What if a drilled hole is too big?

[blup]

Start with a small diameter masonry bit, 3mm, and drill slowly with hammer action turned off. Increase the speed when you have got through the plaster, using hammer action if necessary. Then change up to the correct sized bit, again starting slowly. Allow for 40mm of the hole in the masonry so the plug and screw are tight. Hand tighten the screw as driving it with a powered drill can spin the plug.

 

[Nanako]

It will stop your wondering and your wandering

will it actually prevent the plaster crumbling, or just hide it?

 

[Nanako]

Since its clear that i've not been drilling deep enough, i have just taken delivery of a set of 8x80mm screws and plugs

They are CHUNKY, this might be too much. Is there such a thing as too much? Are there any downsides to drilling excessively deep

 

[robinbanks]

8x80mm is huge.. Are they concrete screws?

I thought you were looking to mount something that would need brown plugs (and 4.5 or 5mm screws)

Show us pictures of what you have bought, fixings wise, and what you're aiming to fix to the wall

 

[Nanako]

8x80mm is huge.. Are they concrete screws?

I thought you were looking to mount something that would need brown plugs (and 4.5 or 5mm screws)

Show us pictures of what you have bought, fixings wise, and what you're aiming to fix to the wall

in this particular instance i was fixing a shelving unit on the ground, so these screws are just to stop it sliding away from the wall, not load bearing. But they have done the job admirably! These shelves are definitely not moving now

Someone mentioned above that screws should go 40mm into masonry, does that sound right?

I figured its better have more than less, and also there is the plaster thickness to consider, so i doubled that.

i only got 12 of these, i'm probably gonna use a few more of them for putting curtains up later this month

Are they excessive? If so, should i get some smaller ones?

 

[robinbanks]

Oh, no, they aren't 8mm screws - the screws will be more like 5mm and the plugs are 8mm (need an 8mm hole)

The general rule for screwing an item to a substrate is that the screw length should be at least 3 times the thickness of the item. In cases where you have some soft layer to get through first, you remove it from the equation..

So if you have a 20mm thing to fix to a hard wall, seek a 60mm screw, 40mm of which will be in the wall.

If the wall has a 30mm layer of soft plaster, use a 90mm screw: 20mm in the work item, 30mm to get past the plaster and 40mm gripping the brick inside the wall

 

[Nanako]

Oh, no, they aren't 8mm screws - the screws will be more like 5mm and the plugs are 8mm (need an 8mm hole)

The general rule for screwing an item to a substrate is that the screw length should be at least 3 times the thickness of the item. In cases where you have some soft layer to get through first, you remove it from the equation..

So if you have a 20mm thing to fix to a hard wall, seek a 60mm screw, 40mm of which will be in the wall.

If the wall has a 30mm layer of soft plaster, use a 90mm screw: 20mm in the work item, 30mm to get past the plaster and 40mm gripping the brick inside the wall

My bad yeah the plugs are 8mm, thats the drill bit i used for them, no idea the size of the screws inside, but i guess that sounds right

Why is the rule based on thickness? Surely the expected weight or load of the item should be factored into this?

Anyways presumably these are minimums, but what about an upper limit? Is there any reason not to drill halfway through the wall for everything?

 

[ATTQ]

Interesting thread this. Because the answer was in the first reply "Tap the plug below the surface" but you didn't catch it, other posts didn't repeat it and made other suggestions and next thing you're buying structural fixings you could hold a wall up rather than for fixing things onto a wall.

If the plaster is 2cm think and the plug is 5cm long you drill a hole that is 7-8cm deep and with a rod or something about the diameter of the plug you tap the plug in with a hammer so it is well down in the hole, all of it in the brick. Then you just need slightly longer screws to make up for the extra depth you pushed the plug in.

 

[Nanako]

Interesting thread this. Because the answer was in the first reply "Tap the plug below the surface" but you didn't catch it, other posts didn't repeat it and made other suggestions and next thing you're buying structural fixings you could hold a wall up rather than for fixing things onto a wall.

If the plaster is 2cm think and the plug is 5cm long you drill a hole that is 7-8cm deep and with a rod or something about the diameter of the plug you tap the plug in with a hammer so it is well down in the hole, all of it in the brick. Then you just need slightly longer screws to make up for the extra depth you pushed the plug in.

Ohhhh thats what that means, huh. i had no idea and it wasnt explained!

 

[ATTQ]

Ohhhh thats what that means, huh. i had no idea and it wasnt explained!

Next time ask what the person means if its not clear enough. People probably assumed you knew what it meant but weren't going with that answer for some reason.

Might be an idea to redo the plugs you already did if they aren't deep enough. You can probably get the plugs out once you've taken the thing off, if you screw the screw back in just a turn or 2 and pull it

 

[robinbanks]

Why is the rule based on thickness?

Because it's easy

Surely the expected weight or load of the item should be factored into this?

Sure; it's a minimum, adequate for most things but you do need to keep your brain switched on. If you're mounting a 100kg TV on the end of a 1 metre long arm, which has a backplate made of 2mm steel, on a stud wall with 10mm plasterboard, obviously a 16mm screw (2 for the plate, 10 for the plasterboard, 4 into the stud) isn't going to cut it, but most things aren't a huge lever generating massive pullout forces, so the clamping friction plus the bending resistance of the screw is enough to counter the shear from the thing sliding downwards/pulling out slightly

Anyways presumably these are minimums,

I did say the words "at least"

but what about an upper limit?

Don't drill all the way through the wall if you don't own the other side of it!

Is there any reason not to drill halfway through the wall for everything?

It would be overkill to drill 150mm into a 300mm wall, to install a resin anchor, to hang a picture

 

[Harry Bloomfield]

It would be overkill to drill 150mm into a 300mm wall, to install a resin anchor, to hang a picture

That depends on the picture. Some of us have extensive family portraiture

 

[opps]

Interesting thread this. Because the answer was in the first reply "Tap the plug below the surface" but you didn't catch it, other posts didn't repeat it and made other suggestions and next thing you're buying structural fixings you could hold a wall up rather than for fixing things onto a wall.

If the plaster is 2cm think and the plug is 5cm long you drill a hole that is 7-8cm deep and with a rod or something about the diameter of the plug you tap the plug in with a hammer so it is well down in the hole, all of it in the brick. Then you just need slightly longer screws to make up for the extra depth you pushed the plug in.

Whilst I agree in principle. In some victorian houses that I have worked in, and which have soft red rubber bricks and 30mm of plaster, burying a single plug can result in the plug being pulled forward when the screw is tightened. I often hammer in two brown (7mm) plugs, so that the deepest cannot be pulled forward.

 

[JohnD]

If I have plugs that are not gripping the brick enough, I clean out the dust and put a dab of builders adhesive in the hole, push the plug in, and leave it to set. The adhesive prevents the plug from moving, and transmits the expansive force to the brick, so the load is carried by the brick and plug. It's an economical and easy method. You can put a long screw a couple of turns into the plug to use as a handle.

Soft red bricks that are a bit damp seem particularly bad, I suspect the damp turns the red dust to slippy mud.