Thinned Epoxy

[11bravo]

No idea where this should be posted; feel free to move it at will.

What are people's ideas on thinning epoxy or JB Weld as to the final strength?
I.e., if I use acetone or denatured alcahol to thin JB Weld enough that it flows*, once the solvent dries/evaporates out will the JB Weld be as strong as it would have been without it?
There is a thread about surface mounting fins and I replied that Shadow Composites uses a high heat epoxy with kevlar pulp to do the fillets in their second video.
The epoxy appeared to be somewhat thin, unlike JB Weld.
I was wondering if thinning the JB Weld would hurt anything.
JB Weld says that it can be thinned with "1 tsp. of acetone or lacquer thinner per 2 oz. (1 full package) of mixed product", but I'll not be using that much.

What do you think?

Greg

*at least isn't so thick, especially with kevlar pulp in it

 

[denverdoc]

Great question. Been wondering the same as I will often use a relatively inexpensive marine epoxy, which is a bit thick for my tastes, and so thin with acetone. This might be a no-no from the material science perspective, but so far have suffered no consequences!
J

 

[shockwaveriderz]

heres what westsystems epoxy has to say about thinning epoxy:

"Acetone, toluene or MEK have been used to thin WEST SYSTEM epoxy and duplicate these penetrating epoxies with about the same effectiveness. If you chose to thin the epoxy, keep in mind that the strength and moisture protection of the epoxy are lost in proportion to the amount of solvent added. "

"There is a better solution to get good penetration without losing strength or moisture resistance. We recommend moderate heating of the repair area and the epoxy with a heat gun or heat lamp. The epoxy will have a lower viscosity and penetrate more deeply when it is warmed and contacts the warmed wood cavities and pores. Although the working life of the epoxy will be considerable shortened, slower hardeners (206, 207, 209) will have a longer working life and should penetrate more than 205 Hardener before they begin to gel. When the epoxy cures it will retain all of its strength and effectiveness as a moisture barrier, which we feel more than offsets any advantages gained by adding solvents to the epoxy."

 

[hokkyokusei]

I'm probably overlooking something, but why do you want to thin it?

 

[11bravo]

I tried posting a reply earlier (like last night IIRC) and now see that for some reason it did not post.
Hmmm?
Anyway, I'm just wondering about making it easier to use.
JB weld is rather thick as it is and with kevlar pulp in it I'm betting it'd be REALLY bad.

Thanks for the replies.
Anymore ideas more than welcome.

Greg

 

[dave carver]

I use epoxy thinned with laquer (sp) thinner to strengthen cardboard tubes and wood. It penetrates like water and slows the hardening time to where it sets after all of the solvent has flashed off.
The wood that I use is real cheap luan, made from Phillipian Mahogany, $12.00 a 4x8 sheet. THe thinned epoxy soaks to the core of the wood vastly increasing the strenght of the fins I make.
One of my rockets, a 5 pounder , stripped it's chute and the rocket fell from about 4000 ft and all that I had to do to fly it again is graft a small piece on the corner of the fin that chipped off, reinforced the corner with some 3/4 oz 'glass and it's still flying 8 yrs later.

 

[kkooch]

Originally posted by shockwaveriderz
heres what westsystems epoxy has to say about thinning epoxy:

"Acetone, toluene or MEK have been used to thin WEST SYSTEM epoxy and duplicate these penetrating epoxies with about the same effectiveness. If you chose to thin the epoxy, keep in mind that the strength and moisture protection of the epoxy are lost in proportion to the amount of solvent added. "

"There is a better solution to get good penetration without losing strength or moisture resistance. We recommend moderate heating of the repair area and the epoxy with a heat gun or heat lamp. The epoxy will have a lower viscosity and penetrate more deeply when it is warmed and contacts the warmed wood cavities and pores. Although the working life of the epoxy will be considerable shortened, slower hardeners (206, 207, 209) will have a longer working life and should penetrate more than 205 Hardener before they begin to gel. When the epoxy cures it will retain all of its strength and effectiveness as a moisture barrier, which we feel more than offsets any advantages gained by adding solvents to the epoxy."

All Valididated!

Build yourself a "hot box" using aluminum backed insulating foam (available at HD) and a 100 watt light bulb. Used exclusively this past year and I've got to say that my layups have not looked better and have more bending/torsional strength at higher temps.

Kevin K.

 

[tfish]

I use Sytem Three T-88. which is a bit thick for glassing. I use de-natured alcohol to thin it down. I have been doing this for a few years now. It does take longer for the epoxy to set up. So far no problems up to just under mach 2.

https://hometown.aol.com/tfish38/page6.html

Tony

 

[SwingWing]

Thinned epoxy may shrink upon cure. Regular epoxy will not shrink. This may not be an issue if you are using it so thin as to soak into cardboard. Most Epoxy companys warn against thinning.

 

[cbwho]

Did anyone experimented with jbweld mixed with alcohol? Does it dry but less hard?

 

[Hobie1dog]

I use a thinned epoxy, it is made by Z-Poxy and it is called " finishing resin ", which is a thinned down epoxy resin that works great for filling in all of the ridges of 3D printed parts, as one layer is self leveling. Come back the next day and sand with 220 and it's a smooth as a baby's bottom
https://www.amazon.com/Pacer-Techno...fix=z+gap+finishing+resin,aps,250&sr=8-1&th=1

 

[MarsLander]

Did anyone experimented with jbweld mixed with alcohol? Does it dry but less hard?

From here...Link-->JBWELD FAQ

 

[kramer714]

Thinned epoxy may shrink upon cure. Regular epoxy will not shrink. This may not be an issue if you are using it so thin as to soak into cardboard. Most Epoxy companys warn against thinning.

Talking Day job stuff here (made aircraft and missile composites as the day job)

Regular epoxy does shrink, how much it shrinks depends on the chemistry and if there are any fillers and what type of filler. If the part isnt fully cured (5 minute epoxy doesn't get a full cure without heat or a REALLY long time). The issue of shrinkage (que George Costanza) also depends on how the epoxy is used. A thick fillet will shrink putting the bond in tension (bad thing). Ever notice how crack appear in fillets over time? This is shrinkage putting the epoxy in tension, A rubber filled epoxy can 'give more' than an unfilled one. Tough resins (look at the T-peel numbers) tend to do better in fillets. JB weld good stuff in shear but really bad in peel.

Some of the shrinkage happens before the resin vitrifies (acts like a solid - this isn't cured just hard). some happens after it vitrifies. If you look a the density of the constituents and the fully cured product, the density is higher than the liquids accounting of the mix ratio. higher density from lower = shrinkage.

Thinning the resin with solvent will reduce the mechanical properties and increase the shrinkage, plus if not done correctly will increase the voids in the bond.

When we would repair dryspots in parts, we used a mixture of laminating epoxy and solvent, would brush on a THIN layer, and use 'just enough' heat to flash off the solvent while letting the resin impregnate the dry spots without curing it, It would take many applications like this to do a repair. After it was re-impregnated we used heat to cure the repair. Having said that we did take a knockdown in strength at the repair.

Mike - Actual Composites Engineer

P.S. with epoxy, hard doesnt = cured Just because a resin gets hard that doesnt mean it is cured or has full strength. We used many different resins that were solid at room temperature, we needed to heat them to mix in a curing agent. There are even prepregs that are hard at room tmeperature, the flow and cure when heated.