Base Plate Rust Treatment

[TheSaintlyOne]

I'm currently in the process of treating the baseplate inside which has suffered some corrosion where water has entered the bow and run to the back where it is deposited via a bilge pump. I have lifted the ballast slabs in sections and scraped all the loose rust. 

The plan now is to use a rust converter either Aquasteel, Fertan or vactan before coating with an as yet undecided coating and then relaying the slabs and then 18mm External Ply Sub Floor coated in cuprinol 

 

Any suggestions about which products 

[frahkn]

23 minutes ago, TheSaintlyOne said:

I'm currently in the process of treating the baseplate inside which has suffered some corrosion where water has entered the bow and run to the back where it is deposited via a bilge pump. I have lifted the ballast slabs in sections and scraped all the loose rust. 

The plan now is to use a rust converter either Aquasteel, Fertan or vactan before coating with an as yet undecided coating and then relaying the slabs and then 18mm External Ply Sub Floor coated in cuprinol 

 

Any suggestions about which products 

Vactan IMHO, Fertan I find almost useless but I have not used Aquasteel.

 

Ensure the Vactan is completely dry before the next step.

[Bee]

Some people recommend laying the ballast onto battens or something similar, I think this is probably wise as in my usually bone dry bilge there is often some moisture under the bricks - probably held in the bricks themselves. In my experience most paint does not like being constantly damp and it bubbles and lifts. I slapped bituminous water tank paint over the inside of my boat and that seems to be perfectly ok but oil and diesel will dissolve it.

[Mike Adams]

Unless you can get the metal to near shotblasted condition I don't think any paint system will work in the long term. I used about 30 litres of Anti Roestvet Grease(anti rust grease, after wire brushing and a nominal coat of red oxide. It is used by heating it up and pooring it into the bilge leaving about a thickness of 3mm, it goes hard a bit like waxoil. I guess it prevents oxygen getting to the metal. You can't use it where you have oily water but in the main part of the boat it seems fine. If you get a water leak it just runs on top of it so you can collect/evaporate it. You need to stop the water running through the boat. Was about £100 for 18Kg. After a couple of years no sign of any rust

[TheSaintlyOne]

Thanks, the boat never had a Cratch Cover installed although a frame did come with the boat. We are now in the process of building a catch cover frame and this will prevent water from entering at the bow and draining through to the back

[1agos]

I use Aquasteel and I am happy with it . I haven't used the others though so can't compare.

[Traveller]

Have used Aquasteel for the last three years now with no issues. Re water running through the bilge - this is what we had on our first boat  (a Springer). We had a self draining deck welded in the front to stop it. A cratch cover is fine but it is not always closed and can suffer damage.

[blackrose]

18 hours ago, Bee said:

In my experience most paint does not like being constantly damp and it bubbles and lifts.

 

That's right. The only paint that will work long term immersed in water is a two-pack epoxy. Single pack primers like international primocon will work underwater too but won't last as long. Red oxide doesn't even work long term above the waterline if it gets damp or wet regularly so it's useless as a bilge paint and a lot of greases or waxoil are fine for stopping rust returning if it stays dry but standing water will lift them eventually.

[Tracy D'arth]

Fertan has to be washed off, what does that suggest?

Vactan will not set off properly with the boat in the water, it needs a higher temperature. Fine if out of the water and the weather is warm.

Best is, as suggested,  2 pack epoxy but you would need to clean back to bright steel and you can never get in the corners.

A good bitumen is about the easiest and stands a good chance of staying put for a while but it will always rust eventually.

Interior rusting is unlikely to thin the base plate substantially,  10mm of rust scale is roughly 1mm of lost steel.

 

Could I suggest waterproof OSB boards rather than ply? Such as Stirling Board.

They last very well even out in the weather, are cheaper and better than the poor quality that is passed as marine ply these days which seems to delaminate at the first sign of damp.

[Taslim]

20 hours ago, Bee said:

Some people recommend laying the ballast onto battens or something similar, I think this is probably wise as in my usually bone dry bilge there is often some moisture under the bricks - probably held in the bricks themselves. In my experience most paint does not like being constantly damp and it bubbles and lifts. I slapped bituminous water tank paint over the inside of my boat and that seems to be perfectly ok but oil and diesel will dissolve it.

A good idea but use plasic tube or strip. Any remaining moisture will cause wood baterns to rot & the fungus is scary.

[WotEver]

5 minutes ago, Taslim said:

A good idea but use plasic tube or strip.

Short lengths of mains flex work well if you don't have anything else - sometimes to be found in skips.

[Man 'o Kent]

 Those + shaped domestic tile spacers work.

