What to do with a gaping flange?

[jono]

Okay, stop sniggering at the back!

But seriously, the fibreglass 'flange' that extends down from the sill and which is then 'stitched' through the structural sill member by a series of screws and washers at roughly 4" centres.

I've replaced the structural members and the old ones had corroded to the extent of disintegration and in doing so the expansion had pushed out and permanently deformed/stretched the fibreglass between each fixing point so that it now looks wavy.

Can anyone suggest a way of making this straight once it's all fixed back in place?

Seems to be a few options - slitting a narrow V cut in the flange between each fixing pointing and glassing it back flat - sounds like a complete ball ache?

I've had another idea that would involve Tigersealing a strip of carbon fibre or GRP to the back of the flange and clamping it before fixing it all back into place.

Has anyone else come across this before and found a way to resolve it?

[h20hamelan]

Probably a crab shoot.
As to the wavy, how do you suspect this happened (rusting and moving metal?). Glass fibre looses any strength once its distorted. Maybe you need to cut this out, and use it as a plug for a template. For concave, gravity problems with glass. Normally I would pre-preg the mat and cloth on a release material. Paying special attention to getting the grp matrix (2”) into the opening. Then adding packing tape overtop to keep the form. Not exactly sure if this information is useful, as I am not totally clear on the exact reference point of location. Post a picture or four.
Typically, the less resin and glass the better. Can you put your hands on rigid (Clark) foam? Actually anything if your repairing with epoxy.
Sometimes, I have used mat. Added removable pieces of whatever (doweling, sticks whatever) inbetween fluffed up mat. So not as to get too much resin on the mat as it weights it down. Just enough to get it wet. This can act as your filler, depending on how much space you have to fill. It keeps it light, and also leaves open spaces for bonding.

[Lotusian]

My sill flanges were also wavy, but, painted matt black (as they should be of course) they miraculously disappear. No-one will ever notice, apart from you. Use socket headed cap screws M6 to make everything smoother - so much better than hex headed bolts which catch the light.

CC40842F-ADE5-4A9F-BF98-5DBB74AC6BD1.jpeg (55.55 KiB) Viewed 877 times

[jono]

My sill flanges were also wavy, but, painted matt black (as they should be of course) they miraculously disappear. No-one will ever notice, apart from you. Use socket headed cap screws M6 to make everything smoother - so much better than hex headed bolts which catch the light.

E0267A7A-6A80-46A3-9E24-ABCA53B1FA97.png

425F90E1-7626-4845-B305-25C4F78C08A1.png

CC40842F-ADE5-4A9F-BF98-5DBB74AC6BD1.jpeg

Thanks for this - yes probably over thinking it and my intention was always to do them black so hopefully it will get 'lost'. However I may try 3M VHB tape to see if that pulls it back a bit.

I've already sourced the screws - 6mm flat head button set screws with 18mm washers and nylocs, in stainless - the original ones were this pattern and I've become an originality anorak this time. What I must remember to do though is etch them with a shot blaster, the paint was always falling off the screws and washers on my last one and needing to be re done every few months

[stugilmour]

That does look good!

The rattle can rockguard undercoating product I used for the sill flange has a mild foaming action that could fill gaps pretty well. Although not a totally stock look it covers the hex bolts well and looks the part. Very durable. I also used it generously to seal the wheelwell end plates; inspected this year and everything is very dry in there.

Perhaps a similar product could be used (more judiciously and suitably masked if you want to still paint the outside flange) to fill the fish mouths from below to prevent moisture issues and give a solid look?

[jono]

Hi Stu,

I used copius quantities of Upol Gravitex on my last car to the underside and also the sill flanges then over painted with black satin - also used it on the inside floors, boot and wheel arches.

It's thick so has 'filling' properties and also acts as a sound deadener. As I don't have spray equipment I just brushed it on in heavy coats then stippled it when it was beginning to go off - I could create the same textured effect as a sprayed stonechip finish.

I will probabaly do the same on this one.

...just back in from glassing up the sill plate areas inside the car and extending 3-4 layups onto the floor and into the corner around the front and rear jacking points (I raise the car on the 2 post in these locations so want them to be nice a strong).

[Plus2cabby]

Hi
When I discovered this issue 20 odd years ago on my last car I bought 2 strips of flat alloy plate, 6 x 25 mm full length of flange , secured with stainless m6 set screws , clamping the wavy fibreglass flat , spreading the load area of the screw and barely noticeable when painted satin black.
Sorry no digital pics back then
Hope this helps
Regards
Mark

[jono]

I've now resolved this issue which also coincided with the 'stitch' holes being worn and oversized and the fibreglass having thinned in the hole areas in addition to some sections of the flange being broken/split/missing.

Being somewhat anal on this build, I ground out and relaminated the fibreglass in the hole areas with 4 layers of CSM to bring it flush with the body flange and also laminated up new sections to replace the missing bits. After that I re worked the entire flange with a DA and finished it with 2 layers of tissue then a thick coat of resin. After flatting back it looks great and the rippling has almost disappeared.

A time consuming ball ache but the body flanges on my last Plus 2 used to irritate me - this one is now perfect and with new cills members is the foundation of a really strong bodyshell. I can now support it on the lift and de-couple it from the chassis then start on the underside and the main body fibreglass repairs.

..who was it once said that an old Lotus is a life sentence?