The lever effect describes how the force applied to a fixing increases as the load moves further away from the wall. Holding a weight with your arm straight down by your side is manageable, but extending your arm outward makes the same weight feel significantly heavier. The same principle applies to wall fixings: a TV mounted close to the wall creates mainly downward shear force on the fixings, but a TV on an extended cantilever bracket, or a heavily loaded shelf projecting from the wall, creates an outward tensile force at the top fixings and an inward compressive force at the bottom. On a dry lined wall, this combination of forces is particularly damaging because the plasterboard has no solid backing to resist either of them.
Why Heavy Duty Fixings Fail on Dry Lined Walls
In brief: Heavy items fall off dry lined walls not because the fixings are poor quality but because standard fixings are the wrong type for this kind of wall. In a dot and dab or dry lined wall, there is a void between the plasterboard surface and the solid masonry behind it. A standard fixing has nothing to anchor against in this void, so the load is carried partly by the plug spanning the gap and partly by the plasterboard, which is not designed to bear significant weight. The bigger the load and the further it extends from the wall, the more likely the fixing is to fail. The solution is a fixing with a rigid steel core that spans the void and transfers the load directly to the solid wall.
(Or… Why is my new TV smashed on the floor?!)
This is one of the most frequently asked questions (FAQs) that our technical support team get asked, or more accurately “…will using Corefix fixings stop heavy items becoming loose or falling off a dry lined or dot and dab wall.” As this seems to be a fairly widespread issue, here is some information that we hope is useful to both professional installers and the DIY enthusiast.
Dry Lined (Dot and Dab) Walls
If you’re working in a modern house or an extension that has been constructed in the last 20 years or so, it’s pretty likely that the external walls will be what’s commonly called “drylined” or “dot and dab” walls. This is where sheets of plasterboard have been fitted over the blocks or bricks on the internal skin to provide a smooth surface ready to accept a final paint or paper finish.
The plasterboard is usually attached by dabs of adhesive or cement, which is where the name “dot and dab wall” comes from. Wooden battens are another option but this takes longer, costs more and is therefore less common.
The result is that there is a gap between the solid material of the wall and the plasterboard finish.
It is this void that lies at the heart of the problem when it comes to supporting heavy loads, and it’s a problem because of the way a fixing works. This is a really simple piece of mechanics and has been around for centuries. Essentially there is a hole into which a screw or nail is inserted that also goes through the item being attached.
The modern method of using a plug in the wall which expands into the hole was developed by John Joseph Rawlings way back in 1911 and although the material used has changed over the years, the basic principle has remained the same. The plug expands as the screw is tightened, forming an excellent mechanical anchor with the solid material that is used for the wall.
The problem with the dot and dab or dry lined wall is that there is nothing for the fixing to anchor with in the void behind the plasterboard and therefore the whole of the weight is being supported by the screw and the plug extended across this gap and the plasterboard finish.
The other issue is that the plasterboard itself is not supported by any solid material behind it and it can easily deform or collapse into the cavity when trying to tighten up your fixing, (frame fixings are notorious for this) and the more weight that is applied the more likely it is for the plasterboard to fail in this way.
As is shown by the image below, when the weight is applied the screw or the fixing can bend in the void or the plasterboard can break up into the void – or both!
Any or a combination of these factors will cause the fixing to become loose or detach and fail completely.
There is the added complication of where the weight is applied. As the diagram below indicates, the further away from the wall the load is placed the greater is the force acting away from the wall. This can also have a ‘lever effect’ which can pull the anchor out of the wall as well. You can experience the difference that this levering effect has on the force applied to the fixing – hold a heavy item in your hand with your arm extended straight down by your side. Now, still with your arm straight, start to move your arm away from your body. You will immediately feel the difference and you’ll need a lot more strength the further away from your body the weight goes.
Typical examples of where these conditions occur are when attaching shelving, wall cupboards, boilers, radiators and of course wall mounted TV brackets.
How to Stop Wall Fixings Failing
There are two ways to stop this problem occurring.
The first is to make sure you screw onto something solid. If the plasterboard has been attached with battens, these can be used to attach the item to the wall using suitable screws. The problem here is that the batten might not be in the desired location.
It is also possible to add your own battens to the wall and this is a technique sometimes employed when fitting cabinets. Basically it requires the plasterboard to be cut out where the cabinet is going to be attached and a batten securely fixed to the wall. The cabinet can then be screwed to the batten. The downside of this is that it is time consuming and unsightly if the item is ever removed.
