Picture framing on penn bluestone

[Pcasserly]

I recently laid a 1.5 inch Pennsylvania Bluestone patio. The joints were filled with polymeric sand, more specifically the Supersand brand. A few days after filling the joints, many of the stones looked wet around the edges which I’ve learned is called picture framing. I’m wondering what causes the stains and if there is any way to safely remove these stains, as I would not like to use acid on the new stones. Thanks

[Tony McC]

We don't get that product in Britain or Ireland - we have plenty of useless equivalents, so no great need to import those you have in North America.

The picture framing stems from the doping oil used to prevent the polymeric curing until used. I'm not sure which oil is used in that partiucular produict but most of the polymerics rely on a biodegradable oil such as rape or linseed, and these tend to weather-out after a few months.....leaving behind a poorly-bonded over-priced sand in the joint.

[Pcasserly]

Thank you Tony!