Can you fix insulated plasterboard to existing plastered walls?

K17 insulated plasterboard

On a DIY forum the question was asked if it was possible to bond the Kingspan Kooltherm K17 Insulated Plasterboard to existing plaster, and if so what would be the best method.

This is something that we have been asked about several times so we thought we would share the details on our blog.

The short answer is that insulated plasterboards can be bonded over existing plaster using gypsum adhesive or proprietary sealant adhesive so long as the plaster is sound / solid and dry. However there are a few more issues that need to be considered before you start. Kooltherm K17 is insulated plasterboard for gypsum adhesive dab / proprietary sealant adhesive bonding and the use of this depends on the type of wall that you are planning to fix it to.

Existing Cavity Wall
If it is an existing cavity wall e.g. if the construction comprises a 100mm blockwork inner leaf, 25 mm + drained residual cavity, 102.5mm facing brick externally and internally lined with a solid plaster finish then the Kooltherm K17 Insulated Dry-Lining System can be used to internally insulate the existing cavity walls.

Solid Masonry Construction
If the wall is of a solid masonry construction we would need to know a few more details before we can confirm the suitability of an adhered system including:

  • What the external finish is (if any)
  • The masonry type & thickness
  • The inside finish
  • The geographical area of the country in which the project is located (this is to determine the exposure zone)
  • Whether the site is exposed or sheltered / protected the building situated on a hill top, near to the coast or is the site protected by adjacent buildings?
  • Whether there is a Damp Proof Course (DPC) running around the perimeter of the building (this should be situated 150mm above external ground level), and if so what type of DPC is it e.g. rigid DPC or chemical DPC?

In this instance we would suggest that you get in touch with our technical services department in order to confirm the details and we can advise on the best solution.

Fitting the boards
Regardless of wall type, if the inside finish is painted plaster, then the plaster would need to be solid / sound and dry otherwise it would need to be removed. If a bonded system is to be used, the paint would also need to be removed from the existing plaster otherwise this can affect the bond. Gypsum adhesive needs suction in order to create an adequate bond / key. The easiest way to remove the paint would be to sand the walls down to the existing plaster finish. Once this has been done, all wall surfaces receiving the insulated plasterboard need to be clean, dry and free from dust in order to provide a good bond for the gypsum adhesive.

There are many different types of masonry and a bonding agent may be required on some substrates in order for the adhesive to key. Plaster would be one such substrate / finish that needs a bonding agent if using gypsum adhesive to attach the Kooltherm K17 insulated dry-lining system, such as an emulsion of PVAC to BS5270-1 or equivalent. Some manufacturers produce their own alternative for high or low suction backgrounds.

The bonding agent is to be applied to the background in bands corresponding to the gypsum adhesive dab / band location.

Once the above preparation has been carried out, the insulated plasterboard can then be adhered to the background with gypsum adhesive dabs. Once the dabs have set, add no less than 2 gypsum nailable plugs per board. Increase this figure to 9 if the insulated plasterboard is to receive ceramic wall tiles.

Alternatively a proprietary adhesive e.g. acrylic sealant adhesive can be used instead of using gypsum adhesive dabs. When using an acrylic sealant adhesive there is, in most cases, no need to use a bonding agent over the plaster first, as it works well on low suction substrates. This therefore cuts down on labour, cost and time. This method can only be used on level walls e.g. plastered walls, concrete or level brick or block walls as only very minor irregularities can be taken out within the depth of the sealant adhesive. When using this method the existing substrate should be sound and flat to within a 5mm tolerance when measured with / under a 2000mm straight edge.

The same procedures outlined above for solid or cavity walls are to be followed when using either adhesive. The installation guidance is very similar to gypsum adhesive except when using acrylic sealant adhesive you can apply the spots / dabs of adhesive to the plastered wall or they can be applied to the back of the Kooltherm K17 insulated dry-lining System.  Apply the acrylic sealant adhesive approximately 25mm in diameter and they are to be positioned at 300mm centres horizontally and vertically.

For more information about fitting Kingspan Kooltherm K17 Insulated Plasterboard please visit our website.

