Epoxy Granite In Practice (Mineral Casting, Polymer Concrete)

Even if you start with a perfect mixed fuller curve of aggregate, if you add 25% epoxy, the different aggregates will separate with the large particles settling out as you fill and vibrate the mould. Not the right path to optimal E/G.
Mark

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Originally Posted by RotarySMP

Even if you start with a perfect mixed fuller curve of aggregate, if you add 25% epoxy, the different aggregates will separate with the large particles settling out as you fill and vibrate the mould. Not the right path to optimal E/G.
Mark

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My next tests will be using 10% and 12% by weight resin. I would like to be able to do 8% by weight resin I just don't see how I can vibrate everything that well. I might test a piece to try it out. Anything over 12% by weight resins were just tests and not suitable, too much wasted resin.

I think that I will probably manage to get a good overall piece using 10%. I just have to take a little extra time to vibrate everything well and limit my pebble size to max 6mm (or thereabouts). I am no longer contemplating using the large jagged pieces as I had in my test samples. My next batch will be strictly quarts sand & quartz pebbles.

I wanted to get everyone's opinion on mixing a batch of quartz epoxy with some graphite powder. I want to rub two surfaces together such that they work as ways. Instead of cast iron ways, they would be quartz epoxy ways. West Systems recommends a maximum of 5% graphite powder mix in their epoxy system for marine use. Can I use up to 5% of my aggregate mix as graphite powder? Would that be too much? What would you all recommend?

Thanks,

What are you using to vibrate your mix? I used a three phase concrete vibrator on my 8% mix, with a VFD on it so I could look for a resonant frequency to help it slump. My mold was pretty small, about 15kg. Got pretty good packing, but still some air bubbles. I think youd need vaccum or 10% epoxy or both to get all the air out.

You want to add graphic to epoxy granite and have that be the lubricant for E/G sliding on E/G? Dont see that working, but give it a go and report back. How would you get these surfaces flat enough? Normally your ways wil need machining after casting. I think you would be better off fixing cast iron in your mould as the way surfaces, and moulding in pockets on the opposing parts and casting in moglice

I put some graphite in my test peices to make a black E/G, just to look cool.
Mark

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Originally Posted by RotarySMP

What are you using to vibrate your mix? I used a three phase concrete vibrator on my 8% mix, with a VFD on it so I could look for a resonant frequency to help it slump. My mold was pretty small, about 15kg. Got pretty good packing, but still some air bubbles. I think youd need vaccum or 10% epoxy or both to get all the air out.

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Hi Mark, I don't have anything as sophisticated. It is just a regular sander that I use to vibrate. Although I thought of using a DC motor to regulate the speed and have it oscillate in a more "controlled" manner.

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Originally Posted by RotarySMP

You want to add graphic to epoxy granite and have that be the lubricant for E/G sliding on E/G? Dont see that working, but give it a go and report back. How would you get these surfaces flat enough? Normally your ways wil need machining after casting. I think you would be better off fixing cast iron in your mould as the way surfaces, and moulding in pockets on the opposing parts and casting in moglice

I put some graphite in my test peices to make a black E/G, just to look cool.
Mark

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Well, I figured that I would have some test molds with the top open. So I have a very level base and sides to the mold and leave the top open. That way, as I fill the top, I allow a small amount to overflow the sides. Hopefully, this will allow the epoxy to "self-level" as opposed to creating those rising sides it does when it is below the top of the mold. This, in theory at least should give me a reasonably flat surface to begin with.

Since I cannot machine the composite once set, it is a matter of sanding or abrading the surface to get it flat. IE the 3 plate method. The reason I want to avoid the inserted steel or iron ways is to see whether something like a graphite infused composite can achieve low friction coefficient. I guess with my tests will find out soon enough.

The only way to mould a flat surface is to mould against a surface plate.

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Originally Posted by RotarySMP

The only way to mould a flat surface is to mould against a surface plate.

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Hi Mark,
I have a surface plate arriving next week. How do you recommend I mould directly on the surface plate? Should I add a layer of plastic wrap (like kitchen wrap)? Or does that create bad finish since I can't guarantee it is flat?

Should I use a release agent that is used for moulds? And then apply the epoxy directly to the surface plate?

Thanks,

On top of your release, sprinkle graphite like a parting dust in foundry casting. The top layer will cling to the epoxy.

I would never (as in NEVER, EVER) cast EG on a surface plate directly without having someone next to me, looking me in the eye and telling me he has actually done that and was able to release, no matter how much release agent I plan to use.

To release a surface of a stiff part cast against something stiff, neither part can bend to release.
That means The entire surface has to release at once, it cannot be peeled.

Think of it as putting two pieces of glass together with water in between and then release them not by peeling nor by sliding.

I'd test using aluminium foil.
You can also use mylar, a polyester, a bit stiffer than most other kinds of plastic film.

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Originally Posted by made2hack

Hi Mark,
I have a surface plate arriving next week. How do you recommend I mould directly on the surface plate? Should I add a layer of plastic wrap (like kitchen wrap)? Or does that create bad finish since I can't guarantee it is flat?

