I often get asked by many hypertufa and concrete garden art enthusiasts where to find “silica fume” and “poly fibers”, also referred to as “fiber mesh”. Depending where you live, it may or may not be very easy to lay your hands on this stuff.

PLEASE NOTE! Silica fume is sometimes confused with fumed silica (also known as colloidal silica and pyrogenic silica). These materials have different derivations, technical characteristics, and applications. Silica fume is very fine like beach sand and completely black.

Silica fume and poly fibers are used as strengtheners, normally referred to as fortifying agents. They help make your cured hypertufa or concrete object stronger. Often, you’ll want to use one or the other for items such as stepping stones or very thin spheres. I do have some recipes sitting on my website that I’ll refer you to, in case you aren’t familiar with recipes and/or projects that utilize silica fume or poly fibers. Here are three of them:

Hypertufa Recipe Using Fiber Mesh (Poly fibers)  (refer to last recipe on the page)
Hypertufa Sculpture Recipe
Concrete Recipe For Very Thin-walled Spheres

How to Locate Silica Fume and/or Poly Fibers

My first suggestion is to call commercial concrete supply companies in your area. Many times they will have either fortifier, and will be willing to sell you a couple of pounds. (You don’t need much of either one in a recipe – unless I guess you’re making something collosal in size! ).

I’ve even read of people walking away with some for free, after explaining to the sales people what they will be doing with the silica fume or poly fibers. Seems the sales people get a kick hearing that Portland cement is going to be mixed with peat moss and water to make an odd concoction called hypertufa!

My next suggestion is to do what else … that’s right, find suppliers who sell via their online store. In doing a Google search today, I found EpoxyUSA.com carries poly fibers for a very reasonable price on the Fillers-Thickeners webpage. Note – I have no affiliation nor experience ordering from them. Perhaps you should contact them first to check shipping charges, etc. before you order. But I’ll wager a guess they are legitimate and probably fine to deal with.

Finding silica fume online seems to be more of a daunting task. I did find this link to the SilicaFume.org webpage. If nothing else, call them and see where you can purchase a small quantity online.

So, there you have it. I hope I’ve helped you locate two ingredients that do help make a difference in strengthening concrete and hypertufa recipes.

I received this email from Trisha asking me:

I have encountered a problem on my patio. After much research your website was the only one that made it clear there was a difference between concrete and cement.

We have a slab in our back yard (like a river rock slab), we wanted to skim it over with a smooth layer. We did so with what the hardware store told us to do it with, which was Portland cement. But it came out with lots of cracks and you can scratch your fingernail in it.

Is it because we used cement and not concrete?

My reply:

Hi Trisha:
First, thank you for telling me how you found my website. Glad my concrete-vs-cement page helped you.

Next … the easiest way to explain cement vs. concrete: cement is the dry, powdery product; once it is mixed with water and aggregate, it is called “concrete”. So no, your problem wasn’t in the terminology … your problem was a very ill-informed salesperson.

What a shame! You were given horribly wrong information!!! Even I know that you can’t put pure Portland cement onto a concrete (or rock) slab! And I’m no concrete expert by any means.

**First … I seriously suggest that you go back and confront the store manager about what happened because you’re not going to like my answer, meaning this isn’t going to be an easy “fix”, nor cheap. (Unless you clean off the crumbling Portland and forget about doing anything further.)

Let me tell you that the husband of a very close friend of mine was a professional concrete finisher and I picked his brain for you … and in a nutshell, here are some guidelines I can offer you:

1. Portland cement CANNOT be used all by itself in this situation! it needs some kind of aggregate added to it … so this was mistake #1;
2. You cannot just put a “skim coat” onto the slab … you need at the minimum a 2″ thick “layer” of concrete … so here was mistake #2;
3. The slab must be prepped with a “bonding agent” … this allows the new concrete to adhere to the slab … mistake #3;
4. There very well might be the need for the bonding agent to also be mixed into the new concrete;
5. The slab might possibly need to be wet down, before the bonding agent is applied;
6. You should use a 5-sack mix (called 5000 lb concrete);
7. The new concrete needs to be kept moist for 28-days – it will reach about 90% of it’s full cure (hardness) in that time frame – spray it down with your hose every day & night to dampen – this will help it to not crack and cure properly;
8. And then seal with a good quality concrete sealer after the 28 days.

And before any new concrete can be laid, you are going to have to THOROUGHLY clean/scrape off all the flaking Portland cement.

PLEASE NOTE: There could be other things to take into consideration before attempting this concrete project. I DO NOT know the particulars. There are many variables when it comes to concrete and the specific project.

***Bottom line … I suggest you call a reputable professional concrete company to add the smooth “layer” for you. Forms have to be built along the outside edges to hold in the concrete; expansion joints may need to be added into the wet concrete; depending on the size of the slab, interior wire “mesh” might need to be laid to help it not crack; the top must be finished off correctly to make it smooth, etc.

