I’m not sure what are you referring to by “gas burner condensate”… is it a condensing boiler, high efficiency furnace, or some other gas burning appliance? The reason I’m asking is that there might be a significant difference in amount of produced condensate.
Assuming that you’re asking about a typical residential high efficiency furnace (90% plus efficiency) has a condensate pH level between 3-5. This is close to a carbonated drink pH and at a lower side of urine pH (normal values are between 4.6-8pH).
Even with a few gallons (amount depends on BTU’s of the furnace) of condensate produced by a high efficiency furnace every day, those pH levels and volume are not considered harmful to plumbing vents
or drains. Since there’s also other waste being dumped into the sewer system it dilutes condensate lowering its acidic content.
Pouring an undiluted condensate directly over the lime based mortar will eventually dissolve it. It will also cause corrosion of many other materials including cast iron pipes. However, high efficiency furnace condensate induced deterioration process inside a clay and / or cast iron sewer pipes being constantly flushed with waste water will most likely take decades.
Just click “comment” below if you have more questions.