Darryl Keil Last Activity 2025-09-09 11:09 AM
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Link Van Cleave

Posts: 8

Joined: 2007-10-16

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Subject : Fairing compound with uni-bond
Posted : 2007-10-22 9:42 PM
Post #34115
Is there such a thing that will work with Uni-bond ? I seem to remember that bondo is not good, nor epoxy type fairing compounds. I have a "fairly" (no pun intended) large curved piece that is mostly fair. Thing is when you are "almost" done you are still a long way away. That is, when the thing is 90% fair and you have a few small hollows here and there if you can't fill them you have to remove that 90% to the level of the lowest hollow. Lot of work not to mention (but I just did ) that I don't want to sand through any plies in my core. Which is 7 layers of 1/8" italian . So any thing that is a sandable product that is compatable with Uni-bond.
Thanks,
Link


 
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Jeff Patrick


Joined: 2004-04-15
Location: Bainbridge Island, WA

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Subject : RE: Fairing compound with uni-bond
Posted : 2007-10-23 1:38 PM
Post #34116 - In reply to #34115
Use Unibond and mix in some cabosil. Or for larger deeper fills, and less strength, use microballoons. These products can be had from a plastics or fiberglass supplier. They are very common in the boat building trade as well as others.




 
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Darryl Keil

Posts: 1455

Joined: 2003-05-22
Location: Maine

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Subject : RE: Fairing compound with uni-bond
Posted : 2007-10-23 4:03 PM
Post #34117 - In reply to #34115
Link,

There is a product called "Durhams Rock Hard" which is a water putty that works quite well and bonds fine with Unibond. Most paint and hardware stores carry it.

Jeff, wanted to let you know the items you mentioned I do not recommend mixing with Unibond. If you're having great results with them then that's great but as the manufacturer of Unibond those epoxy products really are not meant to be used with it and you could get a weakened bond.

Sincerely
Darryl Keil


 
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Jeff Patrick


Joined: 2004-04-15
Location: Bainbridge Island, WA

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Subject : RE: Fairing compound with uni-bond
Posted : 2007-10-24 5:27 PM
Post #34118 - In reply to #34117
Darryl,

Have you done any testing that confirms the addition of cabosil will weaken Unibond's bond? Or are you saying that since the product wasn't designed with additives in mind, then you can't recommend using them? And, would the addition of wood flour also not be recommended?

Thanks,
Jeff


 
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Scott

Posts: 31

Joined: 2006-08-23
Location: New Hampshire

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Subject : RE: Fairing compound with uni-bond
Posted : 2007-10-25 1:40 PM
Post #34119 - In reply to #34118
Just wanted to add the fact that I have mixed and used unibond with as much as 50% cabosil to make it much thicker and have used it for furniture joinery . I find unibond very usefull in glueing up complicated assemblys that require a lot of time to get everything coated and under clamps. In this type of assembly PVA glues set up way too fast and have no gap filling abilitys. Epoxys are way too messy , dont clean up easily and take way too long to set to a ridgid glue line . I have found unibond 800 perfect because it sets in 4 hours, has a long open time, cleans up off the case with water. Also I am able to make it fill gaps nicely by adding a thickener that I use for epoxy called cabosil. It turns the glue from a runny mess (when using it on joinery) to a nice thick gap filling mixture that doesnt run out of the joints. It has worked extremely well for me and I still own the pieces. After many years of use they are still fine. It may not be tested "officially" but in practical use it does work fine. Darryl has addressed my question on a previous post and does not recommend it for good reason but it has worked for me. Just wanted to add my experience.
Scott


 
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Darryl Keil

Posts: 1455

Joined: 2003-05-22
Location: Maine

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Subject : RE: Fairing compound with uni-bond
Posted : 2007-10-25 7:26 PM
Post #34120 - In reply to #34118
Jeff,

As the maker of Unibond 800 I will always take a conservative position publicly about amending the glue, I really have to. I could fill pages with stories of things people have done with Unibond. Many that make me cringe. Its not that adding cabosil and other items will render Unibond useless, its that the more one strays outside what I consider the "ultra safe zone" the more potential for failure can occur. If we have not done lab testing on an particular additive or formulation change I cant give you the green light for that usage.

