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Internal Wall Insulation is perfect for those not able to insulate external walls - and is generally cheaper. There are two different methods to insulating your home internally, this can be done either by a stud wall or rigid insulation boards. A rigid insulation board backed onto plasterboard is generally the easiest method and could help save you up to £380 in energy bills each year. Our handy how to guide will show you how to install in application savings you more money!


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What you'll need

In order to complete this how to guide, you're going to need the following product;

Celotex Thermal Laminate Board PL4000

Plasterboard Drywall Adhesive

Nailable Plug (size varies)

Joint filler 12.5kg

Joint tape 50mm

Finishing Plaster 25kg

Primer 10L


We suggest that you use the following accessories & safety equipment when undertaking this job:

Plaster Adhesive Mixing Paddle

Spirit Level

Measuring Taep 8m

Trowel Finishing 

Plastering Float

Protective Gloves


Combi Drill

Drywall Hammer

Jointing Knife 250mm



Insulating Internal Walls

 Download You can print and download this how to guide here

Internal Wall | Step 1

Prior to installation its important to ensure the wall is sound, secure, free from contaminants and dry. In this method we will demonstrate how direct bonding (dot 'n' dab) is achieved. This method not only saves times but allows for a variable flatness of wall.



Internal Wall | Step 2

Step 1

Drywall adhesive should be prepared, mixed and applied in line with the manufacturer's instructions.
Internal Wall | Step 3

Step 2

Ensure the adhesive is properly mixed with a drywall mixing paddle - This is important for achieving a high suction adhesive that can be used to support the thermal laminate board.


Internal Wall | Step 4

Step 3

In all instances the background should be plumb for alignment making allowances for high sports on the masonry. In older build homes this method is particularly useful in accommodating uneven wall surfaces.
Internal Wall | Step 5

Step 4

Mark chalk lines on the floor and ceiling to establish the new wall plain. Vertical guidelines on the wall should be marked at 1200mm centers to indicate the positioning of the boards.
Internal Wall | Step 6

Step 5

The installation should start from an internal corner, or a window, or door reveal. This is to ensure measurements are correct and the finish will be flush against wall, reveals and all doors.
Internal Wall | Step 7

Step 6

In cases where there are internal openings or reveals, its important to cut these out of the board and ensure the finish meets the measurements around the reveal or opening. Later we show you how to insulate these sills, reveals & cavities.
Internal Wall | Step 8

Step 7

A continuous bed of adhesive should be applied around the perimeter of the wall as well as around any services or other openings. A dab of adhesive approximately 250mm apart should cover the wall ensuring a strong support for the plasterboard.
Internal Wall | Step 9

Step 8

At this point all conduits and piping should be installed prior to the commencement of laying the plasterboard down. The insulating backing of the laminate plasterboard should not be removed to accommodate services.
Internal Wall | Step 10

Step 9

Where reveals and openings go occur we advise cutting the boards so they meet together and ensure no room for thermal bridging. The board should also be cut approximately 15mm short of floor to ceiling height.
Internal Wall | Step 11

Step 10

The board should then be placed on packing strips - this is done to ensure room for any skirting boards and coving on the ceiling.
Internal Wall | Step 12

Step 11

Tap the board with a straight edge to ensure alignment with the chalk lines - At this point the board should be lifted to ceiling level until the adhesive has been set.

Internal Wall | Step 13

Step 12

The alignment of the boards should always be checked to ensure that they are level and that the adhesive setting is not impacting the level of the board.
Internal Wall | Step 14

Step 13

Once set, nailable fixings should be applied at midpoints of the board and approximately 25mm from the board edges. Other boards should be installed closely butted together using the same technique.

Internal Wall | Step 15

Step 14

Once the plugs are arranged in place we always advise drilling the hole in beforehand - This reduces mistakes and ensures the nailable plug securely fits at the correct measurements. 

Internal Wall | Step 16

Step 15

Finally, once the holes are drilled you can place the plugs into the walls and hammer in as pictured. These plugs will hold the entire weight of the plasterboard and assist the adhesive in giving a strong durable hold and finish.


Internal Wall | Step 17

Step 16

If you have door reveals, openings or windows in your internal room - we advise cutting just the insulating backing in a way that ensures when the boards meet these are flush and free from gaps which can lead to thermal bridging.

Internal Wall | Step 18

Step 17

Once the boards are in place and set its important to look at butted joints between the plasterboard. These will have a gap, to ensure a smooth flush finish we advise using a joint filler. Spread this on the butt of joint and smooth over.


Internal Wall | Step 19

Step 18

Once on the plasterboard, feather it to a smooth finish and wait to dry. Two to three applications of this is advised with a joint tape to accompany.

Internal Wall | Step 20

Step 19

Jointing tape should be applied on top of the joint adhesive to ensure a smooth finish. Excuse adhesive should be skimmed off.


Internal Wall | Step 21

Step 20

Use adhesive to lay over the tape securing the overall joint. Ensure two to three coats are applied.

Internal Wall | Step 22

Step 21

Use a trowel to wipe off excess adhesive for a smooth finish. This helps prepare the wall for the plaster finish.
Internal Wall | Step 23

Step 22

A finishing coat of 2mm of plaster should be applied to complete the installation. Apply plaster to the boards and joints with firm pressure, at this point the joint adhesive should be firm but not quite set. Two applications of plaster are required to meet the 2mm requirement.

Internal Wall | Step 24

Step 23

Once the plaster is dry, a final primer coat should be considered if painting or decorating is to be done.


Why not watch the video below to give you additional help & ensure you get the quality finish you want.