Will Permatex High Temp Red RTV Gasket Maker cure properly when applied on hot surface?

mrcolumbia

Hi guys,

I'm trying to plug up a small water drip leak on the union of a steam radiator using some Permatex High Temp Red RTV Gasket Maker. Now even though I've closed the valve and the radiator itself isn't warming up, the metal on the union is still quite hot.

I know once cured, the RTV is designed to withstand very high heat. However, I'm less clear on whether, after initial application, that level of heat will be a problem for the 24 hour curing process itself.

Does anyone have any experience with this? Do I need to wait until spring/summer when the union will be completely cold to apply this fix or can I do it now?

wmgeorge

I can not comment on using to stop a Steam leak? But the new RTV has changed, its not the same. I will need to find something else as the Black I just purchased was a joke, one star.

mrcolumbia

wmgeorge said:

I can not comment on using to stop a Steam leak? But the new RTV has changed, its not the same. I will need to find something else as the Black I just purchased was a joke, one star.

If it changes anything, the leak is technically a water drip leak, not actual steam.

ChrisJ

wmgeorge said:

I can not comment on using to stop a Steam leak? But the new RTV has changed, its not the same. I will need to find something else as the Black I just purchased was a joke, one star.

What happened with the black?
Old RTV won't cure, ever, so you need to keep an eye on the date on the tube. This is actually a big deal and I've been bit by it and it sucked. Had to try and clean the greasy mess off and start over.

@mrcolumbia RTV uses moisture to cure, so I doubt 212F is hot enough to be an issue for curing.
Just make sure there's moisture in the area, winter time dry air often makes it cure slower and don't apply pressure until it's cured somewhat.

wmgeorge

When I worked on motorcycles and snowmobiles I used the Red all the time. The new black was messy, would not spread right and smelled like paint thinner and not silicone.

ChrisJ

wmgeorge said:

When I worked on motorcycles and snowmobiles I used the Red all the time. The new black was messy, would not spread right and smelled like paint thinner and not silicone.

I dunno
RTV should smell like vinegar from the acedic acid until it cures.

BobC

I worked in HV electronics, mostly military and used white RTV because it doesn't have ascetic acid. That acid is conductive and not what you want when sitting at 20-30KV, The white has almost no smell at all and seems to skim over quicker then clear RTV with ascetic acid.

Bob

Hap_Hazzard

What does RTV stand for? Room Temperature Vulcanization. RTV sealants are designed to cure at room temperature. Also, Permatex gasket sealants are intended to be applied to both mating surfaces and allowed to dry until tacky before final assembly. Are you joining two surfaces or trying to fill a crack?

ChrisJ

Hap_Hazzard said:

What does RTV stand for? Room Temperature Vulcanization. RTV sealants are designed to cure at room temperature. Also, Permatex gasket sealants are intended to be applied to both mating surfaces and allowed to dry until tacky before final assembly. Are you joining two surfaces or trying to fill a crack?

From Momentive RTV100 series 




They do not have to be applied at room temperature regardless of the name.  As far as I know silicone rtv doesn't even have issues curing below 0F.  It's just much slower.

nicholas bonham-carter

If the union is composed of the original mated pair, it shouldn’t need any sort of sealing goo between the machined surfaces.
Rock the radiator while tightening the collar to get the faces to fit properly. A little dishwashing liquid will help them align.
if this is a new valve, then it should have a matching spud which should replace the original one in the radiator.—NBC 

mrcolumbia

@Hap_Hazzard @nicholas bonham-carter Yeah, I figured tightening up the physical join was a better long term play than trying to introduce a new substance. I guess I didn't have the guts to put any kind of strain on anything this old while we are still in February in the Northeast. For some context, it's not a crack - just seems to be a misalignment at the bottom of the union that is creating a gap (picture attached, with gap circled in red).

Hap_Hazzard

@mrcolumbia I can't tell much from the picture, but is that union after the shut off? If it is, there's no need to do it while it's hot.

mrcolumbia

@Hap_Hazzard Apologies - I've attached a better picture, plus another from the front to give context. Does that answer your question?:

Alan (California Radiant) Forbes

Just put a little teflon paste or pipe dope on the mating surfaces. Make sure the surfaces are dry when you apply.

Hap_Hazzard

See if you can pick up some Great White pipe joint compound. Apply it to the threads too; it's a good lubricant.

If you can get your hands on a Ford wrench, they work great in tight spots like this.

mrcolumbia

@Hap_Hazzard @Alan (California Radiant) Forbes So if I understand you guys right, I can take some of that Great White and, after making sure everything is dry, putting it into that gap I have circled in the first picture?

