Help understanding why paint failed this way

[JaimeManero]

Hello. Ive been reading many posts of this forum since I got my first boat 3 years ago , and its been extremely helpful in many occasions. This is my first time writing a post

 

2 years ago I painted the inside of the stern hull floor, using rust converter, red oxide, and a top coat of exterior paint.

 

Yesterday, I decided to clean this area, and poking with my finger on the floor i noticed a squishy feeling, like water was trapped  underneath the paint, and even some bubbles of air coming from areas nearby. 

 

Paint cloud be removed in chunks along a thick layer of rust. Any idea why paint failed this way and how to avoid it in the future? 

 

 

 

Its an area frequently exposed to rain water and would pool there. 

 

 

[Tony Brooks]

It is not the paint that has failed, it is the steel that has rusted under the paint. As rust is about 8 times thicker than the steel it formed from, it lifts and cracks the paint.

 

Paint is not waterproof, especially if water is held against it, as it would be in a bilge.

 

Ideally, you will need to grind back to clean steel before applying any type of pant system.  You may find epoxy pain it more waterproof than ordinary exterior paint, but it is getting the steel as rust free as possible that is important.

 

 

[Eeyore]

Preparation will have also played a significant part in the failure, such as needle gunning, wire brushing and thoroughly degreasing the surface prior to applying rust converter. The weather, specifically the moisture content of the atmosphere, and the temperature of the steel in bright sunlight. There also seems to be an undercoat missing from your scheme.  

Edited May 16, 2023 by Eeyore

[Tony Brooks]

From my own experience with the bilge on JennyB, I suspect that the prepped steel was still wet or damp when it was painted.

[JaimeManero]

Thank you for such a quick answer.  Yes, I forgot to mention the undercoat, it was applied. Also i used a angle grinder with a wirebrush, and surface was degreased. I remember I removed a bucket of rust.

 

I also remember I had some rain after applying the undercoat. Wet surface before painting might be also a posibility. 

 

Rust converter is water based, maybe i didn't let it dry totally? It was 2 years ago so i cant remember all the details. It was my first time doing this type of paiting so i wouldn't be surprised of making a mistake on the preparation or wating time between coats.  Red oxide was the only paint oil based, the rest were water based.

 

I didn't know paint are porous.  Im considering going for a epoxy based one to fix this. But i havent use it before. 

 

 

 

 

[Barneyp]

Preparation is key, you need to get back to bare metal and then thoroughly degrease.

You don't say what paint you use, but you really need an epoxy and to use paints that are designed to go together i.e read the manufacturers instructions and use the recommended primer, undercoat and top coat.

Finally temperature and humidity when applying are important, it must be dry when you start and kept dry until the top coat has cured. Assuming the boat is in the water the metal will never get very warm, so check the paint will cure at low temperatures and make sure you leave enough time between coats.

[Bod]

Which rust convertor did you use?

 

Bod

[BEngo]

When painting bare steel in contact with the water the water temperature needs to be higher than the dew point next to the steel.  Otherwise you get a very thin layer of condensation on the steel, which means the metal rusts under the paint and the paint layer fails. 

 

Best time to paint bilges is a low humidity day in late summer when the water is warm, or do it with the boat on the bank.

Use a specialist bilge paint, or one designed for continuous immersion. Ideally try to find one that is surface tolerant too.

 

N

[JaimeManero]

I used dulux red oxide, and a mix of diferent brands for next coats that I cant remember. 

 

Yes, she was on water when I did the job. It was quite warm weather (summer), but It had to rain regardless while the undercoat was drying :/. Im struggling with paint as weather is hardly dry or predictable for that matter in this country.  

 

Im considering using jotamastic 2 part epoxy paint. Anyone had used it before or can recommend another one? Budget is tight but a corroding hull after a bad paint job is even more expensive so...😅. Ill use it for the inside part of the keel too, where access is dificult so its preparation. Also its a place with constant contact with bilge water while I get to fix the roof. I attached a picture where the keel can be seen. Right now it just bare metal, visibly rusting. I dipped a magnesium rod grounded to the hull to try to minimise corrosion while the weather gets warmer to use the epoxy paint. 

 

 

This is the third year after I bought my boat, and refurbishing her while being in continuous cruising have been a tough endeavour. See jobs already failing while I have so much work still left to do is discouraging.  But i guess this is part of the process of refurbishing a boat so ill keep going. 

38 minutes ago, Bod said:

Which rust convertor did you use?

 

Bod

Fuze is the brand. Sold on ebay

[LadyG]

2 hours ago, JaimeManero said:

I used dulux red oxide, and a mix of diferent brands for next coats that I cant remember. 

 

Yes, she was on water when I did the job. It was quite warm weather (summer), but It had to rain regardless while the undercoat was drying :/. Im struggling with paint as weather is hardly dry or predictable for that matter in this country.  

 

Im considering using jotamastic 2 part epoxy paint. Anyone had used it before or can recommend another one? Budget is tight but a corroding hull after a bad paint job is even more expensive so...😅. Ill use it for the inside part of the keel too, where access is dificult so its preparation. Also its a place with constant contact with bilge water while I get to fix the roof. I attached a picture where the keel can be seen. Right now it just bare metal, visibly rusting. I dipped a magnesium rod grounded to the hull to try to minimise corrosion while the weather gets warmer to use the epoxy paint. 

 

 

This is the third year after I bought my boat, and refurbishing her while being in continuous cruising have been a tough endeavour. See jobs already failing while I have so much work still left to do is discouraging.  But i guess this is part of the process of refurbishing a boat so ill keep going. 

Fuze is the brand. Sold on ebay

Personally, I would not buy red oxide from Dulux, I am sure they know how to make paint, but also how to market it to every Tom, Dick and Harry. 

I know it's a grind (!), but it's all about preparation,  determining the various coatings available, read the data sheet and follow the instructions.

If there is any dampness don't start painting. A heater may be required to dry a bilge, but a spell of warm dry weather helps a lot.

This time of year check out the ambient temperature and the dew point.

I was very lucky to get a vacant slot in a floating paint shed, with power, a few years ago.

 I managed to get a lot of work done in less than half the time it would have otherwise have taken, which boosts morale considerably

Edited May 16, 2023 by LadyG

[john.k]

Once there is heavy rust ,abrasive blasting is a costly but sure cure ..........there is an alternative ,and that is flame spalling..........Ive used flame spalling with 100% success doing heavy rust removal.......and the advantage is after wire brushing the steel ,its still hot ,and paint goes on without problems.

[Bod]

@JaimeManero"Fuze is the brand. Sold on ebay"

If I have found the correct item on E-bay, it appears to be one of the Vactan type converters, good stuff.

Your first pictures show a thick layer of rust with paint on the top, what I think may have happened is that water has crept under your prepared area from elsewhere.

 

Bod.

 

[john.k]

Waste of money putting any paint on heavy rust .........rust .converter wont work on heavy pitting ...........wouldnt be surprised if you go over the rust with a chipping(pointed) hammer it will go thru in places 

Edited May 17, 2023 by john.k