How To Block Up A Fireplace With Plasterboard?

July 10, 2023


Blocking up a fireplace with plasterboard - How to do it?

How to block up a fireplace with plasterboard? The truth is that there are ways to do it easily and economically. Trust our tips and make sure that everything serves its purpose well. In this article, we suggest how to block up a fireplace with plasterboard safely, step by step. We hope that our advice is useful and will ease your work!

Why block up a fireplace with a plasterboard?

Blocking up a fireplace is reasonable, and it makes sense, especially because it can add extra space to your room. Not only that, such a change can make your home more heat efficient. It is like that because it is easy for heat to escape from a place such as an old fireplace. Generally speaking, a fireplace is not an efficient way to heat your home.

What's more, having a fireplace in practice means having a lot of work. Not everyone has the time to take care of a fireplace. Lack of time is a main reason for closing off a fireplace, which can be described as “sealing off the fireplace opening or flue system to stop the flow of air to and from your home”.

There are many guides showing the ways of closing: a fireplace with a timber surround, a fireplace with tiled surrounds, a fireplace with a stone or brick surround, brick up an opening, board it up and fit a chimney cowl. Check this one!

How to block up a fireplace with plasterboard in stages?

Blocking up a fireplace with plasterboard consists of a few stages. These are, among others, installing a fireplace insert, constructing and insulating, making marks, cutting profiles, installing them to the floor, ceiling, insulating the back wall of the fireplace, insulating the front wall (existing wall) and a few more steps. We have described everything thoroughly below!

Installing a fireplace insert

The first thing you should do is to install a fireplace insert and to connect it to exhaust pipes or to air supply from the outside if there is one. You need to remember that the ground should be non-combustible and durable. The best option is making a screed. The fireplace insert can be installed on a foundation or a stand. It is especially recommended to mount the fireplace insert on a stand - it is easier, faster, and safer.

After installing the fireplace insert, you should get a fire lit. The aim is to let the paint dry, to check the tightness of the exhaust pipes, and to get rid of an unpleasant smell after curing the paint. Exhaust pipes need to be connected to each other. In case that there are some leaks on the joints of the exhaust pipes, you can use fireplace refractory materials such as high temperature resistant silicone or a special paste to seal everything correctly. At this stage of the process, it is worth mounting a distributor or a pipe “catching” hot air.

Constructing and insulating

The next step in the process of blocking up a fireplace with a straight-edge plasterboard is to make necessary measurements and marks. We need to remember that there should be some empty space around a fireplace insert so that free airflow is possible. How to perform constructing and insulating? Well, this could be done in several ways. Choosing a method with the use of plasterboard is one of the most popular ones (and it's affordable).

Making marks, cutting profiles and attaching them to the FLOOR

In the first place, you need to mark the horizontal UW aluminium profiles on the floor. You have to be precise. Remember about maintaining the proper proportions. Then, cut the profiles. To do this, you can use metal sheet cutting scissors. After cutting, it's time for attaching the profiles to the floor. You should perform assembly on steel pins.

Making marks, cutting profiles and attaching them to the CEILING

Then, you should mark the horizontal profiles on the ceiling. You can use one cut vertical profile and a spirit level - just put the profile vertically to the ceiling in various corners of the fireplace and make use of a spirit level so that everything is well levelled. At this stage of the process, you can proceed to the cutting of the rest of the vertical profiles.

Insulating the back wall of the fireplace

Attach the back vertical profiles first, and insulate the back wall of the fireplace. You can use insulation wool. Attach it from the aluminium foil side turned towards the fireplace insert. Insulation wool boards should be cut in a way that they could be stable between the profiles and on each other. Use heat-resistant insulating tape to connect profiles with plasterboards.

Insulating the floor

When the back wall is insulated, you ought to finish the vertical construction from CW profiles (but don't screw the vertical profiles for good). Also, you need to attach the horizontal profiles that are supposed to provide thermal insulation in a decompression chamber. The floor can also be insulated.

Mounting the profiles around the fireplace's facade

The next stage is all about mounting CW vertical and horizontal profiles around the facade of the fireplace. Keep in mind that you have to leave a small space for a dilatation. Then, insulate the side walls of the fireplace in the same way you insulated the back wall.

Insulating the front wall

Another step is insulating the front wall. Leave the holes for inlet grids and air vents. The holes need to provide an opening for air to get through. They are necessary in a fireplace casing and in a decompression chamber. The manufacturers of fireplace inserts usually inform their customers about the proper sizes of inlet grids (on packaging). Just stick to the guidelines.

Cutting and mounting walls from plasterboards

Then, cut and mount walls from heat-resistant plasterboards. Again, you need to remember about leaving the spaces. The hole for the fireplace insert should be cut in a single plasterboard. Creating a hole from a few connected plasterboards is not a good idea.

Spackling screws

After that, you ought to spackle screws and areas, where plasterboards connect with each other. A fibreglass tape and an angle may prove useful. Let everything dry and finish. Remember that everything you do at this stage will be visible in the final effect. Do it carefully and evenly.


At this stage, you already have a construction and a foundation that can serve as a finish of your fireplace. The way you decide to finish it depends on you and on your budget. You can, for example, use decorative stones, plaques, or tiles. There are plenty of possibilities!

What about the chimney pot?

Chimneys have to be sealed off at the top. It is important to cowl the chimney pot. What should you use to block your chimney breast, then? If you want to block off your chimney, use (for example) a chimney damper - you can ask a professional for help.


Blocking up a fireplace with plasterboard is, despite appearances, not so difficult. Equip yourself with the necessary materials and follow our instructions to do everything properly. The result will be worth the effort!


Urban Splatter

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