expanding bolts in brick

[Chris Holford]

I need to make a very strong fixing to a brick wall using expanding bolts 90mm long. I drilled 14mm dia holes in the brick. After going into the brick about 30 t0 40mm, the drill broke through into a cavity in the brick and then started to 'bite' about 30 to 40 mm further in.

I suspect the bricks are the type with 3 large vertical holes.

Help!

( I have wondered about the following solution;

get a mastic gun and empty cartridge

fill it with wet cement and inject the cement into the brick via the 14mm hole hammer a 12mm wooden plug into the hole to consolidate the cement in the void

drill out the wooden plug after the cement has set

Any comments on this idea? -or alternatives? The fixing will need to take a large load. Thanks

[Dave S]

Is the load in sheer or straight pull? I build a mezzanine in the roof of a garage using Mulitmonti bolts. Theres a ton of stuff on it now. Cross posted to uk.diy as thats probably a good place to get an answer from

Dave

[RubberBiker]

Rather than the uncertain repair that the OP proposes, I would suggest simply filling the original drillings and starting again *with a much longer fixing*.

Is this a single leaf of masonry, or is there an inner leaf? Is the outer leaf possibly not intended to take extra structural loads?

I'd also recommend multimonti - I think some very long ones are available now.

IIRC the data sheet with multimonti covers all common load configurations. I used multimonti (10*140mm), 4 to a joist hanger to support an upper floor in a chapel conversion (all inspected and passed by building control). In that configuration the safety margin from calculations was generous - however, like most building work, quality of workmanship makes a huge difference. I made up a jig to ensure that all pre-drillings were set as accurately as possible, and every single bolt was totally secure (and I set a couple of test multimonti, then tried (unsuccessfully) to lever them out with a very long crowbar).

The OP doesn't say what his application is. Is it safety critical - a roof, floor or structural component? If so, professional or very experienced advice may be necessary, and/or building control oversight.

Are there dynamic factors, wind or snow loading?

Where you're using fixings as critical structural component, I really wouldn't do anything that isn't *certain*, and the repair method proposed sounds far from certain.

[Tim S]

Dave S coughed up some electrons that declared:

Or switch to resin anchors? No doubt that they're strong enough and they won't damage the brick near a cavity.

Cheers

Tim

[fred]

In article , Tim S writes

Prob best used with these to avoid using a cart of resin per hole, pricey though:

or if it's only a few holes, it would be cheaper to fill the void (if it is only a 3 hole brick).

[The Medway Handyman]

Me too. Easier to pull a sailor off your sister than pull one out.

[sm_jamieson]

The only thing I wondered about multi-monti (I've not used them). SInce they cut their own thread, the hole size must be quite critical to the strength. With a slightly wobbly SDS, or slightly crumbly brick, the hole could be a millimeter larger, which could make all the difference ? Simon.

[george (dicegeorge)]

Are the multi-monti better than the bolt things which expand?

Do you just drill a pilot hole with a sds drill then drive them in with an impact driver?

Do they unscrew, or is that that once they're in they're in?

[g]

[Cicero]

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Screwfix give a good description of their usage including drill size(s) required:

[Steve Firth]

Much better in my opinion. They don't expand so they they don't damage the bricks. They also need a much smaller hole.

Yes.

No, you just screw them in with a normal screw driver, nut driver or spanner. They're very easy to drive home. They come with a choice of a normal bolt head or a Torx head.

In general I would use a longer Multi-Monti than an expanding bolt to ensure a good fix.

[The Medway Handyman]

Much less chance of a brick splitting & you can use them pretty close to edges - although not 'right' up to an edge.

Yup. Decent drill driver will put them in, impact driver is obviously faster.

No, you can take them out & put them back no problem, or take them out & resuse them.

Brilliant things. Somebody here put me on to them, can't recall who, but thanks :-)

[The Medway Handyman]

I guess it is, but in practise I've not really had any problems. I use the

6mm with a 5mm pilot & the 7.5mm with a 6mm pilot. You get the odd failure, just like you would with any fixing, but overall they are brill.

[js.b1]

I notice they are carbon steel.

I assume sufficiently oversized w.r.t. corrosion over 40yrs, or is it Build-Like-Barratt these days?

Then again get enough damp to eat a big screw away and even a tough brick can be drilled with a screwdriver.

Anchor bolts are available in stainless, as are resin fastenings, the problem with anchor bolts is they can be very fussy about hole size and stainless needs oversizing being a relatively low grade. Still most roofs are still standing held together with little more than a big nail at an angle with more attention to the finger & cigarette position than wood, nail & hammer.

[Dave Osborne]

I notice that the Screwfix blurb cites "reusable", but the technical approval (sec. 4.2.2) specifically states "The anchor may be used only once".

Also, it seems they are only suitable for static or quasi-static loads and have a design life of only 50 years.

For the 10mm dia. bolt, the nominal hole size is 8mm with a maximum size of 8.45mm. So yes, you need to be careful drilling the hole.

Compare this with a 10mm dia. shield anchor (Rawlbolt) where the nominal hole size is 16mm and the maximum is (not stated by Rawl but) probably in excess of 18mm, so a much bigger hole but much more leeway on the hole size.

[Cicero]

>

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I would guess that this is a case of a specialised product finding a more mundane use because it's so versatile. It's always the responsibility of a user to satisfy himself that an item is fit for purpose. The fact is that these things can be undone and re-used but probably not more than once or twice, and not in critical situations.

Cic.

[The Medway Handyman]

>>> >>> Cic.

I've reused them many times e.g. put them in, realised it wasn't in the right place, re drilled & reused them many times.

Only? I'll be getting a telegram form the Queen before then :-)

Not that careful in my experience. Normal 5 or 6mm bit, bog standard SDS, no real problems.

And much more chance of the expansion cracking the brick/concrete.

Also a 5 or 6mm hole is less stressful to the substrate than a 5 or 6mm hole.

I can only quote from my experience, but the 7.5mm are really easy to use & incredibly strong & reliable.

[Owain]

Why, did you forget to count the corgis before screwing down the last piece of decking?

Owain

[The Medway Handyman]

Don't you mean 'count the gas safes?

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "js.b1" saying something like:

That's a good point and it's just as well for most of us that during construction things tend to stay where they're put. The standard of workmanship I've seen in the construction industry would boggle your mind.

[Robin]

Another vote for resin - also keeps water from entering the hole