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JackB 08-25-2012 09:31 AM

mortar adhesion to bluestone - Question
So often when using Pennsylvania bluestone for outside steps the mortar joints in the slabs will often show a crack along the stone line in a few years. This seems to be because the saw cuts are so smooth it is difficult for the mortar to form a good bond with the stone. Another problem is when some mortar cracks it is almost impossible to match the color several years later and it looks like a patch. We are looking at two alternative options. Butting the stones at the joints and using polymeric sand. There is a question here of water intrusion seeping in and freezing but not sure. The second would be to use an adhesive additive like Weldbond in the mortar to provide more bond strength. Would appreciate any suggestions.

jomama45 08-26-2012 09:23 AM

A few ounces of bonding admixture goes a long ways, and should take care of many of the issues. Getting the edges wet first certainly helps as well, and be sure to compress the joints well to make sure they're as dense as possible. Also, I wouldn't suggest the polymeric sand for a wet-set bluestone application, it will allow too much moisture through........

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