I've been using glass & epoxy to effect some repairs. One surface was
very irregular so the plan was to trowel on thickened epoxy, smooth on the
glass squeezing out any thickened epoxy then add unthickened epoxy if
necessary to wet out the glass.
I normally use Cab-o-Sil to thicken but this time I used micro balloons.
After I finished there was maybe 1/4 - 1/2" of both thickened and
unthickened in little pot pie type pans. The thick went off like gang
busters...once it started, it got rock hard in minutes. It also expanded
by about 3X. Meanwhile, the unthickened had barely gotten syrupy.
What's going on with that? The fast hardening and - especially - the
expansion.
dadiOH
"dadiOH" wrote:
> I've been using glass & epoxy to effect some repairs. One surface
> was very irregular so the plan was to trowel on thickened epoxy,
> smooth on the glass squeezing out any thickened epoxy then add
> unthickened epoxy if necessary to wet out the glass.
>
> I normally use Cab-o-Sil to thicken but this time I used micro
> balloons. After I finished there was maybe 1/4 - 1/2" of both
> thickened and unthickened in little pot pie type pans. The thick
> went off like gang busters...once it started, it got rock hard in
> minutes. It also expanded by about 3X. Meanwhile, the unthickened
> had barely gotten syrupy.
>
> What's going on with that? The fast hardening and - especially -
> the expansion.
-------------------------------------------------------------------------
I'm clueless, but based on your description, sounds like thermal run
away caused the expansion.
I like to use slow hardener with microballoons and limit thickness to
1/4" max per pass.
Using Cab-O-Sil to thicken produces a patch that is a BEAR to sand.
Can you talk to your supplier's tech service group?
Lew
"Lew Hodgett" wrote:
>> I'm clueless, but based on your description, sounds like thermal
>> run
>> away caused the expansion.
-----------------------------------------------------
"dadiOH" wrote:
>
> Could be, it was hot as a pistol. Way to hot to handle.
---------------------------------------------------------
"Lew Hodgett" wrote:
>> I like to use slow hardener with microballoons and limit thickness
>> to
>> 1/4" max per pass.
-------------------------------------------------------
"dadiOH" wrote:
> I had 3:1 hardener and 2:1, used the 3:1
---------------------------------------------------------
Break open the 1/2" piece. If it is foamed like an ice cream soda
inside, two things.
1. You definitely had a run away exothermic reaction.
2. You have a structure that is totally useless.
Time to grind out and start over.
Lew
On 8/5/2014 12:28 PM, dadiOH wrote:
> "Lew Hodgett" <[email protected]> wrote in message
> news:[email protected]
>> "dadiOH" wrote:
>>
>>
>> > I've been using glass & epoxy to effect some repairs. One surface
>> > was very irregular so the plan was to trowel on thickened epoxy,
>> > smooth on the glass squeezing out any thickened epoxy then add
>> > unthickened epoxy if necessary to wet out the glass.
>> >
>> > I normally use Cab-o-Sil to thicken but this time I used micro
>> > balloons. After I finished there was maybe 1/4 - 1/2" of both
>> > thickened and unthickened in little pot pie type pans. The thick
>> > went off like gang busters...once it started, it got rock hard in
>> > minutes. It also expanded by about 3X. Meanwhile, the unthickened
>> > had barely gotten syrupy.
>> >
>> > What's going on with that? The fast hardening and - especially -
>> > the expansion.
>> -------------------------------------------------------------------------
>> I'm clueless, but based on your description, sounds like thermal run
>> away caused the expansion.
>
> Could be, it was hot as a pistol. Way to hot to handle.
>
>> I like to use slow hardener with microballoons and limit thickness to
>> 1/4" max per pass.
>
> I had 3:1 hardener and 2:1, used the 3:1
>
>> Using Cab-O-Sil to thicken produces a patch that is a BEAR to sand.
>
> Quite true. I try to limit its use to places where I don't need or
> intend to sand.
>
>> Can you talk to your supplier's tech service group?
>
> Naah, not that important.
>
>> Lew
>
> Thanks, Lew, appreciated.
>
Microballons act as great insulation, retaining the heat generated by
the reaction. Definitely runaway reaction.
Best I've come up with is to spread the mix out after mixing (as opposed
to keeping it in a mixing cup) in a large shallow COLD tray.
But sometimes even then it if goes Chernobyl on me.
Richard <[email protected]> wrote:
> On 8/5/2014 12:28 PM, dadiOH wrote:
>> "Lew Hodgett" <[email protected]> wrote :
>>> "dadiOH" wrote:
>>> > I've been using glass & epoxy to effect some repairs. One surface
>>> > was very irregular so the plan was to trowel on thickened epoxy,
>>> > smooth on the glass squeezing out any thickened epoxy then add
>>> > unthickened epoxy if necessary to wet out the glass.
