Screwing into a no-fines concrete wall: What screws to use?

[DIYalot]

Hi. Perhaps a bit obscure: I did not think it possible, but workmen were able to attach wood to the no-fines concrete wall in my home. I may need to do the same. Does anyone know what screws I can use? Possibly a flexible type I think. Thanks. Rich

 

[Bonni]

Making holes in no fines concrete walls

House walls are no fines construction. It's a devil to affix things to these walls. I like the idea of using a diamond core drilll, to make say 15 or 16mm diameter holes. The idea would then be to plug with a dowel. Be nice if I could drill into the wall about 100mm or so. Any product...

www.diynot.com

 

[DIYalot]

The thing is, I have used a 16mm diamond tile drill with 16mm oak dowel. It's OK, but when I saw the worker simply screw through the wood (acting as a template) into the no-fines wall, I was gobsmacked and thought, Oh, it can be done, much more convenient than boring out holes. Whether it's good practice to screw directly into a no-fines wall, I don't know. The guy was fitting a false wall in front of the no-fines wall, so not much weight.

 

[Deleted member 174758]

No fines concrete uses flint as the aggregate with a small amount of sand and cement as a binder. The binder us relatively soft, but flint is very hard (Mohs 7 - diamond is Mohs 10, whilst tungsten carbide used in TCT drills is Mohs 9). So you can drill flint with a TCT masonry bit. The problem is that standard 2-flute masonry drill bits tend to skid off the flint, so you ideallt need a 3- or 4-flute masonry bit, some sort of guide to keep them on line, and a stronger hammer action than combi drills offer. So your man may have been using an SDS drill with a 3- or 4- flute drill bit (Heller, deEalt, Hilti, etc) and the lump of wood was acting as a guide. On the rare occasions I drill the stuff U use my corded SDS (3kg, 4.2J) as opposed to my cordless (2J) which makes the job a lot easier

 

[Notch7]

No fines concrete uses flint as the aggregate with a small amount of sand and cement as a binder. The binder us relatively soft, but flint is very hard (Mohs 7 - diamond is Mohs 10, whilst tungsten carbide used in TCT drills is Mohs 9). So you can drill flint with a TCT masonry bit. The problem is that standard 2-flute masonry drill bits tend to skid off the flint, so you ideallt need a 3- or 4-flute masonry bit, some sort of guide to keep them on line, and a stronger hammer action than combi drills offer. So your man may have been using an SDS drill with a 3- or 4- flute drill bit (Heller, deEalt, Hilti, etc) and the lump of wood was acting as a guide. On the rare occasions I drill the stuff U use my corded SDS (3kg, 4.2J) as opposed to my cordless (2J) which makes the job a lot easier

I find the dewalt extreme bits very good for drilling, they work well with a small mains SDS in hard walls and in cordless drills.

 

[DIYalot]

Just to be clear, the worker did not use a drill to make a hole in the no-fines wall, he simply used his portable screwdriver to drive screws into the no-fines wall, using the wood he was attaching as a sort of template. I'm thinking of doing the same.

 

[DIYalot]

Question: There is a kind of punch that has flutes that I have used to punch a hole in a no-fines wall. What is the name of such a punch? I've forgotten. Ta.

 

[robinbanks]

Can you remove one of the screws he used and show us a picture of it?

 

[Deleted member 174758]

Well, never heard of any flexible screws (screws are steel in the main, anyvsteel doesn't bend a that well), and the method I quoted is the one you need to follow if you intend to put any sort of loading onto the fixing. But as Robin says a photo would help

 

[crank39]

Could they have used a Hilti gun then?