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Kingspan Insulation is a market leading manufacturer of optimum, premium and high performance rigid insulation products and insulated systems for building fabric and building services applications.

0 comments on “Can you fix insulated plasterboard to existing plastered walls?
  1. I have a dormer extension which I wish to further insulate.
    Question: Can I fit insulation board to existing plasterboard wall all searches only mention solid walls

    • Hi Luigi

      Our rigid insulation would need to be fixed to the structural component of the wall rather than to existing plasterboard, so to timber studs or masonry. How much insulation you can install would depend on how much insulation there already is, so it would be best to call our technical department on 01544 387 382 so that they can perform a condensation risk analysis.

  2. Hi I’ve got a wall that is constantly soaked from condensation. It’s the chimney breast wall upstairs.
    I’ve tried many things, brand new windows with trickle vents, duhumidifier, don’t dry clothes in house, open windows when boiling food, but I feel the only way to resolve this is to remove the plaster an render and use insulated plasterboard to try and keep the wall from getting so cold.
    Have you come across Any issues like this before.
    Many thanks

    • Hi Adrian

      We suggest that you contact our technical services team on 01544 387 382 with your construction build up. They can perform a condensation risk analysis and will be able to help you pinpoint the problem.

  3. Hi.
    I’m currently insulation all external facing walls of my property. I’m wanting to dot and dab insulated plasterboard and then add fixings to hold in place. However at the builder yard I’ve been told to save money I could buy plasterboard and insulation board seperate and then stick together using dry fix and then dot and dab with fixings. This would half my cost. Anyone recommendation anyone or can this even be done ????

    • Good morning,

      We would not recommend this practice. This is because certain insulation boards do not have facings compatible with plaster dabs, meaning that any adhesion may not be secure and could lead to the facings delaminating and potentially peeling away from the wall. Our advice would be to use a pre-bonded insulated plasterboard, such as Kooltherm K118. You should prime the back of the board (the non-plasterboard side) with PVA and then dot and dab or adhere to the masonry using secondary fixings where required. Our product literature states how many fixings are required per board depending on the type of dab system you are using, so we recommend that you refer to this document before installation.

      Hope this helps,

  4. Hi,

    I am currently converting my single skin brick garage and my architect specified 100 x 50mm studs filled with 100mm foil backed boarding complete with vapour barrier and then finished with plasterboard. I had lots of spare 75 x 50mm timber so I have constructed the stud work from this. The architect has now given me two options. The first is to add an extra 25 mm timber and do the above or infill studwork with 75mm insulation and then use a thermal plasterboard. I am swaying toward the later but wanted to know your opinion and also your material recommendations and application details. Cheers

    • Hi Nick

      It would be much more thermally efficient to use an insulated plasterboard, such as Kooltherm K118 Insulated Plasterboard, on the inner face of the studs, than to use additional insulation that is between timbers, as the timbers create cold bridging through the insulation, but the insulated plasterboard will be in continuous layer giving a higher thermal value.

      Hope this helps.

  5. Hi
    My daughter’s top/7th floor flat suffers from condensation along structural concrete columns and lintels. She has tried to solve the problem with ventilating and a dehumidifies but with limited success.
    Can you advise on suitable products and techniques?


    • Hi Les,

      There could be a number of reasons why this is happening, for instance the current wall make up having no insulation installed within it, roof leaks etc. Without knowing more information it would be difficult to specify a method of insulating to avoid the damp issues. We would recommend getting in touch with your local building authority and asking them assess the situation and advise on appropriate action to take.

      Hope this helps,

  6. I have a solid wall house. I want to put fitted cupboards on an external wall. Will thermal plasterboard added to the existing plasterboard stop any condensation between the back of the fitted cupboard and the e tern all wall. With no insulation any furniture placed on the external wall causes condensation.

    • Morning,

      As long as there is no existing insulation or vapour barriers behind the plasterboard that could potentially cause interstitial condensation, adding a thermal lining will help to reduce the risk of condensation by creating a warm insulated surface.

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