cleaning algae off fiberglass hull

[JAL51974]

I know this one has been posted before but I have some specific questions.

Freshwater lake moored from June-now. Lots of algae and gunk. No hull paint to reduce growth on the fiberglass. Just towed it home on Sat. afternoon and started cleaning it on Sunday afternoon.

I tried 50/50 muriatic acid water solution, painted it on with a bristle brush and let it sit maybe 10 mins. then powerwashed that side of the hull. No real effect on the gunk or stains though. I was afraid to let it sit longer. My power washer was plenty powerful it nicked off a couple of little pieces of the fiberglass. so I have that to fix too now.

What strength do most of you use for the muriatic solution and how long do you let it sit? Is there a way to add a little soap to the solution to make it adhere better not just run off the hull?

Thanks.
Joe

 

[frantically relaxing]

Re: cleaning algae off fiberglass hull

I have a little experience in this area---

Back when our 2007 Bayliner was way less than a year old - no kidding- it looked like this for the same reason yours does--

When we sold in in 2011 it looked like this--

--under the algae was a ton of calcium. And I got it looking like new without ever touching the hull with ANYTHING other than water and muriatic acid--

First, spray off all the algae as best you can with your power washer. When that's done, go to Walmart or Home Depot and pick up 5 or 6 bottles of "The Works" toilet bowl cleaner, it will say "hydrochloric acid 20%" on the bottle. Muriatic acid from Lowes is okay too, ANY is okay as long as it's 20% or higher (HD acid is 14% for swimming pools, ok, but adjust mixture accordingingly)

You'll need a cheap garden sprayer, the $9 ones at HD or Lowes work fine. Mix 20% acid 3 parts water to 1 part acid. You can go stronger, but I've found this works fine.

Get some large trash bags and cover the trailer fenders and frame. Keep a garden hose ON with a spray attachment to keep it off when not needed. Keep the spray away from any bright metal, including stainless, it WILL darken stainless.

pick a 2-foot long area on the hull and start spraying. As long as there's calcium, it will smoke. Spray the spot like your painting, get it wet, then wait about 5 seconds, that's about all the time the acid works before being neutralized by the calcium. Just keep spraying until it won't smoke, then move to the next 2 foot area. About once a minute take your water hose and rinse the boat and the ground, then start up again.

I wore out 2 brushes on our Party Cruiser many years ago before I figured out the acid WILL do all the work.Once all the calcium is gone, then you can wash and wax the hull as needed.

 

[shrew]

Re: cleaning algae off fiberglass hull

I use ON/OFF Hull cleaner and it works great. Get the original fomula. I've tried the gel and it didn't work as well. I do think the active ingredient in that is muriatic acid. All I can say is I was having a hard time with a heavy yellow scum line this weekend and this stuff worked with almost no effort.

 

[crabby captain john]

Re: cleaning algae off fiberglass hull

You are correct-- On/Off is a diluted acid. Cost of On/Off is about $20 per qt, have to pay for that pretty bottle. Muriatic acid is about $5 a gallon. I spray muriatic acid either 90% / 10% water or 100% before the hull is waxed.

I use ON/OFF Hull cleaner and it works great. Get the original fomula. I've tried the gel and it didn't work as well. I do think the active ingredient in that is muriatic acid. All I can say is I was having a hard time with a heavy yellow scum line this weekend and this stuff worked with almost no effort.

 

[JAL51974]

Re: cleaning algae off fiberglass hull

What am I doing wrong. Spent two Sat. mornings applying muriatic acid-water mix and it barely is softening the algae and scum! The second time it was 90% acid to water mix sprayed out of a Lowes sprayer, let it on a section about 3 ft. long less than 5 mins. and rinsed with the garden hose. Didn't really soften it much. Then tried again, same result. third application I sprayed the entire length of one side of the boat so it took closer to 5 mins and rinsed off. Softens it some but it would still take a lot of brush scrubbing to get any really removed. Am I not leaving it on long enough or what? I never see it smoking at all when its applied although it smells pretty strong.

Getting pretty aggravated at this point, time is wasting to getting the boat cleaned up and ready for the colder weather- these good days won't be many the further we get into Oct. in Ohio. Joe

 

[crabby captain john]

Re: cleaning algae off fiberglass hull

I generally do not add any water! If not bad maybe 10%. I've left it on much longer than 5 minutes but always catch it before it dries ---

 

[lfunk11]

Re: cleaning algae off fiberglass hull

I got the muriatic acid from lowes and did 1:1 with water. Sprayed it on and waited a few minutes then went with a brush and gloves to get most of it off. I had to use a green scrub pad to get the worst areas, but only resort to that if you plan on doing a full buff/detail. I boat my boat this year and I doubt it was ever truly cleaned and was kept in a slip all summer so it was pretty grimy.

 

[frantically relaxing]

Re: cleaning algae off fiberglass hull

Muriatic acid has no effect on algae or other bottom growth, you have to blast the algae off the hull as much as possible with a healthy power washer first. That in itself can be a slow process if it's had time to dry, but be patient. Once the algae is off, calcium will be what's left, and THEN the acid can do it's thing...

 

[JAL51974]

Re: cleaning algae off fiberglass hull

I powerwashed it first with a strong washer. even took off 2 small pieces of fiberglass that I have to fix now! I may try it once more with the acid, but between my time and bad back this might be a better job left to a marina to do. Fixing the old back gets way more expensive than having the hull cleaned. Joe