phosphoric acid solution to clean alloy hulls

[hellomister]

Regarding cleaning recently constructed alloy hulls [prior to prime/bog]
Trying to figure out the best solution of phosphoric acid to wash hull prior to priming. We have 85% solution in 20 litre drums and are experimenting with best dilution but it would be great to hear from someone who knows the best ratio.

[Wotname]

Welcome aboard CF, hellomister, interesting first post!

I don't know the best ratio but I reckon it would be pretty low, say less than 5%.

AFAIK, phosphoric acid should never be used on aluminium or aluminium alloys; they are incompatible. Probably makes it pretty clean though as it eats it away

[UNCIVILIZED]

Originally Posted by Wotname

Welcome aboard CF, hellomister, interesting first post!

I don't know the best ratio but I reckon it would be pretty low, say less than 5%.

AFAIK, phosphoric acid should never be used on aluminium or aluminium alloys; they are incompatible. Probably makes it pretty clean though as it eats it away

My understanding as to the purpose of the acid etch step, prior to priming, IS to eat away some of the aluminum. Or rather the protective oxidixed aluminum layer which rapidly self-forms to protect the metal from further oxidation. So the acid etch makes it possible for the primer to get a good grip on clean metal, rather than the aluminum's surface rust layer.

I remember from my chemistry classes, being told that in theory, an airplane should melt in a rain storm. Due to aluminum's being so low on the galvanic scale (like zinc). Except for the fact that with aluminum, when it rusts, the rust (oxide) forms a protective skin/layer over the rest of the metal, protecting it from further oxidation. Unlike say with steel, where oxiation rapidly eats through many layers of the metal, spreading as it goes.

[GordMay]

Greetings and welcome aboard the CF, hellomister.

Table 1: Operating Parameters of PCS Sales Acid Cleaner 342-AC
Cloud Point (˚F) 95 minimum
Temperature (˚F) 95–180
Time (min.) 1–5
Concentration (% by vol.) 8–9
pH 1.5–3.5

➥ www.potashcorp.com/media/bright_dip_manual.pdf

[hellomister]

Ok thanks crew appreciate the replies
Seems this site has a bunch of good fOlk ready to share
Just like the local water hole but global!
So yes thanks for the 5% ballpark cause we came up with 7 to 10 % so means we all close and we can run with that
Yes dont want to eat out 1mm of the 4mm plate in the wash for sure by over doing it
The brand names using phosphoric dont stipulate the solution of course. At least not in this part of the world.
Will update how we go next week for anyone interested

[Mithril Bham]

What type of alloy? Assuming aluminum.

[hellomister]

aluminum 5083-h116 plate
6061 series Ts and bar
standard marine building, mostly 4mm plate

[Captsteve53]

You are probably aware of this but there's time limits for coating after this acid wash, normally max 24 hrs other wise the Aluminium will start to revert back to it's former protective state, actually a lot of the modern aluminium primers are actually self etching!, but agree a good acid wash wont hurt!

In our painting supervision of Aluminium we normally use an etch primer before the epoxy or other primer/under coat-Epiglass used to make a very good etch primer which was applied very thinly (just a mist really) this would actually etch it's self into the Aluminium providing an excellent key,

[hellomister]

roger that
yeah we degrease with detergent, acid wash with phosphoric at a 7 or 10 percent solution and then prime
understanding that we are in a part of the world where brand products are simply not available
we have however sourced a jotun primer which is 'apparently' suitable
shall do some tests and take a good look at the data sheets in the next 2 days.
Wondering is zinc chromete the main ingredient we need or are other etching solutions suitable?
This stage is a fairly big deal as next is the epoxy/micro balloon mix which must stay on for 20 years or more one hopes and im not sure just how cruicial the actual etching solution ingredients are provided they ARE suitable in the first place if you know what i mean
And testing, well, we can test the obvious pre application but im concerned how well be after a season or two in the weather, 10,000 miles and a typhoon or two under the belt
This is a costly and labour intensive part of the build and all feedback is very much appreciated

[hellomister]

by the way captsteve
appreciated.
we are in cebu and i just noted your in subic so any supply hints on materials would be much appreciated
we are having a bitch of a time sourcing tinned copper wire

[Captsteve53]

The thinking on etch primers has moved along over the years hence why it's now hard to find these dedicated etch primers, the new idea is to use a twin pack primer such as below directly after cleaning/acid etching (available in the Philippines). Inter-protect .

I have used this recently in Subic Bay on a complete re paint with a 47 Foot yacht and got some good follow up with the International Tech rep (unusual!), after this the filling and fairing takes place,


https://international-yachtpaint.com...nterprotectard

Feel free to call me @ 09175222971 (Steve)

[model 10]

Originally Posted by hellomister

This stage is a fairly big deal as next is the epoxy/micro balloon mix which must stay on for 20 years or more one hopes and im not sure just how cruicial the actual etching solution ingredients are provided they ARE suitable in the first place if you know what i mean

Micro balloons are not the right material for underwater fairing. The baloons fill with water.

[Captsteve53]

An additional snibit of info to add is: any filling/ fairing under the water line is usually discouraged for obvious reasons but if doing so for any reason then yes a full epoxy filler with no fillers is recommended for smaller areas,

But/and if using micro balloons on larger area's it's better not to use Silica or talc in the mix as these do tend to be hydroscopic more so than the micro balloons them self, We have used micro balloons (note there are numerous differing chemical composition types) in certain applications under water with out any resulting issues noting how ever that after the fairing process is completed the exposed/cut open balloons are sealed with a good coating of epoxy resin followed by epoxy primers/undercoat all rendering the"open"micro balloons totally sealed to water ingress.

[hellomister]

Ok we are ready to go here however just wanted to be sure. We have a jotun product
Jotacote universal
Two part polyamine cured epoxy coating
Suitable for steel and aluminium
No chemical breakdown on the MSDS but the rep says its the right stuff. Looks that way to us too
While not exactly flying blind here it would be great to hear from someone (capt steve) before we go ahead
As to the micro balloons thanks. Weve got what has been used on about 10 boats in the last 5 years with good results no water ingress and correct all fairing is well sealed with at least one coat of straight epoxy prior to prep for final paint