Spitfire Mk3 windscreen/scuttle rust

[Graham Ness]

Wanting to take advantage of the lockdown and the good weather, I decided to attack some of the (hopefully) superficial rust on my Spitfire Mk3.  While I knew the sills needed some attention along the seams, I decided to turn first attention to the dashboard top/scuttle where the windscreen frame rests on the scuttle. Rust was clearly bubbling out from under the windscreen frame seal.  Having removed the windscreen frame it became obvious that a previous repair has included the addition of copious amounts of silicon sealant at the rear edge of the seal - as opposed to the front edge.. where it might have at least impeded the ingress of some water.  I've cleared away the sealant and there is evidence of some (fairly professionally applied) filler in the scuttle already from an earlier repair.  However, creeping rust has eaten into the scuttle and created a few small (<5mm) holes in the metal.

So, how acceptable to clean up the rust, slightly enlarge the holes to remove some more of the rust, apply rust treatment, fill and repaint?  I've already applies Kurust to the affected areas before I proceed further.  The holes are just to the door-side of the left hand screen wiper shaft and normally concealed by the windscreen frame seal, and access underneath is somewhat limited - even with the glove box removed.  Should I consider applying some fibre-glass support under the scuttle before starting on filling above.  I'd quite like to avoid a 'minor' body repair becoming a major headache.

I thought that there may already be a thread on this somewhere, but couldn't find one.  Was I just looking in the wrong place?  Thanks for any constructive feedback that anyone might have,  I am sure this must be a common problem.  Maybe I need to turn my attention to the sills for now and see what nightmare awaits me there.

Thanks.. Graham

[Clive]

Do not, under any circumstances, use normal filler to bridge/fill holes of any type. The stuff is very porous, and will make the car rot even faster. The proper method is cut out/patch and weld.

However, you are in a bind. On my Toledo, (low value) I had rust along the roof edge next to the gutters due it inappropriate use of filler. I was not prepared to start cutting sections out of the roof. What I did (and purists turn away now) was to use an aggressive wire brush in a drill to hack out rust and thin metal. I then used a fibreglass filler called uPol Fibral. It is nearly as "soft" to use as normal filler, but is fire reinforced and waterproof. This was applied, sanded back, reapplied , sanded and painted. 10 years of living outside and still all OK. A genuinely happy punter here. 

So, if you want to do a filler repair, I would again hack out aggressively any rust etc, and treat with a phosphoric acid based converter. Maybe dent the area down a tad. Then apply Fibral filler from on top, no support under unless bigger holes (you don't want air bubbles) Then fill/repair as you wish, prime and paint. I would be inclined to put some thick wax rust prevented under the seal when refitting too, hopefully keep water out. I guess gutter sealant or similar would do similar. 

My tin hat is on for suggesting the above. And off to do some work on the Toledo..

[NonMember]

If the holes are small, I'd agree with Clive. I don't like using just filler on a hole, though, even if it's fibreglass filler. I don't think the access is too bad underneath on a Mk3 - you should at least be able to tape a bit of mesh or fibreglass mat under the hole to give you a surface to apply the GRP filler onto.

[Graham Ness]

Thanks for the feedback.  I am familiar with some of uPol's products, but had not come across Fibral.  I shall do some reading-up now and invest accordingly.  Yes, it may not be the most ideal solution for the purist, but since this car is already a series of compromises and would never be entered for a concours competition, I won't lose too much sleep.

Thanks again.