Screwing into porous wall with air gap

[tobiasger]

Do you have any pictures?

I've been involved in a multi-story building where on the inside of a solid two-brick wall, they nailed up split paneling and then a reed mat with plaster; this is not a very common method but I assume it was done with the idea of some insulation effect with the air gap the paneling on the inside creates..
I'm wondering if you might have something similar..

When you test wood screws, make sure to use at least 5x90mm screws..

I'll try today.

But is there any risk with using the facade plug I mentioned, regardless of the combination of materials in the wall? I mean drilling about 100 mm from the wall's surface into the brick and fastening with an 8x100 mm plug like that? I understand it might be unnecessarily expensive and perhaps overkill, but I'd rather feel that than choose the wrong method.

 

[Testarn]

A plug should generally be fully inserted into the stable material to function as intended. Allowing half of the plug to sit in porous plaster or "air" can result in it not working as intended, and then the screw can be pulled out under load, so yes, it is a "risk" to use those plugs if you do not insert them sufficiently.

If, as Janson insists on believing, there is wood behind the plaster, you should not use a plug. Then you should use a screw with wood thread.

 

[Testarn]

I have never heard or seen reed mat on a brick wall, as these were made on plank walls, see links in my previous posts..

And just because you haven't seen or heard about it, it hasn't happened...?

 

[tobiasger]

And what do we think about testing with lightweight concrete plugs just to see if it grips in the porous material?

 

[tobiasger]

I understand that it's most optimal to know exactly what material you're dealing with and choose the fastener accordingly, but there's something tempting (especially when it comes to facade plugs) about over-dimensioning the choice a bit and going with something that should work regardless.

The brick is somewhat "hollow" so it will partly attach in the air anyway, I think.

 

[Jansson69]

But have you tried a long coarse-threaded wood screw?
If not, do it! It will just be a lot of unnecessary speculation since we don't know the conditions...

 

[tobiasger]

But have you tried a long coarse-threaded wood screw?
If not, do it! It will just be a lot of unnecessary speculation since we don't know the conditions...

Is it best to try attaching a track at the top then, so you have it in place if it seems to work? I assume it's silly to screw only with a screw without a track and then have to screw out and in again?

 

[tobiasger]

Tried screwing wood screws directly into the wall, but they don't hold. I also asked a handyman who was here fixing some other things, and he also didn't think it felt like wood. We both agreed that it's a relatively thick layer of plaster, then some kind of air space, and then brick.

I've bought Fischer DuoXpand 8x100, but realized afterward that the screw that comes with it will be too short, since the Elfa rail adds 16 mm to the depth, so it would be too short. So I guess I have to try to find maybe a 120 mm long screw to use instead. Really complicated this.

 

[Jansson69]

Ok then it is easier if we know what is behind...
You need to make sure the plug goes into the brick or the joint in the brick by driving the plug in with a socket or something similar so that half of the plug is not in the plaster and air gap...
Then a rather thick and long screw is required as the brick/joint is often quite porous...

 

[tobiasger]

Ok, then it would be easier if we know what's behind...
You need to make sure that the plug goes into the brick or the mortar in the brick by driving the plug in with some socket or other, so that half the plug isn't in the plaster and air gap...
Then a rather coarse and long screw is required since brick/mortar is often quite porous...

Sorry for the delayed response, things got in the way.

Okay, so you mean to drill up to the brick, then from there drill the depth required for the plug and then "knock in" the plug so that it sets against the brick and then use a screw that is as long as the depth of the plaster plus the plug?

 

[Testarn]

Sorry for the delayed response, things got in the way.

Okay, so you mean to drill up to the brick, then from there drill the depth required for the wall plug and then "knock in" the plug so that it sets against the brick, and then use a screw that is as long as the depth of the render plus the plug?

Exactly.

Don't forget the thickness of the rail when calculating the screw's length.

 

[tobiasger]

Exactly.

Don't forget the thickness of the rail when calculating the length of the screw.

That's right, good point.

I assume I should drill with the diameter required for the plug? Usually in the apartment's inner walls I need to drill with 6 mm even if the plug is for 8 mm, because the hole gets so torn up. But here I assume it's the brick that dictates, and the drill should have the same diameter as the plug?

What can be used to tap in the plug?

 

[Testarn]

You can drill with a smaller diameter in the soft material, but in the brick, you need to use the size that the plug requires. I usually push the plug in by hand as far as it goes and then with the screw. Otherwise, a träplugg, a dorn, a screwdriver... It's usually easy to push in the plug.

 

[tobiasger]

You can drill with a smaller diameter in the soft material, but in the brick, you need to use what the plug requires.
I usually push the plug in by hand as far as it will go and then with the screw. Otherwise, a träplugg, a drift pin, a screwdriver... It is often easy to push the plug in.

Okay! But isn't it still like drilling directly with a larger diameter in the soft material since I still have to go through the soft material to get to the brick?

 

[Testarn]

Okay! But won't it still be like drilling directly with a larger diameter in the soft material since I still have to go through the soft to get into the brick?

Presumably not. If the hole in the softer material becomes larger than the drill bit, the larger drill bit can be inserted into the slightly larger hole before starting the machine, thus not making the hole even larger. You'll notice the difference when you do it.

Speaking of doing it, I think you've now gotten all the information and tips you can get remotely, so now it's time to put the drill in the wall.
Send pictures of how it turned out.

(If there are large marks/damage from the drilling, there are forum threads for that too. 😉)