[gt40]

I am working a larger epoxy granite vertical mill. The base, sub base, column and table will all be 3-4 cubic feet worth of epoxy granite. I have mixed small quantities but not this much. Could I use a concrete mixer? Suggestions would be really appreciated. Figure 500 lbs/225 kg per batch.

I am looking at just buying a Harbor Freight concrete mixer, pouring the mix into the mold packing and then vibrating.

[Voyager77]

Hey mate,

You'll need some kind of rotary mixer with a lot of torque. If you keep the epoxy content below 10% the mix will have a viscosity that is hard to mix. Perhaps try mixing it dry and adding epoxy once the mineral content has been mixed through. I would recommend much smaller trial batches. I believe epoxy generates heat once the two components have been mixed and the more epoxy there is, the more heat it creates which in turn accelerates the reaction further. Can you get epoxy that sets slowly at lower temps?

Next you are going to need a vibration table that generates vertical vibrations only and copes with 500lb + mold weight.
Take a look here for inspiration

Vibrating tables standard

[CaptainVee]

I've been pondering on the same thing.
As soon as you start requiring serious amounts, mixing really becomes an issue.

As voyager points out, if the stuff gets warm, it'l harden quicker.
To me that suggests that you need to mix all the epoxy at once and then quicly mix with the aggregate.If you leave the mixed epoxy in the tub and try to mix it in to aggregate, bit by bit, to get smaller batches to work with, it is likely to cure without getting the chance to be mixed in to the aggregate.

I've thought of making my own mixers, like cement mixers but using buckets, to make small batches very quickly. I think that having all epoxy mixed with the aggregate will slow it down some, especially if you (can) spread it out before adding it to the mold.

For me, the most important thing is to have a quick and fault free workflow, so I can mix many small batches rather than few big ones.

That means good equipment but also a lot of trial and error. And slow epoxy

But I will never attempt to get a massive casting area to vibrate... Way to many risks. I'd use localised vibration, or manual stamping.

[ger21]

I think that having all epoxy mixed with the aggregate will slow it down some, especially if you (can) spread it out before adding it to the mold.

If you use a slow setting epoxy, you should have several hours to work (the full set time) as long as you mix in the aggregate fairly quickly.

I mixed up a sample with just sand and some US Composites epoxy, and it took a few hours to cure. Without the sand, the large cup of epoxy would have gotten hot and cured in probably less than 15 minutes. The aggregate will keep it from getting hot (exotherm).

[gt40]

If you use a slow setting epoxy, you should have several hours to work (the full set time) as long as you mix in the aggregate fairly quickly.

I mixed up a sample with just sand and some US Composites epoxy, and it took a few hours to cure. Without the sand, the large cup of epoxy would have gotten hot and cured in probably less than 15 minutes. The aggregate will keep it from getting hot (exotherm).

Thanks.

So I am faced with mixing 5-6 gallons of epoxy and then quickly adding the aggregate in one load to do this by using a giant mixer as one choice or do a bunch of small batches one at a time and add with aggregate to slow the cure. After all are mixed I would still have to dump and pack them into the mold.

What if I run out of time? Can I fill the mold with 2 cycles?

FYI I have the US composite with slow hardener.

[ger21]

With the right epoxy, I'd think that you would have at least 2 hours of working time.
If it does start to set up, you have a certain amount of time when it's in a "gel" like state where additional epoxy will still bond to it as if it were one single batch.

If you need 6 gallons, I'd probably do it in 1-2 gallon batches. Put each batch in the mold and compact and vibrate before mixing the next batch.

You might want to read through all the technical documents on epoxy at West System. Lots of good info there.

[Voyager77]

If you do it in multiple casts that cure separately then you get secondary bonds which are weaker and undesirable. You want one cohesive piece that is bonded on a molecular level; can only get it by casting and curing the whole segment. However you should be able to add more material in batches as long as the epoxy has not set/cured yet. The prevalent room temperature is very important. Make sure you research the epoxy and its properties in depth.