[WotEver]

57 minutes ago, Man 'o Kent said:

 Those + shaped domestic tile spacers work.

Good tip

[Man 'o Kent]

4 minutes ago, WotEver said:

Good tip

Only as long as you put them under the bricks and not around the corners between them  .  .  .    

[TheSaintlyOne]

Thanks everyone I have slabs not bricks (Which are all now broken as lifting whole slabs was not that easy as they were wedged in, a little bit of a jigsaw puzzle) but love the tile spacer idea. 

 

Bitumen Rusting???? Forgive my ignorance. Then that could of what's been down before as there seems to be a smooth black layer below whats loose.

 

Is there a bitumen product anyone would reccomend????

 

Will just applying bitumen stop the rust continuing or will I need a product like Fertan or Aquasteel 

 

The grease idea does sound another good one but laying the slabs on it ????

 

Finally had a chance to get some photos uploaded. 

 

In terms of boards for the sub floor it already has about 3/4 of the boat done in 18mm Ply and treated with something like preserver although all loose planks at the mo. So just finishing that off with about 2 8x4 Sheets 

 

 

[Mike Adams]

That looks like a lot of serious corrosion unless the baseplate is a decent thickness (8 -10mm) to start with. You need to know how much metal you have left otherwise you could end up with some holes. The only way to clean this up is with an electric or air powered chisel or needle gun and that is going to find any thin bits so best not to do it in the water! Has the boat had a survey recently? Even that may not give a good indication as the scale could give a false reading. If the boat is out of the water you can drill a few test holes and weld them up later of if in the water try an ultra sonic thickness meter on sample areas after grinding back to metal. Good luck

[Man 'o Kent]

If you are prepared to try a DIY rust treatment then try the following:

You will need the following materials: De-ionized Water, Phosphoric Acid, Tannic Acid and Alcohol.

None of these materials are particularly hazardous but take due care, rubber gloves, eye protection, etc. are advisable.

 

Make up a 10% solution of Phosphoric Acid in the de-ionized water. Tannic Acid is not miscible in water so dissolve in a small quantity of Alcohol first. Mix sufficient Tannic Acid to make a 5% solution and add to the previously prepared Phosphoric Acid.

 

To use remove all loose material before application. This mixture is watery, fine for the bilges of my old boat so I never got around to finding a thickening agent. Apply liberally with a paint brush and allow to dry, the rust will change colour to a  mixture of grey/black/purple/white. Because there is a chemical reaction the oxide layer will change in size, flakes and patches will loosen. It will be necessary to go over the area with something like a wire brush. Any rusty looking spots so exposed will require one or more further application.

 

This particular "witch's brew" was gifted to me by a University Chemistry Department employee, he explained that the Phosphoric Acid converts the iron oxide into more stable Iron Phosphate and explained that the rust pits form a kind of battery that apparently accelerated the conversion of Iron into Iron Oxide. The Tannic Acid in the mixture when dry forms an insulating layer in the pits thus stopping the electrical activity. This was his spiel, I am no chemist so don't blame me, I offer it for what it is worth, all I know is that it worked for me, the resulting surface took paint well and I saw no further evidence of rust during my ownership of the boat.

 

 

[jenevers]

22 hours ago, WotEver said:

Short lengths of mains flex work well if you don't have anything else - sometimes to be found in skips.

Half inch picees of old fan belt. Gives a decent gap above the base plates and cuts down on any vibration.

[james46]

Hi 

Whats peoples view on the side plates on the inside, im about to spray foam insulate, theres rust here and there is it best to just foam over or treat it and red oxide then spray foam.

[Tracy D'arth]

54 minutes ago, james46 said:

Hi 

Whats peoples view on the side plates on the inside, im about to spray foam insulate, theres rust here and there is it best to just foam over or treat it and red oxide then spray foam.

I would take the opportunity to wire brush, Vactan and zinc oxide prime  before spray foaming.

[David Schweizer]

I would consider using a Rustoleum Primer. There is a range of different products, so it would be worth contacting them for further advice:-https://www.rustoleum.com/pages/help-and-support

 

 

Edited December 14, 2023 by David Schweizer

[james46]

3 hours ago, Tracy D'arth said:

I would take the opportunity to wire brush, Vactan and zinc oxide prime  before spray foaming.

Thanks for the reply i was thinking that would be the best way forward 

[Tracy D'arth]

I should of said a zinc rich primer of course.

[james46]

Just now, Tracy D'arth said:

I should of said a zinc rich primer of course.

Yes i looked up which ones are best they said that ive been a welder fabricator for the last 23 years but dont deal with rusty metal 🤣

[Feeby100]

Vactan is great as it primes and look the part but a year on and it crap so steer clear