There are two common methods of creating cast stone , one is the dry cast method and the other is the wet cast process. Both of these methods are to create a simulated natural cut stone look, and the most common finish is like limestone or sandstone.
What’s the difference between wet and dry cast stone?
At the time that the concrete mix is placed into the mold the mix of aggregates and cement is either wet and runny, or it is dry and stiff (just damp enough to hold together). Hence wet cast and dry cast.
More about the dry tamp method
As a kid, did you ever make a sand castle at the beach? You may have had a special sand castle bucket, and your dad may have shown you how to get the damp sand and compact it into the bucket and then flip the bucket over to make the castle.
The dry tamp method is just like making a sand castle at the beach, the main difference is that you add cement to the damp sand, and optionally you use special compacting tools (usually air powered tampers) to compress the sand/cement mixture.
What are the pros and cons of wet cast stone?
- less effort to place the concrete in molds, you just pour it in and perhaps vibrate
- less time to initial cast
- Molds cost less, and are quicker to make (they don’t have to be as strong)
- Less time detailing during demold
- No complicated curing costs
- Conducive to surface treatments such as retarders, and texturing additives in the mold
- less likely to be damaged during demold
- Can be cast to a smooth finish
- Can take larger aggregates for less cost or for exposing by grinding
- Long time before de-molding (usually the next day)
- Early strength not as high as dry cast
- requires more post de-mold detailing to be as clean looking as dry tamp method
- Can only de-mold once per day normally
- Requires more acid etching to get that limestone look
What are the Pros and Cons of Dry Tamp Cast Stone?
- Fast demold time
- Can cast several times a day in the same mold
- Less treatment afterwards to get that limestone look
- Result of Cast stone is very clean and natural looking
- High early strength
- steam curing can be costly to set up
- No surface treatments such as mold applied texture or colors
- requires extra step of detailing during de-mold
- requires extra expertise at casting time
- Cannot create smooth stone
How do you make wet cast stone?
Wet cast stone manufacture is just like baking a cake. Get your mold ready (cake tin) and pour in the cake mix batter.
Here’s a list of the important things when making wet cast stone.
- Mold needs to be perfect
- Mold release is important, chemical release agents result in a better surface
- The mix design of your concrete is important it takes into account surface appearance, workability, surface defects like bug holes, ease of casting, cost.
- No leaks in your mold, otherwise you will have color issues
- If there is an undercut in your piece, you may have to make complicated multi-piece molds
How do you make dry tamp cast stone?
A special mix of sand, cement, admixtures and a low amount of water make a damp sand like mix. This damp mix of sand and cement is placed loosely into a rigid mold and then tamped to pack the mix tightly into the mold in several layers.
Once the mold is full, the excess is scraped off and leveled smooth. Almost immediately the mold can be removed leaving the stiff sand mix by itself.
Please view the video of vibrant dry tamping cast stone from our friends at Advanced Architectural Stone.