How to Fix EPS Insulation Boards: Adhesive, Foam or Fixings

An insulation board is only as good as the way it is stuck to the wall. Get this stage wrong and no render on earth will save the job.

The three ways boards are held on

Cement adhesive. The traditional method. A 2-in-1 adhesive like Ceresit ZU is combed onto the board, pressed home and left to cure. Strong, cheap per square metre, and the same bag also does your mesh coat. The downside is time: you wait a day before drilling for fixings.

Express foam adhesive. Ceresit CT84 is a polyurethane foam applied in beads from a gun. Boards can be adjusted for a few minutes, then set hard enough to sand and fix on the same day. One can does roughly 10 m2. On a tight programme, or in cold weather when cement adhesive struggles, it earns its keep.

Mechanical fixings. Polystyrene fixings are the belt to the adhesive's braces. On almost every Irish external wall you need both.

How much adhesive and how many plugs

Job	Rule of thumb
Bonding boards, cement adhesive	4-6 kg per m2, so a 25kg bag does about 4-6 m2
Bonding boards, foam	roughly 10 m2 per can
Mechanical fixings	5-6 plugs per m2 in the field, more at corners and openings

The plug must reach past the insulation and at least 50 mm into solid masonry, so the length follows the board:

Board thickness	Plug length
50 mm	90 mm
80 mm	120 mm
100 mm	150-160 mm
150 mm	190 mm

Our fixings page lets you pick the length you need, and the calculator on the adhesive works out bags from your wall area.

The mistakes that cost money

• Dabs only, no perimeter bead. Adhesive should run as a continuous bead around the edge of the board plus dabs in the middle, or wind pressure works the boards loose and the edges telegraph through the render.
• Fixing too early. With cement adhesive, drilling before the adhesive has cured pulls boards off the wall.
• Plugs too short. A plug that only bites 30 mm into old rendered blockwork will pull out. Measure the substrate before you order.
• Boards butted badly. Gaps wider than 2 mm should be filled with offcuts or foam, never with adhesive, which bridges cold straight through the insulation.

What about mineral wool?

Wool is heavier and needs more fixings, typically 6-8 per m2, and the adhesive has to be worked well into the fibres. CT84 is rated for wool as well as EPS, which is handy on mixed jobs.

Need a hand with your job?

Send us your measurements and we will put together a materials list with prices. Call 085 868 8459, message us on WhatsApp or email sales@all4building.ie. We deliver across Ireland from our Cork warehouse.