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Old 10-31-2017, 08:09 PM   #1
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Default Strut to hollow precast concrete ceiling?

I'm needing to attach some short sections of strut to a precast concrete ceiling for a run of 2" EMT. Anyone use TapCons for this? Normally I'd use drop ins for a concrete ceiling; however with the hollows in the precast I'm afraid of punching them through when setting.
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Old 10-31-2017, 08:43 PM   #2
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In general if you use a smaller fastener that's easier on the concrete but weaker than you want, you'll want to just use more fasteners to spread the load over more fasteners. But is it even necessary? If you look at the engineering data for tapcons

https://www.confast.com/products/tec...retescrew.aspx

Even the smaller ones with 1" embedment in concrete only 2000 psi are rated for 600# pullout strength. Now 600 pounds is obviously way more than what 10' of 2" EMT filled to capacity with copper wire weighs. So if you have at least one tapcon per 10' section on a minerallac hanger, you'd probably be OK.

Now you probably don't really know what PSI the precast is. And I don't really trust tapcons that much, you wobble the drill and make the hole oval and it isn't nearly as strong. So I'd probably use strut sections with two or three tapcons.
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Old 10-31-2017, 08:48 PM   #3
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Tapcons are too brittle for this application -- IMHO.

You really ought to phone your Hilti rep.

Every time I turn around, Hilti comes out with a new slick, trick, fastener.

If you measure carefully, you can avoid the voids, too.
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Old 10-31-2017, 08:50 PM   #4
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I'm ok with tapcons on wall street where their shear strength comes into play, but I don't like them much in ceilings where they can pull-out.

In you situation I would typically use steel anchors until I hit a hollow, then I would use lead anchors with a hollow wall set tool.

Other times when it's all hollow I would use those steel sleeve anchors that have the spring around them and you drive a lag bolt into.

I've also used 3/8" toggle bolts in hollows with good results.
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Old 10-31-2017, 08:57 PM   #5
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Tapcons with a coating of 3M Scotch-Weld.
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Old 10-31-2017, 09:03 PM   #6
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I was looking at the spec sheet yeasterday and even in something as weak as block they rate the 1/4 (allowing 3/16 SDS bit use) as good for 250lbs tension. I was thinking two tapcons per strut section and a strut section every 3m.

And while I'm a big fan of Hilti stuff I don't have any of their installers available (IE: a 460DX and some X-W6 FP8 would work great); I only have about 12 sections of conduit to install; and I'm a 2 hour drive each way from the nearest rental house. If Tapcons will work they'll suit my specific constraints with a lot less hassle.
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Old 10-31-2017, 09:08 PM   #7
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I used tapcons on the wall but not useally on ceiling not too often.

but for ceiling purpose I use toggle bolts they hold up pretty good as long you know where the hollow cavity is. but whatever you do .,, dont ever hit the prestressed rebar or cable that can get ya., ( unless coredrilling maybe ya can get away with it only in writing ., )
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Old 10-31-2017, 09:26 PM   #8
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In this same type install I've used drop ins with a threaded setting tool, Hilti threaded studs, and lag sheilds.

I'd never use Tapcons in a ceiling.






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Old 11-01-2017, 01:13 AM   #9
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Wedge anchors would not be out of place here.

Sent from my SM-G920W8 using Tapatalk
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Old 11-01-2017, 02:01 AM   #10
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There is something made just for this application. http://anchors.dewalt.com/anchors/pr...dercutplus.php

Quote:
The Mini-Undercut+ anchor is an internally threaded, self-undercutting anchor designed for performance in cracked and uncracked concrete. Suitable base materials include post-tension concrete (PT slabs), hollow-core precast concrete, normal-weight concrete, sand-lightweight concrete and concrete over steel deck. The Mini-Undercut+ anchor is installed into a pre-drilled hole with a power tool and a setting tool. The result is an anchor which can provide consistent behavior at shallow embedments as low as 3/4 of an inch. After installation a steel element is threaded into the anchor body.
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Old 11-01-2017, 07:59 AM   #11
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Quote:
Originally Posted by ppsh View Post
There is something made just for this application. http://anchors.dewalt.com/anchors/pr...dercutplus.php
Yes, here's the same product by Unistrut.
https://www.unistrutohio.com/products/anchoring-products/mini-undercut-anchor/
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Old 11-01-2017, 12:20 PM   #12
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I like drive pins. Just use a few more than you would on a horizontal application.
Same principle as a wedge anchor and much easier as the drill hole is much smaller.

