Bluestone over Concrete Problems -- Major Mortar Fail

by Frank Rothermel
(Bucks County, PA)

Cement Pad -- 4-6

Cement Pad -- 4-6

Cement Pad -- 4-6
Finished Fieldstone Wall & Bluestone Patio
Bluestone Patio -- Mortar Fail closeup
Bluestone Patio -- Mortar Fail overview

Calling all Masons. All stone-hands on deck (please). Ok, learned the stone trade a bit as a kid (not enough as you'll see below), but when our small crew got laid off, decided to make my Mom happy, hung up my trowel, went back and finished college and been a "suit" guy ever since. Fast forward 20 years and my wife and I bought an old farmhouse in Bucks County, PA. Decided to get out my trowel again and build a large stone patio. First, she and I framed the entire area out and poured 55 yards of concrete to create one large, level pad. (Photo #1 attached). Then came back and built the wall (the old Italian way as I'd been taught) with 20 tons of fieldstone. It's about a 100' run, 18" wide, and 30" high with 3' high piers capped with 2" bluestone. After finishing the wall, took a few months to lay 15 tons of irregular Pennsylvania bluestone which was bedded with fresh mortar on top of the fully-cured rough-topped concrete. (Photo #2)

Well, the wall has held up fine but the joints and underlying mortar on the bluestone started to crumble after only 5 years. Now 11 years later it has completely failed. I have no idea what went wrong or how to reasonably fix it. It was a hot summer in 2004 when we laid the bluestone, but we cooled each stone with ice-cold well water, mudded up a moist bedding, and sprayed the joints for a day or two after setting to slow the cure. The mortar recipe was the same one I learned as a kid - 9 shovels of sand, 2 Portland cement, and 1 lime. Didn't use much mortar on the wall so that was all hand-mixed, but did use a mixer for the bluestone given the large quantities needed to bed even 1-2 large stones.

Anyway, many of the joints started to crumble into sand after a few years - it was insane. You could run a slicker straight through the mortar joint and it looked literally just like sand -- no cement visible at all. And as 1 stone went bad, the surrounding stones started to "pop" with the same crumbling mortar-to-sand mixture found underneath. Now all the bluestones are completely detached from their underlying mortar base.(Photo #3 and Video #4). Have checked with some masons over the past years but there was no consensus on what caused it or how to fix it. Some said I never should have used Portland cement; it should have been a strictly lime mixture. Others said the 1 part lime killed the joints because it allowed too much water to wick through. Still others said never do bluestone over cement because the bluestone is porous and needs drainage underneath no matter what mortar you use.

So what do the bluestone pros out there think? If there are any insights or time-honored secrets you or others can impart, I'd be much obliged. I note that the stone steps leading into my house were likely placed when the large addition was built in 1948. The mortar on these steps is still stone hard, tight and nary a crack -- not even one. Unfortunately it serves as a constant reminder that maybe I should have stuck to my day-job ;-)

Well, all my best and again, any and all guidance much appreciated.

/Frank Rothermel

Comments for Bluestone over Concrete Problems -- Major Mortar Fail

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Stone Mason NEW
by: Mike Prock

The only way I've found to make the bluestone stick is to use extertior thinset with an epoxy additive (karalastic) for the joints I use type S with some Portland added basically making it type M mortar

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stone creations NEW
by: STONEMAN

First off sorry to hear about your problems..i have laid thousands of feet of pa stone on concrete pads in 15 years never has one came apart as this.
Just sayin i might be a expert.
my site www.tnstonemason.com shows my work. i have moved from tn back to pa.i live in the scranton area.i now run a buisness www.paflagstonewholesale.com.
Anyways enough to show you i know the buisness.
first problem i can tell from what your sayin is--portland cement to lay stone is a no no.
major reason it wont take the expansion and contraction that stone goes through with the sun..
that is one
was portland used to grout between the stone to? another no no!
and i always use a better mix--1 to2--in otherwords 1 shovel cement to 2 sand--although i use buckets!
feel free to contact me through my site where you can get my phone number..

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