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Heat Shields

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Dave Richards

Dave Richards

Jedi Knight
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After looking at the photos of John Loftus’ restoration, I got thinking about the heat shields…since asbestos shields aren’t much available anymore and probably best advised not to use them anyway, ‘Hardi-board’ makes a pretty good looking substitute, but how much heat do they shield?

I wonder if it would make sense to get 'Hardi-board' shields coated with one of ‘Jet-Hot’s coatings…the color might not be right for the asbestos, but they sure would shield from heat.
 
Yes, I've wondered about this too. I think the Jet-Hot coating is a good idea. I understand the correct color is suppose to be a matte off white (cream or warm white).

Another possibility is to use a thin heat shield material hidden behind the hardibacker. The material could be trimmed slightly smaller than the panel and stuck directly on the metal.

I just bought a laser type thermometer and will take some Hardibacker scrap and gas torch to experiment with. I still have some original abestos shield to compare to. I'll let you know how they compare.

Cheers,
John
 
Hi Dar,
You could call Jet Hot and ask. Their process includes baking the coating on, 800°F for several hours if I remember, not sure if the board would come out unscathed. The shields have a lot of gaps that heat could get through anyway. I think most people wanting to address heat, do it from the interior. There are a few different kinds of shielding people have put under the carpets. Dynamat extreme is the one I chose because it acts as a sound deadener also. Do a search for “Dynamat” and you should get that and the other materials people have used. One thing to note about the search engine, on the bottom right is a section for dates. It defaults to posts only one week old. You have to change these fields to search older posts.
 
Hi Dar100, there is another technique you can use.Instead of attaching the Hardi Board directly to the steel shield support at the fastener locations, use washers cut from the same material to elevate the board off the steel. The theory here is by reducing the direct contact area between the steel support and the board you increase the overall thermal resistnce of the interface.--Fwiw--Keoke
 
These are great ideas, I already intend to insulate/isolate from the interior, but this plate under the Hardiboard and the washers give me the idea that metal plates could be jet-coated, mounted behind the hardiboard and using the washers to create an air barrier. If the exhaust is also jet-coated, the cumulative effect could be a substantial reduction in thermal transmittance to the interior.
 
Someone, I can't remember who, got a torch and put it on one side of the hardee board, and took a reading on the other side with a digital thermometer and was happy with the the readings. I made my firewall shield, and was happy with the results. I plan to use coolmat, dynamat, or one of the other modern types everywhere else.
 
It's a construction product, meant as a durable alternative to wood for external applications. It's a cement fiber procuct made by James Hardie Company. www.jameshardie.com Go to siding products there and a topic called James Hardie near you, to locate a dealer. It may be at Home Depot, or Lowes, or similar. Where are you from in Utah, John, I'm a UTE alumni, I bleed red, not blue!
 
dar100,
I live in Kaysville, right in between Ogden and SLC. We moved here from Texas in 1974. Great place to live, love the weather but it is sure getting crowded! Thanks for your help and have a good day.

John
 
I was there last month, standing behind the Capital Building and looking at the valley towards Draper, it reminded me of L.A. Sorry. Have a good day.
 
You can find Hardiboard at Lowes or Home Depot. Hardiboard comes in large 4'X 4' sheets as well as in strips. The strips are used for home siding and are wide enough to be cut as a heat carb heat shield. My biggest problem was finding rivets to fasten the Hardiboard to the metal. Ended up using small screws.
 
I noticed two types of Hardiboard. One with a grid for scoring/breaking and another with a textured weave on one side closer to the original asbestos (the weave on the asbestos is heavier though .. if you look at my website picture the largest piece that goes under the muffler is original asbestos). The rivets are avail. through British Car Specialists although you might find something to work at a well stocked hardware store.

Cheers,
John
 
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