This does not mean that how you wish to amend the glue is bad, its just not going to get my official stamp of approval. Of course you can give it your own stamp of approval by running your own tests. Once Unibond has completed its chemical reaction it becomes inert and will not change further. Glue up a sample in the species and conditions you will be working and let it sit for a few days to a week. Try and break the joint. Soak it in water for a day, dry it in the sun for another. Generally stress the joint beyond the normal use. If you consider the results successful then you can probably proceed. Remember that some species are more difficult to glue than others so don't assume your test is good for all wood, do a few different kinds to be safe.

To answer your specific questions, no, we have not tested cabosil. It appears that both you and Scott have. Clearly Scott has had good results. Wood flour is already in the catalyst so we know this is an acceptable product. The issue with this additive is how much extra is OK. Test, test, test for yourself.

I don't mean to scare you away from trying these thing with our glue, its quite fine with me. You just don't get the official OK from Vacuum Pressing Systems. As long as your OK with this then feel free to try whatever you like. You wouldn't believe some of the things that I have told people would fail with Unibond only to have them call back and say it worked great. I much prefer it this way than the other way around.

Sincerely
Darryl Keil




 
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Jeff Patrick


Joined: 2004-04-15
Location: Bainbridge Island, WA

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Subject : RE: Fairing compound with uni-bond
Posted : 2007-10-26 1:55 PM
Post #34121 - In reply to #34120
Darryl,Thanks for taking the time to respond to my questions. Believe me, I totally respect your position as regards to your product. I was mostly interested in any known failures you might have learned of by test adding amendments. Since you've no failures to report, I'll assume that my wood won't spontaneously combust if I continue to add a few extra bits of stuff. Scott's experience pretty much parallels my own. I've never been one to always stick with the directions..... guess that's why I work for and by myself. Lets see..... now where did I put the ground up bat wings? Bat wing and unibond oughta make a good ebony substitute.... Yes! I think that idea will fly. (sorry)


 
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Link Van Cleave

Posts: 8

Joined: 2007-10-16

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Subject : Fairing compound with uni-bond
Posted : 2007-10-26 7:34 PM
Post #34122 - In reply to #34121
I have a lot of experience with epoxies, fillers, fairing compounds etc. ( 5 boats plus a lot of repairs and other projects.) I also have no doubt that you can add things to Uni-bond or other urea-formaldehyde glues with success for certain applications. If you don't add so much as to inhibit penetration. Cabosil and wood flour are logical choices. One way to do it is what is commonly done with epoxy. Wet out the joint with unthickened glue and then add you thickener to your mix and use that. This helps insure good wet out and penetration.
All this being said the question or my question to be specific is not what or how much can you add to Uni-bond and still get a good glue but what will Uni-bond stick or adhere to. We know it will stick to wood Will it stick to itself ? That is will it stick to cured Uni-bond. From what I hear, no. Will adding wood flour help it stick to itself. What will it stick too other than wood and what will it adhere to that could be used as a fairing compound.
Darryl I did a few tests and water putty doesn't adhere very well to wood and I don't really trust it in deep holes or feathered out. The Uni may stick to Water Putty but the bond between Water Putty and wood is not up to it for veneering IMO. It is fine for nail holes and fairing out forms but not for substraights.
Finding a good fairing compound would be a real asset when doing thin veneers which is what I find myself doing for this project. Crotch mahogany. The substraight has to be perfect. I usually cut my own veneers a fat 1/16". This thicker veneer besides giving a lot more room to sand takes a fairer curve.
Man I don't like this thin stuff. I am really sweating this one. Final glue up tomorrow.
Link


 
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Darryl Keil

Posts: 1455

Joined: 2003-05-22
Location: Maine

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Subject : RE: Fairing compound with uni-bond
Posted : 2007-10-26 7:49 PM
Post #34123 - In reply to #34122
Link,

You're right about water putty not sticking aggressively to larger areas on wooden substrates. Sorry, I wasn't thinking about that when I suggested it. Unibond will stick to itself if roughed up well with a course grit sandpaper. You could thicken the Unibond a bit extra as the filler since you're not using it to glue with. Sand it and then mix up the glue without fillers for the veneering part.

Sincerely
Darryl Keil
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