Lines after adhering plastic vents to fiberglass hood

[Dave333]

I have a Cervini’s fiberglass hood. I let it cure for a week in the sun, then hit it with 220 and let it cure in the sun a few more days.

Then I took the plastic vents and washed them with Dawn and then Ajax and then back with Dawn and then SPI waterborne wax and grease remover. Sanded them with 180 and the surrounding areas and then used VPA on the area followed by Dolphin glaze.

3 coats of SPI 2k primer and let it sit in the sun 3 days. Saw the lines start to form so sanded the area, another coat of glaze and let that sit overnight. The 2 more coats of 2K primer. Let it sit a few days blocked to 600 wet with no issues.

I did not use a sealer and wonder if I should have shot a reduced epoxy sealer coat.

Base coated and let it sit 22 hours before 5 coats of Universal with 30 minutes dry time between coats.

Sat in the shop overnight with no lines but while baking in the sun I can see them.

Customer says it looks great and they’re happy with it before cut and buff but my question is will this loose adhesion in this area and cause delamination later down the road?

When cutting and buffing should I mask off that area and not touch it?

Thanks for any help. First fiberglass hood I’ve done.

 

[OJ86]

How are the vents bonded to the hood?

 

[Dave333]

How are the vents bonded to the hood?

With Vette Panel Adhesive. I scuffed the vents with 180 on the underside and the hood cut out areas and then sanded any molding lines of the vents flat so they would sit flush and then after it dried I completed the top body work with VPA and glaze.

 

[OJ86]

Ya, I don't see that lasting without cracking and popping out. I feel like that product label is misleading. Atleast I have never bonded dissimilar materials with it. I always use a panel bond type adhesive.

 

[OJ86]

When the panel heats ups, the plastic an fiberglass are going to expand and contract at different rates and I don't see the VPA being strong enough to hold it in place. Also, I am not certain that the VPA will even really hold onto any type of plastic material. But I could be wrong, I don't have the TDS.

 

[Dave333]

Thanks. That’s what I’m thinking too, I think the baking in the sun is already showing a failure. Probably why Cervini’s recommends the 3m tape on these and not glassing them. Appreciate the feedback.

 

[OJ86]

It's not impossible to do it. The hood obviously needs to be redone since the one picture is already showing a failure.

Personal opinion here on how I would handle it..

Pop the inserts out, clean them up and get rid of the VPA from the surfaces. Get a quality panel bond adhesive, 3m, SEM etc.... glue them in place after prepping the surfaces. Once dry, bevel the top surface out where the plastic and fiberglass meet and that will allow the VPA a greater contact area that you can feather out. VPA or Adtech P17 will work, I'd vote for the adtech honestly.

 

[Dave333]

Thanks for the reply. I’ll go ahead and get them out and try the method you layed out.

I think the beveled edge is what it really needs and wish I would have thought of that. I normally weld so fiberglass is new to me. Appreciate the help.

 

[D.A.T.]

The edge of the item inserted into the flange is the problem. It needs to be submerged in a bed of adhesive and the length not allowed to absorb heat. If it is not--no way to give up its heat and you have a ghost line in the sun but not in the shade. All the air in the adhesive layer expelled.

 

[Dave333]

The edge of the item inserted into the flange is the problem. It needs to be submerged in a bed of adhesive and the length not allowed to absorb heat. If it is not--no way to give up its heat and you have a ghost line in the sun but not in the shade. All the air in the adhesive layer expelled.

Thanks. You guys are a wealth of experience and it’s always great to get the explanations of why.

 

[Jim C]

yes this will fail. good advise given by OJ and DAT here. when molding in anything in autobody, it always needs to be feathered out. no straight edges. like when you are doing a plastic or fiberglass repair. the edges on both parts are tapered out to nothing for atleast an inch on both sides then the repair or bond is done in the middle. it should be a big "V". the adtech p17 is high temp and good for i think 450deg so its great for a hood. dont bond with it though. strictly filler. bond with epoxy panel bond then p17 as your filler or blend area.

 

[Dave333]

yes this will fail. good advise given by OJ and DAT here. when molding in anything in autobody, it always needs to be feathered out. no straight edges. like when you are doing a plastic or fiberglass repair. the edges on both parts are tapered out to nothing for atleast an inch on both sides then the repair or bond is done in the middle. it should be a big "V". the adtech p17 is high temp and good for i think 450deg so its great for a hood. dont bond with it though. strictly filler. bond with epoxy panel bond then p17 as your filler or blend area.

Will do. I’ll be removing them tomorrow and picking up some p17, making sure to make a large V and a larger repair area and then use panel bond to adhere the vents.

 

[Jim C]

also, identify what type of plastic the vent is. if its something like abs which i doubt then bonding is easy. if its urethane, make sure its scuffed really well, cleaned with acetone and then flame treat any areas that will see adhesive or filler.

 

[Jim C]

i have worked with cervinis parts before but it was prob 15 years ago. they are local here. mayby 1/2 hour away so pretty popular. back then all their little vents and add on pieces were a off white urethane plastic of some sort. kinda thick and heavy.

 

[Dave333]

yes this will fail. good advise given by OJ and DAT here. when molding in anything in autobody, it always needs to be feathered out. no straight edges. like when you are doing a plastic or fiberglass repair. the edges on both parts are tapered out to nothing for atleast an inch on both sides then the repair or bond is done in the middle. it should be a big "V". the adtech p17 is high temp and good for i think 450deg so its great for a hood. dont bond with it though. strictly filler. bond with epoxy panel bond then p17 as your filler or blend area.

Will do. I’ll be removing them tomorrow and picking up some p17, making sure to make a large V and a larger repair area and then use panel bond to adhere the vents. The vents were black but I didn’t even do a test on the material, I just followed their prep instructions that came with them.