Muriatic acid on old bottom paint?

[ERTF]

How will muriaric acid affect old ablative bottom paint that i want to paint over? I had some really fierce slime on my skiff that my electric pressure washer only could remove about 50%. Then i sanded for about 2 days and have removed about 95-98% of the slime residue.
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My thought is to get the last of the slime with muriatic acid and then pressure wash it off (the topsides need it anyway). But will that comprise the old paint in any way that would cause issues for my forthcoming new coats staying adhered to the boat?

 

[North Baltic sea]

Hi,

I thik antifouling remover chemical is beter, this makes the paint soft and you can scrape it off easily, it's expensive but you don't have much surface left. Here's one example

https://www.international-yachtpaint.com/en/gb/boat-paint-products/antifouling/interstrip-af

NBs

 

[rslifkin]

Were you wet or dry sanding to remove the residue? If dry, try wet sanding it with either drywall sanding screens, or a moderately aggressive scrubby pad. Keep re-wetting it during the process and generally stuff (and some of the old paint) will come off fairly easily.

 

[ERTF]

I was dry sanding. The problem isnt that the sander can't take off the slime. Its that the old paint isnt all the way smooth (so the slime residue persists in some of the flaked areas), plus theres alot of chines to deal with. I'm declaring no mas on further sanding.

 

[rslifkin]

I was dry sanding. The problem isnt that the sander can't take off the slime. Its that the old paint isnt all the way smooth (so the slime residue persists in some of the flaked areas), plus theres alot of chines to deal with. I'm declaring no mas on further sanding.

A scrubby pad (that's not too stiff) with some water will likely take care of that. Unlike sandpaper, it'll have enough give to work around chines more easily and to squish into the flaked areas to get them clean. And the slime will generally come off pretty easily when wet. Just be aware that after a wet scrub, you'll need to rinse it all off and you'll have a good bit of paint in the water that comes off.

If any areas are badly flaked, it might not hurt to drag a scraper over them lightly to knock off any poorly adhered paint before you put new stuff on.

I've used pads like this to get leftover slime off my hull with good results: https://www.amazon.com/gp/product/B079JWGDN9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[Pete Meisinger]

Muriatic acid is not very friendly to the environment. There must be a better way short of a soda blaster.

pete

 

[Jim Cooper]

Muratic acid is some pretty strong stuff and as Pete pointed out, more harmful to the environment than necessary. I've used this stuff from Lowes and it works great...dilute it and spray it on, wait 30 seconds to 1 minute and wash off. Repeat if necessary Hopefully you are doing this in a boat yard that has proper containment protocols.

30 SECONDS 1-Gallon Mold and Mildew Stain Remover Concentrated Outdoor Cleaner
Item #123109

Model #1G30S

 

[ERTF]

Muriatic acid is not very friendly to the environment.

pete

Well the "environment" was STUCK to my boat and i needed it off ?. Trust me when i say half measures were not gonna work.

 

[ERTF]

Muratic acid is some pretty strong stuff and as Pete pointed out, more harmful to the environment than necessary. I've used this stuff from Lowes and it works great...dilute it and spray it on, wait 30 seconds to 1 minute and wash off. Repeat if necessary Hopefully you are doing this in a boat yard that has proper containment protocols.

30 SECONDS 1-Gallon Mold and Mildew Stain Remover Concentrated Outdoor Cleaner
Item #123109

Model #1G30S

I've learned that brand name cleaners are basically always just rebranded basic chemicals. My initial guess was this is bleach like every mildew product. And sure enough it's diluted bleach with a little tsp added. Just an fyi. At least in this case the upcharge isnt too extreme.

 

[Finestkind]

Neutralize!

If you have the ability to ‘catch’ the somewhat ‘acid’ runoff then sprinkling in some diluted baking soda (base) & retesting the area with pH strips would allow you to mitigate this issue in a controlled manor. Use Respiratory Protection - but try not to scare the entire populous.
One of my Haz-Mat instructors used to say the ‘Solution to Polution is Dilution!’
Nothing some folks want to hear; but this is a small scale ‘spill’ and you can control the ‘release’ (perhaps with one of those plastic kiddie backyard pools- like we had for Haz-Mat decontamination!). At least you will have tried! Me thinks 95% don’t.