Using Loctite 290 to seal small cracks and pin holes in boilers

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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#1: Post by phreich »

Hi all,

It might be helpful to include a bit of the discussion that preceded the first post in this new thread in order to get the context of the discussion before it was split from its original thread, so here it is -- Barry had posted a quick comment about using loctite 290 to seal a pinhole leak in a braised joint in a heat exchanger, and I had never heard of that being an application for loctite before and commented on it -- he replied and we got into a productive dialog that eventually lead to to the discussion that follows.

Many thanks to Barry for initially bringing this up -- I had no idea that Loctite 290 existed, or that it worked for this kind of application -- this may save a whole lot of folks some major headaches when pinhole leaks or slight cracking occurs in boilers or heat exchangers....

=================== start of context info ===================
Post by phreich on Sun Jan 02, 2011 11:48 am

I doubt that Loctite will do much good as it's not intended to be a glue that will hold a lasting bond with no pressure holding it in place against the 9 bar pressure in the hx.

Post by barry on Sun Jan 02, 2011 5:08 pm

Clearly, you've never used Loctite 290 on an espresso machine, and it is certainly worth a try before spending the time to take the machine apart, and the money to have the boiler re-brazed.

Post by mhoy on Sun Jan 02, 2011 7:12 pm
Nifty stuff, appears to seal welds.

Loctite 290 Green Threadlocker

Loctite® 290™ Green Threadlocker is a medium strength threadlocker for pre-assembled bolts up to 1/2" (12 mm). Penetrates threads by capillary action. Secures set screws and other assemblies after settings are completed. Seals welds and porous metal parts. Mil Spec: Mil-S-46163A Type III Grade R. ASTM-D5363: Group 2 Class 6 Grade 1.

===================== end of context info ===================

Hmm, seals welds and porous metals, huh? Interesting application for a thread locker. I'm glad to have learned something new -- these forums are nothing if not educational....

Maybe it's worth a try -- but does anyone know about its toxicity and/or the consequences of having it in contact with hot water that is being consumed? Does anyone know if it is specified for food/potable liquid contact use or being used by any of the espresso machine manufacturers, or food equipment manufacturers?

I tried to find a direct answer to this but couldn't. I did find a "technical data sheet" for it (Here's the URL:, and learned the following from it:

Regarding food contact:
NSF International
Registered to NSF Category P1 for use as a sealant where there is no possibility of food contact in and around food processing areas. Note: This is a regional approval. Please
contact your local Technical Service Center for more information and clarification.

However, it goes on to say the following:
NSF International
Certified to ANSI/NSF Standard 61 for use in commercial and residential potable water systems not exceeding 82° C. Note: This is a regional approval. Please contact your local Technical Service Center for more information and clarification.

It might be worth a call to the "technical service center" for clarification as to why they limit the use to "not exceeding 82° C" -- that may be the temperature where it starts to breakdown and outgas or dissolve and release toxic "stuff".

In the same technical sheet it has graphs showing strength in relation to temperature, and it seems to hold at least 60% of its strength to 100 C, but the curve goes down rapidly -- only has about 40% strength at 120 C, and less than 15% strength with exposure to 150 C. IIRC, the boilers at 1 bar get to about 120 C, and the HX inside the boiler gets close to that when it has been sitting idle for a while.

Here are the instructions for porosity sealing with the product (this would apply to sealing pin-holes and small tight cracks):
For Porosity Sealing
1. Clean area and apply localized heat to the area to approximately 121°C.
2. Allow to cool to approximately 85°C and apply the product.

I hope to learn more from y'all about this.


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#2: Post by barry »

I'm talking about a drop of the stuff, only a tiny portion of which would have water contact. I've ingested more than that in the course of using it over the past ten years... (it has a slightly sweet taste, btw)

As for strength, I recommend through experience, not through data sheets. I've used the stuff on several occasions for espresso equipment. Originally, I used it for sealing thermocouple wire penetrations into portafilters (holds just fine against 9 bars). I have used it a few times as a penultimate mend for tedious pinholes or fissures in brazes (the ultimate mend being disassembly and re-brazing). Sometimes it works, sometimes it doesn't. Again, it's worth the try if it means not having to take a machine completely down to take the boiler to the welding shop.

phreich (original poster)
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#3: Post by phreich (original poster) »

