Special backer-rod for fireplace?

I bought some fireblock caulk that I plan to seal the gaps around my prefab fireplace with, but the gaps are large in some places. Do I just use regular backer-rod, or is there a special heat-resistant kind that I'm supposed to use? I didn't see anything like that at Lowes today.
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Go to a store that sell woodstove and fireplaces. There is a fiber gasket material that would make a good filler. Comes in different diaemters.
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I've already got a roll of automotive fiber gasket. If it's made to resist engine heat, it would probably be better than that typical foam backer-rod.
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On 02/05/2011 10:00 PM, ShadowTek wrote:

True but I would still feel more comfortable with something rated for higher temps. Most non-exhaust engine components shouldn't see over 230F; the only gasket that ever would would be the head gasket, and that has metal fire rings around the cylinders.
If an engine uses exhaust manifold or header gaskets (some don't; they just have an ungasketed iron-to-iron joint between the manifold and head,) they are of a vastly different composition than the rest of the gaskets. Aftermarket "high-performance" ones are often just sheets of dead-soft copper.
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