Paint Checking on the Hood

[shorn]

My BJ8 is being repainted as I write. The previous paint job, about 15 years old, checked or cracked badly on the hood, although it was a very good base/clear job. Engine heat, I suppose. What should be done to avoid that on the new paint. I know Moss sells an insulation blanket, Dynamat??, but it would seem that would be somewhat unsightly at car shows, etc. Ideas, anyone??

 

[Dave Russell]

Hi Skip,
I think that engine heat would be the least likely cause of checking. The hood paint on millions of cars survives without heat shields. Below are listed some of the common causes:
----------------
CHECKING:
Patterns of short, narrow breaks in the top layer of paint. Checking occurs when the paint loses its elasticity.
----------------
If the finish on a rod or custom appears to the naked eye as a loss of gloss, it may have paint with crazing or checking. If you examine the paint under low magnification, you can see a large number of small cracks.

This can be caused by excessive stresses in the paint film due to inadequate mixing of materials prior to application, excessive film thickness, or the incorrect use of additives. The only way the problem can be fixed is to sand the affected area to a smooth finish and repaint.
-----------------
1. Insufficient dry time of film prior to recoating.
2. Extreme temperature changes.
3. Excessive film thickness (too heavy coats).
4. Paint not thoroughly mixed.
5. Using incompatible products.
6. Recoating a previous checked finish without proper preparation.
7. Using improper thinner or reducer.
---------------

I don't think it is very likely to happen again if the new surface is properly sanded, prepped, & primed. Good luck,
D

 

[Keoke]

Hi Shorn, If the previous paint is not of a sound condition it should be stripped to bare metal to avoid failure of the new paint. The paint shop should
be responsible for making this decision and guranteeing their work.---Keoke

 

[shorn]

Well, I should be ok then. The painter has taken the whole car down to bare metal including both the hood and its underside, applied epoxy primer, then several coats of K 36 surfacer and block sanded in between,and finally K36 as a sealer. He is about ready for the basecoat. So, I will assume the previous checking was from a mistake by the previous painter.
Thanks

 

[Keoke]

Sounds like you are on the road to success Shorn--Keoke /ubbthreads/images/graemlins/thumbsup.gif