(PHOTO: The stone on the left was made with Rapid Set Mortar. It is almost white, smooth, and no holes or cracks. The stone on the right was made with regular mortar. It has a rough surface, a crack on the top, and many little air holes across the top.)
There are different types of Mortar Mix you can use. Mortar is basically ground up rocks and sand. It is used to build buildings, BBQ pits, patios and flooring. It is designed for outdoor use and is waterproof - perfect for Art Stone making!
I have tried several types/brand. The one I highly recommend is "Rapid Set Mortar Mix" from Home Depot. It is the best I discovered for making Art Stones thus far. Here are the benefits to using the Rapid Set Mortar Mix:
Rapid Set Mortar
• It is ultra strong. It has a 6,500 PSI strength while other mortar vary between 750 and 1800. So your Art Stones are super strong. Less likely to chip or break while hiding outside.
• Rapid Set Mortar doesn't flake like other mortar mixes. With other mortars, the stones may become "flaky". After painting, the stones do not flake, but before they are painted you will have mortar flakes and crumbs all over.
• It's crack resistant. I haven't had any cracks in the rapid set mortar. I have had regular mortar and quikrete mortar crack on me and had to toss several stones a batch.
• No or very few air bubbles (tiny holes) in the Rapid Set Mortar. With the regular mortar there are rough patches and tiny air bubbles and at times big air bubble holes that can form in the stone. So you get a much smoother stone with no/few tiny holes with the Rapid Set.
• It dries to a very, very light gray that is almost white. This eliminates the need to prime the stone before adding your color or background. Other mortars slightly vary from dark to medium gray. And you have to prime them before adding color.
• Rapid set Mortar sets in about 2 hours in normal conditions (70 degrees or higher and average humidity). You can make several batches of stones in one day or make a quick batch and get on with life. With other Mortars it can take 24-48 hours for your stones to dry. It can even longer if the environment is colder than 65 degrees or has high humidity.
• You can paint the Rapid Set Mortar Art Stones in about 2-3 days after removing from the molds. Regular mortars you will have to wait 7 days for them to fully dry and cure before painting.
So Rapid Set Mortar is a superior product. However it is a bit pricey. It's about $13.00 for a 25 lb bag OR $18.00 for a 55 lb bag. A 55 lb bag of Rapid Set Mortar will make about 29 batches of 20 ounce mortar. Depending on the size of the stone here is about how many Art Stones a 55 lb bag makes:
55 lb bag = 406 - 464 Small Art Stones (14-16 stones per 20 ounce batch)
55 lb bag = 174 - 290 Medium Art Stones (6-10 stones per 20 ounce batch)
55 lb bag = 116 Large Art Stones (4 stones per 20 ounce batch)
If you can't find or afford rapid set mortar here are two alternative mortars you can use. But be aware that they both have flaking and cracking issues. They are rougher in texture and dry to a darker gray. These mortars take on average of 36-48 hours to set in the molds. You also need to wait at least 7 days after removing from the mold to paint them. They need additional time to fully dry and "cure" to full strength.
Sakrete Mortar Mix
Sakrete Mortar Mix is available at most hardware stores. It usually comes in 80lb bag. It is fairly inexpensive usually costing $6.00-$7.00 a bag. It will make hundreds of Art Stones. Sakrete mortar will give you a hour of work time (mixing, pour, level and tap). It usually takes 36-48 hours to fully dry before you can remove the stones from the mold. After removing from the molds, you will want to allow the stones to dry and cure about 7 days before painting them. The stones will be dark/medium gray after drying.
Quikrete ProFinish Mortar Mix
Quikrete ProFinish Mortar Mix is available at most hardware stores. It comes in 80 lb bag. It is fairly inexpensive usually costing $6.00-$7.00 a bag. It will make hundreds of stones. This mortar will give you a hour of work time (mixing, pour, level and tap). It usually takes 36-48 hours to fully dry before you can remove the stones from the mold. After removing from the molds, you will want to allow the stones to dry and cure about 7 days before painting them. The stones will be dark/medium gray after drying.
(PHOTO: BACK SIDES OF ART STONES: The stone on the left is a stone made with Rapid set mortar. It has a much smoother surface than the other stone and no cracks. The stone on the right was made with regular mortar. It has cracks, it flakes till painted and has a rough surface.)
WHAT NOT TO USE!
Regular Quikrete Mortar (Yellow Bag)
One product I will strongly advise NOT to use is the regular Quikrete Mortar in the yellow bags. It is not strong, only 750 psi. It also flakes and cracks horribly. It's the cheapest (in quality) mortar on the market! Spend a dollar or two more and use the Profinish or Sakrete mortars if you can't find/afford Rapid Set!
Plaster Of Paris
Mortar Comparison Chart
Here is a comparison chart on the Mortars mentioned in this post
Happy Rocking!
