For some reason you can't provide a link in the first post to a thread, so here it is now...

Here is a link that might be useful: Special types of concrete

Wetting the vermiculite for 24 hours first? I've never done that on purpose. I suppose I'll have to stick a bag outside with the top open on a rainy day. No rain gutter on my studio...I meant to do that.

Does anyone else know this? Anyone who handles my vermiculite concrete dusts off their hands afterwards. I wonder if wetting the vermiculite could reduce this.

Mercedes

I use all bone dry materials, the dryer the better.
But I don't work in construction.
I do concrete art.

I'm making bowls, not bridges, as well. But anything that will lessen the times I've uppacked a stack of bowls to find a broken one sounds good to me. I've had 4 break since Christmas. I'd love to reduce that to zero.

Mercedes

Why do you expect wet materials to be stronger?
I find them less strong.
Getting a good dry mix where the Portland comes in contact with EVERY surface first is much less work then using wet materials.
Mixing dry portland by hand with wet materials requires much longer mixing times and being heavy work I doubt most people do the job thoroughly every time resulting in Portland not coating every surface because of wet material clumping.
Clumping can even occur in a power mixer if you don't add enough water.
I see zero advantages to using wet materials other than to keep the dust down.
No strength advantages at all and my experiments support my view.
But then I don't do construction and never make a mix wet enough that it can be poured.:)

My understanding of the purpose of pre-wetting this particular aggregate is that it is solely to improve it's uniform distribution throughout the mix. Obviously much more of an issue when folding nine yards of concrete at a time for bridge construcion than it is for a bucketful of grots-to-be.

Many "very-lightweight" aggregates exhibit similar resistance to mixing well unless pre-wetted. However, the moisture content of the aggregate must always be taken into account when gauging the total water volume in a given mix. You would never want to add the "normal" volume of water to any mix that contains any damp or pre-wetted ingredients. The same is true even for sand. Masons must routinely accomodate the degree of dampness of their sand by cutting back proportionally on the added water. The same would be true here. I dry all of my sand and store it out of the weather for just that reason...it provides a "known" quantity to help achieve a cosistent mix.

The article mentions foaming agents. Do they work and how do you use them?
How's the markets Runningdog?
Debbie~

Concrete for construction is produced to a recipe, they don't keep adding water and mixing until it is "right". The issue of mixing unusual aggregates is probably mostly in the past, makers of lightweight concrete have some pretty refined air-entraining techniques now, perhaps a little beyond the understanding of the regulatory agencies :)

Possibly the most important difference with construction concretes is that they are poured and pretty much left to their own devices. Rarely do they get cured in water or even sprayed for more than a few hours, probably just covered for a day or two. Such a concrete that included dry vermiculite sucking water away from the cement could be weakened or even crack.

There are two seperate objectives driving the use of air-entraining agents. First, and probably the most common is to provide a measure of freeze/thaw protection. That is what the product was originally designed for. Second, is the "side benefit" of weight reduction which has, in recent years, become an application in it's own right. I use it for both with varying target results and slightly different formulations. Since weight reductions of as much as 15% are now possible, many contractors are doing the same...mixing for specific results.

As for gauging the proper water content of an engineered mix, it is common practice in the US for contractors to use electronic measuring devices to determine the water content of many of their components before calculating the required volume of "added water". This has become an even more important issue in recent years due to the move towards very low water content mixes that have proven to be much superior to the old "wet pour" techniques that were common a generation ago. Superplasticizers for example, allow engineers to achieve much higher flow rates at very low water content levels and have become an everyday tool instead of the "exotic admix" they once were.

Other than autocalved aerated concrete, very few "lightweight" formulations are approved or employed for load bearing structural use at this time. They are most commonly employed in pre-cast decorative and fascia applications where weight is a greater factor than strength. And, as for construction concretes, other than home sidewalks and diveways, most formulations for engineering applications are highly controlled by state & federal regulations that often dictate even the curing processes to be employed. Two reasons you rarely see as much misting and blanketing as you used to on construction sites are; 1). modern formulations are so highly engineered that the mixes themselves contain ingredients that control many of the processes that used to require constant tending after the pour, and...2). the use of evaporation control mediums has become commonplace in flatwork placement, totally eliminating the need for post pour hydration maintenance.

