Rust repairs

[Pdiddy24]

Hi everyone
Looking at repairs and jobs to do on the boat whilst out of action.
I have a 5m pressed tinny and noticing rust spots appearing around the two drain plug bung holes. Is there a fix for this to get on top of it? It appears at some stage (prior to me owning it) that the bungs had been cut out and rewelded. Is this an option as well to eliminate the rust?

Cheers

[re-tyred]

Are they stainless inserts into the Aluminium? Usually plastic. The Aluminium won't be rusting. it has to be either the stainless or the bolts holding them in.
Other metals and alloy are not recommended as they will always corrode. If you have rust you have poor quality stainless and I would get rid of it. Do everything with plastic and 316 stainless steel bolts. Even then you need to put the goop ( name i can't remember) on the stainless bolts and threads.
Rust on trailers etc, I treat with rust converter, then paint with a metal primer then a top coat. small spots i wire brush off and use a cold gal paint then a top coat. you can get all those from a boat shop or BCF and often at a hardware shop. Or online.

[SteveoTheTiger]

Even then you need to put the goop ( name i can't remember) on the stainless bolts and threads.

Sikaflex

Pdiddy, do a search on galvanic corrosion or electrolysis.

[ben475]

When you say rust, do you mean aluminium corrosion? common around fittings with stainless screws, bolts, etc.

Rub back with sandpaper, etch prime and paint is one option.
Most likely the harder you look the more you will find.
In most areas i'd say the aluminium will be slightly pitted and structurally sound but mainly cosmetic.

A Sikaflex type sealant is a very good idea when refitting fixings. Tefgel is a good one for screws or anything you might want to remove, its about $80 for a toothpaste size tube.

[Pdiddy24]

Are they stainless inserts into the Aluminium? Usually plastic. The Aluminium won't be rusting. it has to be either the stainless or the bolts holding them in.
Other metals and alloy are not recommended as they will always corrode. If you have rust you have poor quality stainless and I would get rid of it. Do everything with plastic and 316 stainless steel bolts. Even then you need to put the goop ( name i can't remember) on the stainless bolts and threads.
Rust on trailers etc, I treat with rust converter, then paint with a metal primer then a top coat. small spots i wire brush off and use a cold gal paint then a top coat. you can get all those from a boat shop or BCF and often at a hardware shop. Or online.

I think they are the bolts of some description as you say. The rust/corrosion spots are a pretty consistent pattern with 4 spot areas around each bung. If I get a chance tomorrow I'll try and put a photo up.
Is it a job worth getting a fabricator to do?
That's awesome advice on the trailer too. Will be the next job I reckon.

[Pdiddy24]

When you say rust, do you mean aluminium corrosion? common around fittings with stainless screws, bolts, etc.

Rub back with sandpaper, etch prime and paint is one option.
Most likely the harder you look the more you will find.
In most areas i'd say the aluminium will be slightly pitted and structurally sound but mainly cosmetic.

A Sikaflex type sealant is a very good idea when refitting fixings. Tefgel is a good one for screws or anything you might want to remove, its about $80 for a toothpaste size tube.

Thanks so much for the advice on this.
I think some other areas are just cosmetic and have sandpaper them away pretty easily. For the areas adjoining the bungs they seem pretty deep. I'm thinking that would be too much of an issue for sanding back?
Does the Tefgel loosen the screws or dissolve them or similar? I'll have a google as well

[Pdiddy24]

Even then you need to put the goop ( name i can't remember) on the stainless bolts and threads.

Sikaflex

Pdiddy, do a search on galvanic corrosion or electrolysis.

Thanks Steveo! I'll look into that in a bit more detail

[ben475]

Thanks so much for the advice on this.
I think some other areas are just cosmetic and have sandpaper them away pretty easily. For the areas adjoining the bungs they seem pretty deep. I'm thinking that would be too much of an issue for sanding back?
Does the Tefgel loosen the screws or dissolve them or similar? I'll have a google as well

you put the tefgel on any screw threads, bolts etc before fixing them into aluminium to create a barrier and prevent galvanic reaction.
salt water gets in and the aluminium starts to corrode, if its painted the paint will bubble.

if you do an online search for tefgel im sure there will be a video explaining it.

[Bugatti]

G'day Pdiddy

Yeah, a photo would help as it could be a few things on a few spots.

If it's "white-ish" corrosion, that could be the aluminium. And yes the electrolysis is what would do that. Also "dis-similar" metals doesn't help, but unfortunately unavoidable on an Ali Boat. That's when two different metals are together, which causes the "weaker" metal to corrode (by electrolysis), So Aluminium and Stainless together isn't good, as it causes the Aluminium (the weaker metal) to corrode. But stainless screws are unavoidable as they are great, especially as re-tyred has said 316 is the pick of stainless.

One way to get that corrosion off is with a pressure cleaner. A very focused jet to blast the corrosion off. This would get right into the pitted holes and get most (if not all) the corrosion off. Sandpaper is good but it's hard to get into the pitted holes and get all the corrosion off.

Also the pressure cleaner would get under any loose paint and get that off too. Loose paint is a curse as the "raw" Ali underneath would corrode there faster than anywhere else. Once the loose paint is off, just paint over the exposed Ali.
As ben475 says, etch primer then paint.


Cheers, Bugatti

[Pdiddy24]

Hi Bugatti,

Thanks for the reply on this. I've tried to attach some photos to give you more of an idea.

My hull isn't painted so not sure if that is an advantage or not.

I might look at replacing the screws on other parts of the boat on the back of what you have said and coat them with Teflek stuff mentioned previously. There are no other obvious signs of rust throughout the hull only around the bungs from what I can see. Will lift the floors over winter to give it a good look.

Thanks so much