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Thread: “Thickening up” epoxy

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    “Thickening up” epoxy

    I have a couple holes to fix and need to with body in right orientation. I have used clay to back the spots so the epoxy stays put but it’s hard to get it sealed so it doesn’t run through. If I needed to thicken up epoxy so it wouldn’t run so easily, what’s the best way to do that? I used to have flocking that was super fine but I can’t find that stuff any longer. Can I grind up some set up fiberglass and use the dust? Will it affect strength at all? Some spots will have new holes drilled through so i need it to still be sturdy enough.

    Thanks for your input.
    '33 Hot Rod
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    Back when I was working on satellite structures we used Cab-o-Sil to thicken epoxies and paints. It's a very light, inert material that is basically microscopic silica drops fused together into tiny "molecule" structures. The good news is that it's cheap and available on eBay: https://www.ebay.com/sch/i.html?_nkw...&ul_noapp=true or any other paint or composite supplier website.
    Keith

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    Thanks Keith! Gonna order me some up. Amazon even has it for pretty cheap. I don’t need much lol
    '33 Hot Rod
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    MK4 Roadster
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    I did everything except spray it. She ain't perfect, but she's mine.

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    West Systems sells several products. They have a "fairing fill " that sands very easy and also have a "structural strength " filler. I have used both for rears with great results Currently using it on a friends helicopter.

    Tim Whittaker
    Kootenai Valley Customs

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    Ok, don't laugh, I have used sawdust to thicken resin though the products mentioned are a nicer solution.

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    Quote Originally Posted by Kamp View Post
    Ok, don't laugh, I have used sawdust to thicken resin though the products mentioned are a nicer solution.
    No laughing here, I've used it many times and have a box of 'clean' sawdust for just that. No plywood or other cut up stuff, just from clean wood. However, I've not used in with fiberglass.

    The off white stuff from West System 403 Microfiber I believe is cotton. Used for thickening and filling gaps.

    George

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    I’ve actually thought about sawdust. Just wasn’t sure what it would do to strength. Polyurethane epoxy is all that’s used to make chip board so it should work (I make that stuff). It’s a single component and reacts with the sugar in the wood but the strength wasn’t affected. But I really wanted input from more knowledgeable folks. I appreciate all input you guys have given. I’m gonna try the silica first and see how that works.
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

    MK4 Roadster
    Ordered: 7/10/13. Delivered: 8/20/13. Completed: 10/26/15.
    I did everything except spray it. She ain't perfect, but she's mine.

  12. #8

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    The only thing about sawdust is it absorbs a lot of the epoxy - which makes the sawdust strong inside there but means you use more epoxy to create the mass overall. The solid filler materials add to it but don't absorb it, preferred way to do things.
    Art Quillen

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    Senior Member Fixit's Avatar
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    It might sound goofy, but I make my own "body/seam filler" for my plastic models using ACC/Crazy Glue and Talcum powder.

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    Senior Member Just puttering's Avatar
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    I have used baking soda to fill gaps with crazy glue, it works well but makes the glue set very quickly. I have not done any official strength tests or sanding quality analyzing. But have spanned 1/4 maybe 3/8 of an inch!

    Now im going to have to try talcum powder!
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    Baking soda will make CA (super glue) cure nearly instantly. It’s how they make custom o rings (how I’m gonna make the seals for my cowl covers). They cut the o ring, mate it up with super glue in it, then hit it with baking soda to cure it quickly. The -OH component of the soda reacts quicker than the water in the air does to cure it.
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

    MK4 Roadster
    Ordered: 7/10/13. Delivered: 8/20/13. Completed: 10/26/15.
    I did everything except spray it. She ain't perfect, but she's mine.

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    Senior Member Just puttering's Avatar
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    Thanks, thats good info. Sorry to pull this off epoxy.

    Its almost christmas time, what about the fake snow blankets you see at this time - it looks like its plyester. Not sure how that would react with the epoxy
    Mk3.1 347 AFR 205cc Race Heads A9L EFI siemens deca 60lb injectors MSD 6AL ignition Vortech V-3 3 Link PS/PB

    I like to build cars ... Thats it. Carroll Shelby

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    Quote Originally Posted by Just puttering View Post
    Thanks, thats good info. Sorry to pull this off epoxy.

    Its almost christmas time, what about the fake snow blankets you see at this time - it looks like its plyester. Not sure how that would react with the epoxy
    Perfectly ok man. I don’t mind wandering conversations lol.

    It prolly would work. Maybe even a bit moldable. I’d be worried the epoxy would drain out of it though. Sure a lot would stay but it may not truly thicken as much as give it some fibers. Might have to play with that one day.
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

    MK4 Roadster
    Ordered: 7/10/13. Delivered: 8/20/13. Completed: 10/26/15.
    I did everything except spray it. She ain't perfect, but she's mine.

