? or ?CSF? there are also other brands that work just as good, read the label the see if it contains hydrofluoric acid. There are some other aluminum cleaning products that do not contain hydrofluoric acid available at AC supply stores but I have not tested them. I have been told that they work just as well but not as fast.
This is a very strong acid and should only be used with protective clothing, rubber gloves and a face shield. It MUST be thoroughly rinsed off!! I recommend a power washer for rinsing, one of the electric low pressure ones (1700 psi.) that sell for about $100.00 will work just fine. When you think you have rinsed it enough do it again. I used a sponge mop with a scrubby pad on the back. With a good pair of rubber gloves on dip the mop in a 50/50 water/acid solution and scrub lightly, keep going over the same area until it is clean. Rinse immediately, do not let it dry! I have an 18? boat and it took less than ? gal of acid to clean it. If you use this method you will need to apply something to protect the hull.
A word about hydrofluoric Acid
If left to dry and or not rinsed off thoroughly over time hydrofluoric acid causes a molecular change in the aluminum it will turn brittle to the point that it will crumble and fall apart at even a light touch.
Hull protection:
One of the best ways to protect aluminum is with a chromate conversion coating and it lasts for years. Like the navel jelly it forms a protective oxide on the hull and turns it a golden brown color. The chromate is very poisonous as it comes from the bottle but as it combines with the aluminum it is neutralized. Do not dispose of by pouring down a drain or on the ground. It is best to apply the chromate solution to the hull while it is still wet from rinsing the acid off. It helps to have two people and be careful not to apply acid over the area where the chromate conversion coating has been applied, as it will remove the coating. You can leave a 4? band between what is cleaned and what you are applying the chromate to. A 4? foam paint roller works well, do not saturate the roller or apply pressure to the point it drips, go over the area repeatedly until the aluminum is a golden brown color.
Chromate conversion coatings are getting harder to find because of their toxicity. I purchased some from Chief Aircraft, they have two locations one in Fl. and one in Or. It is listed as (Alodine Coating Chemical for Aluminum 1Qt) 1 qt. will cover up to 200 sq ft under ideal conditions. They will ship it to you using UPS. As of Jan 09? it cost about $25.00 a quart, about $10.00 shipping from Fl. To Va. And there is a $20.00 hazardous material charge for UPS. It takes about 1 quart to coat my 18? boat. Follow the instructions on the bottle. Allow to cure for 24 hours before using the boat.
I have never tried it but I see no reason that after cleaning the hull with hydrofluoric acid you could not apply Navel Jelly to get a protective coating. The cleaning is the hard part with Navel Jelly and the acid does that very nicely. You would have to apply repeatedly to get a good protective coating but at least you would not have to scrub to get to oxide off.
If you have any corrosion problems around stainless steel screws or fittings remove the fitting and clean off as much of the corrosion with sand paper as possible. Clean the last of it out of the metal pores with hydrofluoric acid. Coat aluminum hull and screws with chromate conversion and if the area was painted, paint to match. Assemble using Tef-gel on the screws and nylon washers as spacers between any stainless fittings and the hull.
Link to Chief Aircraft:
http://www.chiefaircraft.com/airsec/Aircraft/Chemical/AlumiprepAlodine.html#Alodine
Link to Tef-gel
http://www.spursmarine.com/tefgel5.htm
These products are available at other places so you may want to do a search, you might find a better deal. I hope this is of help to anyone trying to control corrosion. I have included a photo of my hull after it was partly cleaned with hydrofluoric acid this area took about 20 min to clean.
If any of you try one of these processes please leave a note on here telling everyone how it worked for you, if you had any problems, and what they were and what you did to overcome them.
Thanks
Howard