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The Cardboard Firewall.

I thought I'd simply copy the text from one of the dialogues on the Europa list to this page.  I received many comments from list members on what to do with that firewall.  Read on...

--- In lotuseuropa@yahoogroups.com, "Dave" <p914gtca@y...> wrote:
> A fibreglass car with steel seats and a cardboard firewall. Sheesh!
> Having repaired or improved everything I could find wrong with
> 54/1871, I'm getting ready to roll her onto her belly again,
>except - that firewall. The designer must have laughed himself silly when he chose >masonite to make something called a firewall. British
> humour... Anyway, mine is in good shape, but dirty and ugly.
> Shouldn't it at least be sealed somehow?
> I can sand it clean and:
> Do nothing, and let the painters deal with it.
> Coat it with marine epoxy
> Coat it with marine epoxy and a layer of very fine weave cloth.
> coat it with Polyester resin.
> Coat it with resin and glass it.
> After that a sheet of aluminum might look nice.
> What have others done?
> Thanks, Dave

From:  "tcspcl"
Date:  Fri Oct 17, 2003  5:28 pm
Subject:  Re: Firewall replacement

It's not really cardboard, it's sort of a poor quality strand board -
what we might have called beaver board a long time ago (wonder why it
was called that?). It was probably used to help absorb sound. It
was good as a "firewall' because it soaked up so much water it
couldn't burn. Not very strong, but if yours is in good shape I
would leave it alone after cleaning and painting. The big problem
with it is that it wouldn't stop the engine from joining you in the
car in a severe rear crash.

'73 TCS 2768R

As it turns out my beaver board firewall was actually in decent shape, though there was some failure of the taped joints beginning.   The side facing the engine bay is heavily undercoated, so I can't easily glass it without a lot of prep work, and removing and replacing the entire firewall would be a real PITA, though not that difficult.  There is a reasonably priced polypropylene core material material which seems well suited to the job.  www.plascore.com  www.nida-core.com  I think I'll build me a spiffy new composite firewall!


To begin at the end, I did remove the firewall, here's what it looked like.  I decided to replace it with glass/honeycomb composite panels.   Interested in how to make the panels?

Here's one with the first beaverboard panel removed.   What a tempting storage space, or battery chamber, or subwoofer enclosure or, or....  What should I do with it?  Well, the guys on the lotus list (aka "The collective") seemed to think that since the car will be a ' Tourer' I should install a second fuel tank. (The first in in a similar position on the other side.)  I think they're probably right.

 You can see how it is supposed to work.  The beaverboard panels are supposed to 'land' around its perimeter on specific areas designed into the bottom half of the body, and onto the upper/exterior part below the rear window, then they are glassed in place around their edges.  Here you see the lip molded into the outboard side of the lower body molding where the firewall rests after having been installed from the inside.   You can also see the flat next to the chassis box where the inboard edge of the lower canted firewall panel rests.

 Here's where things don't quite work out according to plan. You can see the piece of beaverboard lying on the floor.  There is an immaculately clean section of body where the board ought to have been glued in place, (beside the three chassis bolt holes) and next to that, a ragged stip of fiberglass with remnants of the board still attached.   The lower mold isn't accurate enough for the lower firewall panel to rest flat on the body on both sides, plus align with the upper firewall panel.  As a result, there's a large gap where a massive joint could be.  The board is only held in place on the underside by the fiberglass mat installed from behind,   No big deal, it was all still sound, but I'll bed my composite panels in epoxy.

Then I noticed another problem, not unexpected.  With the car off the chassis and no firewall, the rear part of the floor was quite floppy and the body shell was far from true.  No problem, we put the chassis on blocks, then the body on the chassis.  It lay flat and straight.  Perfect.

So, using a zip disc, we cutted and fitted  the panel I made.

We then mixed some marine epoxy with silica and chopped glass and heavily coated each  of the surfaces in the car where the upper firewall would land.  After attaching the firewall from the interior with a few sheet metal screws, (lots of pressure isn't a good idea) we mixed up some more epoxy and laid a nice hollow fillet along those joined surfaces from the engine bay side.   Once that hit its 'B-stage', (gelled, rubbery but not fully cured) a quick wipe with an acetone-dampened rag smoothed it nicely.

Here's a picture of the glued but not glassed firewall.  The white bead is a nice smooth concave epoxy fillet.  Awesome stuff.

I'm glad that so far only one side has been fibreglassed.  the board would have been too stiff to easily install with both sides glassed.  It would certainly have distorted the narrow strip of fiberglass below the rear window.    Solid firewalls like aluminum would be very difficult to install, and would - I think - give inferior results in the end.  Maybe other europa firewalls are perfectly flat...

Next is 'tabbing' the firewall to the body.  I pre-laminated 2 layers each of mat and cloth on a sheet of glass covered with waxed paper, then lifted the entire (uncured) patch into place and worked the air and excess resin out with a resin roller.  

This patch will be placed over the epoxy fillet.

After having secured the firewall panel from the rear, and 'tabbing it in from the front as well with two patches (visible in the next picture), I set about fitting and epoxying the the lower panels in place, as was done with the upper panel.

Here you can see the patches securing the firewall from the front, plus the lower panels secured by epoxy.

The layer of mat held in place with a few staples.

And on top of that mat, a layer of cloth was carefully installed.  The edges of the lower panels were glassed in and each joint was reinforced with layers of mat and cloth.


The car was lifted onto the stand from the chassis, and it felt no heavier - it may even be lighter.  It  sure feels much more rigid than it did six weeks or so ago...  

I will close the discussion of my firewall by observing that the results are excellent, and well worth it for a major restoration like this one.  I would estimate around 10-15 hrs was spent and the cost of materials at around $100US.  The worst part is the dust created by grinding away the old fiberglass.   Cover your skin, wear a mask, be prepared for some irritation.  Second worst part is working on your off-hand.  In my case this meant leaning into the drivers side, and using my left hand to fit a reinforcing patch between the top of the firewall and the bottom of the window.  Then knocking over an open jug of resin.  Then dropping my last gooey brush on the floor.  In a thunder then hailstorm in November in Canada. 

Reinforcing along the floor from the back was no joy either, though these things force you to get inventive WRT installation tricks.  I found that laying up a patch on a sheet of waxed paper, then folding it over a piece of cardboard made it easier to place into tight quarters.

At this point, I'll introduce Struan from Oz who shared some helpful pics and instructions on making a similar firewall.  He approaches some details differently, and has made a very nice job of it.