Superformance inner body to outer body bonding

[Craig T]

Hi All. I have an early Superformance MKIII, chassis SP139. The car was built in 1996. I recently purchased the car and as I am just getting to know the car "hands on". I have discovered that the bonding between the outer body and the inner body has failed in several areas. This bonding seems to have consisted of a very heavy bead of black urethane sealer that has failed to adhere to one or both of the inner fiberglass surfaces causing movement between the panels. I first noticed the problem in the right rear wheel wheel behind the rear wheel. Much of the seal had failed and water (flung from the tire, early cars had no splash guard behind the wheel I believe) was allowed to enter the trunk as well the rear outer body/fender had excessive movement. I have since repaired this area buy removing the old sealant (an inch thick in some areas), roughing up both surfaces of the fiberglass then refilling the gap with fresh urethane sealer using embedded 2 inch wide fiberglass tape to reinforce and strengthen the joint, This was not a high stress joint and appears to be holding up.
My problem now that I have since discovered, is that most of the front inner body/engine compartment panels, where bonded to the outer body have also failed. Unless I have missed something I see no structural support (except maybe where the quick lift supports pass through the outer body, but there is no real support here) for the outer nose, fenders and hood. There is in some cases more than an inch (especially at the inner fender and the nose) of space to fill between these panels. Has anyone else experienced this problem and would it make sense to remove the old urethane and again rough up the surfaces and actually fiberglass the inner body to the outer body to create a more rigid structure??
Any suggestions would be appreciated.

CraigT

[Blas]

Craig,
Drop me an email tonight with your phone number and I'll go over what I did with the couple of seams that seperated on mine. Some of the seams in the front narcel are not structural by design, they are more for air control. The product used at the factor is called Silkaflex, it's a marine bonding agent and it's expensive stuff. Very important to have clean sound surfaces when you make the repairs. More later...

[D-CEL]

CraigT & Blas,

I too have this issue on several joints in the front of my car (#239 circa 1998) and have been considering possible solutions. I am not at all happy with the lack of structural support in the front end. I have a small crack around my driver’s side lower QJ rod.
I was thinking about building some support structures. 8-10 inch long 2x2 fiberglass “L” brackets, glassing them to the underside of the nose and welding mating brackets to the Rad core support? What do you guys think?

Blas, Sika has many sealants. Do you know the compound number?

Jason

[1985 CCX]

Automotive seam sealer works as well..............

[m5extc]

I too had this on the front inner fenders and have seen a couple of other cars around the same build time had the same lack of sealant. Mind you, these cars are 2009 and in the 2900 number range. We determined that not enough sealant was used. Cleaned and resealed, no problems now.

Andrei

[Craig T]

As "m5extc" suggests and after a conversation with Blas I think the best way to perform the repair is to do as they have suggested. Cut out the old urethane (I used an old steak knife, it has reach and flexibility, better than an exacto knife or other tools that I tried) and restore the joint with new sealer. As Blas suggested after cleaning, degreasing and roughing up both surfaces, work in and apply a thin coat 1 to 1.5 inches wide of urethane to both surfaces to ensure and promote better adhesion and a wide base of contact.
My next step is to apply a 2 inch wide full length strip of fibreglass gauze (something like fibreglass mesh drywall joint tape, I used a 2 inch fibreglass tape used in sealing high pressure ductwork) and embed it into both surfaces of the first coat of urethane. Next apply a very heavy 3/4 to 1 inch deep filler coat of urethane to the fibreglass gauze and fill the cavity flush, then smooth to blend both panels. The fibreglass gauze does two things in my view:
1) provides a backing for the newly applied urethane to provide a uniform, smooth and regular joint inside the engine compartment even though it cannot be seen in most places. It eliminates the original irregular erratically pumped in mess from the factory. Maybe I just got a bad one.
2) the fibreglass tape will provide additional strength although it may not be needed. The urethane sealer is very strong on its own.
The sealer that I used was from Home Depot here in Canada, "Dap" Polyurethane, "Premium roof and flashing sealant", black in colour, guaranteed 50 years. At $6 a tube.
I think it is close or close enough to the very expensive "Sikaflex" product and will do just fine here. The Dap product has excellent adhesion, flexibility, is waterproof, weatherproof and paintable and cheap.
The front quick lift supports or bumperette supports must be removed to get the best results and access to the joint around the nose and inner fender.
In my view this repair still provides significant support for the front outer shell and provides a strong flexible joint. Hopefully it will also eliminate some or all the front end body "jiggle" and rattles that I currently experience.