Concrete pillars/columns : how long to leave the formwork on ?

[SurinBeach]

I've posted a few Topics recently, am having a few issues with my new garage/sala ...

Current issue, my Farang builder poured the new garage concrete columns yesterday afternoon, then took the formwork off first thing this morning ....

Everywhere I've read states formwork should be in place minimum 24 to 48 hours ...

Am I worrying too much, is this the norm in Thailand/Elsewhere ?

Cheers

SB .....

ps Pillars are 200mm x 200mm, 4 x 12mm Rebar, 3 Meters high ...

[gerry123]

DEPENDS ON THE MIX BUT FULL 48 WOULD BE BETTER

[IMHO]

As a rule of thumb, concrete reaches:

40% strength after 1 day

60% strength after 3 days

80% strength after 7 days

90% strength after 14 days

100% strength after 28 days

You would probably want to wrap those posts in plastic so they get more curing time.

[IMHO]

To clarify,

If the posts aren't already falling apart, there's no issue with the forms already being removed. However, they still need to cure - and for that to happen they absolutely must remain hydrated - concrete should not be left to "dry"... it's not paint, it's a chemical reaction that takes 28 days to complete (well, actually, it goes on longer then that, but after 28 days there's nothing more you can do to impact the curing process).

The cheapest & easiest way to ensure proper curing for posts is to wrap them in plastic - heavy duty stuff on wide rolls can be purchased from any building supplies store:

For things like beams, the best solution is normally just to leave the forms on.

Edited March 3, 2015 by IMHO

[eyecatcher]

Another concern I would have is that whilst they are still "green" they are prone to site damage....especially if there is a lot of activity going on.

If you cant obtain the cling film wrap pronto then rig up a hose pipe with a sprayer nozzle and give them a dousing every few hours.

[IMHO]

Another concern I would have is that whilst they are still "green" they are prone to site damage....especially if there is a lot of activity going on.

If you cant obtain the cling film wrap pronto then rig up a hose pipe with a sprayer nozzle and give them a dousing every few hours.

Yep. A spray of water before the plastic goes on is all that's required though. From there, the post will keep itself sufficiently hydrated as it 'sweats'. Indeed, when it stops sweating, that's when the plastic can be removed - job done

[krisb]

Yep form work can come off once it's set.

[topt]

Another concern I would have is that whilst they are still "green" they are prone to site damage....especially if there is a lot of activity going on.

If you cant obtain the cling film wrap pronto then rig up a hose pipe with a sprayer nozzle and give them a dousing every few hours.

Yep. A spray of water before the plastic goes on is all that's required though. From there, the post will keep itself sufficiently hydrated as it 'sweats'. Indeed, when it stops sweating, that's when the plastic can be removed - job done

Presumably spraying water on the plastic is not required then? The reason I ask is that when they built behind my place they wrapped the pillars in plastic and left it on for a long time but I am pretty sure I remember the "foreman" spraying the concrete fairly regularly including the pillars - it was 4 years or so ago so memory may be faulty................

[IMHO]

Another concern I would have is that whilst they are still "green" they are prone to site damage....especially if there is a lot of activity going on.

If you cant obtain the cling film wrap pronto then rig up a hose pipe with a sprayer nozzle and give them a dousing every few hours.

Yep. A spray of water before the plastic goes on is all that's required though. From there, the post will keep itself sufficiently hydrated as it 'sweats'. Indeed, when it stops sweating, that's when the plastic can be removed - job done

Presumably spraying water on the plastic is not required then? The reason I ask is that when they built behind my place they wrapped the pillars in plastic and left it on for a long time but I am pretty sure I remember the "foreman" spraying the concrete fairly regularly including the pillars - it was 4 years or so ago so memory may be faulty................

Well, if the plastic is properly applied, the water isn't going to get in

My guess is he was hydrating the slab, and maybe spraying the tops of the posts if they weren't also sealed with plastic.

[SurinBeach]

Thanks for the replies Gents (and ladies?).....

They did wrap the columns in film but I still would have preferred the formwork stay on for 48hrs ....

Cheers

SB

[IMHO]

Thanks for the replies Gents (and ladies?).....

They did wrap the columns in film but I still would have preferred the formwork stay on for 48hrs ....

Cheers

SB

Our standard is forms on for minimum 3 days, as it helps the forms come off cleaner - but, so long as the posts didn't suffer from early removal, and plastic has been applied, it should be all good

I guess I should also point out that even a 5mm hole in the plastic can result in a 5% weakening of the finished result - it really is important to make sure the post is fully sealed. I should also point out that fully controlled curing (28 days) results in a design life in excess of 100 years. (assuming correctly mixed concrete).

Edited March 3, 2015 by IMHO