Primer on top of antifoul?

[Murv]

I think antifouling is one of those areas where there's almost a little bit too much info out there!
So, we've acquired our first boat and she needs antifouling.
Have no idea what was applied before so we were advised to primer the hull before painting to ensure no risk of incompatibility.

So, we've bought all the stuff, but I now have a nasty feeling that the primer needs to go on a clean hull.
I don't want to remove the old fouling, if it really comes to it then I'd rather take a chance by painting new on top of old and if it comes off, I'll accept the consequences.
Or, can I just slap the primer on top of the old antifoul?

 

[richardbrennan]

If you paint over the existing A/F with something like Primocon I think you will be OK. However, I would check the website of whoever manufactured your chosen A/F, they usually have a table of compatibility which includes "unknown".

 

[sailorman]

http://www.international-marine.com/products/products-home.aspx

 

[PhillM]

Give it a really good scrape then prime. You can then AF on top of the primer.

 

[maby]

I think you have two issues to address - one is compatibility of the new AF with the old, and the other is the condition of the old AF irrespective of how compatible it is with the new.

Some AFs don't sit comfortably on others and that is where the special primers come in - they are designed to be pretty much compatible with anything and serve as a binding and isolating agent between the old and the new.

Like any paint job, you need a decent surface to receive the primer and if the old AF is flaking or there is any indication of underlying rust, then you need to clean back to a sound surface before priming and overcoating. There are "soft" and "hard" antifoulings and the soft ones can get quite powdery as they age - again not a recipe for good adhesion of the new stuff.

Apart from the compatibility question, it's similar rules to repainting a door in your house - if the underlying paint is in good condition, just wash it thoroughly, give it a light rub over, then prime and overcoat. But if the underlying surface is not well bound, you need to rectify it first, otherwise all your new (and expensive) AF will simply flake off.

 

[prv]

I would check the website of whoever manufactured your chosen A/F, they usually have a table of compatibility which includes "unknown".

Yep, and the answer to "unknown" is almost always "paint over it with our primer as a barrier first."

You don't need to take the existing paint off unless bits of it are falling off, in which case they'd obviously take all your new stuff with them when they do.

Personally I'd go at it with a plasterboard sander on the end of a pole, with a bucket of water and a hose. This will knock off any bits that were coming off anyway, smooth the transitions between those bits and the bits that are staying, take off some of the existing buildup (how much depends on how much elbow grease you put in), and give a key for the new primer to stick to. Then two coats of primer from the maker of your new antifoul, then the antifoul itself.

Pete

 

[Robert Wilson]

If you paint over the existing A/F with something like Primocon I think you will be OK. However, I would check the website of whoever manufactured your chosen A/F, they usually have a table of compatibility which includes "unknown".

Exactly what I did two years ago with Primocon+Cruiser Uno - after general rub-down with sandpaper I achieved a smart and smooth finish with the primer. The Uno went on well and looked very acceptable, but the racing boys would probably have tut-tutted.
Cruiser Uno again last year. No problems, that I can see and A/F has done what is says on the tin.
But there again, I might just have been lucky to get away with it.

 

[Murv]

Fantastic info all, thanks very much

 

[ianj99]

Fantastic info all, thanks very much

This company sell an excellent primer for antifouling as well as AF itself.

http://www.discountantifoul.com

It has anticorrosion prroperties, is quick drying and thixotropic so easy to apply without runs or drips. (it is the consistency of Greek yoghurt or soft butter and is very quick and easy to apply by brush or roller).

Their AF is the equivalent of Micron at half the cost.

 

[KellysEye]

>Have no idea what was applied before so we were advised to primer the hull before painting to ensure no risk of incompatibility.

I don't know who advised to to apply primer but there is no reason to do that. As others have said find out if the new antifouling is compatible with the old or preferrably use what was used before, ask the previous owner what it was.

 

[maby]

>Have no idea what was applied before so we were advised to primer the hull before painting to ensure no risk of incompatibility.

I don't know who advised to to apply primer but there is no reason to do that. As others have said find out if the new antifouling is compatible with the old or preferrably use what was used before, ask the previous owner what it was.

That does assume they can remember! I honestly cannot tell you what we used last time.

 

[johnalison]

It used to be common practice to reprime before each annual anti foul. It improved adhesion but added to the thickness of non-eroding paints. In recent years I have had to touch up areas of flaking paint around the waterline and always prime after removing flaking paint and feathering off the edges. The results have been good on Optima and whatever the builder put on originally.

 

[Sans Bateau]

I think the issue here is if you were to use s two pack antifoul system then it would not work over a one pot scheme. Use a basic standard antifoul over what exists and see what happens. If you can cadge a couple of paint brush fulls off someone in the yard it will save you having to buy/open a new tin. Give it a week or so, if it hasnt fallen off, use it. Forget the Primcon, IMO.

 

[maby]

I think the issue here is if you were to use s two pack antifoul system then it would not work over a one pot scheme. Use a basic standard antifoul over what exists and see what happens. If you can cadge a couple of paint brush fulls off someone in the yard it will save you having to buy/open a new tin. Give it a week or so, if it hasnt fallen off, use it. Forget the Primcon, IMO.

That does rather assume that you can dry the boat out! When we anti-fouled our boat last, the craneage to get it out and back in again cost a fair bit more than the materials. I would prefer to waste a few pounds on unnecessary primer rather than pay for an extra Iift.

 

[Sans Bateau]

That does rather assume that you can dry the boat out! When we anti-fouled our boat last, the craneage to get it out and back in again cost a fair bit more than the materials. I would prefer to waste a few pounds on unnecessary primer rather than pay for an extra Iift.

If the antifoul does not do anything nasty with the boat just sitting in the yard (assuming it is out of the water for winter) then it should be OK once immersed, why not?

 

[johnalison]

That wasn't our experience with poorly-adherent A/F around the waterline. Each year I would deal with the loose bits and each year new bits would flake off just after re-immersion. The bits I had dealt with remain OK.

 

[maby]

If the antifoul does not do anything nasty with the boat just sitting in the yard (assuming it is out of the water for winter) then it should be OK once immersed, why not?

Ah, but mine is in the water all the time!

 

[Sans Bateau]

Ah, but mine is in the water all the time!

Yes but its not your thread.

PS, so is mine, but I have Coppercoat

 

[maby]

Yes but its not your thread.

PS, so is mine, but I have Coppercoat

So do we - wonderful stuff!

 

[Neeves]

We ran a trial in Oz with a variety of AF. We primed a board and then applied a variety of AF. The issue of incompatability, this is between a new AF on a new primer - but different manufactuers, did not appear for weeks. We have since re-done the trial as panels on a yacht - but we applied the AF over primer from each AF supplier. Each primer was simply applied over an old AF. We have had no issues, its been 4 months. The yard where we did the work, as a matter of policy, apply primer over old AF unless they actually know what the old AF is.

Good luck

Jonathan