Do you need to shotblast hull to remove old antifoul before blacking?

[pebble77]

Hi all

 

I have a boat that I need to black for the first time.

I have been advised I need to shotblast is so the blacking can adhere- is this right?

What is the usual procedure?

 

Thank you for your advice!

[pete.i]

Shotblast if you are going to use two pack epoxy coating

but high pressure wash if you are using bitumin blacking.

[pebble77]

Thanks for your comment. The guy has reccomended shotblasting for blacking but it costs a fortune. Hopefully we can just powerwash but is it risky?

[DandV]

Shot blasting and two pack epoxy is by far the best. Both blasting and the epoxy are expensive. 

But if you are going to spend the money on shot blasting the extra cost of epoxy, instead of bitumen is definitely worth it.

I think it is rated for about 10 years with a water blast and touch up, or perhaps full overcoat at about 5years.

So an accumulated  saving on the hassle of dry docking and application  costs over the shorter lifed bitumen.

 

For Bitumen blacking, I am not sure that shotblasting, instead of  water blasting only, would extend the life of the coating enough to justify the extra expense.

 

The best access to the underlying steel is always prior to the first coat of anything. And repairing any wasted steel is by far the most expensive option.

For good paint systems removal of mill scale is vital, hence the blasting requirements, And mill scale is suprisingly resistant to wire brushing or similar.

For blacking it is more of a race between what looses adhesion first, the blacking or the mill scale.

 

Edited February 10, 2023 by DandV

[john.k]

Mill scale is most cheaply removed by allowing the steel to rust somewhat ,the scale will simply fall off....................another cheap way of removing all sorts of mill scale and flaky rust is flame spalling..........paint can also be removed ,but there is likely to be lots of smoke ,which may be a problem.

[rusty69]

Do you know what type of antifouling paint it has on it? 

 

If it is the self eroding stuff, a powerful pressure washer may be enough. 

 

 

There may, of course be another coating beneath the antifoul which ideally needs to be identified before a decision is made. 

 

I suppose grit blasting would likely remove all previous coating, to avoid that decision, but at great cost, and perhaps unnecessarily. 

 

You may get some idea by scraping a bit off. This could be done with the boat in the water if you are able to lean it a bit, and it isn't left too long before the new coating is applied. 

Edited February 11, 2023 by rusty69

[Paul C]

If its a canal boat, it won't be antifoul on the hull.....if it is, be very concerned.

[rusty69]

2 minutes ago, Paul C said:

If its a canal boat, it won't be antifoul on the hull.....if it is, be very concerned.

It's possible it was a boat kept on the coast that has now moved to the inland waterways, so there is every possibility it has previously been antifouled. 

[Paul C]

15 minutes ago, rusty69 said:

It's possible it was a boat kept on the coast that has now moved to the inland waterways, so there is every possibility it has previously been antifouled. 

Of course it is, but I'd say the fraction of canal boats in that situation is very small. So its worth pointing it out. I suspect its just a confusion of terminology from a newbie, and a "boatyard" giving erroneous or over-cautious advice to milk a newbie punter. That's much more common!!!

[rusty69]

3 minutes ago, Paul C said:

Of course it is, but I'd say the fraction of canal boats in that situation is very small. So its worth pointing it out. I suspect its just a confusion of terminology from a newbie, and a "boatyard" giving erroneous or over-cautious advice to milk a newbie punter. That's much more common!!!

Certainly worth pointing it out yes, but looking at OPs previous posts, they talk of recently looking at having a Dutch steel cruiser craned in on the K&A. 

[Paul C]

35 minutes ago, rusty69 said:

Certainly worth pointing it out yes, but looking at OPs previous posts, they talk of recently looking at having a Dutch steel cruiser craned in on the K&A. 

 

You spend longer researching posters than me! If that's the case, fair enough.

[pebble77]

Thanks for all the replies! as mentioned above by rusty69, it is a dutch cruiser that has been in the sea. The antifoul layer is starting to flake off a little.

I do feel like the boatyard is pressing me down the overly cautious road tbh... he has now 'ordered a part' for the shotblaster for the job so is going to be annoyed if I say cancel it. God its all so overwhelming!

