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How To: Descale and Descum a Boat


Reflections Detailing of Utah gets to deal with a fair number of boats here in Utah, and boat detailing is not “glamorous” to many detailers.  I really like detailing boats because the turn around in appearance can be drastic.  Boating in Utah is a family affair and after a long day on the water many boats just get put in storage till the next week, this weekly trend continues until the problems not addressed build.  The major problems are; hard water spots, dirt, grime on the seats, carpets with all matter of spills, and boats that stay in the water all season.  This later situation presents the topic of this blog;  How to remove hard water scale and algae scum build ups on a boats hull.

Boats are a huge amount of work due to the nature of the material you are working with (gel coats, fiberglass) and they are typically have a much harder coating in comparison than clear coats.  The angles you are cleaning or polishing stress your back, and many body parts you don’t use frequently.  Imagine holding a rotary buffer above your head while trying to keep it in control on the surface of the boat as that surface slants away from you!  The chemicals used can be harsh, and an agitation to human skin, eyes, and respiratory system.  Added to all this is the fact that many owners only get the boats “detailed” when the problems build to such a condition that you are not maintaining the boat but restoring the boat to the best possible state.  Restoration is far more intensive than maintenance work, and boats are no different.  In reality a boat should be wax/sealant twice a year…….at a min.  I give the recommendation of every 7 days on the water you need a new protective coating on the gel coat.  UV protective coatings to the canvas and vinyl materials of the craft need to be applied often, which really means the more times you use the boat the more you need to clean and reapply these protective coatings.  Here in Utah boats get hammered by high UV rays (due to the altitude) and mineral content of the water and boats in general get more harsh rays of the sun due to reflective nature of the water, owners should wipe down and clean the boat after each use to maintain optimal protection of the boat.



Distilled water

Zep hard water remover

3M abrasive pads (I like white 07445) they are much less abrasive than the well known green ones…  They make grey ones that are softer than the wite, but for boats they are too soft.


Chemically resistant spray bottles

Paper mask

Eye goggles

Yellow dish washing gloves

Bottle of  baking soda and distilled water (to counter act the mild acid of the cleaner)

Bucket of water with Grit Guard


I thought  I would see how many of you would like to see something other than cars being worked on.  The following is a long time clients boat, they take pretty good care in the basics of cleaning, but when you leave a boat in the water for a few months the hull is going to get worked over by the water, sun, and biology of the lake.

The condition of the boats hull after a few months sitting in the lake water exposed to sun.

Close shots of the hull…….. you can see the Yellow scale, and the green Algae


It’s time to introduce the cleaning team.  

I always try to clean hard water stains and build up with the least aggressive method first…… this case that is Vinegar.  In case you were wondering why use an acid on the boat lets go back to some basic chemistry.  There are acids and bases and they are scaled from 1 – 14, with water being about 7 on the pH scale.  Acids range from 1-6.9 in comparative strength, and bases (alkaline) from 7.1 – 14.  Without going deep into chemistry let use this example:  If I have a base solution of 14 pH and I wanted to get that solution to a 7 pH, I need to combine an acid solution to the mix of 1 pH.  Hard water is a base so to neutralize that base you need an acid, the stronger the base the stronger the acid you will need to neutralize that base.

So a mild acid like Vinegar (acetic acid) will usually help with soft to mild hard water stains and spots.  It works very well on glass too.  In this case I needed to use a stronger acid, the acids in Zep are a bit stronger.  I also dilute Zep with distilled water in ratios of 1:1 or 1:2 or 1:3, again starting with least first (1:3).  Warning:  Add acid to water   Get your goggles on, yes goggles to avoid spray from the sides, and your yellow gloves, a long sleved shirt also helps…..If you have a bald head like mine wear a hat.  Be over protected!!!  Wet down the trailer, and flooring underneath to dilute the drip and spray, error on the side of precaution.  I also have a bottle of baking soda mixed with distilled water.  I like to add 1 cup / half gallon of water this will act as a neutralizer of the acid mix.  Acids like to keep “burning” until neutralized.  I spray down the trailer with soda water and if it gets on my skin.  The mask is because the vapors of the reaction sometimes cause respiratory irritation.  Now the acids in the ZEP are mild, BUT why take a chance protect yourself always.


I don’t recall what the Yellow pad is called, when you soak it in water it becomes plyable and softer.  It’s great for use on bugs on the front end of a car.

Spray on the acid mixture, allow to dwell, don’t allow to dry, and then scrub with the white or yellow scrub pad.  You will see the acid bubble on the surface of the gel coat, this is the reaction with the hard water scale (base)…..allow this to happen. Keep spraying until the reaction ceases.  Start scrubbing! Having a bucket of water to rinse your pad is very helpful.  It’s a bunch of work!  But if your ratio is correct it will help speed up the process greatly.  Rinse the area when you have reached as clean as possible.  Some staining might be left behind from the scale and scum, I have another chemical trick that I cannot share to remove that yellowing.  You can remove it with a strong compound if you want.  Most hulls are not perfectly buffed, so don’t OCD on it unless you must.

The stainless steel can dull in the presence of acids.  The brass WILL stain and oxidize, you will need to polish or scrub to increase the appearance.


After I’ve descaled and descumbed the hull, I will wash it really well with a strong soap such as Chemical Guys Citrus Wash and apply a good Wax/Sealant to the boat.  My favorite sealants for boats is called Finish kare 1000P.  You can also use collinite 845, and Meguiars flagship marine wax is also good.  Most car waxes, unless a hybrid wax will not last in the harsher environment of marine life.



