Plasterboard
Scrim tape for board joints before skimming
- where
- joint length (m)
- boarded area to skim (m²)
- board width (mm)
- boards butt end to end: 1 = yes, 0 = full-height boards
- board length (mm)
- internal angles to scrim (m)
- scrim needed (m)
- waste allowance (%)
- whole rolls to buy
- scrim roll length (m)
Explain this equation
This works out the scrim tape needed to reinforce plasterboard joints and internal angles before skimming, and how many rolls to buy.
The joint length J comes from the area divided by the board width (long-edge joints) and, where boards butt end to end, by the board length (end joints), plus the internal angles Li. S adds waste, and R is the roll length, typically 90 m.
Each board width across the area produces one long joint, so long joints total about A ÷ B. Dividing by 1000 turns millimetre board sizes into metres. The rolls are rounded up because they are sold whole.
Sense check: a 30 m² room boarded in 2400 × 1200 sheets with 10 m of angles needs about 50 m of scrim, comfortably one 90 m roll.
Watch out: external corners take angle bead, not scrim. The estimate is slightly generous on a single small wall.
Length of scrim tape to reinforce plasterboard joints and internal angles before a skim, and the number of rolls.
Enter your values to see the result.
Good to know
Thistle ProTape FT50 self-adhesive scrim is 50 mm wide in 90 m rolls. Scrim all board joints and internal angles; fill wider gaps with finish plaster first. External corners take angle bead instead of scrim.
Common mistake
Skipping scrim on ceiling joints, the place where cracking is most visible.
Limits
Same joint-length approximation as the jointing calculator: slightly high on a single small wall.
Sources
Results are calculations from the published methods and manufacturer figures shown, and depend on the data you enter. Always follow the manufacturers’ system and product data, BS 8212, BS EN 13914 and Building Regulations. Coverage rates vary by product, background and thickness. Check prices, VAT and CIS rules with your own records and HMRC.