And I absolutely agree that the research & technology leap that the concrete industry has seen over the last decade or so has greatly outpaced regulatory understanding. A good example of this is flyash. While some states have embraced the benefits evidenced by a great deal of scientific study...others absolutely restrict it's use based on the old notion that it was merely a way for contractors to cut the cost of their concrete. And while flyash does indeed produce very significant cost savings over "traditional" concrete...it also yields a vastly superior end product in virtually any application where concrete is employed. Old notions are hard to let go of and beaureaucrats tend to move slowly.

Just to keep you all up to speed with my experimentation (which has been proceeding very slowly due to lack of time)...

Last Saturday I half-filled a bucket with water, then added in fine vermiculite until the bucket was full. The water seeped up through each layer as I added it. Had to do a bit of mixing to damp down the final couple of layers. Covered the bucket. Did a casting on Monday. I mixed the dry ingredients in bulk (1 white cement to two crushed white limestone). Although I'm not great at mental arithemetic, I reckon that to get a 1:2:3 mix (1 cement, 2 sand, 3 vermiculite) I then have to take just one bucket of the cement/sand for every bucket of vermiculite. Hope my figures aren't way out!

Anyhoo, it worked out pretty well. I was casting a couple of small items, so got a cat-litter tray, put in a quantity of vermiculite, equal quantity of pre-mixed cement/sand, and mixed thoroughly with gloved hands. It was very easy to mix, didn't clump, because the vermiculite wasn't really wet, just damp. It didn't start clumping until I added a bit more water. It was quite like mixing a pastry-dough, just a question of breaking up the lumps as you mixed. Then pushed the mixture well into the mould.

I'm stripping the moulds this morning, so will upload photographs this afternoon, and report whether it worked or not.

Well, it turned out OK. I was a bit rough and damaged a lower rim, so had to cut back the other side to match - those areas are pretty obvious in this attached photo.

I'll be more careful in future.

Here is a link that might be useful: {{gwi:66560}}

The other slight problem was a pooling of the release oil. I couldn't see a puddle of oil when casting, but it was obviously there. I'm wondering if I need a release at all, as the top layer of sand remained behind on the mould surface...

Here is a link that might be useful: {{gwi:66561}}

RD --- What kind of mold are you using? That is often the determining factor for selecting the right release. Love the texture, BTW!

The mould is made from silicone (the type you buy in a hardware store, for sealing round baths, windows etc.).

{{gwi:66562}}

HMMMMMMMMM...is a puzzlement. Never used silicone sealant as a mold material myself. I know it's done a lot, but I also know that different rubber compounds require different release agents and I'm afraid I haven't a clue what would be compatible with er..ah...glue. Some of the adverse reactions between different rubber & release agents can be profound, so my recommendation would be to call or Email the folks at Reynolds Advanced Materials. They have releases for every type of mold compound they sell and are very knowledgeable and helpful. I'd hate to see you put something into your mold that might turn it to jelly.

Best of luck...oh, and knowing how beautifully the original was detailed, I'd love to see a casting done in a finer mix. Have you considered it? You can always etch it back to get the "aged" look.

Here is a link that might be useful: Mold Material & Release Info Source

Hi running_dog,

the planter(?) in the picture that you've linked to looks marvellous.

I'm trying to imagine (no casting experience) how you would do such a piece. Would this need to be a mold made of two pieces, a front and a back? I'm also curious about the layer of sand that you mention; part of the casting process, or just the mix?

Any rate, looks great,

Sean

I made a one-piece mould, but reinforced it at the back and slit it with a sharp knife right up as far as the rim. So I can pull it open, then prise it off. Bit of a tug-of-war, but it comes off OK. The detail actually came out much better than I expected - it's only that the speckles don't show up the detail.

I made a damp but not wet mix, took handfuls and squeezed them onto the surface - did the face first, then packed up at the back and worked my way all around. It was pretty easy.

As regards the sand - normally when a concrete cast comes out of the mould, the mould is left clean. This time the whole inside of the mould has a fine layer of sand left all over it, which must have come off the surface of the cast. The cast is quite delicate, I'll have to wait to see how it cures.

