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Author Topic: False bottoms and fire shield  (Read 523 times)

Offline 410trailrunner

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False bottoms and fire shield
« on: December 06, 2017, 02:35:05 PM »
I am loving the wealth of information found on this sight although I am finding it difficult to search for certain questions. I am assuming most if not all stoves require a false bottom, what are people using for theirs? I am also considering placing a heat shield between the stove and the tent as well as wood kept in the tent. I am wondering though if there is a "safe" distance. I've seen numbers from 12 to 24 inches and that makes sense when you take size into consideration. I will be running a SnowTrekker 8x10 and their small stove 19x10 inches. What are people using as heat shields? I've even talked to one person who uses a cookie sheet but wasn't sure if he was pulling my leg so I didn't respond  ::)
Thanks in advance. 

Offline Dave Hadfield

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Re: False bottoms and fire shield
« Reply #1 on: December 06, 2017, 02:58:52 PM »
Putting in a false bottom reduces warping, but isn't absolutely necessary. I don't travel with one usually. And in winter, when you can't easily find any dirt or sand to throw in, I lay 5 or so small split logs on the bottom, round-side-up. Then start the fire on that. By the time they burn down to the metal, it's mostly ash, and not all that hot.

The simplest fire-shield to stop melt-away around the stove, and perhaps your sleeping-bag, is Typac house-wrap. It's cheap, light, and quite fire-resistant.

I tape widths together and use it for a ground sheet -- much preferable to poly tarp.

In this photo you can see some of the typac, on the left, laid there and spiked with twigs to stop melt-away under the sleeping area.


Offline Bothwell Voyageur

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Re: False bottoms and fire shield
« Reply #2 on: December 06, 2017, 03:57:25 PM »
Do you mean Typar?

I wouldn't feel comfortable running a stove that close to the wall of a cotton tent without a reflective shield. Dave H has obviously had no problems but having felt how hot the fabric gets I just prefer not to risk it. Maybe with more experience I would be prepared to risk it but for now I would rather play it safe.

A silver surface will reflect almost all the heat back into your tent, increasing the efficiency of your heating system as well as reducing the fire risk. Cookie sheets, aluminum flashing or even Reflectix bubble insulation will all work though the latter will melt big time if it ever touches the stove and it is difficult to stand up.

All the same stuff will work fine under your stove and again will increase efficiency by reflecting radiant heat back into the tent. Undersky uses a neat folding piece of ply wrapped in flashing which also creates a nice stable platform for the stove legs.

Presumably the Typar is also blocking radiant heat as well. It simply puts whatever is behind it into the shade. Difficult to tell but it looks like there is a healthy pile of logs under the stove as well to block the heat.
www.canoepaddler.me.uk for canoe tripping and winter trekking photos and fireboxes

Offline AunNordDuNord

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Re: False bottoms and fire shield
« Reply #3 on: December 07, 2017, 01:01:00 AM »
Here is an exemple of a stove to close to the tent wall... I got hired to make the repair!!
https://photos.app.goo.gl/RRQ4ezVUaMPG6CaE2

Dave, Is Tupac the same as Tyvec and Typar? Don't you find it slippery? I know for a fact that Tyvec wouldn't be good for behind the stove cause it's known to some time melt when use as an underlayment on roof covered by tin in the summer months!

Offline Dave Hadfield

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Re: False bottoms and fire shield
« Reply #4 on: December 07, 2017, 10:56:42 AM »
Oops, too many names. It's Typar, not typac.

It doesn't melt when used this way. I have had that piece 16" away from the red-hot spot on the side of the stove, and the material in unaffected.

It's the best thing I've found for reflecting heat because it's light, for transport, and folds up very small. (Every piece of specialized, single-purpose equipment you bring along adds to the pain-factor on the trail. Humans are lousy sled-animals.)

As for the back wall being close, it's about 18". The perspective may be off a bit in the photo. That's plenty. This tent is made from fire-retardant-treated horrible 11 oz polycotton for the corner where the stove is. (The rest of the tent (8 x 10 x 7high) is made from 4 oz uncoated ripstop nylon. Total weight is 14 lbs. And it stows into a small bird-seed sack.) On the outside, I have an additional tie-out for the side-wall right there, behind where the stove is. This ensures that when the wind blows, and the fabric flaps, it doesn't contact the stove.

Offline Dave Hadfield

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Re: False bottoms and fire shield
« Reply #5 on: December 07, 2017, 11:22:00 AM »
Here's a photo of the tie-out behind the stove.


Offline Dave Hadfield

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Re: False bottoms and fire shield
« Reply #6 on: December 07, 2017, 11:25:32 AM »
The wonderful thing about cotton is that it is quite reflective. You can have it quite close to a very hot surface and it won't deform.

A plastic fabric melts. Cotton will stay intact until it gets heated to the point where it will char, and then it catches flame. it's far better stuff.

