We recently had a irregular bluestone patio installed -- on a base of 5-6" of crushed stone, the bluestone was set and leveled using a good bit of cement. The gaps between the stone range from 1/2 inch to 3 inches and the contractor used a mixture of about 10 parts quarry dust and 1 part portland cement for the grout. This mixture was swept in dry and then sprayed with a garden hose. Most of the grout is now not solid and is getting tracked into the house--nevermind the fact that it comes out when you sweep the patio. What did the contractor do wrong and what would you recommend to fix this?

 

Dear Stephan:

The proportion 10 : 1 is very poor, and the technique is also not appropriate with that kind of wide gaps. That is the right way to go (proportion and method) only when you install pavers or bricks, and leave a gap of approximately no more than ¼” ~ ½”. For installations like yours you have to actually use either heavy sanded, ready-to-mix grout (which will need to be pointed on a yearly basis or so, depending on the harshness of your winters), or a mix of quarry dust or river sand and Portland cement in a proportion of approximately 7 : 3 or even 6 : 4. Even this second way of grouting will need to be pointed periodically. There are also flexible, ready-to-use grouts for outdoors. Expensive stuff to make sure, but I love it. It is the one that lasts the longer (it will always be gummy-soft to the touch). However, I do not know its performance with up to 3” grout gaps. You should inquire with the manufacturer for advice.

And please, do NOT seal your stone outdoors. If you like a richer and deeper color you could use a good quality stone color enhancer like MB-6. But that is it!   

May I ask you now to please read and e-sign our Statement of Purpose at: http://www.marblecleaning.org/purpose.htm?

Ciao and good luck,

Mauri zio Bertoli

 

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