Expandable Bolts


Old 04-01-04, 08:04 AM
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Expandable Bolts

Hi -

Can someone explain to me the correct method of getting an expandable bolt to work with concrete? I'm not having any luck in getting it to expand.

An example of the bolts I'm using can be found here:



Old 04-01-04, 01:58 PM
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I checked the link you provided ... and IMHO they appear to be pretty typical concrete fasteners.

All expansive concrete fasteners rely upon sevaeral factors to work properly and to offer maximum pullout strength, including but not limited to a hole drilled to the right depth AND more importantly a hole drilled to the right diameter.

The hole must be at least 1/4" deeper than the fastener to allow a pocket for drilling debris to locate AND the diameter must be drilled to the exact size specified for the fastener of choice. Too small a diameter and the concrete will fracture or crack when the expanding fastener is tightened; too large a diameter and the expanding fastener will spin or will not properly engage and embed itself in the hole.

If the hole is too large the fastener can not offer the proper pullout resistance, and it's tensile, yield, and shear strengths also become limited.

Each box or package of expanding concrete fasteners *should* have a printed sheet stating what diameter hole to drill. Some fasteners produced by top-of-the-line companies even have the drill size stamped on the fastener.

Of course there are other factors that affect a fasteners performance, and these you may need to consider; such as the age, condition and make-up or type of the concrete.

Old concrete, improperly cured concrete, or concrete that has been repeatedly exposed to cold/hot temperature cycles with high levels of moisture may not offer a sound base for the fastener; it may just crumble away when the fastener is tightened.

I suggest you first verify the diameter of the hole required for the fastener of choice.

If you're using the right diameter bit and the concrete isn't up to par you might try using one of the many concrete-to-steel epoxies on the market. The instructions usually tell you to fill the hole with epoxy, insert bolt, wipe excess and tighten. Modern epoxies add tremedous resistance to pullout.
Old 04-01-04, 02:53 PM
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Thanks for the reply. I was interested in knowing what makes the bolt expand - hammering it? Is it when the bottom of the bolt hits the bottom of the concrete hole that it expands?
Old 04-01-04, 03:30 PM
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There are indeed concrete fasteners that need a hammer blow to activate the embedding sleeve; but, and of course with some exception, they are for the most part considered obsolete.

Concrete fasteners should not "bottom out" in the hole, there should in nearly every application be at least 1/4" space ... a relief pocket for dust and debris to locate and space to allow for the bolt to slightly expand during any high thermal cycle. The larger in diameter the fastener the deeper that relief needs to be.

The bolt expands when it it tightened. On split sleeved fasteners, on embedding collared fasteners, and on lead-plastic-fibre anchors the expansion and embedding act is created by the threaded shaft which is larger than the sleeve, collar or anchor. Key point: That's why the hole drill diameter is critical. That sleeve, collar or anchor MUST fit tightly or with little tolerance in the hole for it to engage and embed itself. Sloppy, oversized, or out-of-round holes will not permit this critical engagement and embedment. The proper diameter hole is the primary key factor.

Some concrete fasteners have internal conical shapes that force the collar or piece to expand when the threaded shaft is turned. They also rely on the proper diameter dimension of the drill used to make the hole.

Hope this helps .... I suspect you will get other opinions. I'm retired and have worked part time ... when I feel like it ... but for over 10 years at my cousins fastener business. Concrete fasteners is a big part of his business. No fastener leaves the place until the buyer is told what size bit to use. It's the key to having them work right.
Old 04-01-04, 09:11 PM
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Thank you, this answers my question. I was indeed sold a drill bit matching in diameter to the bolts, but the person who sold it to me led me to believe it was the hammering which I had some doubts about. That's why I posted the reference to that picture of the bolts, so you'd know which type I was referring to.

Thanks again!!
Old 04-02-04, 06:46 AM
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Just a follow up; Once at work I did several data searches on your fasteners ... expandable bolts ... manufactured and distributed by plakabeton.

I was unable to locate any customer surveys or product rankings under that brand name. There also does not appear to have been any product recalls or safety alerts issued.

Manufacturers offer product data information to importers, distributors and engineers; and also provide ample samplings. We do not have any samples on hand here, just CD and printed media. From that info we have I can not find, in the English version, directions that state these fasteners need to be mechanically charged by a hammer blow.

They simply have typical conically shaped shafts that expand an embedding collar when tightened; and rely on a hole drilled to minor tolerances for resistance to pullout, and to also maximize the fasteners tensile, yield and shear strengths.

Unlike US and Canadian companies, the manufacturers data I found does not specify drill bit size ... that is, quite frankly, unusual; and it also does not provide any extensive testing data for concrete types and conditions. Usually concrete fastener companies provide test data about their product's strength ... mainly pullout resistance ... in concrete, cement block, bricks, mortar joints, and in sometimes in specially formulated grouts and special concretes (such as lightweight, high density, air entrained, metal aggregrate etc, etc).

IMHO your fasteners are typical ... so hole diameter is primary issue ... condition of concrete is other factor. Good luck!

PS: From time to time a customer will experience problems with a fastener. Customer satisfaction is Job #1 so we will try them AND his bit and his drill in one of our concrete test pads in our shop. It not at all unusual to find that the problem is caused by using an improper sized bit, but we have also found from time to time that the drill machine is worn ... has slop and play ... and that it is drilling an oversized hole or an out-of-round hole. This could also be presenting you with a problem ... check your drill.

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