The easiest way to overcome the problem is to choose a fixing which bridges the void between the plasterboard and the masonry and transfers the load directly to the solid masonry behind. This means the fixing is not reliant on the strength of the plasterboard.
Copper pipe is sometimes used to sleeve the fixing to tie the plasterboard into the block work behind although once again this requires extra work and can be quite time consuming if a lot of fixings are needed.
At the Metex we focus on practical innovations that bring real benefits to the construction industry with the objective of saving both time and money as well as making everyday tasks easier to complete.
We researched the problem of fixing heavy loads to dot and dab walls and came up with a simple but highly effective and practical solution. The Corefix Connect wall fixing for dot & dab walls has a steel sleeve that fits inside the plastic plug (as shown in the diagram). This stops the plastic plug from bending or deforming in the void when a load is applied. Furthermore as the diagram shows, the weight is now supported by the masonry and not the dry lining so the plasterboard will not cave in or fracture and collapse into the void.
Corefix Connect fixings are easy and quick to fit and require no special tools. They can also support substantial loads, having been independently tested and certified to a safe working load of 100kgs using just four fixings in fact in-house tests have securely supported 250kgs.
So, to finally answer that original question, heavy loads become loose or fall off dot and dab walls simply because an unsuitable fixing has been used.
If you have any questions at all please don’t hesitate to contact us. You can email us or call us for free on 0800 130 3646.
Frequently Asked Questions
Why do heavy duty fixings fail on dry lined walls even when they reach the masonry?
The problem is not whether the fixing reaches the masonry but what happens to the plasterboard in between. On a dry lined or dot and dab wall, there is a void between the plasterboard surface and the solid blockwork behind it. When a standard fixing is tightened, the screw pulls the plug inward toward the masonry, and because there is nothing supporting the plasterboard from behind in that void, the board gets dragged along with it. This crushes and distorts the plasterboard, damages the wall finish, and leaves the fixing without a stable contact surface. The heavier the load and the longer the fixing is in place, the worse this distortion becomes.
What is the difference between a fixing that fails suddenly and one that fails gradually on a dry lined wall?
Most fixing failures on dry lined walls are gradual rather than sudden. The plasterboard material around the fixing crumbles slowly under the sustained load, the fixing becomes progressively looser, and the item on the wall begins to tilt or shift before eventually coming away entirely. This gradual process can take months or even years, which is why a fixing that feels secure when first installed can fail long after the installation is complete. Sudden failure is more likely when a fixing is overloaded quickly, for example when additional weight is placed on a shelf that was already at its limit, or when a cantilever TV bracket is extended fully for the first time.
Can adding more standard fixings solve the problem on a dry lined wall?
Using more fixings spreads the load over a wider area and can reduce the stress at each individual point, but it does not solve the underlying problem if the wrong type of fixing is being used. If each fixing is still relying on the plasterboard rather than the masonry to carry the load, using four inadequate fixings instead of two still leaves the plasterboard doing work it is not designed to do. The correct solution is to use fixings that bridge the void and transfer the load to the masonry, regardless of how many are used. Once the right fixing type is selected, using the recommended minimum number or more gives the best result.
What types of items are most commonly affected by fixing failures on dry lined walls?
The items most commonly involved in dry lined wall fixing failures are televisions, kitchen and bedroom wall cabinets, floating shelves, radiators, and boilers. These all share the characteristic of being relatively heavy and often mounted on brackets that hold them away from the wall, which increases the tensile force on the fixings. Televisions and shelves are also often loaded unevenly or have additional weight added after installation, which can push a marginal fixing past its limit. Boilers and radiators carry the additional complication of thermal cycling, where the repeated expansion and contraction of the unit as it heats and cools gradually loosens a fixing that is not solidly anchored in the masonry.
How does Corefix Connect solve the problem of fixing failures on dry lined walls?
Corefix Connect addresses the root cause of the problem rather than just the symptoms. Its steel core spans the void between the plasterboard and the masonry, transferring the load directly to the solid blockwork so the plasterboard carries none of the weight. A built-in shoulder stop inside the plug prevents the steel core from pushing through when the screw is tightened, which means the plasterboard stays flat and undistorted throughout installation and in use. The result is a fixing that behaves on a dry lined wall as a good masonry fixing behaves on a solid wall, with the load path going through solid material rather than relying on a weak intermediate layer.