Can you fix insulated plasterboard to existing plastered walls?
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 e.g.is 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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