View Full Version : Paint sloughing off block chimney

Ernie Simpson
02-20-2021, 12:55 PM
I did an inspection yesterday for a homeowner (fun to find an old flexible gas connector from the distant past - the owner confessed he put it on himself. Not the issue, however). The home has a concrete block chimney (built in 1945). No internal problems from what I could tell (new gas liner and recently checked clay tile liner for new oil-fired heating system). The chimney has either a very thin veneer of mortar covering or a thick coat of some type of paint. Gross peeling and sloughing off. Past input from masons has not been helpful.
The owner wants to know what to do with the chimney as paint adhesion problems have been chronic. He wants to sandblast - which I told him was a 'no go'. The photos show a whitish stain which I believe may be the residue of an old paint that is not allowing adhesion of new paint. I think that he may just need to keep removing the old stuff as it loosens and keep painting with a latex masonry paint. Does anyone have a better idea?

Jim Robinson
02-20-2021, 05:17 PM
Where I live they would nail lath to the block and stucco it. You would (in theory) never have to paint it again. I would recommend a metal cap however, as I almost always find cracks and problems when they use the stucco on a horizontal surface.

Markus Keller
02-21-2021, 09:15 AM
Blast clean down to raw block; grind and tuck point, put a domed/sloped metal cap on top and ensure the cap to flue liner joint is properly sealed, finish outside as desired. Don't let some moron put a flat cap on there that will end up concave all too soon.
Conditions at that chimney are indicative of water soaking down into the block from what appears to be a large / wide / flat cement cap. Those caps always have cracks or are old more porous cement. Water soaks through the cap down into the block causing those problems. If you seal the top end after all the other work the new coating should have good live span.
See abatron.com for some good product options.
and no I am not affiliated with them.
Or the other option, take it down, install a properly sized B-vent either exposed or within a nice looking enclosure

Jerry Peck
02-21-2021, 05:54 PM
"flat cement cap"

Man, autocorrect/spellcheck can be a pain at times ... turning concrete into cement ... :)

Gunnar Alquist
02-21-2021, 08:13 PM
Man, autocorrect/spellcheck can be a pain at times ... turning concrete into cement ... :)

Yeah, it's even worse when it happens twice. Here in CA, the shoulder and crown are capped with mortar rather than concrete.

Ernie Simpson
04-15-2021, 04:23 PM
Thanks all.

Ernie Simpson
04-15-2021, 04:33 PM
Thanks all.