Sanding acrylic paint for smoothness fails?

[Avi]

My problem: sanding my build scratches away paint.
 

Working on the hull of my USS Constitution build, I sealed the wood, primed it with two coats, then put on two coats of copper below the water line and black above. Primer and paints are Vallejo acrylics Model Color. 
 

Once fully set (I waited days) I tried sanding to smooth down the paint where needed, etc. I used 2000 grit wet, which should be high enough. I moved very gently in circles, using only light thumb pressure.
 

It didn’t go so well.

 

It smoothed it beautifully, but also removed paint, to the point where I could see the primer or wood underneath. That definitely wasn’t the goal. 
 

what am I doing wrong? Isn’t high grit wet sanding supposed to be good at smoothing it without scratching away the paint?

 

 

[Jaager]

Painting is not something that have much experience with, but I have been thinking that the reason to sand any layer of paint is to provide tooth for the next layer.  I would think that nothing good would come from abrading the final coat,  I am guessing that a smooth finish would either require that the consistency of a brushed coat be relatively thin or that an airbrush be used to apply it.

[Roger Pellett]

It depends on what happened.  If small areas sanded off, then the sandpaper did its job.  It removed high spots. 

 

If on the other hand, paint came off in sheets, it failed to adhere to your sealer.  This means that paint and sealer were incompatible.

 

Post a picture to help us diagnose the problem.

Edited December 27, 2021 by Roger Pellett

[vaddoc]

Always test on scrap wood, not the model!

[Chuck Seiler]

    What did you prime with?

 

    My limited experience with painting models (I only paint sections, like the wale or a panel...and I don;t complete many models) is that I seal the wood only.  Then I use what I believe Chuck P. refers to as 'carriage process'.  I thin the acrylic (using artist acrylics) to just thicker than water.  Apply.  Let dry, Apply a second coat. Let dry.  Buff with a micro fiber cloth or very fine (600+) sand paper.  Apply/dry/buff at least 2 more, maybe 4 more coats, depending on color.  It takes time but the results are worth the effort.

 

    I understand that painting the wale is much different in scale than painting the whole hull...

[mtaylor]

I wouldn't use sandpaper on paint at all.   Maybe rubbing compound or even toothpaste.  Learned that when painting a couple of cars.

[Nirvana]

Only two component paint would withstand the 2000 grit paper.

As previous members wrote, with acrylic paint from Vallejo/Tamiya and others sanding can remove a lot of paint.
Besides do test runs before applying your desire to your model. We have all been there, with a lot of work afterwards.

I know you will find your solution.

 

[wefalck]

Acrylic paint retains a slightly rubbery consistency for a long time. This is due to the time it takes for the water to diffuse out of the interlocking mat of acrylic molecules. It may not be possible to sand for weeks, depending on the thickness of the paint layer. For the same reason, acrylic paint will initially not adhere that strongly to most surfaces and can be easily peeled off. Building up the paint from very lightly sprayed layer accelerates the overall process.

 

Rather than using paper and perhaps even a sanding block, I would use very fine steel-wool (say 0000). Another possibility is pumice applied with a humid paper towel.

 

However, as others have asked, why would you want to sand the paint at all ? If there are specks of dust or other imperfections, the above methods will help.

[allanyed]

I agree with Eberhard.  Clean surface and totally dust free environment, no wool sweaters (learned this from an esteemed builder/MSW member quite a few years ago).  Spray paint in light coats (four or five) and if needed steel wool between coats, then several clear topcoats .     Light spray coats should yield a flat surface with no bumps or runs if done correctly.   NEVER start or stop the spray on the model, but rather off to the side a few inches when beginning and ending the movement across the model.  Of course spray methods need taping and such to block any overspray.   

Allan