Quote:

.. I thought things were perfect...they came in small patches....so I did my second wetsand with 600 thinking that would clear things up.

on my fourth coat I have some major orange peel and the same small patches of micro-bubbles...this all occured ONLY where I had wetsanded the previous "mistakes".

so I have two questions:
do you think those areas were contaminated somehow?

will the final 1000/1500 wetsand and the polish remove this? or do I need to sand again with 600 and lay another coat down and then do the finalsand/polish/wax?



Ok... here is what I am thinking... Imagine that you went to a tanning shop and got a lovely tan on your skin. But on your way home you tripped and your arm scrapped against a wall.

What would happen is that you now have two different surfaces. One is 'well cured' ( the unscraped area with the tan ) and the other surface is the area where you scraped your skin, removed the tanned layer and exposed the skin below the top layer of skin cells. And we all know that the lower scraped surface of skin is going to have to scab ( create a new hardened outer layer ) and then heal ( reach the same level of health or cure ) as the outer layer, before you will be able to properly tan the area that was damaged.

Ok... so picture this scenario over to the paint job. The paint we add to our car bodies goes on in coats. Each coat goes through three phases when you apply a layer :

The first phase is when you apply a coat. In this phase the paint is one wet layer.

0000000000000000000 <....wet paint added
0000000000000000000 <.../
XXXXXXXXXXXXXXXXXXX <- body surface

In the above picture the two rows of 'o' are actually all one layer of wet paint. I show it as two rows only for the convenience of showing the transition in the following pictures.

----------------------------------------------

The second phase is as that coat is drying. In this phase a skin forms on the outer layer and a wet layer exist between the subsurface and the outer 'drying or hardened' skin.

xxxxxxxxxxxxxxxxxxx <....dried outer skin layer
0000000000000000000 <...trapped wet layer drying
XXXXXXXXXXXXXXXXXXX <- body surface

In the picture above that trapped wet layer is trying to evaporate its gases from the carrier through the hardening outer skin layer.

-------------------------------------------

The third phase is when that coat has fully cured or hardened. In this phase the wet layer that was trapped between the outer skin layer and the subsurface has fully cured to the point where there is no difference between the trapped layer and the outer layer for dryness/hardness.

xxxxxxxxxxxxxxxxxxx <....dried outer skin layer
xxxxxxxxxxxxxxxxxxx <....dried inner skin layer
XXXXXXXXXXXXXXXXXXX <- body surface

In this picture I am trying to show that the 'x' layer is now all one layer of fully cured paint.

------------------------------------------

Ok... my initial thought is that the 600 grit sanding may have opened up the flesh and exposed some of the still uncured paint that was still trying to evaporate the carrier ( mineral spirit ). This is a problem that we experience as humans. We tend to look at 'dry' paint as 'all' being 'dry' or 'cured' without realizing that a chemical reaction may still be occuring beneath the surface of what we see as 'dry' paint.

It is not as obvious to the human eye or touch as say a layer of ice floating above a layer of water. Yet in a way this is how you have to envision things when you are painting or working on the layers of paint. You wouldn't skate on 1 inch thick ice... you would wait until the water below the ice surface has hardened and also turned to ice.

If you add paint over uncured paint, where the carrier is still trying to evaporate the mineral spirit ( so it can harden ) what happens is you will get micro-bubbles. Which is basically the evaporatiing 'carrier' getting trapped under the new hardened outer skin of the fresh paint.

It's like your sanded paint is swimming in the bath and farted. The gas rises to the surface and little fart bubbles break the surface of the water's tension.

The answer would probably be to allow more time for the coatings to dry. Patience is a virtue and helps ensure that the previous coating is not still evaporating when you add the next coat of paint.

The temperature you are working in will help determine just how long you need to wait between coats. But the key is to key in on how long it takes each coat to fully harden and not just appear to be hardened. You want each previous layer of paint to have reached the point where the trapped layer between the outer skin and the subsurface are cured to the point of being one layer and not a dry outer layer and a still curing layer beneath it.

Do your sanding and walk away from the project for a few extra days. Hopefully your subsequent coats will not have any adverse reactions.

Marq

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Last edited by Marq; 05/24/07 09:11 AM.