>>> >
>>> > I normally use Cab-o-Sil to thicken but this time I used micro
>>> > balloons. After I finished there was maybe 1/4 - 1/2" of both
>>> > thickened and unthickened in little pot pie type pans. The thick
>>> > went off like gang busters...once it started, it got rock hard in
>>> > minutes. It also expanded by about 3X. Meanwhile, the unthickened
>>> > had barely gotten syrupy.
>>> >
>>> > What's going on with that? The fast hardening and - especially -
>>> > the expansion.
>>> ---------------------------------------------------------------------
>>> I'm clueless, but based on your description, sounds like
>>> thermal run away caused the expansion.
>>
>> Could be, it was hot as a pistol. Way to hot to handle.
>>
>>> I like to use slow hardener with microballoons and limit thickness
>>> to 1/4" max per pass.
>>
>> I had 3:1 hardener and 2:1, used the 3:1
>>
>>> Using Cab-O-Sil to thicken produces a patch that is a BEAR to sand.
>>
>> Quite true. I try to limit its use to places where I don't need or
>> intend to sand.
>>
>>> Can you talk to your supplier's tech service group?
>>
>> Naah, not that important.
>>
>>> Lew
>>
>> Thanks, Lew, appreciated.
>>
>
> Microballons act as great insulation, retaining the heat generated by
> the reaction. Definitely runaway reaction.
>
> Best I've come up with is to spread the mix out after mixing (as
> opposed to keeping it in a mixing cup) in a large shallow COLD tray.
>
> But sometimes even then it if goes Chernobyl on me.
Yes, and warnings about exothermic runaway are found in every
manufacturers technical notes. I've seen a pot of mixed epoxy catch fire
whe something went wrong with the part fit so it didn't get used
immediately as expected. The reaction rate typically doubles for every
10 deg K rise in temperature so if you are using a fast hardener and
larger volumes of mixed resin its very easy to get into trouble when the
self heating runs away. If you are using epoxy in warm weather you
should always consider using a slow hardener.
Another problem is melting the mixing pot. I favour polyproplyene
plastic pots because cured epoxy doesnt stick well to them so they can
easily be reused, but for safety you need to put them in a tin in case
you get a runaway batch and it is always a good idea to have something
heatproof handy to grab them with and chuck them out the door or into a
drum of water.
Just hope you never get an in-situ exothermic runaway - that rarely ends
well!
Except for pure volume filling, I wouldn't use just microballoons. The
cured epoxy tends to be too brittle. Adding microfibre (cellulose
fibre) makes it a lot tougher but not significantly harder to sand.
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL
"Lew Hodgett" <[email protected]> wrote in news:53e14d62$0$61246
[email protected]:
>
>
> "Lew Hodgett" wrote:
>
>>> I'm clueless, but based on your description, sounds like thermal
>>> run
>>> away caused the expansion.
> -----------------------------------------------------
> "dadiOH" wrote:
>
>>
>> Could be, it was hot as a pistol. Way to hot to handle.
> ---------------------------------------------------------
> "Lew Hodgett" wrote:
>>> I like to use slow hardener with microballoons and limit thickness
>>> to
>>> 1/4" max per pass.
> -------------------------------------------------------
> "dadiOH" wrote:
>
>> I had 3:1 hardener and 2:1, used the 3:1
> ---------------------------------------------------------
> Break open the 1/2" piece. If it is foamed like an ice cream soda
> inside, two things.
>
> 1. You definitely had a run away exothermic reaction.
> 2. You have a structure that is totally useless.
>
> Time to grind out and start over.
>
> Lew
2. You have a structure that *MAY* *BE* totally useless.
So far we understand you applied a skim coat of thickened epoxy to an
irregular surface then glassclothed over it.
If you have any blistering or discolouration then Lew is right and you've
had an exotherm in-situ. Grind out and start over, with slow hardener at
a cooler time of day.
If you had any holes in the original surface bigger than a pea, you may
have a problem. If they are near an edge or the part is under
significant stress or it is going to be immersed, you should consider
investigating further e.g. drill through the glass cloth with a 1/16" bit
in a hand drill (not a power drill) then probe with a mounted pin to
check the epoxy underneath isn't spongey. Make good with a dab of
thickened epoxy.
However if it exothermed in the pot at least 5 minutes after you finished
working on the surface, and the surface's cure rate appeared similar to
the unthickened leftover pot, you've probably got away with it this time.
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL
"Lew Hodgett" <[email protected]> wrote in message
news:[email protected]
> "dadiOH" wrote:
>
>
> > I've been using glass & epoxy to effect some repairs. One surface
> > was very irregular so the plan was to trowel on thickened epoxy,
> > smooth on the glass squeezing out any thickened epoxy then add
> > unthickened epoxy if necessary to wet out the glass.
> >
> > I normally use Cab-o-Sil to thicken but this time I used micro
> > balloons. After I finished there was maybe 1/4 - 1/2" of both
> > thickened and unthickened in little pot pie type pans. The thick
> > went off like gang busters...once it started, it got rock hard in
> > minutes. It also expanded by about 3X. Meanwhile, the unthickened
> > had barely gotten syrupy.