Now remembering why I gave up casting concrete ornaments the last time :o(

tango - one of the reasons I like the dry-ramming method is that I don't have to acid-dip. I'm working in my sister's conservatory, have to traipse into her kitchen for all water, don't think she'd appreciate a dustbin full of acid in her back garden!

Ah-hah. Thanks; it sounds like something I might want to avoid for the moment, as a beginner, but the result is great,

cheers,

Sean

tango - I think now that the reason the layer of sand was left inside the mould was simply that the mix was so dry. As I mentioned in another thread, I've started to make the mixes wetter. Haven't released one of the 'wetter' casts yet (tomorrow is D-Day) but I'm expecting the cast to be a bit stronger, and not to have sand flaking off as happened with the dry mix. Will post photos... :o)

We.e.e.l.l.ll, I'm having great success with the wet-casting method. I keep forgetting to take photographs - I'm working in my sister's conservatory, so I'm being so careful to clean up after myself, not leave stuff lying around, that everything gets packed away in plastic bags, and I'm in my car driving home before I remember the pics.

The first few days I had quite a few failures, all to do with releasing too soon from the moulds. Here's a typical example - the cast came out perfect, but with a chip in a noticeable spot.

{{gwi:66563}}

I don't know why I never used this method before! It's SO much easier than lifting heavy moulds up on to a vibrating table, and having to acid-dip everything to get rid of the surface bloom.

So many advantages
1. Only half the weight to transport
2. Don't need a vibrating table
3. Don't need to bolt the mould casing - that's very time-consuming - I just tie the two halves of the casing together with bandages now (a tip read on this forum :o) )
4. Seam marks or imperfections can be scraped away easily.
5. A light brush with water gets rid of the surface bloom.

Disadvantages

1. Not as strong as the casts made with crushed granite aggregate
2. Using a 1 cement/3 granite mix, a mould could be used once a day, if not twice. This vermiculite mix is much weaker and needs to stay in the mould for 4 days. So more moulds are needed than with a cement/granite mix.

All in all, I'm very pleased with the results I've been getting by using the pre-wetted vermiculite. I'm using the fine mix, and it's really 'damp' rather than 'wet'. The sand and cement are mixed together first (by hand), then I mix small quantities with the vermiculite as I pack the moulds. The quantities I mix at a time are so small that even a small mould (like the item in the photograph) takes about three mixes. That way, I know that the ingredients have been mixed really thoroughly.

If you wet the vermiculite overnight, the next day you can tip the bucket over on its side and allow any excess water to drain out. That leaves the vermiculite just damp, and easy to mix with the sand/cement. The (fine) vermiculite is still light and fluffy and 'separate', it isn't stuck together in clumps. I've had no problems with clumping.

I will definitely take some photographs today!

RD ---Great looking work as always! I'm glad to see that you've been able to record the detail that makes that wonderful face so endearing. And it sounds like you have the pre-wetting process for the vermiculite down to a tee. Not "wet"...just damp. All you need now are a few more molds because I don't believe there will be any shortage of buyers. I rarely buy "art for my garden"...but if this were available in the US, I would have to have one. Consider presenting your (copyrighted) design to someone like Smith & Hawkens. They are a purveyor of high-end, high quality garden wares and, to my mind, would be fools to pass up a chance to have something this wonderful in their stable of goods.

Wish you all the best & much success.

lol - I'm blushing ;) I don't think that what I make will ever be big sellers, though. Plus too pernickety to make for a commercial outfit.

I'm starting to think that a buff/beige sand might look better with the vermiculite than the white sand - once I scrub off the surface fines the vermiculite is making the surface look a bit spotty.

I'll post a few photos. Plant-containers first...

Here's a nun

{{gwi:66564}}

{{gwi:66565}}

This is quite large, about 2 ft long

{{gwi:66566}}

This is for holding a candle. I made it originally for planting ferns in, but it looks better with a candle.

{{gwi:66567}}

{{gwi:66568}}

I based this on a photograph I saw in a magazine of an antique stone Indian niche. I've cast a mirror (acrylic) into the back, to reflect light. The mirror was damaged by the damp, but I really like how it looks so next time round I'll seal the back of the mirror using plastic sheeting and silicone.

For this cast, and the 'ugly man' above, I used cheap grey sand just to see how the finish compared to white sand. I quite like it, it looks very stone-like.

