Stabilising aluminum OTS doors / paint prep

Someone mentioned awhile back that body metal changes shape when exposed to the hot sun. I expect that’s true, especially aluminum. Now that I’ve got my OTS door skins flat and drum tight I’m wondering how to keep them that way, or at least mitigate the effects of temperature during our hot summer days.

Seems to me a thin, rigid sheet material of some kind bonded to the inside of the door would help to stabilise the skin, keep it flatter in the sun. It would have to be a material that’s fairly light weight, that will absorb and dissipate heat without softening or expanding.

My doors originally had an 1/8" thick tar paper like material bonded to the inside, but I think this was more for sound deadening than stabilisation.

Has anyone explored this?

Nick. I would be concerned that bonding a different type of metal to the aluminum would possibly result in bowing due to a bimetallic strip effect. Perhaps a thin aluminum honeycomb sheet would work if you were able to source it.

Are the doors wood framed?

Is there a turnbuckle brace running from on corner to another?

The 1/8" tar paper seems like that might stabilize for a couple of reasons.

Not sure what material you could use to fasten/attach another piece of metal. If the thermal cycling of the skin, because it is aluminum, is that great, I’d worry about shearing the adhesive?

I would also say, a full sheet seems overkill.

I’d be more worried about the edge crimps on the perimeter. Seems to me, if they are tight enough, that would cause an issue, as would these crimps being loose allowing movement.

How about some light weight Ali angle bonded using 3M VHB tape (very high bond)

Thanks for the input, gents. The doors are all aluminum and well put together. Any movement would be across that long expanse of unsupported sheet between the edges, that is the aluminum will expand with heat.

I figure the total crown across the front leg of the rear wing, the door and the front wing quarter panel is around 1/4" and visually unbroken so it looks almost like a straight line, but I can visualise the door skin expanding with heat will add crown and present like a bulge in the bodywork. It would disappear once the metal cooled back down so maybe I’m overthinking this.

I’m thinking I will at least bond the long, internal horizontal stiffener to the inside of the door skin with something like Sikaflex, same stuff that’s used to bond the flanges to E-type bonnets, which also get hot but keep their shapes.

still thinking

Hexcel hexagonal core material, bonded to the inner skin?

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Now that looks interesting, Wiggs. Wondering where one might source maybe 4 square feet of the stuff, though.

Contact Hexcel: they used to be pretty good at supplying ‘engineering samples’" and you’d hardly need more than 4 square feet. Not to mention, wrt having supreme knowledge of how to bond the stuff, there are few rivals to Hexcel.

Tell’em your intended use, they may just shout ya a sheet!

From experience (building nifty geophysical toys) when this stuff is bonded on thin aluminum, I can/did stand on it, with little flex.


Nick, there’s a reason they but a slight crown on all these old panels. You are shooting for the moon!! I’ll bet you will get as close as can be got. Seems doubtfull any sun induced expansion, would be permanent. Much more likely to suffer from someone planting thier big ass on your door! :tired_face:

My dad always advised me to shoot for the moon but to be satisfied with the stratosphere :wink:

Right. We say XK sides are flat but they must have a crown else would be flabby. I’ve just taken a short video of where I’m at today. Will upload it onto YouTube after dinner.

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I’ll look for it then!

Similar to “flat windshield” Bugs: they aint flat.


Also, the top of older RollsRoyce radiator shells: they, too, had a very slight crown, to make them appear flat.

Right you are. All goes to perception. Remember the spats on that beautiful XK120 just acquired by GTJoey? They’re probably dead flat and look fine in the flesh but appeared convex in the photos.

Here’s the video.


Holy Body Worker, Nick!!

I am in awe of your craftsmanship, and I ain’t awe struck by much or many!

I hope to come visit your faire neighborhood, in the future, maybe about the time you drive it for the first time.

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Honeycomb core and panels

I used to buy a lot of airframe bolts from Aircraft Spruce. They also have all kinds of materials for strong, lightweight composite structures, including honeycomb. You might also want to look at the array of rigid foam panels they offer. Anchored to the interior aluminum of the door skin with a urethane foam, it might be just stiff enough without being too stiff.


Thanks for the conversation. Some great ideas and leads.

Now to figure out how to bond the honeycomb.

Here’s a FRP composite reinforcement that you could whip up at very little cost. It would easily accommodate any panel curvature.


Getting fiberglass resin to bond durably to either aluminum or steel, is not a trivial process.

Hexcel makes specific epoxies to do this, and I’d wager a honeycomb no more than 1/8" will suffice.

There’s maybe a half inch of clearance between the door pocket and the skin. Something 1/4” thickness would fit, 1/8” better!