Best way to patch up drilled holes in a concrete wall?

[oldmanriver]

I've been trying to mount a kitchen cupboard to a concrete wall by drilling a couple of holes and using rawl plugs. I can drill one of the holes fine, but the other hole refuses to turn out neatly. It feels like the drill hits something hard and instead of going any deeper, it starts to expand the hole. I have tried various places near my original hole and there seems to be the same problem. I think with a little work I might be able to get through it, but the problem is that I have more or less used up all of my potential drilling sites.

Is there anything I can fill the holes with (if necessary, after expanding them), which will be sturdy enough to drill into and support the unit? The holes are not massive; they are drilled with a 6mm masonry drill bit, but their edges have been somewhat eroded, so a rawl plug doesn't sit safely inside.

 

[Symptoms]

old - you've probably drilled in and hit one or the steel rebars (reinforcing bars) which your masonry bit won't touch. Obtain a 6mm HSS (high speed steel) twist drill, sometimes known as a 'jobber') and deepen the hole with this 'till you get through the steel then further with a masonry drill through the concrete if necessary. Get a couple of jobbers as it's not uncommon for a slip to happen and a breakage to occur (wear safety specs).

 

[oldmanriver]

Thanks for the reply, Symptoms. I will look into getting hold of one.

Regarding the holes I have already drilled, it has been recommended to me to remove the debris and fill them with cement, and then drill into the cement once it is dry. However I am concerned that the weight of the unit might be too much for a rawl plug in drilled into the cemented patch. There isn't much room for maneouvre, so ideally I would like to put the holes in the same place as I tried to the first time. Is this feasible?

 

[Bilioustrumpstaine]

Just using cement will not provide the best fixing.

If you can drill through the metal bar (you are sure that it isn't a gas pipe ) then use a longer screw with a rawlplug punched into the wall, the head of the plug will catch on the bar, good solid fixing.

 

[oldmanriver]

I'm not really sure whether there is metal behind the place where I'm drilling, because some of the holes seem deep enough, just too wide now. My guess is that I have hit a particularly hard bit of concrete. I couldn't say for sure, though.

The hole was drilled with a 6mm masonry drill, but has become a bit wider. If we assume that there is no metal bar behind, and that I am able to drill deeper by, say, breaking it down with a masonic nail and hammer, what could I fill the hole with so I am able to drill again in the same place?

 

[rebuke]

Could you not drill the hole bigger (e.g. to 8mm) and then use a larger (e.g. brown) rawlplug (and a larger screw if necessary)?

 

[oldmanriver]

Thanks for the reply, rebuke; I think I probably could get a bigger rawl plug to sit firmly in the hole, but the mouth of the hole was expanded a bit when I hit whatever hard surface is behind. If the rawl plug grips the wall deeper in the hole, can I just use filler to patch up around the mouth of the hole?

One other thing; I'm not sure what my wall is made of, but I'm starting to think it is plaster over brick. I live in student accommodation (yes, we are allowed to drill away), and since my room is next to a staircase, I have access to both sides of the wall. It is certainly brick on the other side. If it is plaster over brick, does that mean I have to drill deep enough to go through the brick? And if it is indeed brick I have hit, what could explain the relative ease with which I could make the other hole?

 

[rebuke]

If it's plaster over brick, then you should try to have the rawlplug gripping in the brick, as the plaster will just crumble if it gets any load on it. Unfortunately, some rawl plugs are designed with a ring at the front so they sit flush on the surface, hence often don't go deep enough - the proper ones will go into the hole, and then with a screwdriver you can just tap them in until they go beyond the plaster.

It's possible the first hole you drilled you hit mortar between bricks. I'm assuming here that you're using a hammer drill, so I'd be surprised if it would really struggle to drill through brick. The plaster around the front of the hole may crumble a bit (particularly if it's old plaster), so I wouldn't be too worried about that, as long as you get the plug properly in the brick, it should be fine (you can then use polyfilla or similar around the front, but if it's going to be hidden by your cupboard anyway then I wouldn't bother).

(Note I'm not an expert, just a DIYer, so no guarantees what I'm telling you is accurate etc!)

 

[foxhole]

SDS drill and bit required, will go thru like a hot knife thru butter.

 

[oldmanriver]

Thanks for the tips, guys. It seems that my drilling assistant wasn't completely familiar with the correct technique, as I was able to drill into the brick myself without any major complications by not drilling at full speed.. (If a job's worth doing..) Now the problem is that all the places where I could feasibly put the holes have already been drilled, and none of the holes are of any real use. What can I do? Help please, before I collapse my wall in frustration!

 

[foxhole]

Just drill where you need to but deep, go to about 75mm and use long screws.