jeffc wrote:
wrote in message
oups.com...

jeffc wrote:
wrote in message
ps.com...
I think etching becomes less of a requirement for older concrete. The
purpose of etching is to give the concrete a rough surface so the paint
will stick. If the floor has become rough over the years from wear,
for example, then I wouldn't etch it.

Actually, sometimes concrete becomes "polished" and smooth over time, and
is
in the most need of etching. Fresh concrete rarely needs it.


That's just totally false. Read any paint can or guidelines for
painting concrete and see what they say. Etching is always required
for new concrete.

No it's not. Really new concrete is going to be very alkaline which is a
problem. Obviously concrete can be poured and finished in a variety of
ways, some more smoothly, some less smoothly. Now this guy is talking about
a crawlspace which obviously doesn't get any traffic. But concrete that
gets traffic definitely gets smoothed over time. Not only that, but the
tiny nooks and crannies can get filled in with dirt and grime. In addition
to etching you should clean and power wash (clean first, etch second, power
wash third to get the concrete particles removed.) You think you need to
etch concrete that's "rough" like a sidewalk? No.



Seems some folks who should know disagree with you about not needing to
etch new concrete:

From Behr Porch and Floor Paint product instructions:

Preparation **
All surfaces must be clean, sound, dry and free of any dirt, oil and
grease. Eliminate mildew stains with BEHR No. 62 Multi-Surface
Deck-Prep Cleaner & Mildew Stain Remover.
New or weathered wood; use BEHR No. 63 Wood Cleaner Brightener
Conditioner.
Uncoated Concrete or masonry surfaces; allow new surfaces to cure 30
days. Use BEHR 990 Concrete Cleaner & Degreaser and follow with BEHR
No. 991 Concrete Etcher & Rust Remover.


Or how about this from another manufacturer:

Why is it necessary to etch my concrete surface before I apply Mason's
Select Concrete Stain or Mason's Select Clear Finishes.

It is necessary to etch hard-troweled or very dense concrete surfaces,
such as garage floors, in order to open up the surface and allow the
Mason's Select Product to penetrate. If you are not sure whether to
etch or not, it is always best to etch the surface. Sometimes, very
dense surfaces require etching twice to make the surface porous enough
to stain. The surface should feel like 120 grit sandpaper

Is etching recommended on new concrete surfaces?

Yes. All concrete with a smooth surface or that does not allow water
to penetrate should be etched prior to applying Mason's Select Concrete
Stain or Mason's Select Clear Finishes


Or how about this from DIY on how to paint concrete:

Step 2: Acid Etching: New interior walls should be acid etched before
painting (see instructions below.) Existing coatings can be repainted
where the coating is sound. Any bare spots (including areas revealed
when scraping loose and peeling paint) should be acid etched before
painting.