I have read that rhododendrons that also are supposed to love acid soil can grow in alkali soil if there is lots of magnesium in the soil. I don't know about the azaleas, but maybe it' s the same for them.

Did you test the soil exactly where the azaleas are? Even within one garden there can be pockets of different soils. Also is it possible the builders amended the planting holes, in which case the azaleas might start to suffer as they get older.

Regarding your final question, if the azaleas are fine why do anything? Just keep an eye on them.

Just curious what chirt is? Looked it up on dictionary.com but there was no entry...?

Try chErt....

Chirt is decomposed limestone. Goo9gle chirt into your computer and you can find pictures of it.

Azaleas shrubs comprising of 2 of 8 subgenera of the genus Rhododendron.
Epsom salt is the way we get magnesium in the high acid soil/sand in S.C.
I have read in new paper many years ago, that azaleas tolerate low pH more then enjoyed it.
If you are not growing Blue Berries & your flowers are doing well, then enjoy.
Blue berries will do better in a pot in a high pH soil.

Chirt is decomposed limestone. Goo9gle chirt into your computer and you can find pictures of it.

Must be a regional or local term, no viable google searches and despite coursework in geology and soil science, I've never heard the word. Now chert...

I get some 61,000 hits for chirt on google none that I saw which related to limestone. There were some 6,000,000 hits for chert most of which I saw defined cheert as decompossed limestone.
I saw a lot of Rhododendrons and Azaleas growing wild on the cliffs of Dover when in England some years back and the cliffs of dover are limestone. Could a very high level of soil organic matter help explain why these plants that appear to need an acidic soil can grow well in soils that are closer to neutral?

Even then chert isn't decomposed limestone, since it's silica based. However, it may be what's left around after the limestone around it weathers.

Sorry I asked!~