Anyway, this tent has been used fairly often since 1987. The combination of fabrics -- treated canvas and light nylon -- has been very practical.]

Now if I only had a place to clean it...

Offline AunNordDuNord

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Re: False bottoms and fire shield
« Reply #7 on: December 07, 2017, 01:28:10 PM »
Hybrid tents are not a bad way to go, some on weight and bulk!!The design I'm working on would be hybrid, for the same reason Dave have mention! On a 8 panel tent, I would have 3 panels where the stove would be in teated cotton, and the rest some kind of lighter synthetic fabric, I'm thinking a somewhat heavy SilPoly or SilNylon....

Offline Bothwell Voyageur

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Re: False bottoms and fire shield
« Reply #8 on: December 07, 2017, 01:47:01 PM »
Hybrid tents are not a bad way to go, some on weight and bulk!!The design I'm working on would be hybrid, for the same reason Dave have mention! On a 8 panel tent, I would have 3 panels where the stove would be in teated cotton, and the rest some kind of lighter synthetic fabric, I'm thinking a somewhat heavy SilPoly or SilNylon....

Probably cheaper too!

Making the sides in poly and the roof in cotton would retain breathability and stop the indoor snow I get in the morning with my nylon tent. I wonder if you could get away with an uncoated synthetic? Maybe Wiggy has something?

Back on topic, as I said. If you are happy with the system that is good. Rather like putting your finger on top of the log being split, the folk who are good at it will tell everyone that it is a great technique. The rest of us may want to have a wider margin of safety.

And new cotton reflects about 60-70% of the mid infrared and has an ignition point of 300 deg. C.

Washing your tent in the bath works fine or get one of those kiddies paddling pools for the summer.
www.canoepaddler.me.uk for canoe tripping and winter trekking photos and fireboxes

Offline Dave Hadfield

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Re: False bottoms and fire shield
« Reply #9 on: December 07, 2017, 02:07:54 PM »
Most of the tent in the photo is exactly that, uncoated synthetic. 1980's rip-stop nylon. I refused all coatings because I wanted it to breathe.

However there is still condensation on it in the mornings because I let the stove go out. And frost will condense on a spider web, let alone breathable fabrics.

One other factor about the fire risk -- the back of the stove doesn't get as hot as the sides. I'm always raking the coals forward, toward the door, in use.

Offline southcove

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Re: False bottoms and fire shield
« Reply #10 on: December 07, 2017, 04:31:11 PM »
There are buliding wrap materials (like Typar) that are mandatory underlayments for many fire prone areas out west in the US (that I know of)... these go between the siding and the sheathing underlayment whether plywood, foam insulating board or OSB type materials.   

Like Dave has experienced, they seem to have more reflective properties and higher rated heat melting points than anything I can buy through my business here in the NE US.   They might indeed work more efficiently than our common thin sheet metal (flashing), they'd certainly be easier to pack on the sled and hang behind the stove.  And be quieter too.

In AUS, where there is a very high building standard in fire prone areas, Moondog here has fairly recently done over the siding on his house, that fire resistant house wrap material is called "sarking" I believe and I have  piece of it on my desk.

A fast perusal of 3 industry catalogs for building supplies offered ony Tyvek clones.   None offered up melting point specs only vapor permiability numbers.   

In our big wall tent we use a fibreglass based fire suppression blanket behind the stove, but it's annoying to cart around, hang and attracts schmaltz of every sort.


Offline Bioguide

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Re: False bottoms and fire shield
« Reply #11 on: December 07, 2017, 06:09:54 PM »
Snowtrekker sells their bottom heat shield material (aluminized fiberglass cloth) in linear feet. The fabric is 60” wide and I bought 1 yard of it and cut it length wise and use one piece along the backside of the stove in both of my tents. Relatively light and easy to store... i.e. roll it or fold it.


Online chimpac

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Re: False bottoms and fire shield
« Reply #12 on: December 07, 2017, 06:28:46 PM »
I love the heat that comes from the bottom of my stove.
I use it to broil ribs or other tasty meat. The food gets nice and brown sometimes a bit of burn. There is no need to watch it close like frying with thin kettles.
To get more broil heat I moved my bottom ash grate lower to the very bottom of the stove body, so ash collects in a pan outside the stove.
If I am not broiling I warm my feet under the stove or I lay a reflector under the stove to direct the radiant heat out to me.

Offline AunNordDuNord

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Re: False bottoms and fire shield
« Reply #13 on: December 07, 2017, 08:00:27 PM »
Bioguide, I should get myself some of that stuff too!

Offline Bothwell Voyageur

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Re: False bottoms and fire shield
« Reply #14 on: December 08, 2017, 07:49:20 AM »
Bioguide, I should get myself some of that stuff too!

Definitely the deluxe option, goes very nicely with a Ti stove!
www.canoepaddler.me.uk for canoe tripping and winter trekking photos and fireboxes