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Thread: Patchy piece of Bondo after applying new layer of Bondo

  1. #1

    Question Patchy piece of Bondo after applying new layer of Bondo



    Picture in link:




    Good Morning,

    I am new to bodywork, and I applied a fresh layer of Bondo.

    However, although the rest of the dogleg is smooth→ there is a patchy area (red circle in the pic) which for some reason is not as smooth as the rest of the newly applied layer.

    What is the cause of having a patchy area, *right after* applying fresh bondo?

    Thanks!

  2. #2
    Join Date
    Nov 2006
    Posts
    2,048

    Default

    Hard to say what caused it. Maybe itís from not using enough pressure on the spreader, maybe itís air bubbles. No matter what caused it, you still need to sand it flat. Sand it down and add more filler if itís low. If you find air bubbles you canít fill them. Trapped air in the bubble will push the new filler out. The way I remove them is to take a 1/4Ē drill bit and twist it with my fingers until I get to the bottom of the bubble. After enlarging the bubble like that you have a wide shallow hole that will accept filler.

    Bob K

  3. #3
    Join Date
    Nov 2005
    Posts
    41,213

    Default

    Apply more Apply more pressure on the first pass so that the filler gets pressed into the scratches and bonds well with the surface. Also, after block sanding the filler you may have low areas that don't get block sanded, you should scratch those low spots so that the next coat of filler will adhere properly.

  4. #4

    Default

    GUIDE COAT VS SPRAY PAINT

    What advantage do I have using guide coat over just buying a cheap can of spray paint or even primer?

  5. #5

    Default

    Quote Originally Posted by Len View Post
    Apply more Apply more pressure on the first pass so that the filler gets pressed into the scratches and bonds well with the surface. Also, after block sanding the filler you may have low areas that don't get block sanded, you should scratch those low spots so that the next coat of filler will adhere properly.
    GUIDE COAT VS SPRAY PAINT

    What advantage do I have using guide coat over just buying a cheap can of spray paint or even primer?

  6. #6
    Join Date
    Nov 2006
    Posts
    2,048

    Default

    Guide coat is more like stain than paint but it wonít sink into surfacer. It just makes a color on the surface but doesnít add thickness like paint would. Paint can plug your sandpaper when you sand it off and those pills of paint on the sandpaper can damage the surface that you are trying to make flat. Buy a can of guide coat and donít use much of it in each application. It will last a long time. We all have cans of spray paint laying around but most of us that have tried using it have switched to guide coat after one use. Donít make trouble for yourself to save the $7 you could invest into a can of guide coat that will last years of moderate use. I use dry guide coat on filler and spray on guide coat on surfacer.

    Bob K

  7. #7
    Join Date
    Nov 2005
    Posts
    41,213

    Default

    We use dry guide coat on body filler and aerosol guide coat when wet sanding but the aerosol can also be used on body filler, I just don't like using it multiple times in a confined area then breathing the fumes. The dry guide coat is a black powder that is applied with a large powder puff that comes with the kit, wipe it on then sand it off.

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