{{gwi:66569}}

{{gwi:66570}}

No need to blush OR be modest. Every bit of your work that I have seen is vastly superior to most of the commercial junk that's out there. Any of these could be very meticulously replicated with standard quality urethane production molds for scaled up production. You might consider simply "licensing" your originals for reproduction in multiple markets including the US. I think they would be very consistent sellers. In fact, I work with a mold making/casting operator here in Texas who might be interested if you would consider it. I see a lot of this type work, and yours is quite special. Think about it.

"I'm starting to think that a buff/beige sand might look better with the vermiculite than the white sand"

Have you seen pool filter sand?
It's beige, orange, and brown and about 5 times as course as regular sand. It makes astounding finishes.

Thank-you for the pics running dog.
Your work is wonderful!!!
I remember the stone niche pic you posted I've been hoping to do one ever since.
I hope your markets are going well.
Debbie

Debbie - I'm not doing the market at all, for several reasons. First, the market that I wanted to use is run by my local council, and you need Public Liability insurance. That was going to cost Â250 for the year. The pitch rental was Â40 for one day. Then I'd have to buy a stand of some description. Then...the stuff would have to be shifted twice - once laying out the stand, then again taking away anything that didn't sell. I have only eight moulds, cast into them twice a week, so once I looked into the idea, it became apparent that it wouldn't be worth my while - I'd be working to pay for the stall and insurance.

I have a friend who has a concrete yard, with a very nice display area, he'll do a small display stand for them. Then I can cast at my own pace.

tango - licensing is always difficult, because you've no way of knowing how many moulds have been made, or how many casts are being sold. Also, if I was making things for commercial production now I'd design them very differently - certain items, like the nun and the ugly man, would be just about impossible to do commercially. Also, when I made these originally I was thinking in terms of how they looked as I made them, not in terms of 'how will they look when people put plants into them?'

I'll e-mail you...

david - thanks for that tip. I'll have a search here and see if I can find a supplier.

Runningdog, They are just beautiful. I especially like the reclining, long haired woman. Billie

RD I probably sent you on a wild goose chase. I suspect silica filter sand is whatever color found in your area.
But check it out anyway. For your kind of work the very course
sand would be great. The size is very uniform in filter sands so ask to see the different sizes. The stuff I use is very rounded and uniform and approx 2mm in size.
It is wonderfully tactile. If you use a sealer it gives the piece a wonderful bumpy smooth shark skin feel.
My customers have remarked several times on how wonderful it feels. Nothing like concrete at all.

And if you are looking for something really interesting try oyster shell that is fed to chickens.
Amazing rough smooth rock like texture that looks terrific in the sunlight..
Cheap as well, but it must be washed and dried before using. The fine dust really effects strength.

david - are you using a lightweight aggregate as well, with the filter sand? And are you scrubbing back after releasing from the mould?

Re. the oyster shell, does washing succeed in getting rid of all the salt? And, again, are you using it combined with a lightweight aggregate?

Hi RD
Yep I use cryogenic perlite or fine vermiculite in most of my work. Cryogenic perlite is like using weightless fine white sand. I love the stuff.

I scrub back all my work to expose the aggregate either with wire brush, brass brush or a small sand blaster. After it cures I brush it again with vinegar to remove the cement film off the surface of the aggregate to get the most from the natural color.

There seems to be no salt in this oyster shell. I tested by filling a bucket with the stuff and water. There was no salty taste even after a week.
The pieces of shell are roughly 1/4 inch in size so you get a very rough/smooth surface. very nice.

Must see if I can source that in Ireland. Probably won't be able to :(

Best of luck with your sales at the concrete yard!!!
Debbie

RunningDog, I love the clean lines of your sculptures. I guess these are cast from a mold of original sculptures you have done. What are the original sculptures made of?

Jean

Jean - the originals I modelled in clay. At that time I was making urethane moulds, so had to then make plaster of paris masters - urethane won't cure on anything damp.

One more note about clay models and urethane molds. Anytime you plan on making a urethane rubber mold...you MUST use a totally sulpher-free clay. Otherwise there will be a chemical reaction by the urethane to the sulpher that will prevent it from ever setting properly. Instead of a mold...you wind up with a master covered with goo. Not fun.

