3 Steps to Install a Defence Grid

3 Steps to Install a Defence Grid


– Focus on the defence grille

– Step 1: Locate the location of the grille

– Step 2: Case 1: Sealed installation

– Step 2: Case 2: Installation with fixing plates

– Step 3: Finishing work

The defence grille allows securing a room while acting as a guardrail when installed on a window.

Available in kit or ready to install, the defence grids are made of metal (steel, iron, aluminum…) for more excellent resistance to break-ins.

There are two different ways to install this type of fence:

– the installation in a table;

– the installation in frontage.

In both cases, you have the choice between two types of installation: the bars are either sealed or screwed into the masonry.

Attention: the sealed installation is the most secure; it would be easier to unscrew the fixing plates in case of a break-in attempt.

Here is the following method to install a defence grille on a window.

Focus on the defence grille

Here are some tips on how to choose your grille:

– Remember to choose a grille approved by insurance companies to avoid inconvenience in case of burglary: it is advisable to choose a model whose vertical bars are spaced at a maximum of 12 cm. The diameter of the bars should be 20 mm or 4 cm for square bars.

– Before purchasing, take all the measurements of the outer and inner frame of the window to select a suitable grille.

– Before installing the grille, choose a type of installation: in front of the transom, embedded or fixed.

There are many styles of defence grilles and many shapes: straight, spiral, forged… It’s up to you to choose the one that best suits your home.

Equipment to secure your window



Cat’s tongue



Chemical sealant kit


Spirit level


Rustproof paint


Fixing plates

1. Locate the location of the gate

Depending on the model you choose, you will need to locate the location of the gate and any fixings. To do this:

– Assemble the different elements according to the manufacturer’s instructions.

– Mark the location in the window frame for a panel installation or on the wall for a front installation.

– Check the alignment of the marks.

2.1 Case 1: Sealed installation

A defence grille can be sealed in the wall directly in the window masonry with mortar, whether you have chosen a façade or a transom installation. This is the safest way to prevent break-ins.

Attention: protect the glass with a plywood or medium board before drilling.

Start by drilling the fixing holes. To do this, mount a drill bit on the drill:

– Mount a drill bit on the drill press appropriate for the type of support and larger in diameter than the bar.

– Drill the holes to a depth of 8 cm. If necessary, mark the drill bit with tape.

– Clean the holes well to remove any dust.

Note: you can also make these holes with a sharp chisel and a sledgehammer. The holes should be large enough to fit the iron bars.

To seal the grate:

– Use either sealing mortar or a sealing kit. Refer to the manufacturer’s instructions to prepare the product.

– Place the iron bars in the holes (tilting them will make it easier).

– Prepare the mortar or chemical sealant.

– Insert the cannula/nozzle into the space between the iron bar and the wall.

– Put chemical sealant generously in the 2 holes of the same bar (right and left sealant). Act quickly, as chemical sealant has a reasonably fast setting time!

– Hold the bar horizontally during the setting time. You can use a wedge to help you.

– Remove excess mortar or resin.

– Follow the same steps for the second bar.

2.2 Case 2: Installation with fixing plates

A defence grille can also be screwed into the wall, on the facade or in the picture.

Attention: this installation is less safe than the sealed installation!

Start by preparing the fixing holes. To do this, you must

– Drill the mounting holes for the grille with the drill.

– Place the mounting plates on the holes.

– Fasten the screws in the holes with a screwdriver or a screwdriver, then position the grille.

Note: You may want to seal the grille fasteners into the wall for added strength. To do this, drill upper holes and proceed with the sealed installation either with a bit of mortar or a sealing kit.

3. Finishing work

Once your installation is complete, you still have some finishing work to do:

– Fill in any holes with a conventional concrete filler.

– Sandpaper the bars.

– Paint the bars, taking care to choose paint for exterior iron. This paint usually has a built-in anti-rust treatment.

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