Hi all,

I wanted to know more about this product (Loctite 290) and it's potential for use in repairing small cracks and pinhole leaks in espresso boilers so I contacted the manufacturer and talked to them about the product at some length. I talked to Sandy Adams, one of their Technical Customer Service Agents. She told me the following information:
1. The 86 C degree rating is a NSF standard that applies to all products rated for cold water potable water contact. The 86 C degree limit is not related specifically to this product -- just to the NSF standard.
2. Loctite doesn't have a product that they've asked to be rated for higher temps through the NSF testing labs. It doesn't mean that this product can't handle temps up to around 120 C, but they haven't paid NSF to test for it.
3. She mentioned that, to her knowledge, none of the materials in the product are toxic. She went on to say that in the past, one of their engineers used to eat some of the product during demonstrations to show that it was nontoxic. She didn't recommend that anyone do this though ;-).
4. She said that it would work just fine on regular steel, copper, and brass, but would not work on stainless steel or aluminum without priming, or without extended curing times.
5. She said that to speed up curing time, the product could be baked at around 300 F for 30 minutes (but not longer, or it would start to weaken).
6. She said the product, when cured, forms an acrylic plastic.
7. She said that the product will not cure when exposed to air -- it needs to be in a tight-fitting place like the threads of a screw, in a tight crack in metal, or in a pinhole pore in metal. In those applications, the surface exposed to air won't cure, but the material under the surface will.
8. She cautioned, in an application where a crack or pinhole leak is being filled, not to put too much of the material on or it could flow through the crack or pinhole and come out the other side. The material coming out on the other side would not cure because it would be exposed to air. What this means to me is that you should use just enough to cover up the pinhole or crack, but no more -- otherwise it could flow through into the boiler and the product that flowed through would not cure and would then dissolve into the water in the boiler.
9. She said the product should be used on dry materials -- so the boiler should be drained and the area being repaired should be completely dry. (probably a heat gun or hairdryer could be used to do this if the repair is being done "in-place".)
10. She did say that this product was commonly used to seal pipe threads -- which is why they paid to get the NSF 86 C degree potable water rating.

Bottom line, she said it should be safe for use in espresso machines, although it has not been rated for this.

I hope this information is helpful. I think that it might be a good idea to copy this entire discussion about Loctite 290 and put it in a separate thread so that it can be more easily found in the future. I'll send a request to the forum moderator to this effect.


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#4: Post by barry »

Sweet, Phil! Thanks for the investigation & write-up. I'd always had it in my toolbox because I'm notorious for forgetting to put on threadlocker before cinching up threads. It got put to espresso use just because it was on hand and seemed to do the job.

I agree that too much is bad (sometimes I'll put a drop and wipe off the excess); heating definitely helps cure times; and things need to be dry.

It has saved my butt on more than one occasion.

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#5: Post by bobpaule »

JB Weld holds up to 600 Fahrenheit.

My FR8 had 2 repairs with this, never failed.

My Isomac Millennium developed leaks at the boiler inlet/outlet
fittings so i used it on it 3 years ago. Still holding like a charm.

It is specifically designed for high heat and some expandability.

Just make sure the surface is level because although the magic
gray paste looks and feels thick, it will drip.

Correction: DavidR correctly pointed out that JBWeld is nontoxic,
contrary to what i wrote earlier. My bad.
Never get between a man and his ristretto, ever!

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#6: Post by David R. »

bobpaule wrote:It is also highly toxic
JB Weld is not toxic, though some people find it a skin irritant (I don't).

I used some to plug a fairly large blowhole in a Vesuviana boiler almost 25 years ago, the patch still holds.
David R.

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#7: Post by bobpaule »

OK, i always take the EPA labels seriously, but you are right, from wiki:
Health Issues: Avoid contact with eyes or with skin (wash with soap and water); bonds with skin; non-toxic if ingested
Never get between a man and his ristretto, ever!

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#8: Post by JohnB. »

bobpaule wrote:JB Weld holds up to 600 Fahrenheit.
It might but the company website states that it is only resistant to 500*F.

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#9: Post by earlgrey_44 »

Previous suggestions here that JB Weld be used have not met with approbation:

Repairing leaks in a copper boiler
Trust your taste. Don't trust your perception.

David R.
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#10: Post by David R. »

earlgrey_44 wrote:Previous suggestions here that JB Weld be used have not met with approbation:
I wouldn't suggest it as the repair of choice, if one is interested in something permanent, but it is there in a pinch. Probably if I had the same problem now with the Vesuviana, I would drill out the hole a little, dab some Permatex red around the hole, and drive in a screw (if I could find one from metal whose galvanic index was not far from the aluminum of the Vesuviana boiler). With a serious machine and no urgency I'd spend the money and get the boiler brazed (or dig out the torch and rods and try myself, though my success rate on DIY brazing is pretty close to zero).
David R.