13 replies to this topic

[Mitchell Duke]

I have a 12" pier that has been curing for 3.5 days. The setup on top would weigh 210 Lbs. Do you think it would br ok to use the pier now?

[MarMax]

I'd wait 7 days minimum. Longer is always better.

[sevenofnine]

+1 on MarMax. Wait a week according to this:   

 

https://www.concrete...uring-concrete/.

[KTAZ]

I always wait 7 days. Been doing concrete for 40 years. It's just good practice.

[Mitchell Duke]

Thanks thats what I was looking for!

[ex-Bubblehead]

Of course, the secret that KTAZ doesn't want to get out is that, unlike a watched pot, a watched pier WILL set faster. At the risk of higher probability of clouds after you mount your gear on it.

Edited by ex-Bubblehead, 13 August 2024 - 10:53 PM.

[Skywatchr]

I have a 12" pier that has been curing for 3.5 days. The setup on top would weigh 210 Lbs. Do you think it would br ok to use the pier now?

Nope.  Concrete takes time to cure enough to have enough strength for the anchor bolts to hold.  I myself usually wait about 2 weeks, or longer depending on the "mix" I had used.  Be patient because if you crack or break the concrete, you're in for a "treat" trying to start over.

[duck]

concrete strength history

3 days = 50% of 28 day strength

7 days = 70% of 28 day strength

 

there's no way you are stressing the concrete to 50% of its 28 day strength with a 210lb load on a 12" diameter pier.

 

other interesting facts

470lbs cement / cubic yard of concrete is "5.0 SACK" and unless the supplier uses junk aggregates will easily make 2500 psi in 28 days.

 

Beware of sacked concrete like you can get from Home Depot....no telling what the cement content is.

 

Easy enough to mix concrete in a wheelbarrow.   3 parts rock, 2 parts sand, 1 part cement - add water to achieve the proper consistency (called slump in the business)

[cahanc]

I have a 12" pier that has been curing for 3.5 days. The setup on top would weigh 210 Lbs. Do you think it would br ok to use the pier now?

No.  Wait at least 7 days before loading it at all. It would really suck to have to do its all over a second time. I made a 12" diameter 6' deep base that narrowed into 10" diameter just above grade. I did it in 2 pours with rebar. I waited 7 days after the second pour to use it and have not had any issues. Good luck!!! You're going to love having a pier. It makes everything so much quicker and easier. It is easily the single best thing I ever did for this hobby. 

[Skywatchr]

concrete strength history

3 days = 50% of 28 day strength

7 days = 70% of 28 day strength

 

there's no way you are stressing the concrete to 50% of its 28 day strength with a 210lb load on a 12" diameter pier.

 

It is not the load weight, it is the force on the anchor bolts holding the pier, which can easily exceed a half a ton squeezing the concrete to the failure point.

 

Pouring a footer, a slab, sidewalk, driveway, etc. is a completely different ball game. 

 

There are many different mixes of concrete too.  Your "hardware store" variety of pre-mixed is the weakest blend. But plenty good enough if it cures at least a week or more. I tend not to use it, because many times it has already seen moisture and comes out of the bag half cured and lumpy. Yes, the bags have a plastic liner, and yes, many times not sealed, and/or punctured from rough handling.  Been there, done that.

Edited by Skywatchr, 14 August 2024 - 08:45 PM.

[KTAZ]

It is not the load weight, it is the force on the anchor bolts holding the pier, which can easily exceed a half a ton squeezing the concrete to the failure point.

^ This. Tightening those nuts down on uncured concrete is a bad idea.

Edited by KTAZ, 14 August 2024 - 08:45 PM.

[duck]

I presume you are using a nut on the underside of the pier plate and have the cg of the entire mount and scope reasonably over the center of the concrete.  If this is the case,  there should be no problem with 3 1/2 days of cure.

 

Don't bolt the pier directly to the concrete...that's a bad idea.  Use nuts on the underside of the pier plate.  If you like, you can us non-shrink grout to fill the gap. The concrete will never be flat enough to allow an even distribution of load if you try to bolt the pier directly to it, beside generating pullout forces on the anchor bolts.

 

 

That's a very heavy scope and mount, guessing about 1200 lbs.  The anchor bolts are 1 1/4" diameter.  The RA housing sits on nuts on the anchor bolts.  Nuts on the top side clamp the bottom plate of the RA housing.  This scope has a dead-beat response to slew taps on the hand paddle.  No grout fill.  Keep the exposed anchor bolt as short as possible.

 

 

Edited by duck, 14 August 2024 - 09:29 PM.

[Mitchell Duke]

I presume you are using a nut on the underside of the pier plate and have the cg of the entire mount and scope reasonably over the center of the concrete. If this is the case, there should be no problem with 3 1/2 days of cure.

Don't bolt the pier directly to the concrete...that's a bad idea. Use nuts on the underside of the pier plate. If you like, you can us non-shrink grout to fill the gap. The concrete will never be flat enough to allow an even distribution of load if you try to bolt the pier directly to it, beside generating pullout forces on the anchor bolts.

ImgIMG_0740rs.jpg

That's a very heavy scope and mount, guessing about 1200 lbs. The anchor bolts are 1 1/4" diameter. The RA housing sits on nuts on the anchor bolts. Nuts on the top side clamp the bottom plate of the RA housing. This scope has a dead-beat response to slew taps on the hand paddle. No grout fill. Keep the exposed anchor bolt as short as possible.

Thanks for the info! I just hit day 5 of the curing process. This is my third concrete pier build. There are three 5/8" j bolts. The pier plate will rest on the nuts which allows perfect leveling. Im now sure that the pier can easily handle the weight.

[Skywatchr]

Thanks for the info! I just hit day 5 of the curing process. This is my third concrete pier build. There are three 5/8" j bolts. The pier plate will rest on the nuts which allows perfect leveling. Im now sure that the pier can easily handle the weight.

After 5 days you should be pretty much safe to proceed. Just don't "bang" on anything for a few days yet just to be on the safe side.  I used 4 anchor bolts on my pier (with nuts underneath too) to make the final tweaking a little easier, and quad directional for weight shifting for a large GEM.  Although 3 should do just fine.