Removing concrete forms too early?
Mark
seen. My neighbor poured a concrete wall yesterday, and today he removed the
wooden forms. The concrete was plain ol bags of concrete mix from HD. It is
not a quick setting mix. I usually leave forms on for up to 3 days for this
slow drying concrete. As expected, the now exposed concrete walls look damp
and are damp. Has anyone seen concrete fail like this? What do think will
happen? The wall is only 24" tall, 7" wide and about 8 feet long. I'm not
sure if the wall sits atop earth or the old concrete driveway. I kinda think
it is atop earth. He did put rebar in it. After 30 minutes now, the wall
has not yet moved. Weather is 72 degree's and the skies are mostly clear. No
sign of rain.
I'm am expecting a bulge to develop along the lower 6" and maybe even a wall
collapse. Any one have a crystal ball?
Mark
Eric Ryder
"Mark" <MCHA...@kc.rr.com> wrote in message
news:pK4q8.42036$A67.11...@twister.rdc-kc.rr.com...
Steve Ridley
If it is indeed sitting on the ground it "may" crack eventually.
If it didn't slump when the forms came off it probably ain't gonna.
Sometimes it's better to be lucky than good :)
Steve
>
>
Gilbert Smith
> I've worked with concrete quite a bit but there are some things I have never
> seen. My neighbor poured a concrete wall yesterday, and today he removed the
> wooden forms. The concrete was plain ol bags of concrete mix from HD. It is
> not a quick setting mix. I usually leave forms on for up to 3 days for this
> slow drying concrete.
Concrete doesn't "dry"........it hydrates, or "cures". Bagged concrete or not,
if it's made of Portland cement and aggregate it's not going to cure any slower
or faster than any other concrete without additives. Curing takes place
relatively rapidly in the first few days, but if internal moisture is allowed to
escape full curing will be delayed or prevented.
When my house foundation was poured, the contractor removed removed the forms
the next day, much to my dismay, but even that was after considerable persuasion
on my part, because he initially planned to remove them the same afternoon. The
problem with removing forms too soon is not necessarily related to the early
strength of the concrete........after 24 hours with favorable temperatures
concrete has considerable strength. The problem is that removing the forms
exposes more surface to the air, and moisture that's needed for the hydration
process to take place leaves the concrete through evaporation. No damage is done
if the concrete is wet cured using blankets or mats, etc., but this is not often
done for residential projects. The result of improper curing is concrete that
lacks the full strength for which it was designed, has high permeability, and is
inferior in it's resistance to abrasion, freezing and thawing, and chemical
attack.
Bottom line.......the concrete has probably reached 25% of it's design strength
after a day or so, and it's not going to fall down. The problem is now that the
hydration process is being adversely influenced by exposure to the air it will
probably never surpass 60% of it's potential strength.
Mark
morning and as you predicted, it is still standing. Since the wall is
heavier than the small volume of earth it is holding, I guess he may never
notice it's weakness, unless the wall cracks from being atop soil, or flakes
off. This person is the same guy that covered an old cracked sidewalk with
1" of concrete (or was it morter) last year. It survived the first winter
without cracking, but it was a mild winter. He is indeed lucky.
Mark
"Mark" <MCHA...@kc.rr.com> wrote in message
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Mike
> Thanks Steve and Gilbert for your replys. I just checked the wall this
> morning and as you predicted, it is still standing. Since the wall is
> heavier than the small volume of earth it is holding, I guess he may never
> notice it's weakness, unless the wall cracks from being atop soil, or
flakes
> off. This person is the same guy that covered an old cracked sidewalk
with
> 1" of concrete (or was it morter) last year. It survived the first winter
> without cracking, but it was a mild winter. He is indeed lucky.
>
> Mark
>
have you ever seen concrete stairs ever wonder how how they get them
troweled out smooth?
I did one several months ago after pouring the stairs the risers were
stripped about 2 1/2 hours after the pour
and then they were troweled
Gfretwell
few days. If the surface dries out before it is properly cured that surface
will spall off the first time it freezes.
Mark
will mention to him about keeping it wet.
Thanks
Mark
Tony Miklos
They removed my foundation wall forms the same day they poured them.
They also sealed the outside with tar that same day, so at least one
side couldn't dry out too fast. I hosed down the inside quite often for
days, I know the concrete was wet all the way through because after
wetting it with the hose, the tar on the outside started forming "water
blisters" from the excess water. They were in no hurry to back fill
since they were busy on other jobs. After a week I stopped wetting the
walls, and then the blisters stopped popping up, I gave it another coat
of tar. When they poured the floor, I kept that wet also for a week or
two. I couldn't believe the contractors had no idea what I was doing.
When I told them that the longer it stays wet, the stronger it cures,
they shook their heads and walked away. Keep it green as long as you
can, and even if it looks white, it's probably green inside yet, so
keeping it wet a while longer doesn't hurt it.
--
Tony