Should I use a release agent that is used for moulds? And then apply the epoxy directly to the surface plate?

Thanks,

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I release parts made with epoxy from rigid molds every day of the week so I can offer some practical advice on this.

If the aim aim is to replicate the flatness and smoothness of the surface plate in your casting, then pour directly onto it. Don't try to add layers of clingfilm or foil etc. if you absolutely have to, use some proper smooth release film. It is sold in every composites store. If you use a release film, stick it down with a temporary spray adhesive (also sold at composites stores) and use a roller to smooth it down against the surface plate with no trapped air pockets. This is not as easy as it sounds. I use my laminator for this like that....

If you want to cast on the surface directly (which is what I would do), you absolutely need mold release and you need to apply it correctly. I use a combo of mirror-glaze wax and purple PVA mold release.

You apply the wax first in thin layers using a cloth as if you were applying wax to your car. If you apply it thin enough, you shouldn't be able to see it. Buff each layer so it appears glossy smooth before applying the next. Use an automotive buffing cloth. I find that it works best if you leave the first layer to dry overnight before adding the rest. The following day, I apply 3 to 5 more layers allowing 15 minutes of drying time between each. It will look glossy smooth when you are done buffing the last layer. There should be no visible clumps of wax. I like to leave the last layer to dry for a few hours.

When the wax is dry, I apply the PVA mold release. Make sure to buy the purple one, not the green or the one-coat clear version. I wipe on the PVA using a folded piece of kitchen towel. It can be sprayed but I find this easier. Don't use anything thin like toilet paper or you'll end up with white clumps stuck in the pva. Wipe it on thin and smooth. Wipe off any visible excess pools of pva before it dries. Think karate kid - wax on, wax off technique. If you have done it right, you shouldn't be able to see the pva when it's dry. Less is more. Allow 15 minutes for each layer to dry. I apply 3 layers of PVA. Some people use more but whatever.

Don't skip the PVA. Don't use a different type of wax. Don't try to use PVA on it's own. Without the PVA, the epoxy will fisheye on the wax. Without the wax, it will get stuck together. You have been warned....

Even though PVA is compatible with epoxy, I prefer to apply a layer of epoxy black surface coat before pouring the rest of the epoxy. You can buy it at ACP composites. It will pretty much guarantee a nice easy to release finish. It has a honey-like consistency and easily sticks to vertical surface without running off or pooling like other epoxy products. It leaves a nice hard wearing surface too.

When it has cured, you can release the casting using a screwdriver or compressed air to seperate it from the surface plate. Once you get one corner to seperate, the rest will be easier. Just work around the edges. You might still have to take it slowly to avoid damaging the casting. It's not a fun step but it's worth a little patience. Some people cast with a triangular silicone wedge stuck in one of the edges to make it easier to release.

If the casting feels stuck, you can use warm water to help it release. The pva layer will desolve in water (as it is meant to do).

Make sure to cast the epoxy part thick enough or it will warp and you'll lose that nice precise flat surface. I added carbon fiber to my epoxy granite mix for this reason. Long epoxy parts will warp and bow if they aren't strong enough.

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Originally Posted by Goemon

I release parts made with epoxy from rigid molds every day of the week so I can offer some practical advice on this.

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Forgive me for being critical but do you actually release cast epoxy granite from surface plates?

But very good info nevertheless, thanks!

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Originally Posted by CaptainVee

Forgive me for being critical but do you actually release cast epoxy granite from surface plates?

But very good info nevertheless, thanks!

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It doesn't make a difference what it is being release from. The method I described is universal. There is nothing special about granite that makes it more difficult to release epoxy from than anything else.

I have used this to release epoxy granite from various surfaces and I have also used it to make sure epoxy does not stick to my granite counter-tops. I most commonly use it for releasing carbon fiber with epoxy parts from molds.

In my experience, the easiest parts to release are from flat smooth surfaces (like a surface plate). The most difficult are from molds with deep complex crevices and espiecially when the parts are long and thin (easy to break). In either scenario, I would use the same mold release though.

I used a front surface mirror to cast flat epoxy granite parts where a perfectly flat surface was needed. These are far more expensive than any surface plate I have ever seen if that makes you feel better about my level of confidence in it. I would risk a surface plate before any of my molds too.

I can understand why you might be nervous about it though. I used to be the same until I gained confidence in the mold release products I use. You should practice on a cheaper surface first to gain some comfort with the process.

The other reason why I would have no worries with epoxy releasing from a granite slab is the incredibly high surface hardness of granite. If epoxy did get stuck to it (which it won't if you follow the process), it can be chiseled off fairly easily without damaging the granite.

I think the concern is there are posts in the mega thread and utube videos showing having to chisel out the part, destroying the mold. I'm pretty sure the video mentioned using mold release though I don't know the steps followed.

[edit]and the granite countertop comment sparked a thought. Pick up a sink drop or broken piece from a granite dealer (or pulled countertop at habitat for humanities shop) and practice technique prior to gluing your part to a surface plate.