> >
> > What's going on with that? The fast hardening and - especially -
> > the expansion.
> -------------------------------------------------------------------------
> I'm clueless, but based on your description, sounds like thermal run
> away caused the expansion.
Could be, it was hot as a pistol. Way to hot to handle.
> I like to use slow hardener with microballoons and limit thickness to
> 1/4" max per pass.
I had 3:1 hardener and 2:1, used the 3:1
> Using Cab-O-Sil to thicken produces a patch that is a BEAR to sand.
Quite true. I try to limit its use to places where I don't need or intend
to sand.
> Can you talk to your supplier's tech service group?
Naah, not that important.
> Lew
Thanks, Lew, appreciated.
--
dadiOH
____________________________
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Taxes out of hand? Maybe just ready for a change?
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"Richard" <[email protected]> wrote in message
news:[email protected]
> On 8/5/2014 12:28 PM, dadiOH wrote:
> > "Lew Hodgett" <[email protected]> wrote in message
> > news:[email protected]
> > > "dadiOH" wrote:
> > >
> > >
> > > > I've been using glass & epoxy to effect some repairs. One surface
> > > > was very irregular so the plan was to trowel on thickened epoxy,
> > > > smooth on the glass squeezing out any thickened epoxy then add
> > > > unthickened epoxy if necessary to wet out the glass.
> > > >
> > > > I normally use Cab-o-Sil to thicken but this time I used micro
> > > > balloons. After I finished there was maybe 1/4 - 1/2" of both
> > > > thickened and unthickened in little pot pie type pans. The thick
> > > > went off like gang busters...once it started, it got rock hard in
> > > > minutes. It also expanded by about 3X. Meanwhile, the unthickened
> > > > had barely gotten syrupy.
> > > >
> > > > What's going on with that? The fast hardening and - especially -
> > > > the expansion.
> > > -------------------------------------------------------------------------
> > > I'm clueless, but based on your description, sounds like thermal run
> > > away caused the expansion.
> >
> > Could be, it was hot as a pistol. Way to hot to handle.
> >
> > > I like to use slow hardener with microballoons and limit thickness
> > > to
> > > 1/4" max per pass.
> >
> > I had 3:1 hardener and 2:1, used the 3:1
> >
> > > Using Cab-O-Sil to thicken produces a patch that is a BEAR to sand.
> >
> > Quite true. I try to limit its use to places where I don't need or
> > intend to sand.
> >
> > > Can you talk to your supplier's tech service group?
> >
> > Naah, not that important.
> >
> > > Lew
> >
> > Thanks, Lew, appreciated.
> >
>
> Microballons act as great insulation, retaining the heat generated by
> the reaction. Definitely runaway reaction.
>
> Best I've come up with is to spread the mix out after mixing (as opposed
> to keeping it in a mixing cup) in a large shallow COLD tray.
>
> But sometimes even then it if goes Chernobyl on me.
Thanks. If I have occasion to do it again I'll keep it on ice.
--
dadiOH
____________________________
Winters getting colder? Tired of the rat race?
Taxes out of hand? Maybe just ready for a change?
Check it out... http://www.floridaloghouse.net
"Lew Hodgett" <[email protected]> wrote in message
news:[email protected]
> "Lew Hodgett" wrote:
>
> > > I'm clueless, but based on your description, sounds like thermal
> > > run
> > > away caused the expansion.
> -----------------------------------------------------
> "dadiOH" wrote:
>
> >
> > Could be, it was hot as a pistol. Way to hot to handle.
> ---------------------------------------------------------
> "Lew Hodgett" wrote:
> > > I like to use slow hardener with microballoons and limit thickness
> > > to
> > > 1/4" max per pass.
> -------------------------------------------------------
> "dadiOH" wrote:
>
> > I had 3:1 hardener and 2:1, used the 3:1
> ---------------------------------------------------------
> Break open the 1/2" piece. If it is foamed like an ice cream soda
> inside, two things.
>
> 1. You definitely had a run away exothermic reaction.
> 2. You have a structure that is totally useless.
>
> Time to grind out and start over.
>
> Lew
Yeah, the suppy batch was foamed. What I was working on was fine.
My garden tractor grill - plastic - was broken when a repairman pushed it
too hard onto his trailer and bumped the front wall of the trailer. I
would have preferred ro buy a new grill but they aren't available. There
was one piece missing so the I covered some thin cardboard with celluose
tape and used that taped to the inside to get a contour and to contain the
thickened epoxy. Once set, I took out the cardboard and glassed over the
repaired area. Looks terrible, but functions fine :)
--
dadiOH
____________________________
Winters getting colder? Tired of the rat race?
Taxes out of hand? Maybe just ready for a change?
Check it out... http://www.floridaloghouse.net