[CAS14]

When I took shop (woodworking) in high school, sometime around 1960, we used hot plates to melt horse hooves for really strong glue. Later as a research assistant in grad school, we used hot plates to heat epoxy for making slides of rock thin sections for the microscope.

So...............I am looking on the internet for hot plates and all I see is very expensive industrial hot plates, and a bit too expensive hot plates for cooking. I guess the cooking hot plates would work fine for warming epoxy.

My plan is to attempt to salvage some nice red cedar that is hard and cured, but badly cracked. I think that if the sticks are warmed next to the fireplace, and the structural epoxy is heated on a hot plate to lower the viscosity, that the epoxy will penetrate far more deeply into the sticks and make them workable.

Has anyone bought a hot plate in recent years?

Recommendations?

 

[NightKnight]

Sorry, I havent ever looked into them before. Let me see what I can find. What is your price range?

 

[JJireh]

well you aren't trying to boil it necessarily, you could use anything from a coffee warmer to a cheap crock pot/pot pouri warmer, or even an old coffee maker.

 

[CAS14]

Price range: seems like $10 - $15 should do it. My Mr. Coffee cost only $20 including a pot.

Just a simple rheostat, no fancy digital display to drive the price up.

 

[CAS14]

I am reading about the many kinds of epoxies. Temperature seems to affect strength in different ways, depending on the formulation.

I have been using System 3 T-88 Structural Epoxy:

According to the instructions:

Lap-Shear Strength vs. Temperature:
(Aluminum Tensile Shear):
67°F ................................................................................. 2500 psi
75°F ................................................................................. 2000 psi
150°F ............................................................................... 1300 psi
180°F ............................................................................... 1000 psi

I interpreted this incorrectly. This is the strength of the cured epoxy when exposed to these temperatures, NOT a list of epoxy temperatures during application with the resultant strengths.

The manufacturer's representative said that heating prior to use would not impact strength and only minimally impact viscosity. He said that the addition of a minute quantity of lacquer thinner would reduce viscosity (and penetration) without reducing strength excessively.

It looks like I will have to experiment some, unless someone here has already been through this exercise.

 

[Rad]

CAS -- I know nothing about hot plates, but we used cast iron melting pots for melting lead, with a propane fire -- could you do something similar? I know, it's probably not the same kind of heat. We also played with mercury in science class -- all very healthy pursuits

 

[CAS14]

Rad, thanks, a good thought, but I think a hot plate will be cheaper than cast iron and a propane bottle. I could use a ceramic tile to place on the hot plate to heat the epoxy. I'm not confident in the manufacturer's rep's opinion that heat will not reduce epoxy viscosity. I plan to test the concept, not with temperature and viscosity measurements (a paddle wheel viscometer is an expensive and complicated device), but just with empirical observation of the apparent fluidity of the epoxy as it heats up. If heat does the job, then I won't add lacquer thinner.

 

[CAS14]

Procter Silex for $22-something after tax. Lowest setting makes epoxy boil - bad. However, the tile stays hot a long time, so I just removed the tile.

The epoxy gets runny - that's good but you have to figure out how to apply it. A watercolor brush might have worked better than the little wooden sticks that I used.

I will find a small, cheap ceramic bowl to contain the very fluid heated epoxy. The T-88 structural epoxy did harden well after 24-hours. Only time will tell whether the epoxy actually bonds well.

 

[CAS14]

The tile wasn't a good idea, so I bought a cheap Pyrex pie plate, or whatever you call it. No fluid epoxy could run off the edge. It retained heat for a long while after minimal heating. The epoxy seemed to thicken more rapidly after heating, but maybe that's my imagination.

My second cracked red cedar stick just had structural epoxy applied.

Here is the plate I used.

I still don't know whether this procedure is more effective for adding strength than the normal approach to applying epoxy.

 

[Rad]

The tile wasn't a good idea, so I bought a cheap Pyrex pie plate, or whatever you call it. No fluid epoxy could run off the edge. It retained heat for a long while after minimal heating. The epoxy seemed to thicken more rapidly after heating, but maybe that's my imagination.
My second cracked red cedar stick just had structural epoxy applied.
Here is the plate I used.

image.jpg
I still don't know whether this procedure is more effective for adding strength than the normal approach to applying epoxy.

CAS -- I know it's been a while since you did this, but I was wondering: After the epoxy has hardened and cooled in the dish, can you reheat it and use what was left over another time?

 

[CAS14]

CAS -- I know it's been a while since you did this, but I was wondering: After the epoxy has hardened and cooled in the dish, can you reheat it and use what was left over another time?

Rad, I haven't used it since. I have rasped and sanded down that stick enough to see that most of the epoxy penetrated well (perhaps 1/8"-1/4") I'm wondering whether this is just too complicated an operation. Perhaps a good wood glue injected with a needle is a simpler approach, I don't know.

 

[nameless]

And, to think of all the time i might have saved!

When I had to restore elderly stix, with some deep cracks, I used superglue.

First, anyway. That penetrated right down to the black hole where is all seemed to be going until, eventually, I began to see a consistent cured glue line. That is the patch that goes 'to the bone'!

That does require many of the 'little bottles'.. *__-

And the fumes are toxic!

And the time involved in the application of layers.

And you cannot add the superglue, or the epoxy, to different sides of the stick, if there are multiple crevices to repair.

More time and personal contact!

On top of that, though, epoxy works; adds a bit to the 'toughness factor'.

After all that, there is plenty of 'mana', 'spirit', in the stick!

So, warm epoxy would be just as capillary sucking good?

 

[CAS14]

CAS -- I know it's been a while since you did this, but I was wondering: After the epoxy has hardened and cooled in the dish, can you reheat it and use what was left over another time?

I don't think so, it seems to soften but not get fluid. I don't know whether this is worth the trouble. It may be that heating the stick would do just as well as heating both.

The result was good but I don't yet have enough experience to know which alternative works best.

 

[Chiricahua Jack]

I'm coming in late on the hot plate question but wanted to offer an idea I have used and that is the bottom heater plate from an old popcorn popper. You can easily add a cheap rheostat in order to control the current, and therefore the heat. Remember using them to heat soup or Ramen noodles in college? Some people even use them to roast coffee beans.