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Originally Posted by rocketflier

I think the concern is there are posts in the mega thread and utube videos showing having to chisel out the part, destroying the mold. I'm pretty sure the video mentioned using mold release though I don't know the steps followed.

[edit]and the granite countertop comment sparked a thought. Pick up a sink drop or broken piece from a granite dealer (or pulled countertop at habitat for humanities shop) and practice technique prior to gluing your part to a surface plate.

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The world is full of idiots that get surprised when epoxy sticks to things when they didn't use mold release. There is an even greater number that ruin stuff by cheaping out and assuming that they can use any old wax instead of proper mold release wax. That should not deter the rest of the population from using epoxy.

It is a simple fact that epoxy can not and will not chemically bond to a surface when there are layers of meguiars mirror glaze wax and pva mold release in-between.

Anyway.... I've led the horse to water.... drink.... don't drink.... makes no difference to me.

From what you write you seem way more experienced in releasing epoxy than I am.

But me being crytical is not about the release agent.

"the easiest parts to release are from flat smooth surfaces (like a surface plate)"

Have you actually used a surface plate for casting epoxy granite?

After casting epoxy granite on a surface plate there is literally no open space left between the surfaces.
And there are voids in the surface plate so there are peaks on the casting.

I believe that means that in order to release the two, one or both of the parts must bend (which on this scale, they can't) so the surfaces can peel away from each other or the whole surface has to release at once.

A friend of mine has actually done this and even though the parts were small, he had a very hard time to get them to separate. And he is well used to working with epoxy.

Also consider that the epoxy granite mix has abrasive aggregates in it, and when vibrated and compacted, these abrasives can compromise your release agent/film.

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Originally Posted by CaptainVee

From what you write you seem way more experienced in releasing epoxy than I am.

But me being crytical is not about the release agent.

"the easiest parts to release are from flat smooth surfaces (like a surface plate)"

Have you actually used a surface plate for casting epoxy granite?

After casting epoxy granite on a surface plate there is literally no open space left between the surfaces.
And there are voids in the surface plate so there are peaks on the casting.

I believe that means that in order to release the two, one or both of the parts must bend (which on this scale, they can't) so the surfaces can peel away from each other or the whole surface has to release at once.

A friend of mine has actually done this and even though the parts were small, he had a very hard time to get them to separate. And he is well used to working with epoxy.

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The assumption that the parts have to bend to release is wrong. Carbon fiber parts made with epoxy don't bend and they release just fine from rigid molds. There is nothing in an epoxy granite mix that increases adhesion over pure epoxy or epoxy with cf. Nothing.

The thing that will prevent a clean release is if you create a mechanical lock. Mold release only prevents a chemical bond. It won't compensate for a lack of common sense in this respect. If the surface has holes that resin will find it's way into and create a mechanical lock, these holes should be filled in before you start. In the composites world, it is common to use filleting wax for this. You wouldn't want the casting to have a rough surface anyway. The whole point of using a surface plate is that it's super flat....

Small textures in the surface that won't create a mechanical lock or prevent you applying mold release will not prevent parts releasing.

No matter what shape you cast, if it is on a surface plate or a pattern with complex curves, there is never a gap between the part and the mold until you create one. The liquid resin will conform to whatever shape you put it on. The mold release allows you to create a gap. As I said, this can be made easier by casting with a silicone wedge at the edge. Or, you can buy a wedge from a composites store that allows you to feed air from a commpressor into the gap to seperate it faster. I just use a blunt knife and ease it into the gap gently after running some warm water over it.

If the surface plate is poor quality and has tons of voids, I wouldn't bother using it at all. You can create a flat and level surface with good bartop resin and, if needed, an isopropyl alcohol mist on top. It might even give you a flatter surface that casting against a surface plate.

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I just use a blunt knife and ease it into the gap gently after running some warm water over it.

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The fact that you can ease a knife in gently implies that something is flexing. If there's no flex, than the part is either released, or it's not. There's no middle ground, when both bodies are rigid.

Yes, I also think one part definitely has to bend. I work with carbon fiber everyday, and carbon/epoxy mix definitely bend, otherwise it would be nearly impossible to take the part out of the aluminium molds. I''ve also built EG machine a year ago and have some experience with that too. Using only PVA, without wax, was more than enough. But I wasn't trying to replicate surface plate as I had metal inserts.

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Originally Posted by ger21

The fact that you can ease a knife in gently implies that something is flexing. If there's no flex, than the part is either released, or it's not. There's no middle ground, when both bodies are rigid.

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No it doesn't. It means the two rigid surfaces are being forced apart creating a gap. The layer of mold release being washed away also creates a small gap but it's mainly about the two parts being seperated. Try it yourself with two pieces of metal you know you don't have the strength to bend. Lay one on top of the other and then force a knife into the gap.

I suggest a practical experiment for everyone that believes it is more likely that they are bending 3 inches of steel or granite than it is that the mold release is just doing it's job. I can see that learning from my experience is not going to be possible here so a few trial parts will let you see for yourself.