Concrete Question?

[MountainDon]

Anyone have an idea on how long it would be best to let concrete cure before drilling and using expansive type anchors?

[Redoverfarm]

Anyone have an idea on how long it would be best to let concrete cure before drilling and using expansive type anchors?

In air after 3 days is 80%, and In air after 7 days is 90%.  Normally takes 28 days to gain close to it's maximum cure time.  If you have time to wait keep the surface moist, covered to gain maximum.  Of course all of that depends on relative humidity, temperature and % moisture of the mix at the time of pour.  So unless you are in a hurry I would wait at least 7 days.

[firefox]

I am wondering if it wouldn't be better to drill the holes now while the concrete is softer.
Then wait the 7 to 28 days before placing in the anchors. This would also help to get moisture in to the inside of the holes which might help with the strength of the material around the holes.

I have no knowledge of this, just curious.
Bruce

[Redoverfarm]

I am wondering if it wouldn't be better to drill the holes now while the concrete is softer.
Then wait the 7 to 28 days before placing in the anchors. This would also help to get moisture in to the inside of the holes which might help with the strength of the material around the holes.

I have no knowledge of this, just curious.
Bruce

Only problem with that Bruce is that while drilling "green" you could not keep a consistant diameter.  The bit would also want to walk off the location.  Unlike lumber, concrete is something that is better worked cured than green. Not much you can do working with concrete while 

Back in the late 70's there was a powerplant  coolingtower construction just a few miles from where I lived that partially collasped killing some 51 workers. It was considered the worst construction accident in the US.  I think one major contributing factor was that they had attached scaffolding to green concrete which failed.

http://en.wikipedia.org/wiki/Willow_Island_disaster

[rick91351]

I don't like drilling green concrete or even plating it for about three days.  I have this thing about stressing it too soon can cause cracks and tear-outs.  I have never seen anything in writing or anything like that just a feeling.

That said when I was working in concrete we would pour a footing on the morning, walls in the evening and the framers were laying out joists the next day

[MountainDon]

My feeling is that it is best left alone, left to cure, for at least a week. That drilling now could result in having the drill bit wander. No problem keeping it moist.

Not that I'm in a hurry, but I would like to get the anchors in around 10 days or so from the concrete having been placed. Just wondered if there was a best practice...

[JRR]

I try to avoid drilling concrete ...by using "nut" or threaded-rod inserts.  They are available "store-bought", or you can make your own, especially if you have a welder.  A nut, tacked to a large washer, buried deep in the wet concrete makes a pretty good anchor.
Use a temp threaded rod to locate ... protect the threads on the rod with a plastic or metal sleeve.  Unscrew the thread rod after concrete cures.

All this assumes that enough information is available to precisely pre-locate the connectors.

[rick91351]

I would ten times rather drill than embed.... 

No matter how careful stuff is planed and measured..... it can go wrong   

[MountainDon]

All this assumes that enough information is available to precisely pre-locate the connectors.

Which is the reason I did not want to embed an anchor. Placement would have been +/- 0.125", more or less.  I've never been able to maintain the anchor bolt position with such accuracy when placing concrete.   But then even drilling can go awry if an extra dense chunk of rock is encountered. 

[Redoverfarm]

It is possible to be accurate with embeded bolts but a little extra preparation is needed.  You can use a 2X4 drilled as a jig to hold the bolts in the right position as long as they are built as part of the form high enough to finish the concrete on grade and aroud the J-bolts.  But like any other form work I like the grade surface to be daylighted for a good finish.  Can it be done Yes but is it worth the effort No.

[firefox]

Thanks Redoverfarm for the good explanation. That makes a lot of sense.
I personally like to use the 2x4 to hold the "J' bolts in place and pour.
Bruce

[Squirl]

You also have to make sure the holes are drilled just right in the board and the J-bolts stay at a perfect 90 degrees.  On my sill, some of the holes were a little loose, or maybe just a little off.  This had two bolts slightly bent in towards each other.  It effectively locked in the board.  I had to use a drill to widen the hole to get the board off to install the sill seal.

[flyingvan]

I thought J bolts ALWAYS came out crooked.  I just spin a nut on to protect the threads,  slip a length of pipe over, and bend them plumb.

[rick91351]

I thought J bolts ALWAYS came out crooked.  I just spin a nut on to protect the threads,  slip a length of pipe over, and bend them plumb.

Or nut it up and hit with large hammer for regular sized j bolts.  Hint number two - Don't unpack the beer cooler until the j-bolts are in and set.   

[rick91351]

I would ten times rather drill than embed.... 

No matter how careful stuff is planed and measured..... it can go wrong   

I am talking special embeds like horizontal embeds for like deck ledgers as I see called for a lot lately around here.  In fact the inspector says leave them out and just drill'em in.  It is a lot less hassle and less damage to the forms and brackets when you go to set them.  Seems one or two will always drift into the bolting pattern no matter how hard you try. 

For 1/2 inch or 5/8 inch j bolts they pretty no brainer and if you mess up a little there is a ton of things you can do.....  Drill out the hole a little or nut it up and bend or my most likely hit it with the double jack sledge hammer.