FYI - Hardie Board for Heat Shields not Recommended

[MikeAH100M]

Like many AH'ers, I was searching for ideas to reduce the heat transfer from the engine/exhaust to the passenger compartment. I saw several posts here and on other BCF's proposing the use of Hardie Boards. I contacted the manufacturer, James Hardie, and they strongly recommended NOT using their product for this application because the it has a very high heat transfer rate and offers no insulation value, even with an air space behind it.

 

[RDKeysor]

It will be back to the drawing board for those of us who recommended Hardie backer. I particularly don't look forward to dropping the muffler again when I find a substitute. Perhaps this explains why I didn't realize any noticeable improvement in my car after installing the full complement of "insulation" pieces.

 

[Lotuswins]

Hi Mike,

If you look how the original shields were designed, with standoffs to hold them away from the sheet metal, it is apparent that they were meant to prevent the effects of radiation heat transfer, not conduction (direct contact) nor convection (fluid transfer I.E. air moving around in the engine compartment/muffler area). So, considering that, even if you put a sheet of copper or aluminum in their place, which we know has a much better heat transfer coefficient, it would still block the radiation, and since air is circulating around them, they won't achieve the temperatures that the muffler or exhaust piping attains and therefore won't re-radiate and transfer the heat to the sheet metal of the passenger compartment. So, considering this bit on the configuration, I think even hardie backer does achieve a measure of insulation while still simulating the appearance of the original asbestos pieces.

As an aside, Moss does offer a muffler insulator that appears to be a better alternative to the hardie backer, but a bit pricey.

 

[Keoke]

Well I am just curious as to how a product alleged to be made up of cement and sand can have a high thermal conductivity.

Generally, materials that are not highly conductive in the electrical sense are also Poor thermal conductors.

 

[MikeAH100M]

Just passing along what two Tech's at James Hardie said so can't answer the questions. I did let them know about having an air space which diud not change their recommendation.

For between the floor and muffler, I found this ceramic product with aluminum facing and spacers that fit and works well. https://www.tomsimport.com/new/parts/parts.asp?sect=28&new=1

Also found a hear shield kit on AH Spares that I plan to check into. Have been very pleased with their products. https://www.ahspares.co.uk/austin-h...ls-IBP101-to-IBP286A/HEAT-SHIELD-KIT-RHD.aspx

 

[Keoke]

Just passing along what two Tech's at James Hardie said so can't answer the questions. I did let them know about having an air space which diud not change their recommendation

OK Michael I understand you;

They probably were just side stepping any potential liability for this application.

 

[steveg]

Keoke wrote:

...They probably were just side stepping any potential liability for this application.

That sounds reasonable. It's hard to believe having a sheet of hardiebacker is the same as not having anything there at all.

One would think the air gap would be doing most of the insulation work, anyway. Someone should try applying several layers of reflective mylar on the back side of the hardiebacker plates. How to measure the heat transference with and without the hardiebacker...

Too bad none of us is in high school - this forum would be a good source for ideas for science projects!

 

[HealeyRick]

I don't think the use of Hardie Board was ever meant to be anything other than something for the originality folks to use as a similar looking replacement for the original asbestos shields. Just look at the firewall. Above the original asbestos is an uninsulated panel of sheet metal with bunches of holes that just lets heat pour into the cockpit. I'm convinced there are a number of different ways to keep our cars cool using modern materials. It becomes a lot more difficult (perhaps impossible) to do so if you try to keep it concours. If I was trying to keep a stock appearance, I'd use Lizard Skin https://www.lizardskin.com/ throughout the interior and try to put some other insulation between the original asbestos or Hardie Board.

 

[TimK]

I still have the original asbestos insulation in place. It is not hazardous unless you break it up. So it is probably worse to remove it than leave it. On the other hand, it doesn't seem to keep my car cool at all. I put some rock wool insulation with an aluminum shield between the muffler and the floor. I also covered the floor with Dynamat Extreme. The transmission tunnel is probably a major source of interior heat as are the holes in the fire wall.

 

[glemon]

I did a two phase heat reduction plan on my old 100, not planned but just because phase one didn't work that well, phase 1, was this aluminum foil looking stuff with the bubble layer in between you can use as water heater insulation etc. in the floors and tranny tunnel, it helped, but the cockpit was still hot, phase two was sealing up air leaks, especially around the tranny tunnel both where it meets the floor and where it meets up with the firewall, and also the various holes in the firewalls. After phase two the cockpit was pretty much as cool as whatever the ambient air was, even on a hat day with the motor fully warmed up.

One of the reasons the cars run hot, and probably the reason the factory put the vents in the front fenders of the rally cars, is that the air that comes through the radiator doesn't have an easy exit, so it tries to get out wherever it can including seeping into the cockpit, before I did the sealing up the heat wasn't just radiating into the cockpit, it was blowing in pretty hard (with the car going at highway speeds) through the various leaks, also forgot to mention it likes to come through the shift boot too if that is not all sealed up.