Hello everyone,
I am building up my racing car and i am making all the pressure tubes in carbonfiber by hand layup.
The reason for this is that i have built a huge 3d printer which can print the exact pipe size and shapes i want.
All of this is already accomplished with succes.

However now i am standing at the finishing part of the tubes and some weird patterns shows up after sanding the surface.
I am following the carbon skinning tutorial and only replacing the XCR epoxy with the EL160. Postcuring has been done to 40ºC so far and final temperature is going to be 170ºC.
The post cure cycles will be followed to 170ºC and polish after that when everything works on this test piece.

My process so far for this tube:
1. Glass fiber hand layup of the tube with EL160 post cured to 170ºC (Glassfiber is just better here)
2. Sanding 120grid
3. Carbon sleeve hand layup with EL160
4. 24 hours cure +25ºC
5. First sanding down dry 120 grid
6. Surface cleaned with brake cleaner (Alkanes)
7. 3 coats of EL160 was applied by waiting between passes approximately 6 hours until sticky "B" stage.
8. 24 hours cure + 2 hours 40ºC cure.
9. 180 grid wet sanding + 500 grid wet sanding + polish some places.

Please see pictures of the imperfections shown best before the polish process.
It is like the layers is not properly bonded together.

Looks like you have sanded a bit soon.  EL160 can be slow to cure to the point where it sands properly.  Moisture can be absorbed into the resin while it is still not fully cured as the resin in a part cured state is hydroscopic.

The resin will turn white as it absorbs moisture and as you sand through the layers this leaves the white rings you are seeing.  Leaving the resin to cure longer before starting the sanding process is the best method to stop this happening in future.

You want to sand through the current layer to remove the rings and leave it  to harden off a bit more before going near it again. The El160 can have quite a slow cure time so I would be looking at 48 hours minimum  to be on the safe side.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Hello Warren,

Thanks for the quick answer .

I will try leave it for the longer cure time before proceeding.

Is this still possible to coat 3 times with approximately 6 hours between passes when the cure is in the "B" stage, or should the epoxy cure (48hours) between all layers?

Another possibility: brake cleaners are often  chlorinated and leave a chlorine residue behind - which happens to be white. 

Dont use brake cleaner for prep work, it isn't designed for that purpose. Use a 'clean' solvent that doesnt leave a residue, like acetone or wax and grease remover.