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I need to repair a leak in the plumbing behind my shower. There is an access panel, and enough room for myself and my torch, but not much else.

How do I apply the flame to the fittings (for the final installation) without burning down my house? It seems that no matter how I direct the flame, it's hitting something that burns (drywall, wood, myself, etc).

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9 Answers

up vote 18 down vote accepted

I bought a piece of fireproof 'cloth' at the hardware store. I'm not sure what's in it - fibreglass? In any event, it's about 10x10 (or less) and you can just slip it behind the thing you are working on (I usually duct-tape it to the wall behind) and it protects the wall. I actually cut a slot in mine so that I could slip it around a pipe stub where the stub came out of the wall.

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The best method is to point the flame away from wood, etc., although your ability to do that varies from situation to situation.

If you are completely unable or mostly unable to accomplish that, the best method is probably using some metal to absorb the heat, with a small piece of welding blanket behind that. Not all welding blankets are the same. Some can withstand temps of 1000F, while others can withstand temperatures of 1800F and higher. Try to get the higher temperature stuff, and understand that you cannot hold the flame directly to a welding blanket, as even a propane torch puts out temps of 2000F and higher.

On top of that, you can also use a damp rag to shield heat-sensitive parts that are nearby, especially if they are attached to the pipe itself. Evaporation sucks up the heat, protecting nearby parts.

If it is difficult to juggle everything, keep in mind that you only need the solder near the end. Try to secure the sheet metal and welding blanket before hand as much as possible without ruining anything, and then go at it with the torch and damp rag. After 30 seconds, swap the damp rag for the solder. Once you're done soldering, use the damp rag once again to cool the nearby pipe, but avoid the soldered location, as a quick cooldown will weaken the joint slightly.

MAKE SURE YOU DO NOT DROP THE TORCH, ESPECIALLY IN CONFINED SPACES. IT MAY BURN YOU OR FALL INTO AREAS FROM WHICH IT CANNOT BE RECOVERED. NO MATTER WHAT YOU DO, MAKE SURE YOU DO NOT DROP IT OR POINT IT AT ANYTHING OTHER THAN THE PIPE, JOINT, OR OPEN-AIR, AWAY FROM EVERYTHING. ALWAYS HAVE A FIRE EXTINGUISHER NEARBY.

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Be very careful when using any type of metal as a heat shield. If your like most home owners and pack a typical propane/mapp one pound tank with a mounted torch, the flame control is very limited and the wide flame will impimge on the shield. It could easily conduct enough heat to get the structural items in the area (studs, sheathing, etc.) to ignition temperature if concentrated on the metal shield for a prolonged period, particularrly on older dimentional lumber. The metal is better than nothing but don't let it, or the cloth heat shield, pull you into a false sense of security.

Compression is the way to go, if you have the clearance to do so. the few extra dollars are well spent. A great many fires are the result of welding/burning/ soldering projects gone awry. Should you decide to go ahead with it, as most of us do, I recommend stuffing the area (usually a joist channel) both above and below the solder joint with fibreglass batting. Should ignition occur, this will halt a fires natural upward progress and catch any ignited material from falling down into the channel and igniting what is usually a collection of dust, wood shavings, and other easily ignitable material. This will also compensate a bit for the lack of "firestop" bridging that may be absent in older homes with balloon type framing. Having a pressurized water can nearby and being familiar with local fire dept. contact info is never a bad idea, should things not go according to plan.

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I have welded metal pipes, right next to wood, without starting a fire. Although I was just using the wood to hold the pipes where I wanted them while welding, so it didn't matter how damaged the wood became. Since we are talking about structural members of a building, you may want to do something to protect the wood.

Just make sure you aren't pointing the torch directly at any flammables, and use something that is fire-resistant to deflect the heat, and you should be fine. You could even use a spray bottle before hand, to lightly spray nearby flammables to help deflect the heat.

You can also go and check on it after a while, just to make sure nothing is going to catch fire.

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Good point about the spray bottle. –  user558 Sep 15 '10 at 16:00
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There are MANY ways to do this.

You can buy a piece of heat resistant cloth made specifically for this purpose.

You can use a piece of metal as a backing. In fact, this is what I do, since I've got a box full of scrap metal in the shop. Scrap aluminum flashing is especially good, since it is flexible and cheap.

You can use compression fittings, so no heat produced at all. They are not cheap of course.

I've even seen a tube of stuff that is essentially glue for copper pipe - you squeeze a bit on the joint, slip the pieces together and give them a quick twist, and in a few seconds it sets up. No heat required. Again, this stuff was not cheap, and if you solder only infrequently, the tube will probably dry up before you need to use it a second time.

Finally, you can just be careful. Skill with a torch will keep the flame where it belongs - on the pipe, not on the wood behind it. Of course, until you have gained that skill, you might end up burning down your house.

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I usually use a piece or two of aluminum flashing to sheild the areas behind the pipes. Its cheap, easily bent and dissipates heat well.

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If you have any unused piece of tin ventilation or flashing you can snip out a piece of that and set it behind the pipe. My dad used to do this because it was always readily available and easy to snip to whatever size you wanted.

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when faced with a similar situation I was really paranoid and took two cookie sheets and cut a relief cut so I could put each sheet over the pipe in the opposite direction and then soldered the new shutoff valve in place and still be able to get the sheets off.

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You could try using a chunk of cement board as a sort of heat shield. Another option would be to just use compression fittings instead (if that's possible for what you are doing).

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Perhaps what you call cement board is different to what we have here, as anything with real cement in it will explode when the sort of heat we're talking about is applied. –  John Gardeniers Dec 30 '10 at 23:32
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