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    Senior Member AC Bill's Avatar
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    Will HSRF not work for what you are doing?
    How big is the hole? Maybe body filler would work?

    https://thefactoryfiveforum.com/show...filling-a-hole
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    Could you use epoxy putty? That stuff stays where you put it.
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    Senior Member AJT '33's Avatar
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    Quote Originally Posted by Svtfreak View Post
    I have a couple holes to fix and need to with body in right orientation. I have used clay to back the spots so the epoxy stays put but it’s hard to get it sealed so it doesn’t run through. If I needed to thicken up epoxy so it wouldn’t run so easily, what’s the best way to do that? I used to have flocking that was super fine but I can’t find that stuff any longer. Can I grind up some set up fiberglass and use the dust? Will it affect strength at all? Some spots will have new holes drilled through so i need it to still be sturdy enough.

    Thanks for your input.
    OK, been watching this thread and finally I cant hold back not commenting on this anymore. Please take the following as helpful advice and experience over the last 12 months of body work with a lot of help from professionals I know.

    First, stay away from epoxy! The parts you have are made from a Polyester or Vinylester based resin, you should continue with the same resins. The main reason is that once you use epoxy nothing will stick to it after UNLESS you start using epoxy based products, and even then you need to prepare the epoxy such that there is NO shiny or smooth surfaces left, epoxies don't stick to epoxies once applied. Epoxies are great for adhering fiberglass or in marine applications where impermeability to areas that are underwater needs to be sealed to alleviate osmosis.

    Thats first, next, if you have a hole and it goes through the laminate you need to re-laminate over that hole (or place a layer underneath which is easier, otherwise anything that you put over it will pop eventually. A simple layer of 2oz mat with some polyester resin will do the trick. If there is a deep gauge or low spot that is greater than 1/16", use some fiber filled resin like what bondo has similar to this: https://www.3m.com/3M/en_US/company-...8711351&rt=rud, this will not only adhere very well but it will never crack, filled resins or filled epoxy can and depending where it is, will over time. Once you have your area filled and as even as possible (I use a 1/16" thick by 1-1/2" wide by 24" long piece of aluminum as a batten to check if the surface is fair. An 18" steel ruler works well too), then do the balance of the fairing with a quality putty like Rage Gold or Rage Ultra, you can the use a polyester based primer as a base fairing coat to see how fair your surface really is. You will most likely need to then fill and fair a lot more as you will find all those pin holes that you couldn't see, once they are repaired, and the entire surface sanded again, you can go ahead and spray another coat of polyester primer (like form HOK SP1600) to ensure that your surface is smooth, recheck that it is fair, then you can long board sand it to get ready for your paints base primer, sand it again, do your base color coats and then clear. I wrote a procedure I used that I sent to another blog colleague on this forum in a PM on Messenger, if your interested I can send it to you as well for insight, as he was using the HOK system for point as well, I would be more than happy to copy and paste it here if you would like.

    Again, just trying to provide as much insight for you as possible so you don't go through the issues that I have gone through. Have fun, take care.
    Black & Copper ("The Mistress" as per my wife! ) #1028
    Brought home: Nov. 2017, GoKart: May 2018, Plated & on the Road: ??? 2019??
    Andreas

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    AJ, I certainly appreciate any input!

    First, let me say that I am not using epoxy. I am using vinylesther resin from US Composites for all my repairs. I’m sorry for using the generic term of “epoxy”.

    So, what you are saying is I should cut out more than just the holes I want to fill and fill it with cloth and resin? Not just “plug” the holes (they are 27/64” diameter to be exact lol) with thickened resin? Trying to see how to explain what I think you said... kinda like countersink the hole, seal the back (I use clay normally) and fill the countersunk with clothed resin?
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

    MK4 Roadster
    Ordered: 7/10/13. Delivered: 8/20/13. Completed: 10/26/15.
    I did everything except spray it. She ain't perfect, but she's mine.

  22. #18
    Senior Member AJT '33's Avatar
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    Quote Originally Posted by Svtfreak View Post
    AJ, I certainly appreciate any input!

    First, let me say that I am not using epoxy. I am using vinylesther resin from US Composites for all my repairs. I’m sorry for using the generic term of “epoxy”.

    So, what you are saying is I should cut out more than just the holes I want to fill and fill it with cloth and resin? Not just “plug” the holes (they are 27/64” diameter to be exact lol) with thickened resin? Trying to see how to explain what I think you said... kinda like countersink the hole, seal the back (I use clay normally) and fill the countersunk with clothed resin?
    Glad to hear your using a vinylester resin I did the same and its easier to work with, excellent. Based on the hole size I would simply take some 2" tape and put a piece on the backside of the part and then taper the hole like you said, the thumb rule in the industry is 4 time the thickness for the taper up to a 1/4" thick laminate, this gives the proper bond for the new laminate you would add. Basically for the size of hole your looking at, a nice clean 45 degree taper will be the best then a couple layers of 2 oz mat to fill the gap or using a fiber filled resin would be more than appropriate to get the best adhesion. Just make sure that your exposed fibers are clear of any remnant dust.

