Keel paint bubbles

[Blinky]

Last week my 7 year old Bavaria 32 was lifted to enable me to change the sail drive gator, not really a difficult job if you have a practical back ground and basic engineering skills. Anyway while I am waiting for the parts to arrive I decided to have the keel sand blasted and treated. I used Symblast a local company who did a good job quickly and professionally. I decided to use the Ecosea preparation method recently featured in one of the magazines. As recommended the keel was pressure washed which removed most of the antifouling and all of the growth. It was then left for 7 days to dry out. The keel was blasted leaving a fantastically clean surface ready to prime. It was primed within 15 -20 minutes as recommended to prevent flash rusting and given a second coat 6-7 hours later………………….. Now here is the problem; on returning to the boat this morning the keel has the pox! There are hundreds of small blisters in the paint and some tiny pinholes.
Is this salts absorbed in the cast iron from its immersion? Or water / humidity trying to escape from the CI ?
Has anyone else had this problem?

Blinky.

 

[bluedragon]

Sounds like moisture to me. I used to get this problem on wood I thought was dry. Could also be residual water reacting with the primer causing out-gasing. Was it an epoxy primer? Epoxies are especially prone to this.

 

[Seajet]

Sorry to say this but it sounds a real pain.

I realise you are proficient, but think it sadly needs a re-take ?

How about after a real blasting a thorough dosing of alcohol degreaser ( I'm talking about something which would make Oliver Reed flinch ).

My keel is a mild steel ( lifting ) plate with a cast iron ballast bulb; I don't find much trouble with the C/I bulb, but the mild steel has had to be replaced - then again after 32 years I & treatment co's have learned better...

I have tried EVERY steel / 'metal' treatment going, and I mean every, I used to work in a chandlery; nothing really was the holy grail ( asking a lot from a lifting keel, even proper long timed hot dip galvanising scrapes off in time ) but this stuff seems by a very wide margin to be the best I have ever come across; Dulux Pro Metalshield, primer & topcoat.

Yes, I'd have laughed at 'Dulux' too, but this is the business, I could send photo's if you PM me, including the previous keel I had to replace ( £Ouch ! But at least still available ) despite every treatment previously, with high trestles to get at the keel - essential for all lift keel boats - for years.

I am in no way related to Dulux or any retailer etc.

 

[OGITD]

A little late...sorry!

Phosphoric acid for removal of rust.
One of the most common phosphoric acid uses is to remove rust from surfaces of metals. Phosphoric acid can be used as a rust converter with the help of direct application to rusted iron, or steel tools and other rusted surfaces. The phosphoric acid converts reddish-brown iron, that is, ferric oxide to black colored ferric phosphate. After treatment with phosphoric acid, the black ferric phosphate coating can be scrubbed off, thus, revealing fresh metal surface. However, there may be need for multiple applications of phosphoric acid before all of the rust can be removed. The black phosphate coating can be left in place though, so that it provides further corrosion resistance. Rust remover is sometimes a greenish liquid that is suitable for dipping but it is more often formulated as a gel.

I have used Phosphoric in the past, but I now use Kurust which seems to give better results with pitted Cast Iron.

 

[Blinky]

Paint bubles

I have stripped back the coatings locally using a small sand blaster, back to the clean cast iron again. There is no rust, no moisture visible, no contaminates just clean cast iron. I think I will washin down again and leave it open for another week or so, then re blast wip down with r40 degreaser and try again!

Blinky

 

[Blinky]

update!

Update for you who may be interested.... Lift out in Feb .... No rust no problems dried out against piles today to jet wash. Still as good a the day I did it.

Blinky.

 

[Blinky]

Update for you who may be interested.... Lift out in Feb .... No rust no problems dried out against piles today to jet wash. Still as good as the day I did it.

Blinky.

Further update.......... Jan 2013. My keel is still without a blemish there is no peeling or de-lamination of the paint treatment it is holding the anti-foul. I am impressed!! Well worth the investment.

Blinky.

 

[VicS]

Phosphoric acid for removal of rust.
One of the most common phosphoric acid uses is to remove rust from surfaces of metals. Phosphoric acid can be used as a rust converter with the help of direct application to rusted iron, or steel tools and other rusted surfaces. The phosphoric acid converts reddish-brown iron, that is, ferric oxide to black colored ferric phosphate. After treatment with phosphoric acid, the black ferric phosphate coating can be scrubbed off, thus, revealing fresh metal surface. However, there may be need for multiple applications of phosphoric acid before all of the rust can be removed. The black phosphate coating can be left in place though, so that it provides further corrosion resistance. Rust remover is sometimes a greenish liquid that is suitable for dipping but it is more often formulated as a gel.

I have used Phosphoric in the past, but I now use Kurust which seems to give better results with pitted Cast Iron.

I think you will find that the blue/black coating is ferric tannate and is produced by tannic acid based rust converters such as Kurust and Fertan.

Ferric phosphate is off white

 

[oldsaltoz]

Hi Blinky,

Moisture would have the original problem, cast iron is porous with many small defects and often contamination.

Drying out after a light blasting is essential then a thorough dry blasting and rapid application of a suitable primer or epoxy then primer.

I use a brush on a stick and follow the blast nozzle so it has no chance of flash rusting.

Sounds like a good result for you though.

Good luck and fair winds.