8 replies to this topic

[SFC_Allen]

Well trying to cover up the T-tops here for a CHP car. I used Bondo glazing $ spot putty but it keeps cracking when it dries.

At first i was wet sanding, then i went to just sanding and it would still show hairline cracks like you see in the bottom right of the first pic.

i did all the other chipping to start over.

Should i be doing something else to cover this up? Thanks in advance Earle

[Fat Brian]

What is underneath it? It sounds like the Bondo isn't able to adhere to whatever that orange stuff is. You might need to remove all of the Bondo down to that orange layer and primer over it then put the Bondo over the primer.

[SFC_Allen]

Should have put this in there also... i primered the car (t-tops were clear) then added the bondo glaze and then reshot primer and again cracks.

The orange is the bondo glaze. Doesn't happen all over just small area's different times...getting to be a pain in the ...

[1972coronet]

Incompatible materials ?
Insufficent dry time of the Glaze ?

Maybe there's a chemical reaction (in this case , oxidation ) ?

How long are you allowing the glaze to setup before you start working with it ?

Also , wet sanding is to be used *only* after primer coats are built-up over the filler / glaze . Primer absorbs moisture , as do fillers (plastic and polyesters) . It may be something as simple as allowing the H₂O sufficent vapourisation before primering / painting .

Best of luck !

Edited by 1972coronet, 25 November 2012 - 02:54 PM.

[SFC_Allen]

I was letting it sit for about an hr ( what the tube recommended), maybe I'll let it sit longer and see what happens.

Should I strip all the rest off or leave it and cover it up? Thanks Earle

[Craig Irwin]

Is your "Bondo Glaze" an air dry product? (without a hardener?) If it is remove it completely and use a product that uses a hardener. I use Evercoat Metal Glaze.

[Casey]

First suggestion would be to use a liquid cement, such as Ambriod ProWeld, Tenax7R, Testors in the glass jar, etc. and literally plastic weld the T-top panels to the roof, making it all one piece. The liquid cement will melt the plastic a little, and ensure the parts are permanently bonded.

Next, did you scuff the body and T-top panels before you primed them? If they are clear panels as found in the Monogram 1/24 '79 Camaro Z/28 and '77 Trans Am kit, the panels themselves will be very smooth and glossy, a surface paint does not like to stick to very well. It looks like the red oxide primer is still bonded to the plastic, but the filler you used isn't bonding to the primer...

The glazing putty is meant to be used for thin imperfections, and it always helps to sand the primered roof to give the glazing putty something to "bite" into. Not sure if you sanded the roof or not, nor which kind/brand of primer you used, though.

I would sand it down to bare plastic using 400, then 600 and 800 grit wetasanding paper, then assess the situation. Ideally, the roof panels and surrounding roof will be level and the joints between them eliminated, thereby eliminating the need for any filler.

[hicksie]

Strip all of it off. Then scuff with 80 grit paper. Wash with soap and water them with a wax and grease remover. Allow this plenty of time to dry. Apply a body filler. Not glazing putty. allow plenty of time to dry. sand starting at 180 and work you're way to 1000. Write off and apply glazing putty only if pinholes are there. Then sand out again.

[plowboy]

I agree with stripping it and starting over. One other thing I would suggest is to run a bead of crazy glue around the perimeter of your T-tops inside and out after you glue them in with liquid cement. It will fill whatever gap you have between the tops and make the bond stronger.