Hello RD --- As I understand, you are casting hypertufa into molds? While my experience is limited to concrete mixtures, here are a couple of techniques/products I am familiar with that might be of value.

First, the problem with lime is generally much overrated and latex admixtures made specifically for concrete do indeed inhibit leaching as well as effloescence (No data available on the use of latex paint, though). And if you seal the interiors as well as the exteriors, leaching is a non-issue. The best sealers are the solvent-based, penetrating sealers made for concrete. These are available in either gloss or a "natural" that does not affect the color at all and is virtually invisible. And, unlike water-based sealers, which sit on the surface like paint, they do not wear away requiring constant reapplications to keep water and stains out.

Finally, if you are looking to "antique" your work, there is a much better product than woodstain. It is called "antiquing mold release". It is formulated for use with stamped concrete texturing molds used to simulate brick & stone patterns on walks, floors and driveways. I have also seen it used to achieve the same effect with closed molds. It is available as either a dry, sprinkle on product or a liquid and I have seen casters use both. They come in a fairly good selection of colors as well and are excellent for highlighting details.

And if you want enhance colors a bit or get a low-luster sheen, a final light top-coat of beeswax can be applied and buffed for a very pleasant look. And the wax adds another level of water-proofing as well. I finish of my Faux Bois tables with food-grade beeswax for both the look and the added protection. It is also very simple for owners to maintain.

Best of luck. If your "small" work is anything like the large-scale I've seen here, you should be a tremendous success. Very nice work my friend and do keep us informed.

Hi RD:

I agree with Tango and think that the lime problem with plants is a little over-rated, but I've read you can neutralize the pots with white vinegar, or with 1/2 oz of Potassium Permanganate to 3 gallons of water. Also, wouldn't a water bath for a couple of days go a long toward in leaching out?

Just curiious: If you're selling your hypertufa projects as planters, why do you want to seal them? One of the good points of hypertufa is that it's somewhat pourous so that the water drains out and some moisture/water is absorbed into the planter walls with watering, rain, etc. (also helps those people who overwater from drowning their plants :) I also have holes in the bottom (usually just bore them in with a drill hammer after the pots have cured -- seems to make customers feel more warm and cuddly (also prevents the aforementioned drowning...).

Just some thoughts.

I have used latex paint diluted with water on the outside of some pots -- sometimes green, sometimes white, whatever your taste. It gives that antiquey look; cananot vouch for the years it will last, but have had some pots out for a couple of years and they still look good -- old and worn. I figure if it's okay for the outside of my house for 10 years or so, it's okay for my pots!! This may eventually completely wear off. Maybe someone out there has a better idea of longevity on this.

Hi RD, From what I understand also any sealer will prevent moss or lichen growing on the cement. If that's not a problem then I've seen this sealer work very well. I did not buy it myself or apply but saw the 2nd year results and it was still doing a great job of sealing on a heavily used surface. So I think it'd work well long term for any pot you make.

It reacts with the lime in concrete so this would solve the one concern of yours about that. I don't know if it or similar product is available to you where you live but it's an interesting read.

Here is a link that might be useful: Concrete sealer

Thanks for the suggestions - I'll probably go with a bit from each post :o) - use watered-down latex paint to antique, then use a sealer on top.

I'm not making hypertufa with peatmoss. Just using vermiculite in the mix so that I can get a very closed smooth surface.

Here's a very bad photo that I know I've posted before, it will give an idea of why I want to antique and seal it. This version is slip-cast terracotta, I've also made it in full (heavy) concrete (crushed granite and white cement, acid etched), but this time round I'm using 1:1:2 cement, white crushed granite and vermiculite.

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That is one great face! Is that also a planter, or just a beautiful decorative piece. Must be fairly heavy made with the cement, granite and vermiculite.

I've made some things with vermiculite and no peat moss with the History Stones planter mold, and they don't appear to be porous, and like you said, are closer grained. Also, seems easier to get the ledges of the mold stronger than with the peat moss mix, but have finally figured it out (patience :). I use the metal effects paint on the vermiculite one, and plan on leaving the "peat moss" ones alone and let them weather. Can never tell what people want -- I'll bring my paints to the markets with me just in case!!

When someone says "hypertufa" I just assume they mean using peat moss, and want the finish to be rough and erode away over time.

Not that this has anything to do with the subject, but does anyone go to the antique fairs at Brimfield, MA in the spring, summer and fall?

Beautiful work! Excellent scuplting! Have you ever tried a fine crushed limestone/white portland mix? It acid etches very nicely for an "antique" look. Another trick is to apply some baking soda to the inside of a damp mold. After pouring & setting, the baking soda washes away clenly (with no reaction from the cement) and leaves a slightly "pock-marked", faux ancient artifact surface. Also makes each piece unique, as no two ever turn out quite the same. BTW...what size is that piece?

That baking soda tip is great! I'll try that.
I used to acid etch the granite/white cement mix, but I'm sick of dipping heavy lumps of concrete into dustbins full of acid :o( Baking soda sounds like it would be a lot easier.

That face isn't very large - maybe 6 inches all round. It's smaller than the original, because the terracotta shrinks at least 10% when it's fired. Can't find the original mould, so had to take a mould from this terracotta piece. And yeah, it's basically a pot. When I cast, I put a cork in the bottom, not quite pushed all the way through. Then people can plant straight into it, or knock through a drainage hole.

I've been looking at crushed white limestone. It's very expensive - Â7 a bag, almost the same cost as the white cement. But I won't be able to resist experimenting lol.

When you paint on the baking soda, have you already oiled the mould?

We've been using a "self-lubricating" urethane for most of our molds that don't require a release, however a little spray-on release or water does help hold the baking soda in place while pouring.

Depending on how heavy-handed one gets with the soda clumps, the effect can be made to resemble anything from light weathering to heavily worn and deeply pitted surfaces. My casting partner often pours out a small pile, then mists it lightly with water. Once damp, he hurls fairly large amounts into his big architectural facade molds where it sticks for a very deeply pitted effect. It's a bit much for me, but he sells huge quantities to architects who love it.

The face really is very finely executed. Do you ever work in any Celtic design motiffs?

Not really. The nearest to Celtic that I've done is a set of three stepping stones based on prehistoric carved stones in County Meath (see one of the masters at link) for a friend who manufactures paving.

Here is a link that might be useful:

Very Nice Petroglyph. Looks like the spiral patterns in the burial mounds. What media did you work the original in?

That's plaster of paris (I buy it as 'fine casting plaster' in builders' suppliers' yard). I love carving POP when it's very fresh (24 hours old or so) and before it dries out completely. It's like butter then :) I made a few test-moulds in urethane, now the master is going to a tool-maker/mould-maker to have an aluminium version cast, then vacuum-formed moulds will be taken from that.

Getting back to casting plant containers...a disadvantage to 2- or 3-part moulds is that water seeps out through the seams when you vibrate the mould, taking the fines with it. So that would destroy the effect of the baking soda. However, this time round I'm going to seal the seams with silicone - lubricate the moulds as normal, then run a line of silicone all around the seams, assemble the mould, and tape the rubber parts together before putting them into the casing mould. As long as the seams are oiled the silicone will just lift off afterwards.

We've never had any problems losing the bakaing soda from multi-part molds, but most of our mixes are either GFRC (glass fiber reinforced concrete) or a "stone" mix like the limestone. The baking soda seems to stay put in spite of vibrating. We use both vibrating tables and old fashioned mallets (to whack them with). And getting clean seams is always an issue. It mostly comes down to how well the mold parts all fit.

Keep us informed as you progress.