Does this overview of things-to-do help you? I hate to hear of problems like this. If nothing else, you deserve all your money back for whatever supplies and such that you bought for this project!

~~~

Trisha wrote back:

Thank you very much Claudia. Your info is extremely helpful!

We must be on the right track because yesterday we bought that same 5000 concrete mix and blended it with the Portland cement. It made a smooth finish like we wanted. It does not have the best appearance but it bonded and it is concrete. HA!

It is just a small 16 x 20 fenced in back patio, so anything done to the slab is better than what it looked like before.

Again thank you for all your info.

I received an email from Sue, who wanted to share with me this rather interesting bit of info:

You are my hero! I’ve been after the instructions on duplicating Little & Lewis spheres for a year!

I did some on my own and they exploded on my driveway (cold ball from house, 90 degree day= mess.) I just had to tell you about this recent disaster – maybe others can learn from this.

Sue

My reply:

Hi Sue:
Well, gee  Thank you for the compliment. That was very kind of you to take the time to say thanks!

Ummm … the only thing I am confused about is that you say you’ve been “after instructions” for a year to make hollow concrete spheres?? Did you search on the internet?? Because my hollow sphere articles have been available much longer than that. Maybe you mean you were thinking about it, because you just sent me into a panic that my Google rankings had dropped. But no, they are still at the very top! My rankings are:

how to make hollow concrete spheres — #1 and #2
how to make hollow concrete spheres — #1 and #2
how to make hypertufa hollow spheres — #1 and #2
concrete hollow spheres — #1 and #2
concrete spheres — #1
hypertufa spheres — #1 and #2

So you see, my instructional hollow sphere how-to pages are sitting up there at #1, waiting to be easily found.

Anyway … please know my information and how-tos should point you in the proper direction. And I am glad you found my site.

Wow, exploding concrete spheres!!  Now that’s a new one on me! If you had the video of the actual explosion, I’d be begging you to let me put it on my website so we could all learn from it, and maybe get a laugh, too?? (I’m not laughing at your mishap … just the mental vision of the sphere blowing up! ha ha)

But this incident goes to prove that temperatures CAN have a huge influence on the outcome of projects that use inflatable forms and Portland cement – both in the curing and otherwise, as your explosion proved! And this also proves that when making a hollow sphere the temperature of the air INSIDE the inflatable ball needs to be the same as the temperature in the area where you’ll be curing it.

Thanks again for sharing your concrete hollow sphere escapade!

I received an email from Debbie asking me:

In the instructions given for the Hypertufa Hollow Garden Sphere, one of the materials needed was a deflatable ball.

Can you advise me where I would get such a ball? What size does it come in and what type material is it made of? (Guess you can see I don’t have any young kids at home nor any grandchildren. )

Thanks for your help. Oh by the way, I love the project info you send. My neighbor and I have tried a lot of the projects you have sent to me in your great little Newsletter. Debbie

My reply:

Hi Debbie:
I’ll be happy to explain this for you. You can use a plastic blow-up (inflatable) beach ball like the kind you’d toss back and forth to each other while frolicking on the beach which you can buy at most drug stores, Wal-Mart, etc. Just depends upon the climate zone where you live as to whether you’ll be able to find them year-round. Stores don’t usually stock them during frigid winter months. Or of course I am sure you’ll find them on the internet. And they’re pretty cheap.

The main thing, though about using these balls for a hollow sphere mold (form) is that they can deflate S..L..O..W..L..Y and without it being noticeable in the beginning. Most normally this is due to a pin-sized hole that allows the air to escape. I know in my case, as a kid, sometimes I’d find that my new beach ball was pretty much totally deflated within about a day. This was probably caused by a tiny pinhole leak.

Now … add the weight of a heavy, wet ‘tufa or concrete recipe pressing down on the ball. The weight helps to accelerate the air escaping. Some crafters have reported that when they came back the next day to inspect their sphere to see how it was curing – yikes! They found a pretty sad looking deflated and slumped down sphere.

Now … perhaps this “disaster” might prove to be an interesting sculptural form that once cured can be painted and utilized in some other fashion, but let’s just say most folks end up having to trash the project. So … “cheap” beach balls are quite OK most of the time and hold air without causing a project failure … but just be aware of the potential deflation problem.

Or you can get one of the big heavy-rubber inflatable types that people use to exercise with. These can be found at Wal-Mart or Target in the exercise depts. (as examples) and just the other day I saw some at T.J. Maxx for sale. This size ball would of course be used if you want to make a really big garden sphere. But deflation problems from small leaks most likely won’t be an issue for you.

Now, there are other smaller, sturdier type balls you could use, but you asked about inflatable/deflatable, so I am mentioning the most often used balls. You want something with a stem you can blow into or can hook-up an air supply to for automatic inflation. And the stem allows you to deflate the ball easily after your sphere has cured enough.

Good luck with your hollow sphere project!

I received an email from “Stoner” asking me:

I have been using a regular pre bagged “sand mix” cement for my concrete leaves. Is there a benefit to using something that I mix together myself ? Thanks. Stoner

My reply:

Hi Stoner:

Well, not necessarily. I mean, if you are very successful with and happy with the results of using the premix … “if it ain’t broke, don’t fix it!”  But of course, mixing your own ‘tufa or concrete recipe(s) allows you to tweak it, so that the recipe accomplishes what you want it to “do”.

Such as – maybe you want a really thin, yet very strong leaf casting. In this case, you might want to use an even finer sand than what comes in your premix, etc.

And then of course, you might want to add reinforcing fibers or a bonding agent, but of course that could be added into your premix.

I guess the point is, “it all depends” upon your desired outcome.

And perhaps mixing up your own might be a cost savings … don’t know what you’re paying for premix versus non-premix.

Good luck with all your projects!