Question
Hi Mark,
 I saw that you answered some questions about rock quarry for a patio. I have a question concerning a sealing issue as well. We recently had this put in. I don't know anything about it, so we trust the landscapers did what they were supposed to!

 They put sand over the top of the rock quarry and swept it into the cracks. Later they came back and told us they sealed it with another type of sand and they spread it in to the cracks and then wet it down. The lady said it should act almost like a rubber sealant. However, it never "rubberized" and it's really quite irritating because there is sand EVERYWHERE!! It tracks in to the house and gets all over our feet. I have tried to contact them with any suggestions to this problem, but they haven't gotten back to me. I'm wondering if you have any suggestions.

 It doesn't seem to me that they even sealed it. I saw in a previous answer that you don't recommend sealing it. With cracks being in between the rocks.. is that going to mess anything up? We couldn't grow grass in this area so that's why we decided to put in the patio.. it doesn't seem that adding grass between the cracks could be a solution. I'm just at a loss for what to do. I guess having the large cracks wouldn't hurt anything.. I just don't want our children to trip and fall. My biggest complaint is the massive amounts of sand I'm having to deal with.

Any suggestions are appreciated! Thank you SO much for your time!

Deborah

Answer
Hello,

Perhaps the binding agent added to the sand used failed or if a pre-mixed paving joint sand compound was used,perhaps it was not handled properly. The sand could be too fine and is now washing out. If what was used was some kind of semi-dry mortar mix,perhaps the mortar to water ratio was not right. A relatively coarse sand such as concrete sand would be more desirable than a finer sand in a larger joint. A fine sand can have a tendency to wash out because it will not bind as tightly as a coarse sand,although a binder can compensate for this tendency. A semi-dry mortar mix would be a cheaper option but may have less flexibility of movement than a sand mixed with an organic or synthetic binder. The paver joint material has to move as they expand and contract without cracking. Also,it takes a few passes with a thin layer of sand to get it properly swept in and compacted in the joints. It may be desirable to wet it down after a single pass and then come back the next day and sweep another layer in and then repeat the process. If the sand was swept in hurriedly and in 1 pass then it may not have settled properly.

A fine sand,such as masonry sand can be effective to seal joints where the joints are relatively narrow such as with brick or concrete pavers but I would not recommend it for a larger jointed stone installation. The bond of fine sand is weaker than coarse sand. Sand with a binder added has a superior bond.

The fact you have not been called back by the contractor is a big red flag and indicates that poor workmanship and poor materials were used. Situations like this illustrate how a designer can protect you. A designer can write specifications outlining exactly what type of materials are to be used and how they are to be handled and applied.

I question why the joint sand was placed in 2 layers. Seems it would have been better for one layer of either plain coarse sand or one layer of sand with a binding agent.

After removing the old sand,the following,listed from least expensive to most expensive, could be options for you:

Plants,such as creeping thyme,in the joints.

Coarse sand,such as concrete sand.

Semi-dry mortar mix or wet mortar mix.

Paver joint sand with an organic or synthetic binding agent. Or perhaps you could mix the existing sand with a binding agent.

Polymeric sand.

Hope this helps. Good luck.



Mark Harshman


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