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FREE WASTE GUIDE FOR DRYLINING CONTRACTORS

Dot and dab: dab spacing and how much adhesive you need

Dot and dab, or direct bonding, fixes plasterboard straight onto a masonry wall with dabs of gypsum adhesive, plus a continuous ribbon of adhesive around the edges.

British Gypsum says a 25kg bag of Gyproc DriWall Adhesive will fix two 2400 x 1200mm boards in normal use, which is about 5.76m². Walls that are out of plumb or out of line take more.

The figures on this page come from three of the biggest UK manufacturers: British Gypsum, with Knauf and Siniat in brackets where theirs differ. They vary from product to product, so always check the bag or the data sheet for the adhesive you're using.

How much dot and dab adhesive do I need?

  • British Gypsum (DriWall Adhesive)

  • Knauf (Plasterboard Adhesive)

  • Siniat (Universal Bonding Compound)

  • Two 2400 x 1200mm boards, about 5.76m²

  • 4.6m²

  • 8m² on internal walls, 4m² on external walls

Manufacturer

Coverage per 25kg bag

To work out your order:

  1. Work out the wall area: length x height for each wall.

  2. Take off the doors and windows.

  3. Add 5% for waste: the bottom of the bucket, mix that goes off, and dabs scraped back.

  4. Divide by the coverage for your adhesive and round up to whole bags.

The manufacturers don't say whether their coverage figures allow for waste, so 5% is our suggested starting point. Adjust it to suit the job. The thicker the dabs need to be to bring the board out to the line, the more adhesive you'll use.

Worked example

A room 4m x 3m, walls 2.4m high, with one door (0.9 x 2.1m) and one window (1.2 x 1.2m).

  • Wall length: 4 + 3 + 4 + 3 = 14m

  • Wall area: 14 x 2.4 = 33.60m²

  • Less the door and window: 33.60 - 1.89 - 1.44 = 30.27m²

  • Add 5% for waste: 30.27 x 1.05 = 31.78m²

  • British Gypsum: 31.78 ÷ 5.76 = 5.52, so order 6 bags (Knauf 7 bags; Siniat 4 bags on internal walls, 8 on external)

  • Boards at 2400 x 1200mm with 15% waste for the openings: 30.27 x 1.15 ÷ 2.88 = 12.09, so order 13

The spread between manufacturers is why the bag matters. For more on board numbers, see how many sheets of plasterboard do I need.

Dot and dab spacing

British Gypsum asks for dabs in a regular pattern, following BS 8212 and BS 8000-8, so that at least 20% of the board is in contact with the wall. Its data sheet doesn't give a dab size.

Knauf and Siniat both spell the pattern out, and they agree:

  • dabs 250mm long and 50 to 75mm wide

  • 10 to 25mm thick, enough to bring the board out to the line

  • 300mm centres up the wall

  • columns at 600mm centres for 12.5mm board, 1200mm wide, which gives three columns per board

Thinner or insulated boards need the columns closer. Knauf uses 400mm centres for 9.5mm board 1200mm wide, and Siniat uses 400mm for its thermal boards. Siniat also keeps dabs at least 25mm in from the board edges.

Continuous ribbons, not just dabs

British Gypsum asks for a continuous ribbon of adhesive:

  • around the whole wall perimeter

  • around door and window openings

  • around socket boxes and other service penetrations

(Siniat also runs a ribbon along the head and base of each board, about 50mm in.)

The ribbons seal the cavity behind the board. Without them, air moves behind the lining, which hurts airtightness and thermal performance. A continuous vertical line of dabs down the centre of a board can also form a cavity barrier on long runs, where one is needed.

Mixing, working and set times

British Gypsum's figures for Gyproc DriWall Adhesive:

  • 13.5 to 14.5 litres of water per 25kg bag

  • leave it 10 minutes after mixing before you apply it

  • maximum working time 90 minutes

  • minimum set time 2 hours

  • shelf life of four months, with a use-by date on each bag, so use them in date order

Mix only enough for one board at a time (Knauf). Keep boards at least 10mm off the floor (Knauf). With insulated plasterboard, British Gypsum adds two nailable plugs per board at mid-height once the dabs have set.

Before you dot and dab a wall

  • The wall needs to be reasonably flat, dry and sound. On a crumbly or very uneven wall, British Gypsum recommends a mechanically fixed lining in place of dabs.

  • Brush off dust. Dense or very smooth concrete may need a bonding primer in bands where the dabs go.

  • Check the adhesive suits the board. (Knauf says its plasterboard adhesive shouldn't be used with moisture resistant or vapour check boards.)

  • On external and separating walls, British Gypsum recommends a 6mm sealing coat of Gyproc SoundCoat Plus on the masonry first, for airtightness and sound. Check the system specification.

Get the free Drylining Waste Guide

Adhesive is one line on a lining job. Our free Drylining Waste Guide gives waste allowances for plasterboard, metal stud, track, insulation, screws and fixings, jointing compound and tape, plus five rules for ordering.

Common questions

How many bags of dot and dab do I need per board?

British Gypsum says one 25kg bag of DriWall Adhesive does two 2400 x 1200mm boards in normal use (Knauf's figure works out at about one and a half boards per bag). Check the bag for your product.

How far apart should dot and dab be?

Knauf and Siniat both put dabs at 300mm centres up the wall, in columns 600mm apart for 12.5mm board that's 1200mm wide. British Gypsum asks for a regular pattern that gives at least 20% contact.

How thick should dot and dab be?

Between 10mm and 25mm (Knauf and Siniat), depending on how far the board needs to come out to reach the line.

Can you dot and dab onto a plastered wall?

British Gypsum allows it on pre-plastered walls that are reasonably flat, dry and sound. On plastered backgrounds its DriLyner Dab system uses Gyproc Sealant in blobs at 300mm centres in place of adhesive dabs.

We're building QFitout, drylining quoting software that applies these allowances for you when you price a job.

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