Failed thrubolts... so what next, resin anchors?

[Lobster]

I've been using M12 thrubolt anchors like these...

to attach a joist parallel to the wall, but they haven't 'worked' at all well, in that one just pulled out of the wall when I tightened the bolt; and when I removed the joist to try to rectify this, another one failed as well when I replaced the bolt and retightened it. (The remaining two are well anchored and work fine).

Looking at the actual fittings, they seem to me to fundamentally flawed: they have no sleeve, so that as you tighten the bolt, the anchor moves outwards, and relies on achieving enough friction with the wall of the hole to enable the conical 'plug' to engage with the anchor and splay its legs outwards. It doesn't seem any surprise to me at all that this is very hit and miss, and that mine just slid straight back out of the same hole they went in. Holes were drilled 12mm as specified, into red brick, with placement such that anchors were in the middle of bricks in all three planes. Am I doing something wrong?

Anyway, to rectify matters... I need to reinstate the two missing bolts, preferably without removing the joist again, and have been searching the archives for resin anchoring methods which I've never seen or used. Am I right in thinking that this is an appropriate application for this? Could I just fill the holes (ie through the joist) with resin and then just ram a length of M10? M12? threaded bar straight down? Would certainly solve a lot of grief!

Thanks David

[urchaidh]

I'd think so, though I'm talking from the limited experience of having researched and used these on one job. I posted the details to another thread on the subject.

I filled through the PFC channel I was fitting so I can't see any problems there, the applicator spout was very long and could easily have coped with another 100mm. Get the hole as clean as you can, brush and blow a few times. The system I used specified a 75mm deep M10 hole for M8 studs, so use studs 2mm smaller than the holes you have.

If the bricks are hollow then you may have problems, I think you need a liner of some sort for those cases.

[Phil]

The ones in the URL adon't look like they were intended for a blind hole fixing (ie/ one sided) - they look like they were intended to be inserted right through the workpiece from the non-fixing side....

For blind fixings, a washer goes behind the joist, and with the nut on the outside this means the bolt 'head' in the blind hole has to expand as the nut is tightened.

[Lobster]

well, that would explain my lack of success suppose, and I did wonder about that; but why would a fancy fitting like this be needed if you had access on both sides? Surely an ordinary bolt, washer and nut would suffice and do the job much better?

If I understand you rightly, wouldn't that make the anchors open up extremely close to the surface of the brick I'm attaching to (especially as it's plastered! although I suppose that could and maybe should have been removed), and very likely to burst out?

Thanks David

[Dave Plowman (News)]

Think I'd stick to the normal 'Rawlbolt' type. Those can't pull out while tightening as they sort of pull against themselves.

[mark_begbie]

I used some (outwardly identical versions) of these bolts in a very similar situation - attaching the header board of a deck to a brick wall. The thing seemed to be that the anchor was a very tight fit in the hole to start with - they had to be driven in with a hammer. The protrusions then bind in the hole, and the whole thing locks solid when it's tightened. I'm guessing that if the hole was a little large to start with the process might not bootstrap properly and all that would happen is the device would gradually pull out.

Does it sound like this might be what happened?

regards,

Mark

Phil wrote:

expand

[Chris Bacon]

You should drill a hole of the correct depth and diameter (same as the bolt) and hammer these in, then do up the nut. I've never used these in brick, only concrete - are they supposed to be suitable for brickwork? The hole diameter needs to be accurate. Perhaps loose rawl bolts would be better? What are you actually fixing?

[Phil]

The washer 'stops' against a shoulder at the end of the thread. The sleeve then transfers this foce down the hole to the 'speady outy bit' at the end....

[Phil]

The hammer in versions have a length of unthreaded bolt on the end of the thread to hit them in with....

[Lobster]

Thanks for all the replies.

Yes, sure. Mine certainly weren't that tight; I had to tap them in with a hammer but it didn't take much effort. Soft brick? Too-heavy Ferm SDS drill wobbling in the hole? The thread on the fittings is M12, and the pack specified a 12 mm hole, which is what I drilled in the brick (would that be expected to yield a very tight fit?)

David

[Lobster]

Mm. will do next time!

Can anybody else (ie as well as urchaidh!) confirm that my 'resin' plan is a good way forward now?

David

[bigcat]

'worked' at

Resin is the best, used kilos of the stuff and it gives A1 fixing performance. If you use the non-epoxy types, move fast, as it sets very quickly indeed. Inject resin, stick threaded rod in, let set. Much superior to expansion fixings.

NT

[Dave Plowman (News)]

In what way? Cheaper?

I've used loads of rawlbolt type fittings around the house and never had one fail. Dunno about fixing into lightweight blocks, though.

[bigcat]

they bond better to the brick, as theyre bonding to every square mill in the hole, not just some of the area. Also they put no forces on the brick, so dont tend to break it, which expansion fixings sometimes do. Also they bond the material round the hole togther, which again expansion fixings dont. Theyre especially recommended for near-edge fixings, where expansion fixers would simply break the material.

NT