    Wherever there is a major gap or crevice, I prefer using a proper laminate, however, the base laminates of the car, if you dont break through its nominal thickness is way more than strong enough. You will want to grind and fill those mold joints properly. If you can add 2 or more layers of mat then the fiber filled putty is the route to go with. To convince yourself, lay a 1/8" thick layer of putty on a piece of wax paper and do the same with the fiber filled putty, let it set and then see how much effort each takes to bend and break.

    20180623_Marked up.jpg This is how I showed another builder on how to taper the glass so it doesn't bulk up to relevel his doors, he had the same situation as me.

    Have fun!!
    Black & Copper ("The Mistress" as per my wife! ) #1028
    Brought home: Nov. 2017, GoKart: May 2018, Plated & on the Road: ??? 2019??
    Andreas

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  24. #19
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    When I was building radio control aircraft we used a product called microballoons to mix with the "epoxy" to thicken the resin. I'm not sure if it would work with the vinylesther.
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    Senior Member AJT '33's Avatar
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    Quote Originally Posted by HVACMAN View Post
    When I was building radio control aircraft we used a product called microballoons to mix with the "epoxy" to thicken the resin. I'm not sure if it would work with the vinylesther.
    100% however it still does stay runny when mixed at the set ratios otherwise it becomes too brittle when dry. Cabosil or Aerosil are two thickeners/fillers that are widely used with fiberglass resins.
    Black & Copper ("The Mistress" as per my wife! ) #1028
    Brought home: Nov. 2017, GoKart: May 2018, Plated & on the Road: ??? 2019??
    Andreas

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  28. #21
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    I used the cabosil today to thicken some up. Worked great and didn’t run out once mixed up.
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

    MK4 Roadster
    Ordered: 7/10/13. Delivered: 8/20/13. Completed: 10/26/15.
    I did everything except spray it. She ain't perfect, but she's mine.

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    You guys are having to much fun with this. Grind front and back and use mat or roving, not cloth. Lay your patch pieces on cardboard and wet them out with a 1-2in chip brush. Wetting out on cardboard keeps resin at a minimum. Wet the repair area and add the patch pieces and try not to add any more resin. Scrape the resin out of the brush and use the tip of the brush to stipple over the repair to help float out the excess resin. There is no strength in the resin, it's the cloth or mat resin mix. In this case strength is not an issue. The issue is "SHRINKAGE" Resin shrinks, less is best. If you have some HSRF you could prep it just the same way and fill it with HSRF. ..da Bat

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  32. #23
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    Thanks for the info, da bat.

    HSRF=? High strength rxxxx filler?

    Does resin shrink immediately during cure or over time?
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

    MK4 Roadster
    Ordered: 7/10/13. Delivered: 8/20/13. Completed: 10/26/15.
    I did everything except spray it. She ain't perfect, but she's mine.

  33. #24
    Senior Member AJT '33's Avatar
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    Both, however it achieves 90% hardness (Barcol hardness) in the first 24 hours roughly and further shrinkage essentially ceases.
    Black & Copper ("The Mistress" as per my wife! ) #1028
    Brought home: Nov. 2017, GoKart: May 2018, Plated & on the Road: ??? 2019??
    Andreas

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  35. #25

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    Quote Originally Posted by Svtfreak View Post
    Thanks for the info, da bat.

    HSRF=? High strength rxxxx filler?

    Does resin shrink immediately during cure or over time?
    Shrinks and shrinks and shrinks......very little but enough that if you were to just fill a hole you would keep seeing a shrink ring for years to come......you could color sand and polish it away and at would be back in a few weeks....ya couldn't feel it but you can see it. Also known as picturing..da Bat

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  37. #26
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    Mr Jeff, what about filling it slightly low and covering it with thin layer of body filler? Would that hide the shrink?
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

    MK4 Roadster
    Ordered: 7/10/13. Delivered: 8/20/13. Completed: 10/26/15.
    I did everything except spray it. She ain't perfect, but she's mine.

  38. #27
    Senior Member AC Bill's Avatar
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    Quote Originally Posted by Svtfreak View Post
    HSRF=? High strength rxxxx filler?
    This stuff. It has vinyl-ester resin, as is commonly used in the marine industry, so perfect for our cars.

    https://www.3m.com/3M/en_US/company-...3087022&rt=rud

  39. #28
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    Quote Originally Posted by AC Bill View Post
    This stuff. It has vinyl-ester resin, as is commonly used in the marine industry, so perfect for our cars.

    https://www.3m.com/3M/en_US/company-...3087022&rt=rud
    Thanks, Mr Bill. Mr Jeff got me on the right track. After discussing with him what I need, he thinks filler will be just fine in my application.

    On another note, I have met and been able to talk to some of the coolest dudes I’ve ever made aquatintances with since building this car. Thank you all.
    '33 Hot Rod
    Ordered: 3/25/17. Delivered: 5/6/17. 1st start: 8/24/18

    MK4 Roadster
    Ordered: 7/10/13. Delivered: 8/20/13. Completed: 10/26/15.
    I did everything except spray it. She ain't perfect, but she's mine.

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