primer left for a year,advice on prep to paint please

[tired old pirate]

Got a neighbour who has asked me if I will help her paint her boat over the summer, i had a good look at it last night and am not sure on the scale of it, its a 2year old liverpool boat which was delivered in grey primer and seems to have stayed that way.

 

Looking closely last night theres alot of pinprick type rust spots all over, what would people do to prep it? All I know about boats that have been primered is not to leave them like that! If i just clean it seriously and coat with international primer will I seal the surface or do I have to go back to metal?

 

Any thoughts appreciated

[Sir Nibble]

A light rub down with wet and dry should suffice, (having treated the rust spots of course).

[tired old pirate]

A light rub down with wet and dry should suffice, (having treated the rust spots of course).

 

brilliant thanks, thats what I was hoping

 

whats the best rust treatment around at the moment? (preferably available in buckets!) anyone got any favourites?

[HYBRID]

I would speak to the boat manufacturer.

As I understand some primers are not impervious to water, they will allow the steel to rust. The other problem is the primer retains some moisture that you will seal in with the gloss, rusting will continue under the paint and the top coat may blister within 12 months.

If the primer has absorbed water the only option is to return the steel back to bare metal and start again, as the gloss will store up problems for the future.

It maybe possible that the boat has been painted with a fancy primer that is sealed like gloss, I am a bit out of touch with latest technology paints but the fact you have rust forming already suggests otherwise.

[Hairy-Neil]

Wet and dry is so old hat, there are far superior dry abrasive systems around now that the old wet and dry need only be used for flatting newly applied paint.

[tired old pirate]

I would speak to the boat manufacturer.

As I understand some primers are not impervious to water, they will allow the steel to rust. The other problem is the primer retains some moisture that you will seal in with the gloss, rusting will continue under the paint and the top coat may blister within 12 months.

If the primer has absorbed water the only option is to return the steel back to bare metal and start again, as the gloss will store up problems for the future.

It maybe possible that the boat has been painted with a fancy primer that is sealed like gloss, I am a bit out of touch with latest technology paints but the fact you have rust forming already suggests otherwise.

 

Thanks Hybrid, Good idea. I had a chat with them and they agree with you, looks like back to bare metal! groan. That is obviously the reason youre not supposed to leave primer unpainted...

[Gary Peacock]

A pearl of wisdom here.

 

Boat builders prime boats to provide a minimum protection during transport, they do not prime boats for a base for the topcoat.

 

The preparation before will range from minimal to non at all.

 

The official advice is to remove it before any attempt at top coating is made.

 

If the boat is exposed to the elements primer is porous so rusting will occur painting over this is then asking for problems.

 

Now don't blame the boat builders for this, preparation for painting is expensive and people want cheap hulls so that element is stripped out.

Edited June 13, 2007 by Gary Peacock

[tired old pirate]

consensus is looking like primer off and complete restart then. Poo. Next, whats the best way to get back to bare metal? I've only ever used a sander on mine, Dont suppose theres an easier way!?

 

Thanks Gary by the way thats really helpful

Edited June 13, 2007 by tired old pirate

[Hairy-Neil]

Next, whats the best way to get back to bare metal?

 

Shot blasting........

 

Well you didn't say it had to be cheap or DIY friendly.....

[tired old pirate]

Shot blasting........

 

Well you didn't say it had to be cheap or DIY friendly.....

 

Ok rephrase! what about the best cheap DIY friendly way to get back to bare metal?!

[blackrose]

Ok rephrase! what about the best cheap DIY friendly way to get back to bare metal?!

 

Belt sander?

 

About 9 years ago when I was cc-ing I sometimes used to moor up near a couple whose new josher style narrowboat boat was primed in red oxide. About 18 months later, in the days of foot & mouth when we were prohibited from moving, I happened to be moored next to them and I noticed that rust was starting to come through the primer. Not realising that this was a porus paint they had neglected to put a topcoat on and were now in for some real work.

Edited June 13, 2007 by blackrose

[tired old pirate]

Belt sander?

 

About 9 years ago when I was cc-ing I sometimes used to moor up near a couple whose new josher style narrowboat boat was primed in red oxide. About 18 months later, in the days of foot & mouth when we were prohibited from moving, I happened to be moored next to them and I noticed that rust was starting to come through the primer. Not realising that this was a porus paint they had neglected to put a topcoat on and were now in for some real work.

 

Probably the only way, nitromors crossed my mind but I think that would kill the canal a bit. Theres not going to be any easy way I think, just hard slog and lots of time!

[ChrisPy]

unfortunately stripping off all the primer will not leave bare metal. It will leave steel plate with a coating of millscale. I would try stripping a bit of paint to see what lies beneath. If you find nothing but the rust spots you started with, it is likely the millscale is actually protecting the steel from general rusting.

 

Then you have a choice -

1. remove the millscale by gritblasting or leave the millscale exposed for 12 months to fall off by itself.

2. just treat the obvious rust spots then paint over.

 

I had spotting occurring on the roof of my boat - I had used 2 undercoats and a deck paint. Unfortunately I think the paints were porous to water. I sanded the surface down with the random orbital, washed the flatted surface with milkstone remover (diluted phosphoric acid) and waited for 2 months. Not a sign of rust. Repainted 1 undercoat and 2 gloss (Weathershield). Watch this space.

[Hairy-Neil]

unfortunately stripping off all the primer will not leave bare metal. It will leave steel plate with a coating of millscale.

 

Yes, most people that 'bare metal' their boats really only get it down as far as polished corrosion........

[Speedwell]

Ok rephrase! what about the best cheap DIY friendly way to get back to bare metal?!

Those big scrapers with the razor sharp replaceable blades are very effective and far less messy than power sanding. Millscale is rarely removed from boat sides. Zinc phosphate primer can be used to get a base on it.