[G59]

This is no biggie. I think you are over thinking this. You can mix in 1 cubic ft batches if you wanted. As long as you don't exceed pot life you will be fine. Pour in first batch. Ha've an orbital sander mounted on the bottom side of your mold, running, while you prepare the second batch. Then pour over first batch. I mean, how long do you think you have to mix for?
It's the same as making a concrete floor with a small mixer. In the end you can't tell from each individual batches.
Here at work we commonly bond hard and soft Urethanes together, and the bond is at the molecular level, meaning a true indistinguishable and inseperable bond between two different durometers. Epoxy works the exact same way.

[ger21]

You want one cohesive piece that is bonded on a molecular level; can only get it by casting and curing the whole segment.

Yes, if one section cures than you'll have a poor bond. But he should have a few hours before it actually cures, and as long as you add the next batch before the previous batch cures, it'll cure as one piece.
See the "gel" stage here:
WEST SYSTEM | Use Guides - Epoxy Chemistry

[gt40]

This is no biggie. I think you are over thinking this. You can mix in 1 cubic ft batches if you wanted. As long as you don't exceed pot life you will be fine. Pour in first batch. Ha've an orbital sander mounted on the bottom side of your mold, running, while you prepare the second batch. Then pour over first batch. I mean, how long do you think you have to mix for?
It's the same as making a concrete floor with a small mixer. In the end you can't tell from each individual batches.
Here at work we commonly bond hard and soft Urethanes together, and the bond is at the molecular level, meaning a true indistinguishable and inseperable bond between two different durometers. Epoxy works the exact same way.

Thanks for the info. Do you think I could get away with a harbor freight concrete mixer like this:

Cement Mixer - 3-1/2 Cubic Ft. Cement Mixer

I could just mix the aggregate and then add mixed resin...

[G59]

Yes, why not? The biggest problem I can see, will be the cleaning after you're done. Try small batch first and see how well it folds the aggregate when it is turning. Too big a batch means longer mixing.

[G59]

It's been my experience, the closer you get to the mixer's maximum capacity, the longer it has to spin for it to be a consistent mix.

[rowbare]

I've thought of making my own mixers, like cement mixers but using buckets, to make small batches very quickly. I think that having all epoxy mixed with the aggregate will slow it down some, especially if you (can) spread it out before adding it to the mold.

For me, the most important thing is to have a quick and fault free workflow, so I can mix many small batches rather than few big ones.

Sven,

Can you get the OdJob mixer in the Netherlands? That might do the trick.

https://www.google.ca/search?q=odjob...w=1512&bih=862

bob

[NeoTech]

So my plan for this subject is to calculate the amount of 10kg batches i need and premeasure everything, start mixing number 2 while a friend pours number one and so on going thru all the batches.. that way i can use a 1200W hand held blender and large mortar buckets..

[gt40]

I looked at the Home Depot cement mixers- they have a polymer barrel 6 cubic feet one for rent. Should definitely do the job mixing but my concern is cleaning it. Will the epoxy granite clean up? I am thinking between the plastic and a gallon of paint stripper, I could get away with just renting it. Here is a pic:

Attachment 270966

[NeoTech]

Only problem i can see with a fall tumbler that its not really forcing the components together and well coating all the gravel properly. Because of the viscosity of the epoxy is not nearly close as that of water used in concrete. =)

[CaptainVee]

That is not a problem, epoxy creeps everywhere, just does it a bit slower than water.

Cleaning the mixing equipment may go well with vinagar.

[NeoTech]

Well acetone breaks the bonds in epoxy and shouldnt touch most polymers or steel so. Can later be used to clean epoxy castings as well, not able to break it when cured. =)

[gt40]

Update:

I found a 90 gallon giant mixing tub at a local building supply house and went with that. I had to friends helping and we would mix 1 1/2 gallons of epoxy hardener in a five gallon bucket and add that to a 130 lb batch of pre mixed aggregate. 2 people working the tub with hoes worked really fine and with the US Composite 635 / slow hardener system, we had enough time to make all 4 130lb batches. It set up really well without pooling any epoxy and was warm to the touch 3 hours later. This morning I was greeted to a 2ft x 4ft x9" "rock". Anyway, mixing tub works fine for 600lb + batches. Just get some help because it is a lot of work!

Here is the tub i used: Attachment 273688

[CaptainVee]

Would not mind a picture of the rock