Oil based paint over acrylic

[Jim Wortelhock]

I want to  re paint my NB roof. 

I have always been wary of painting oil based paint over water based paint. I have seen the results where cracking occurs because the oil paint is less elastic. 

My roof appears by the texture to be International Interdeck (polyurethane). I would like a finish that is more likely to deflect water and dirt and Rylard do a low gloss called Raddle Sheen (oil based)

The interdeck is in good nick apart from some flaking where the coal has been kept.

Any thoughts?

[bizzard]

2 minutes ago, Jim Wortelhock said:

I want to  re paint my NB roof. 

I have always been wary of painting oil based paint over water based paint. I have seen the results where cracking occurs because the oil paint is less elastic. 

My roof appears by the texture to be International Interdeck (polyurethane). I would like a finish that is more likely to deflect water and dirt and Rylard do a low gloss called Raddle Sheen (oil based)

The interdeck is in good nick apart from some flaking where the coal has been kept.

Any thoughts?

Generally oil based paint will go over anything, it's the other way round you might get a reaction.

[Jim Wortelhock]

Thanks for the reply.  In my experience with house painting I've seen some ugly results of oil over acrylic,  especially in bathrooms. 

[bizzard]

7 minutes ago, Jim Wortelhock said:

Thanks for the reply.  In my experience with house painting I've seen some ugly results of oil over acrylic,  especially in bathrooms. 

Are you sure it wasn't cellulose paint, that really reacts badly, pickles up if oil paint is put on top. Not heard of Acrylic reacting.

[Jim Wortelhock]

The acrylic doesn't necessarily react but in areas where there is moisture and varying temperatures the oil based paint contracts and expands at a different rate hence the crackling.  Maybe it's different with boats. If there is a chance of this then I'll go with Interdeck but I trust oil paint over polyurethane. 

[bizzard]

10 minutes ago, bizzard said:

Are you sure it wasn't cellulose paint, that really reacts badly, pickles up if oil paint is put on top. Not heard of Acrylic reacting.

Forget that. other way round. I meant painting cellulose paint on over oil paint or other other paint, it will react.

[Tony Brooks]

6 minutes ago, Jim Wortelhock said:

The acrylic doesn't necessarily react but in areas where there is moisture and varying temperatures the oil based paint contracts and expands at a different rate hence the crackling.  Maybe it's different with boats. If there is a chance of this then I'll go with Interdeck but I trust oil paint over polyurethane. 

 

One think is for sure, the steel underneath expands and contracts a lot from normal weather. Many narrowboats are long enough for the expansion on a hot day to  show with gaps in the lining etc.

[bizzard]

8 minutes ago, Jim Wortelhock said:

The acrylic doesn't necessarily react but in areas where there is moisture and varying temperatures the oil based paint contracts and expands at a different rate hence the crackling.  Maybe it's different with boats. If there is a chance of this then I'll go with Interdeck but I trust oil paint over polyurethane. 

I had that trouble painting water based paint over oil paint, had to re do it again with oil paint.  Why not use Acrylic again.

[Jim Wortelhock]

2 reasons.  I trust oil based and the Interdeck finish goes black/green very quickly 

[Mad Harold]

5 minutes ago, bizzard said:

I had that trouble painting water based paint over oil paint, had to re do it again with oil paint.  Why not use Acrylic again.

I found the opposite.

Flatted back the original (oil based?) paint and painted the (steel) top with Dulux Weathershield Satin water based.

That was in 2018, and the paintwork still looks good.

[bizzard]

2 minutes ago, Mad Harold said:

I found the opposite.

Flatted back the original (oil based?) paint and painted the (steel) top with Dulux Weathershield Satin water based.

That was in 2018, and the paintwork still looks good.

I quite like water based paint. I find it dries really hard and doesn't scratch easily.

[LadyG]

1 hour ago, bizzard said:

Generally oil based paint will go over anything, it's the other way round you might get a reaction.

Note to OP, you must buy paint which is recommended for metal paints. 

 

I buy from SML, section, marine paints. 

Apart from my epoxied hull, i never use two pack as they are not compatible with one pack.

One pack good moderm paints are almost as good as two pack once were, IMHO. 

Preparation is the key, pun intended. 

Sand down, wash down, undercoat, light sand if gloss topcoat. 

If your prep is such that it looks as though it has been undercoated, unlikely but possible, a modern topcoat may not need an undercoat. 

Some marine undercoats are so good that they don't need a topcoat, I tried this approach on my NB roof, but this year I need to attack dirt and rust on the angle twixt roof and cabin sides, so I will be using something like Hammerite smooth, after a rust killer. Just for two inches along the angle. 

Rust is the enemy in a metal boat. 

There is a huge difference between paint qualities, I am currently  painting a cream over a mid green inside, using Wilko satin, now on fourth coat. 😢 Day three. 

I used Zinsser exterior satin over the rest of the interior, one light coat, one standard coat. Tough and good colour direct over rough dark ply, Zinsser paint cost twice as much per litre. Job done in 24 hours. 

Edited April 2, 2022 by LadyG

[Jim Wortelhock]

6 hours ago, LadyG said:

Note to OP, you must buy paint which is recommended for metal paints. 

 

I buy from SML, section, marine paints. 

Apart from my epoxied hull, i never use two pack as they are not compatible with one pack.

One pack good moderm paints are almost as good as two pack once were, IMHO. 

Preparation is the key, pun intended. 

Sand down, wash down, undercoat, light sand if gloss topcoat. 

If your prep is such that it looks as though it has been undercoated, unlikely but possible, a modern topcoat may not need an undercoat. 

Some marine undercoats are so good that they don't need a topcoat, I tried this approach on my NB roof, but this year I need to attack dirt and rust on the angle twixt roof and cabin sides, so I will be using something like Hammerite smooth, after a rust killer. Just for two inches along the angle. 

Rust is the enemy in a metal boat. 

There is a huge difference between paint qualities, I am currently  painting a cream over a mid green inside, using Wilko satin, now on fourth coat. 😢 Day three. 

I used Zinsser exterior satin over the rest of the interior, one light coat, one standard coat. Tough and good colour direct over rough dark ply, Zinsser paint cost twice as much per litre. Job done in 24 hours. 

Wholeheartedly agree.  I have used Zinsser for years despite the price premium.  It just works.  On a side note, I was in a hardware store in the US and said paint was about $6 a litre (or quart)

[XLD]

Any precautions when painting over Silicon Alkyd paint? The word "silicon" worries me😬.