Print through why and any fix.

[ArAKern]

Hello et All

Would like some guidance on what caused print through and can it be fixed.
So I have some very light layup GRP panels, I am assuming the construction was thin layer of gel-coat then two layers or woven rovings only. Now these panels are old 15+ years we just had them repainted
and they looked fantastic, finish smooth as glass but 2 week later after being removed from the shed I can not only see print through but feel it is a rough as the underside roving's are.

How is 15 year old GRP moving so much paint job is ruined just look a mess.

 

[rwatson]

How well do polyester resins rate?
..... The mechanical properties of resins are measured by tensile strength and tensile modulus (stiffness), which are significantly lower in polyester than epoxy resin. Polyester also exhibits a relatively high rate of shrinkage of up to 8%, which contributes to built-in stresses that can weaken a component and lead to 'print through' of the reinforcing fibers into the surface finish.
Resin Systems - Voodoo Hot Rods - http://www.voodoohotrods.com/composite_faq/resin_systems/

 

[ArAKern]

But why would I be getting shrinkage now 15+ years after the panels were made?

 

[Mr Efficiency]

The "cruel light of day", perhaps ? May have looked less obvious indoors. A high-build epoxy primer undercoat might hide it, but the sanding will be a chore. And of course, paints can look more slick when first applied, but when the solvent escapes, conforms more to the texture of the substrate. I don't think the old laminate has moved.

 

[JamesG123]

What kind of paint was used? Maybe it reacted with the poly?

 

[Beamreach]

Painters sanded away gel coat and more, did not replace it with anything other than top coat paint?

Like to paint ourselves; works out OK other than smell/toxicity of the paints...

 

[Mr Efficiency]

What kind of paint was used? Maybe it reacted with the poly?

I can't think of any paint or paint solvent that would do that.

 

[Blueknarr]

"Cruel light of day" says it all.

15 year old gelcoat was oxidized to matte or other low gloss, so printthrugh was unnoticeable. New paint is much higher in gloss. Now weave is highlighted.

Over zealous sanding that removes gelcoat and exposes glass fibers will result in printhtrug.

Solution: fair and repaint
+felt texture will come back if no fairing compound used
+seen, but not felt can be blocked down and heavily primed
+low angle lighting shows surface variations better than overhead lighting

Good luck

 

[ArAKern]

The paint job was semi professional. Gel coat was sanded and all imperfections filled then 2 coats of epoxy primer was applied left to cure 14days then 3 coats of high build primer applied this was faired and blocked to perfection left for 7days and then 2k base coat 3 coats followed by 3 coats of 2k clear/lacker. This was left to cure for 14days at this point it all looked perfect then once refitted and taken outside within 2 days we could feel the print through.

 

[Blueknarr]

The roving weave should not be telegraphing through that regime.

There are other ways texture is introduced to a paint film. Are you sure that it isn't orange peel or alligatoring?

Need pictures or all is speculation and conjecture.

 

[Mr Efficiency]

The paint job was semi professional. Gel coat was sanded and all imperfections filled then 2 coats of epoxy primer was applied left to cure 14days then 3 coats of high build primer applied this was faired and blocked to perfection left for 7days and then 2k base coat 3 coats followed by 3 coats of 2k clear/lacker. This was left to cure for 14days at this point it all looked perfect then once refitted and taken outside within 2 days we could feel the print through.

Sounds like an enormous amount of work, but to what end ? What was the intended usage ?

 

[ArAKern]

Ok was harder to photograph than expected to much reflection.
This is what I can feel in certain areas in others it is visible and else where there is nothing.
IMAG0102.jpg https://drive.google.com/file/d/1YSVPvFdnZiBT-j2lfrgmkiC7QdnjTnUq/view?usp=sharing

and this is orange peel
IMAG0103 (1024x759).jpg https://drive.google.com/file/d/1WEv9uaEUC-BfQBiC_xNc5iA0vgQ56iFX/view?usp=sharing

 

[rwatson]

They are pretty bad photos. I don't see obvious "print thru", which would look like random chopped strand patterns.

After your explanation of the process, I think you might be experiencing incompatible paint types.

 

[ArAKern]

Yes looking at the online images they are bad sorry.
You will not be able to see any CSM as it was not used only rovings.
The diamond pattern on the right half of the first image is what I am trying to show notice there is no distortion in the reflection left hand top corner.

Will try and get some better images next weekend

 

[Mr Efficiency]

I thought I was looking at a masterpiece of abstract art !