Painting over 'old' paint? whats going wrong?

[noddy]

Hi,
New to the forum! and I need your help/advice.

I have just begun to repaint a 55 year old car. The original paint is in superb condition (the car is 38k miles & 1 previous owner!) - however I want to change the colour.
I have started spraying the door shuts, engine bay etc (with panels off) before doing the whole body. But I have noted a problem - the new paint doesnt adhere to the old paint very well - it is very easy to scratch off - even with your fingernail.

My question is ... how do I prepare the old paint to accept the new paint? but I dont want to strip back to bare metal.

Thanks in advance.

Roger.

 

[steveo3002]

engine bay a red scotch pad should do it , outer panels 800 wet or 400 dry

what did you prep it with?

 

[noddy]

Thanks Steve,

To prep the bits I have done, I just quick wet 'n' dryed it with 1500 - but just very gently and nothing else.
I assume from your reply, that if I use 800 or less I will give it more of a rough surface to key into?

Cheers,
Roger

 

[steveo3002]

yes 1500 isnt really suitable , somewhere in the 600-800 range wet will be ideal

red scotch pad for the hard to reach corners etc

 

[zardoz]

No need to strip it back to bare metal. What are you painting with ? Primer or colour ? If it is primer make sure you are not accidentally using etch primer on top on anything except bare metal.

 

[noddy]

Thanks guys - it looks like I need to use a different grade!

Zardoz - I'm just spraying on a cellulose topcoat - no primer!

Cheers,
Roger.

 

[langy]

yes 1500 isnt really suitable , somewhere in the 600-800 range wet will be ideal

red scotch pad for the hard to reach corners etc

As Steve said 1500 is too fine 600 would be better