How heavy?
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Old 11-01-2017, 05:53 PM   #13
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Run you a bead of silicone on the strut before you attach it. Whenever I tapcon a disconnect or something to brick I put a little blob on the back, really firms things up.
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Old 11-01-2017, 07:14 PM   #14
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Quote:
Originally Posted by matt1124 View Post
Run you a bead of silicone on the strut before you attach it. Whenever I tapcon a disconnect or something to brick I put a little blob on the back, really firms things up.
Funny you mention that...

I do use silicone sometimes but I was wondering if there is something stronger? Would construction adhesive like liquid nails work better?

Recently I had to do a panel change in a house that the customer just bought. The panel was in this little closet and there was a safe glued to the wall that was in the way. I have no idea what they used to glue it to the cinderblock, but hammering it with a sledge didn't budge it. Opening the door and both me and my helper putting all our weight didn't budge it either. I had to use a 4X4 post and a floor jack to break it off.

What type of glue could they have used that was so strong?
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Old 11-01-2017, 07:39 PM   #15
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Quote:
Originally Posted by HackWork View Post
Funny you mention that...

I do use silicone sometimes but I was wondering if there is something stronger? Would construction adhesive like liquid nails work better?

Recently I had to do a panel change in a house that the customer just bought. The panel was in this little closet and there was a safe glued to the wall that was in the way. I have no idea what they used to glue it to the cinderblock, but hammering it with a sledge didn't budge it. Opening the door and both me and my helper putting all our weight didn't budge it either. I had to use a 4X4 post and a floor jack to break it off.

What type of glue could they have used that was so strong?
I use "MasterSeal NP 125" made by BASF
All Purpose Clear Sealant and Adhesive
Liquid Nails is obsolete
You'll probably have to go to a building supply or online
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Old 11-01-2017, 08:48 PM   #16
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Quote:
Originally Posted by HackWork View Post
Funny you mention that...

I do use silicone sometimes but I was wondering if there is something stronger? Would construction adhesive like liquid nails work better?

Recently I had to do a panel change in a house that the customer just bought. The panel was in this little closet and there was a safe glued to the wall that was in the way. I have no idea what they used to glue it to the cinderblock, but hammering it with a sledge didn't budge it. Opening the door and both me and my helper putting all our weight didn't budge it either. I had to use a 4X4 post and a floor jack to break it off.

What type of glue could they have used that was so strong?
Most construction adhesive is polyurethane based like Gorilla Glue and IMO overrated, it's decent when used as directed but not super strong. Epoxy is usually a lot stronger.
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Old 11-01-2017, 10:02 PM   #17
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Here is a very good option.

https://www.hilti.com/anchor-systems/flush-anchors/r232
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Old 11-01-2017, 10:43 PM   #18
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So the local fastener supply house suggested the UCAN STUBi drop in (which appears to be similiar to the HILTI HDI-P JohnJ65 linked) which is designed for this purpose along with the specified depth limited SDS drill bit. I'm going to give them a try and will report back.

JohnJ65 have you actually used the HDI-P?
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Last edited by Gnome; 11-01-2017 at 10:47 PM.
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Old 11-01-2017, 11:43 PM   #19
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Hollow wall set tool and lead anchors. The hole your drilling will not harm the precast.
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Old 11-02-2017, 08:25 AM   #20
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I have used a metric ton of lead anchors with a hollow wall set tool in ceilings, and they work great.

But, then I learn that they are not allowed to be used in ceilings (in some areas) due to becoming soft during a fire and causing it to rain conduit racks.

I still do not have good info on this, what does everyone else know about this issue?
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