The boat is on hardstanding, I'll go tomorrow and start scraping to try and identify potential 'layers'

[Paul C]

5 minutes ago, pebble77 said:

Thanks for all the replies! as mentioned above by rusty69, it is a dutch cruiser that has been in the sea. The antifoul layer is starting to flake off a little.

I do feel like the boatyard is pressing me down the overly cautious road tbh... he has now 'ordered a part' for the shotblaster for the job so is going to be annoyed if I say cancel it. God its all so overwhelming!

The boat is on hardstanding, I'll go tomorrow and start scraping to try and identify potential 'layers'

 

In that case, I can see why they're being cautious - he probably thinks its the right thing to do, to remove every trace of the old antifoul, 1) because it might interfere with the new layer of paint, 2) because antifoul is not permitted on canals.

[rusty69]

11 minutes ago, pebble77 said:

Thanks for all the replies! as mentioned above by rusty69, it is a dutch cruiser that has been in the sea. The antifoul layer is starting to flake off a little.

I do feel like the boatyard is pressing me down the overly cautious road tbh... he has now 'ordered a part' for the shotblaster for the job so is going to be annoyed if I say cancel it. God its all so overwhelming!

The boat is on hardstanding, I'll go tomorrow and start scraping to try and identify potential 'layers'

If he is buying a bit for his existing shotblaster, it seems likely that it has had some previous use, and so will probably have future use. Unless you have already agreed to have it shotblasted, I wouldn't feel too bad about it if you decide not to go ahead with it. Afterall, it usually costs a fair bit of money, even on a 30 ft boat.

 

Has he quoted you a price for the blasting yet?

[David Mack]

6 hours ago, Paul C said:

2) because antifoul is not permitted on canals. 

Says who?

[Paul C]

14 minutes ago, David Mack said:

Says who?

I'll open it up to others. I thought it wasn't allowed but I'm not sure where or who makes that a regulation (if it is one). 

[john.k]

If its old antifouling,it may be something like tri methyl tin..which is a toxic waste............anyhoo,if the blaster is a mobile guy ,then he probably wont be too worried ,as the waste will be left onsite.

[Tracy D'arth]

Is it not grit blast? Shot blasting is a metal treatment not cleaning.

[peterboat]

Mine was blasted with glass then Zinga coated, it's a messy job but the long term protection is outstanding.

Now on a practical side now is not the time of year to be doing the job, it's to cold and damp, tell them so the blacking has every chance of falling off. These jobs are best done under cover in the summer 

Edited February 12, 2023 by peterboat

[pebble77]

I think I have basically agreed to the shotblasting. He has quoted 800 for it. The blacking will be done undercover, but I see what you mean about the temperature being a potential issue peterboat. Not sure if i have a choice here though.

 

They have quoted 1600 for epoxy 2 pack and I just don't have the money to afford that.

[peterboat]

Just now, pebble77 said:

I think I have basically agreed to the shotblasting. He has quoted 800 for it. The blacking will be done undercover, but I see what you mean about the temperature being a potential issue peterboat. Not sure if i have a choice here though.

 

They have quoted 1600 for epoxy 2 pack and I just don't have the money to afford that.

Then don't have it done or do it yourself, February is not the time to have bare metal it will be going rusty as soon as its blasted totally a waste of time and money. The blasting is cheap though very cheap

[pebble77]

Sorry, I'n not sure I understand. are you saying you think I need to epoxy it at this time of year?

[Richard10002]

5 minutes ago, pebble77 said:

Sorry, I'n not sure I understand. are you saying you think I need to epoxy it at this time of year?

He is saying you should do nothing now, and wait until later in the year when it is warmer and dryer.  I'd be suspicious of a yard suggesting/agreeing the work is done in February. 

[rusty69]

Think I would get them to do the blasting. Seems reasonable cost wise, and then 2 pack epoxy it myself, but not until the weather warms up a bit, unless it happens to be in a heated enclosure.

 

Maybe cost just over 1000-1200, maybe more with slip charges.

 

If money is really tight, then investigate the bitumen route.

Edited February 12, 2023 by rusty69

[pebble77]

Definitely going to consider this thank you!