Hi everyone,

I am a artificial rock contractor (pool and spa) and an expert with specialty concrete mixes - specifically vermiculite which is also commonly known as "pool base". I have read through this thread and there are a few things I wanted to offer some clarity for:

1) The reason that you should pre-water the vermiculite is becasue vermiculite is incredibly absorbant. If you do not pre-water it will leech water from your concrete depriving it of moisture and likely leading to hairline cracking and crazing if the surface layers. The mix itself can still be "dry" as someone eluded above that concrete that is too wet becomes weak. This is extremely true. Pre-watered vermiculite is much easier to proportion and regulate the water in the mix.

2) Soap in concrete mixes is an "air entrainer" as discussed in a post above however soap has long since been used as an ingredient in vermiculite concrete mixes for different reasons. Vemiculite concrete is very sticky and can be difficult to trowel. Adding a tiny bit of soap, like dish soap, makes the concrete smoother and less inclined to cling to the tools.

3) It was posted above that concrete for construction does not get adjusted for water content. This is not true. Concrete is and can be adjusted on the fly in almost every mixing condition to account for changing conditions, heat, direct sunlight, concrete consistency, slump etc. There is a point past which you should not hydrate the mix but before that it is no problem at all to adjust slump. Every single mix through a mixer gets individually watered. Ready mix concrete will ask you if you are happy with the slump of the mix when they arrive to your site and will wet it up if you want them to.

4) Use water reducer to achieve desired placement slump without compromising the strength of the concrete. A tiny bit too much water equals a substantial loss of finished strength.

5) The best release agent for silicone is wax based release agents. In most cases if you are not sure what to use you should use wax based.

I hope this info helps some of you out. If you want more information on lightweight concrete mixes check out the link below

Here is a link that might be useful: Lightweight Concrete Mixes

First - thanks for the great information,

Some of the people that post now to this forum make hypertufa containers. So my question regards making Hypertufa -
My questions - Use of Liquid Acrylic in lightweight mix or Hypertufa, Will it add strenght to small projects like garden troughs, and Acrylic is different than Bonding Agent and if you are looking for strength - use L Acrylic?

thanks

Liquid Acrylic
Acrylic is a retarder, meaning that it slows the initial set time of concrete. This is the opposite effect of calcium flakes. This would be used for applications where you need additional time to place, work and finish the concrete before it sets up. Additionally liquid acrylic will change slightly the working feel of the concrete giving it a smoother and stickier overall consistancy. Acrylic also helps to increase the finished strength of concrete and is a common ingredient in specialty and engineered concrete mixes.

Liquid acrylic concrete admixture is not to be confused with concrete bonding agent. Liquid acrylic is viscous similar to milk where concrete bonding agent is very similar in texture and smell to white wood glue. Acrylic is not a good choice for bonding concrete.

If I were making hypertufa I would probably use some liquid acrylic in the mix. You would see a noticable change for the better in the consistency of the mix and an increase in strength that could be described as negligible. If you want to make the mix stronger then you need to look at your aggregates, your ratios and your admixtures. Liquid acrylic is an admixture that improves the strength property but does minimal impact on the finished product when used alone. When combined with an advanced aggregate blend that has been engieered and tested and a proven water content and cement ratio (and likely some glass fibers also) you will realize the full benefits of liquid acrylic.

If you want to increase the strength of the mix I would use the bonding agent (thick liquid glue) instead of liquid acrylic. Be careful as the bonding agent will speed up your initial set time. Pre-mix it in the water for your mix for even distrobution.

If you need more information on admixtures and their effects on concrete mixes there is some good info at the link below

Here is a link that might be useful: Concrete Additives

Aloha again, CC,
I meant to ask about fibers - from what I've read, the alkali-resistant PVA fibers seem to have several advantages. Since I want to reduce weight in very large containers and troughs, would it be reasonable to leave out the "basket" of concrete reinforcing wire and rebar hoops embedded in the planter? Many mahalos for your reply!

WHat is very large? Can you provide a photo?
Small hypertufa containers, I use no reinforcment wires nor fibers. If the container is - say 24 " round and larger , I may use fibers. I have rarely used wires to reinforce, but my largest trough was about 3ft x 2 ft. Would like to here is others or doing it different.

Aloha!

Mike