Millscale is very difficult to deal with as it is so hard. It's a few thou thick itself and has scale filled pits at least as deep underneath. That may not sound much but imagine trying to get that off all over the boat !

Arthur

[Gary Peacock]

Not all boats have millscale, it's common practise these days to use de-scaled steel.

 

I doubt there are many builders still using scaled plate?

[Speedwell]

Not all boats have millscale, it's common practise these days to use de-scaled steel.

 

I doubt there are many builders still using scaled plate?

Hi Gary

I'm sure you're right and probably the only was to go if you want a quality plate. However, if you start off with millscale, it's not not an easy DIY job to get rid of.

Arthur

[DHutch]

We went for the grit blasting aproach, which has worked well.

- But it isnt done for free, and to do a good job you need all the windows and fittings out...

- Infact, if you want to do a proper job, you should proberbly be doing the inside as well...

 

However at this stage, i would be very tempted to wait for a line of good dry summer days, give it a half decent rub down, get some topcoat on, and see what it looks like in a year time.

 

 

Daniel

[ChrisPy]

Not all boats have millscale, it's common practise these days to use de-scaled steel.

 

I doubt there are many builders still using scaled plate?

hmm ................. but if the biggest builder still does, that's a large proportion of the new boats out there ..............

[Timleech]

hmm ................. but if the biggest builder still does, that's a large proportion of the new boats out there ..............

 

I see plenty of newish boats which are painted over millscale.

The (cabin) paint can last surprisingly well, provided any scratches are fastidiously touched up, but that's not a recommendation to leave the scale on.

Doesn't help the OP, though, it sounds as though his is beyond that stage.

Dilute HCl is one way to get it off, but probably doesn't do the fishes a lot of good.

 

Tim

[John Orentas]

In my experience the description 'de-scaled steel' cannot be taken quite literally, all they do is put a bit of texture on the steel which helps the paint to adhere. Some years ago a few builders would recommend that the shell was left outside for a few years to allow it to rust, the mill-scale then expands by a very large factor allowing it to be ground or blasted off. Whether this advice was intended to be taken seriously or if anyone ever accepted it I am not sure.

 

In my experience all new shells are still in mill-scale at the time of painting, as one who has attempted to grind off even small areas of scale off new steel I know the job is near impossible.

Edited June 15, 2007 by John Orentas

[Guest]

The shipyard where I have my fit-out has an official International Paint Station on site, I've asked them to paint my hull and their advice to me is that they want to leave the primer as is so that it rusts to remove the mill scale, They reckon when it is ready, 1 to 2 years, they should be able to prepare it for painting by just pressure hosing rather than grit blasting. They also told me that when they fit out a steel hull they like to sink it in the river for 6 months so as the rust gets to the mill scale - makes it easier to remove. I have tried to wire brush it off and grind it off and only seem to be able to polish it but I have seen that where there are small patches of rust the mill scale can easily be removed with an high pressure air jet. So maybe there is a bit of sense in what they say - I hope so.

Phil

[Gary Peacock]

"In my experience all new shells are still in mill-scale at the time of painting, as one who has attempted to grind off even small areas of scale off new steel I know the job is near impossible."

 

 

At the risk of stating the very obvious, you do know that if you pay for it you can use pickled and oiled bright steel?

 

This steel is bright no rust or scale. The scale is removed by acid and the sheets are then coated with a protective oil before they leave the steel mill.

 

The cost of this process is about £450.00 extra on a narrowboat and this includes having the D bar supplied shot blasted too.

 

The picture below show a hull being built from pickled and oiled steel next door.

 

 

The next picture shows a sheet of pickled and oiled 6mm sheet laid on top of a mill scaled 6mm sheet you can see that it is black. (That is the scale.)

 

 

 

 

The last two pictures show a Heron boat with some of the primer removed the black patches are also scale.

 

 

 

These were discovered after the primer and scale started to come away.

 

There is no reason other than the cost saving to work with scaled steel!

Edited June 16, 2007 by Gary Peacock

[Phil Speight]

Got a neighbour who has asked me if I will help her paint her boat over the summer, i had a good look at it last night and am not sure on the scale of it, its a 2year old liverpool boat which was delivered in grey primer and seems to have stayed that way.

 

Looking closely last night theres alot of pinprick type rust spots all over, what would people do to prep it? All I know about boats that have been primered is not to leave them like that! If i just clean it seriously and coat with international primer will I seal the surface or do I have to go back to metal?

 

Any thoughts appreciated

There is nothing in all the above responses that hasn`t been thoroughly explored within the group before - I mean no offence , there is much good sense throughout , but there is no point in me covering it all again.

So give me a ring if you want - and I`ll be to happy offer whatever advice seems appropriate ( or help you pick which of the various answers already offered above that most ideally suits your situation). Office number 01384 485554 - I`m usually in here up to about 9.30 a.m and early in the evening.Avoid ringing between Friday 2.00p.m and Monday though - it`s Goodwood on Saturday and National Alfa Day on Sunday. I`ve had me anorak cleaned specially.

Cheers

Phil

Edited June 21, 2007 by Phil Speight

[Alec Gatherer]

No two ways about it - millscale or no millscale - PRIMER OFF!!! The primer itself will have absorbed moisture and will cause pin-prick, blisters etc in whatever you attempted to put on top.

All and any primre should be top-coated as soon as you can after application to prevent moisture absorbtion.

May I repeat my mantra about Bonda Rust Primer? It's a zinc-rich 1st stage primer - a sort of smart-arsed red oxide- that I have been using for donkey's years to give a reliable bond between bare metal/rust treated bare metal and paint system primer/fillers. I swear by it.