Some Q's about cement-additives for DIY pots (plasticizers & structural reinforcements)

[SU2]

I've been trying to build an inventory of pots for a massive spring re-potting session, and while I've made a good amount of small ones I'm starting bigger containers and have some Q's..

Firstly, I'm not quite sure where the line is for needs/doesn't need reinforcement - I just use cement/sand (1/2.5 ratio) in my forms for small pots, but I've got a 16" wide circular pan form that I'm about to make - is that too-large (16" wide, 4.5" deep) to be made w/o internal structuring?

Secondly, additives/strengtheners/plasticizers: I've heard about these a lot and want to get into them, using acrylic additive liquid instead of water to increase strength and things like that (chemical, not mechanical like fiberglass-shard additive*), however I don't know what is/isn't 'bonsai safe' so any&all additives that you guys can tell me, like specific products/models, would be hugely appreciated so I know what I'm getting is safe!

[* where can I get those baggies of fiberglass strands? Home Depot hasn't had them and that's the only place I could think of, I'd realllly like to be using those in all of my mixes but just can't find the stuff, any reco's for where, whether online or just types of places IRL I should seek, would be greatly appreciated!!]

Happy '18 to you all and thanks for any insight on this!!

 

[Lionheart]

I bought shredded fibers on Amazon.

 

[Lionheart]

I've recently bought some plasticizer (also from Amazon), used it once thus far. It did seem to give the usually un-plastic cement a little bit more workability. I'm going to use a little bit higher percentage next time and see if it helps.

The term we used to use in ceramics for clay that would not hold together was "short". Concrete/cement seems to be inherently short. The same term applies to dough for bakers.

 

[Lionheart]

I've also been using liquid Acrylic admix in addition to water (not instead of), to impart more strength to my mix. I bought that off the shelf at Home Depot.

My mix by volume is basically:
1.5 Sand
1.5 Fine gravel (aggregate)
1 Portland cement

Then use water and acrylic admix at approximately 5:1 ratio, and some acrylic fibers. The amount of fiber is hard to quantify. I think the cement doesn't care how much fiber is mixed into it. It's going to cure anyway with either none or a ton. But to approximate what I do, I'd suggest about 1/4 cup for 2 gallons of mix. If you don't know already, mix all your dry ingredients first.

Additionally, I use liquid colorants. These are made by Quikrete. I've seen these at Home Depot a few times and not at other times. So, I bought mine again at Amazon.

 

[SU2]

I bought shredded fibers on Amazon.

jesus a pound!? You'll never run out!! I used to get it in little baggies lol

I've recently bought some plasticizer (also from Amazon), used it once thus far. It did seem to give the usually un-plastic cement a little bit more workability. I'm going to use a little bit higher percentage next time and see if it helps.

The term we used to use in ceramics for clay that would not hold together was "short". Concrete/cement seems to be inherently short. The same term applies to dough for bakers.

Would love if you could elaborate a bit more on your description of how the plasticizer-enhanced mud felt, what you wrote sounds like a *very* desirable property!!!

Re 'short', I'm taking that to mean 'insufficiently wet', is that what you mean? That's the only way I can read it but you then say that it's inherent to cement which confuses me...when I make mortar for this I can make it very close to optimal by eyeing it, but then I use a spoon and start adding tiny amounts of cement or water (depending which direction it needs to go!) until it's just right, there's a certain viscosity that's just ideal (I want to say 'slump test' is how it'd be phrased by the industry, googling that would expand on what I'm getting at here), and when you've got that dialed-in the end results are just so much better because if your mix isn't wet enough it won't be strong / will be crumbly, and if it's too-wet then - aside from being a PITA to get to take-form - then you'll have both shrinkage of the product as well as a lower overall strength in the finished/cured product....so perfect mixing is critical, and it really can seem like a razor's-edge where 1/2tsp of water or cement would tip it out-of-balance, but it's not inherently 'short' it's just there's a crazy-small range that's optimal!

 

[Lionheart]

Yes, I bought a pound, mainly because it didn't seem like too much. But it probably is/was.

I think you're right regarding water. To me "short" just means a little too crumbly to hold together, and the remedy is more water. As you said, added cautiously.