Hap_Hazzard

It never dries, but it will prevent leaks if there isn't a perfect fit, but since it also lubricates the threads, you can get the nut tighter with less torque (be careful you don't break it) which will compress the faces of the union.

mrcolumbia

@Hap_Hazzard Yeah, when I said "after making sure everything is dry", I was referring to the leak itself, not the Great White since @Alan (California Radiant) Forbes said the surfaces need to be dry. That sounds like a plan. Out of curiosity, are you suggesting this instead of the RTV because the Great White will definitely be effective with high temps?

Chris_L

mrcolumbia said:

@Hap_Hazzard @Alan (California Radiant) Forbes So if I understand you guys right, I can take some of that Great White and, after making sure everything is dry, putting it into that gap I have circled in the first picture?

You want to put a very thin layer of the joint compound on the mating surfaces. To get to the mating surfaces, you have to loosen the union nut. If the two halves of the union don't separate on their own, you'll need to push them apart so you can see the two mating surfaces.

That is where the seal is made. Apply the joint compound. Then put the union back together and tighten.

Hap_Hazzard

mrcolumbia said:

Out of curiosity, are you suggesting this instead of the RTV because the Great White will definitely be effective with high temps?

I'm suggesting it because it's made for sealing pipe joints. I use it on everything except brass fittings and gas piping. It's similar to what @Alan (California Radiant) Forbes recommended, except it's a PTFE paste and pipe joint compound in one product.

ChrisJ

Chris_L said:

mrcolumbia said:

@Hap_Hazzard @Alan (California Radiant) Forbes So if I understand you guys right, I can take some of that Great White and, after making sure everything is dry, putting it into that gap I have circled in the first picture?

You want to put a very thin layer of the joint compound on the mating surfaces. To get to the mating surfaces, you have to loosen the union nut. If the two halves of the union don't separate on their own, you'll need to push them apart so you can see the two mating surfaces.

That is where the seal is made. Apply the joint compound. Then put the union back together and tighten.

With all due respect unions are intended to seal without thread joint compound on them.
Some guys use it on the threads to lubricate them to help get them tighter, or to help them come back apart later on but never on the machined sealing surfaces. Even if that does seal, it'll likely encourage a leak down the road.

The same goes for flares and compression fittings.

Hap_Hazzard

ChrisJ said:

With all due respect unions are intended to seal without thread joint compound on them.
Some guys use it on the threads to lubricate them to help get them tighter, or to help them come back apart later on but never on the machined sealing surfaces. Even if that does seal, it'll likely encourage a leak down the road.

The same goes for flares and compression fittings.

That's true, but this one's leaking, and he can either replace it or try to fix it with a little pipe joint compound. Some people here with more experience than me use it all the time and recommend it. Personally, I only do it to stop a union from leaking until I can get around to replacing it.

ratio

That gap on the back side of the union nut isn't part of the sealing surface. The mating surfaces are in between the two parts of the union. I found a PDF with not only a section, but a 3D animated model that shows how & where they mate & seal at. It's actually pretty neat, take a look at it.

NB: It appeared to open safely on my computer (I had to allow the animation to run), but YMMV.

Chris_L

ChrisJ said:

Chris_L said:

mrcolumbia said:

@Hap_Hazzard @Alan (California Radiant) Forbes So if I understand you guys right, I can take some of that Great White and, after making sure everything is dry, putting it into that gap I have circled in the first picture?

You want to put a very thin layer of the joint compound on the mating surfaces. To get to the mating surfaces, you have to loosen the union nut. If the two halves of the union don't separate on their own, you'll need to push them apart so you can see the two mating surfaces.

That is where the seal is made. Apply the joint compound. Then put the union back together and tighten.

With all due respect unions are intended to seal without thread joint compound on them.
Some guys use it on the threads to lubricate them to help get them tighter, or to help them come back apart later on but never on the machined sealing surfaces. Even if that does seal, it'll likely encourage a leak down the road.

The same goes for flares and compression fittings.

Yep, the mating surfaces of unions are intended to seal without pipe joint compound. But a thin layer of compound acts as a lubricant on the mating surfaces and helps the surfaces mate better.

That is a trick a pro taught me years ago. I use it routinely on unions, and I don't have leaks.

ChrisJ

I don't want to offend anyone I just watched a video from a popular "home improvement" store and they show using tape on compression fittings.


I think it put me in a mood
  

Chris_L

ChrisJ said:

I don't want to offend anyone I just watched a video from a popular "home improvement" store and they show using tape on compression fittings.


I think it put me in a mood
  

Watch this video: https://youtu.be/_m2xg5e6RpE?t=180 about lubricating malleable iron unions before assembling. Maybe it will put you in a better mood.

Hap_Hazzard

The ones I've used don't have that much taper, but they have a brass face on one side that helps it conform.