Greg Nichols Reflections Detailing
Greg Nichols
Reflections Detailing
Logan, Utah

19 comments on How To: Descale and Descum a Boat

  1. Great article Greg! 🙂

    You should come to MN and do all the boats for me! Back breaking work is an understatement! 😉

    • greg nichols says:


      Thanks for the kudos.

      Boat detailing is hard on the body, the angles are odd, the material is tough, the chemicals can be harsh, and many boats are in rough shape when a detailer gets them. However, if you stick with it the turn around is amazing.

      I don’t think I would like a MN winter, in addition one amazing detailer in MN is enough.


    • Nichole Wolbeck says:

      Chad, where in Minnesota can we find your detailing services. Our boat was on Lake Zumbro for a few weeks and I am sad to say it’s in need of a good cleaning.

  2. James Wentworth says:

    Great work Greg! Very helpful for me becaues I am in the process of gaining a few clients who have boats and this will help a lot! Also, I noticed you said you didn’t know what the yellow pad is, is it spungy? I imagine so because you stated that its good to use on cars with bugs and it would have to be to not cause to many scratches in the paint. What polish do you recommend for the metal surfaces? All I use is Optimum Metal Polish, that might work well no…

  3. Tim Buxton says:

    Great article with some very helpful information Greg! Fantastic work and pictures also!

  4. Sean Woodward says:

    That is a fantastic detail !

    Question, how long did this detail take? Better question, how long did it take to clean the hull with your ZEP?

    There is a new product on the market from Hayward, California available through West Marine that removes:
    Scale, rust-mildew-exhaust stains very quickly. It removes fiberglass oxidation and hard water stains with minimal agitation.

    Before I detail any gelcoat or metalwork, I apply a thin coat to affected areas and allow it to work for a few minutes, then agitate as required. Rinse well and continue to your preferred compound/polish/wax.

    FSR Fiberglass Stain Remover

    Feedback on this product would be fantastic for this detailing community!

    • greg nichols says:

      Thanks for the comment.

      I like ZEP as a starting point the acids in it are less aggressive than other. The product you mention has Oxalic acid so it should work well too. IF the build up is bad you might need to use Muriatic acid in a PROPER dilution and since that has a higher risk I won’t go into that method.

      If the company wants I’ll test it over other methods……….my experience with most over the counter is they are chemically designed to be much safer and that usually translates into less effective.

      I think the time needed for just the hull was 2hr to do the ENTIRE underside not just the the water line. So I had to climb under at times.


      • Sean Woodward says:

        I will give ZEP a try, for sure. As for Oxalic Acid. It works extremely well on rust, applying it to chrome rims does wonders for it’s simplicity.

        I am not much for laying on the ground for standard details on boats where the owner has failed to keep the bottom clean for years on end.

        Maybe there is a way to dip a brush into your mixture and apply it to perform a quicker process, saving the top detail procedures for hands on cleaning? Or using a large wand type pressure sprayer to get into crevices (carpeted areas)?

  5. Eric says:

    makes me want to do another boat!!! The turn around on this thing was HUGE! Nice work man!

  6. Gail says:

    Greg……Fabulous article sent to me by my son-in-laws brother…….BUT; my problem is not the bottom but the painted hull. We are in saltwater 100%, and the salt and sun oxidize the hull drastically. I am looking for something that will last longer than it does at present. I have a great team of girls that uber clean and polish the boat twice a year when we are in port. The problem is; that when I wash it, I don’t always have the luxury of drying it and the same spots keep recurring every time. The forward hull is not bad as it flares out and the product and the sun do not get to it as much. I am currently using McGuire’s Gel wash and have tried numerous others to no avail. We travel the North East coast from Maine to the Bahamas all year with stops to get maintenance done and the boat cleaned. Please make any reccomendations you can as I am tired of a dull boat. (56′ motor sailer) Factory painted.
    Regards, Gail

  7. hyrum evans says:

    Help !, I’m looking to buy a 1997 Bayliner Capri . The owner has painted the hull and the outboard section of the motor. The owner stated that painting would keep off the slime build up. This boat has seen a lot of salt water time. The zinc’s look new.

    Am I looking at trouble and a money pit ? Could damage to the hull of the boat be possible?

    • Greg Nichols says:


      Not knowing what Painting system is on this boat is very hard to say. If the paint starts to peel off, you are in for a nightmear. Did they use anti foul paint? That is what ocean going boats use, and it will help prevent a lot of issues associated with ocean organsims, salt, some scale build up etc. Its important to find out, act a bit niave about it and see if the owner truely fesses up. If they use some “home depot” special run fast……..

      Hope this helps.


  8. Al says:

    I have a 16′ Lund with a black painted hull that I use in a BC fresh water lake with hard water. It normally will sit in the water through the summer from May-October and has a significant scum and algae buildup on the hull. To date, the best cleaning solution that I have found is using vinegar with 15-20 hours of arm strong application. Cleaning has involved scraping every part with either my thumbnails or using a plastic bread tag. I normally apply a couple of good coats of carnuba wax which works somewhat but, at the end of the season, it still needs significant work to clean. Would ZEP be a better alternative or do you have other recommendations?

    • Greg says:


      You might have to step up to the 3 parts water 1 part Pool acid and spray it on. do a test spot and find out how it works. Sounds like you have HEAVY scale.


  9. Tom Gibbs says:

    Any suggestions to help remove heavy scale on my painted aluminum jon boat?
    I have some Zing to use, i can dilute it down 1:1, what would you recommend for a scrubbing pad??

    Thank you

  10. Kamila says:

    what is the eqivalent in mg to 5 cbd

  11. Its like you read my mind!

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