Wednesday, May 5, 2021

Common Reasons that Hypertufa Cracks

Why Hypertufa Projects Crack

This article presumes that you are familiar with the basics of making projects with hypertufa.  If you aren’t familiar with the process, or just need a refresher, you may want to first go to our Hypertufa 101 article by clicking here.

Hypertufa projects are made by combining various aggregates (such as Peat Moss, Vermiculite and Perlite) and binding them together with Portland Cement.  The mix can be molded into nearly any shape or size.  

The number of projects you can create is only limited by your imagination.   And best of all, hypertufa projects can last for years and be left outside for the winter.


Long Does Hypertufa Last?


A project created with the common recipe of 1 part Peat Moss, 1 part Vermiculite or Perlite and 1 part Portand Cement will normally last ten years.  Adding a strengthener like sand or synthetic concrete re-enforcing fibers can extend that shelf life to 20 years.

Here are the most common reasons why hypertufa cracks.


Hypertufa Cracks during DeMolding

Anyone who has made a number of hypertufa projects has run into de-molding problems.  

The de-molding process must be done slowly and carefully.  How long a project will take to cure to the point where it’s safe to remove the mold depends on a number of factors including the humidity and temperature of the area where it’s curing and the size of the project.

To prevent a demolding problem, many people like to grease the mold with Vaseline, cooking spray like PAM, vegetable oil, mineral oil or even WD40.

Once you find the mold and project stuck together, though, here are a few tricks you can use to help de-mold that challenging project.

  • Put ice cubes in a plastic mold to shrink it a bit and then slide out the project.  Some people have put a smaller project in the refrigerator for a time to get the same result.

  • Release any suction that’s built up between the mold and the project by drilling a hole in the bottom of the mold.  If it’s a planter, you will need drainage anyway.

  Hypertufa Cracks When It’s Moved

Hypertufa projects need to cure to a certain stage before being handled or moved.  The best practice is to leave a finished project where it was built for at least a few weeks.  

If you know you will need to move the project soon after building, build the project on a sturdy piece of plywood to make the move easier.

 Hypertufa Breaks off in Large Chunks

 Recipe/Mix Problems

 1.     Not enough Portland Cement

Since the Portland Cement is the binder, I never use less than a third of it in a mix recipe.  Not using enough Portland Cement weakens the entire project.

 2.     Not Dry Mixing

Thoroughly mixing all the dry ingredients together to the point where you cannot distinguish one from the other before adding any water is very important. 

Why?  You will be assured that there is no weak area where there is no Portland Cement.

Too much Perlite in one area will cause a weak spot.  Globs of peat moss will rot away and eventually cause holes.  Peat Moss should be sieved to remove any lumps or sticks that may stick together. 

If you substituted organic material for peat moss, like bark, pine needles, dried grass clippings or leaves, if these materials were clumped together, it will form a weak spot.

The Portland Cement must be mixed in well with all the other additives.

3.  A watery mix

Too much water in the mix, even though the mix may cling onto your project while you’re building, is a recipe for disaster.  

You want a mix that, when fisted and released, stays together like a nice hardy meatball.  See the photo above.  It should never be watery enough that the mix pours like a liquid.  

If your fisted “tufa meatball” leaks water, it’s not the right consistency.  Add more dry mix and fist again until the meatball holds together but doesn’t leak any more than a few drops of water.


The Main Body Cracks into Pieces 

Lack of extra strength.

Projects like stepping stones that will take some abuse need to be stronger than other projects. Larger projects, like large planters or troughs, will also need some added strength.

Here are some ways to strengthen a project.

My go-to s extra-strength recipe is 1 part Portland Cement, 1 part peat moss and 1 part sand.  (The sand replaces the usual Vermiculite or Perlite)  The project will be heavier, but stronger.

Mixing in a handful of synthetic concrete re-enforcing fibers or chicken wire will also give a project added strength.

Embedded Items Crack

The above picture is a perfect example of that.  The blue inserts were pieces of a blue plate that I inserted.  It only took one winter for the ceramic pieces to break and begin to fall off.  

The leaf in the middle is actually metal so it holds up well.  Lesson learned.

    Hypertufa Edges Crack or Break Off

One of the most important considerations while building a hypertufa project is ensuring that the edges are as thick as the body of the piece.  

Thin edges will crack much more easily.  Double checking the thickness in these areas will reward you with a project that will hold up longer.

The above picture shows edges that have broken off when I was attempting to use a wire brush to remove sharp edges.  I could leave it as is and enjoy the uniqueness of the planter or plant a plant in it that will drape over the edge and cover it.

  Older Hypertufa Planters Crack

Plant roots can grow quickly, and if the roots have made their way into the cracks and crevices of the planter, that will quicken the breakdown process.

If I were to leave this So Sweet hosta in this planter for a third year, the roots would certainly crack the planter.

Repeated excess water in a project can cause the hypertufa to break down over time.  Be sure not to place hypertufa in a place where excessive rain will pool in or around it, especially over the winter.

An insufficient amount of drainage holes in the planter will also cause pooling of water and will slowly deteriorate the hypertufa.

No hypertufa project will be perfect, but neither is nature.   Some of the imperfections in my final hypertufa projects have actually made the final project more unique, natural looking and beautiful.

Hypertufa is one of my favorite garden projects.  The internet is full of great ideas, designs recipes and tips. 

By avoiding some common pitfalls, there is no limit to the number of great garden projects you can do – and best of all, they will last for years!


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