Fit 47" 30kg LCD tv to cavity wall

[ssb1973]

HI,

I'm not sure if this is a cavity wall or not. I am planning to hang a large tv above the fireplace on a bracket. The house was built in 2001, so it is likely to be a cavity wall?

There are a few holes already in the wall above the fireplace, and I have measured that the thickness of the plasterboard is 2cm, and then there is a 2cm air gap behind the plasterboard, then there is masonry.

Is this a cavity wall? If the screws that come with the bracket are longer than 4cm, then could I just drill the screws into the masonry behind the cavity gap?
What are the best rawl plugs to use?


I have previously hung a heavy mirror on the plasterboard only using strong rawl plugs but drilled in at 45 degrees.

 

[big-all]

what you probably have is dot and dab

you "must" fix into solid masonary
at minimum you need to space out the bottom off the bracket and not overtighten the top otherwise it may pop the plasterboard

incidently half the weight tends to be in the base so assuming the base is removed

 

[ChrisFrost]

I'm not sure if this is a cavity wall or not.

As Big-Al said, what you have is Dot-n-Dab which is how a plaster fixes plasterboard to the walls: Dots of adhesive then the plasterboard is pressed in to place.

Cavity walls are going to be the ones on the outside walls of your property, not the chimney breast.

The brickwork of the chimney breast will probably be a single brick thickness. Inside the tunnel of the chimney will be a flue lining of some sort. It's important that you don't drill through the brick and damage the flue lining. Make sure you use a depth gauge on your drill so you know how deep you are drilling - a bit of tape on the drill bit will do.

I presume you want to complete the install in a day? If so then you need to plan for the cable runs (power & signal cables) as well as how to best anchor the bracket to the wall.

You have already found that your wall lining is dot-n-dab, so you know that you have plasterboard/2cm air gap/brick. The challenge you now face is how to support the bracket so that when you start to tighten the fixings so that the plasterboard doesn't cave in. What you need is a way of fixing so that the TV & bracket are solidly supported by the brick wall, but that doesn't put any pressure on the weaker plasterboard fascia. There is a product designed for this LINK. The cost is £18 for a set of four from Screwfix. With a large TV I'd tend to use more than four fixing points; 6 or 8 depending on the size and weight of the TV.

Apart from cost the only criticism I have of the rigifix dry wall anchors is that they use a conventional style wall plug. The problem with that is two fold. First, the fixing is only as good as the grip it gets inside the fixing hole. If the material is crumbly, or you drill a hole a little too large, or your hole hits the mortar between two bricks, or you hit the edge of a brick which then fracture when you tighten then the strength of that fixing is compromised. The second issue is that the anchor material is soft plastic - it can be damaged if overtightened, and there is also the risk of the plug working loose over time.

My preferred solution for hanging heavy valuable items is to use a quick-setting liquid resin anchor. Drill the holes, pump in some resin and insert a short length of threaded rod. The resin dries in 10 - 20 minutes, and because it fills all the little nooks and crannies it gets a really good grip. You then have 6 or 8 threaded studs on to which you can run some nuts front and back of the TV bracket so it's held securely without pressing on the plasterboard. Have a look at screwfix and search for resin anchor

 

[maltaron]

Another good way is to use 6mm Rawlbolts and relace the bolt with a suitable length of 6mm studding. Cut 6mm steel tube to the depth of plasterboard and gap less the thickness of a washer. Drill the hole in the masonry for the rawlbolt, insert the rawlbolt with washer and spacer, then mount the fixing bracket, fit washer and nut and tighten. I have fixed 35kg loudpeakers to dot and dab with 3 of these fixings with no problems.

 

[ChrisFrost]

I have fixed 35kg loudpeakers to dot and dab with 3 of these fixings with no problems.

Don't you mean through rather than to, right?

 

[maltaron]

Well spotted, you are correct.

 

[ssb1973]

Thanks all for your responses. I have taken them all on board, many thanks for taking the time to help.

The rigifix product looks like it will do the trick, another one I have seen is called dryline pro. Anyone have any experience of using dryline pro?

 

[ssb1973]

thanks for all your help. I did this over the weekend with meticulous planning and measuring. I made six 10cm depth holes in the plasterboard using a 12mm drill piece, inserted 6 pieces of Rigifix M6 bolts. Attached the bracket to the wall.

The supplied bolts that came with the bracket were 16mm and 40mm, and were too shallow or too deep for my tv VESA slots, so I had to get some M8 25mm roofing bolts, which fitted perfectly.

The TV is now up on the wall and looks nice. It seems like an easy job in a few sentences, but took me 1 and a half days which included travelling between B & Q, Wickes and homebase, every now and then.

The only worry at the moment is whether I've drilled into the chimney flue, how deep are chimney flues from the plasterboard, I drilled 10cm from the surface of the plastboard.

 

[ChrisFrost]

The only worry at the moment is whether I've drilled into the chimney flue, how deep are chimney flues from the plasterboard, I drilled 10cm from the surface of the plastboard.

Go to the outside corner of your house. Look at the bricks, you'll see log sides and short ends. The short end is the depth of the brick you drilled in to. If the depth of the brick + the thickness of the plasterboard and gap all combined is less than 10cm then you have potentially got a problem....but I very much doubt it is.

 

[ericmark]

Beware my house has a flue brick and the gas tight skin is only about an inch or so thick one has to be very careful not to drill into the flue.

 

[ssb1973]

I've looked on the outside and the short end of the bricks are about 10cm.

I measured the gap from plasterboard to wall before drilling -

The plasterboard is 2cm thick, the air gap is another 2cm (dot and dab wall), so I must have drilled 6cm into brick, or breeze block? The house was built in 2001 if that helps