I'm working on a project that I'm hoping won't go up in flames... literally! It's a table top (made out of wood) for a fire pit. I planned on protecting the bottom with this High Heat Ultra Spray Paint, but I'm not sure what kind of finish to use for the top. Normally I would use Thompson's Water Seal for outdoor furniture, but I believe that finish isn't fire resistant. Is there a finish out there that would protect this project from catching fire when placed over a smoldering pile of ash?
Use Cumaru hardwood (aka Brazilian Teak or Golden Teak). My internet searching seems to indicate that this wood has a Class A fire rating and is as resistant as concrete to fire.
This link includes a number of results from test data backing this up.
The type of testing that these hardwood decking and siding species were tested for is commonly referred to as ASTM E84-10 "Standard Method of Test for Surface Burning Characteristics of Building Materials". This fire testing standard was established by ASTM International (formerly known as American Society of Testing and Materials). A Class A fire rating using the ASTM test method is the equivalent of a Class A fire rating from the following test methods and agencies:
- ANSI/NFPA No 255 from the American National Standards Institute/National Fire Protection Association
- IBC 8.1 from the International Building Code
- UL 723 from Underwriters Laboratories
In short wood is not the right material for this, I think you should re-think the requirements... coming to the inevitable conclusion that metal is very likely the way to go. Every fire-pit cover I can recall seeing was made from plate steel.
But if I'm reading the following right you already have problems you'll need to address!
a firepit made out of wood.
There's a reason barbecues and so forth are made from metal, brick or concrete, just sayin' ;-)
Even if you coated it with a thin sheet of steel - which you'll never get to burn with a wood fire - a wooden lid would char badly.
You need to keep the temperature of the wood low with a decent layer of insulating material if it's going to go over the top of glowing coals. You might be able to achieve this with a steel sheet against the wood, then an air gap, then another steel sheet, but long term I doubt it.