Does it Really Matter?
The issue of whether to finish walls with wet or dry plaster has created debate ever since plasterboard came on the scene in the 1940s. But your choice will have an impact and you need to pick the finish that most closely matches the other elements of your design.
Wet plaster is favoured by many because it matches the look and feel of traditional materials, offers better soundproofing and doesn’t cause problems in fixing items to the walls (unlike some boards). But plasterboard has advantages, too — it offers speedy installation with no drying period or cracks.
Option One: Wet Plaster
Preferred by masonry lovers, wet plaster uses either cement renders or gypsum backings trowelled onto blockwork. There is little to choose between gypsum and cement in cost terms, and both are finished off with a thin skim coat of gypsum (Thistle).
Simple to understand and gives a smooth, durable finish. It’s ideal for difficult areas like door or window reveals and dormers. It also gives a good seal around openings — offering superior airtightness.
Because it’s wet, it takes a long time to dry and this can also lead to hairline cracking issues with unwelcome callbacks and redecorating costs. It’s a skilled process and good plasterers can be hard (and expensive) to find.
Note: A scratch or ‘key’ coat refers to a base coat which is lightly scratched before the plaster dries and the top coat/s are applied. The next layer of plaster enters the scratches to form a bond.
A Natural Choice
There is a small but growing interest in traditional materials, principally lime mortars and clay plasters. They are expensive and tend to be used by people interested in natural materials, or wanting breathing wall designs. In restoration work, there is sometimes calls to go back to the plastering used by our forebears: instead of plasterboard ceilings, you can use chestnut laths and then plaster them with lime mortars mixed with horse hair. Horse hair has its modern equivalent with fibres, which are now sometimes added to plasters to stop them cracking when drying out.
Plasterboard: Skim it or Tape & Joint?
There are two rival methods for finishing plasterboard. Skim-coat plasters are trowelled on to produce a smooth, gloss finish ready for painting. The joints between the boards are covered with scrim (i.e. hessian), and this is often the weak point in the method because the scrim doesn’t always mask the gap and cracks appear if the backing timber moves, which tends to happen in new builds. The alternative method (taping and jointing) is to use tapered-edge boards, tape and fill over the joints and nail holes, and to then sand the surface before painting. It’s quick and crack-free but many people don’t like the rough, matt finish it produces.
Option 2: Board on Dabs
An alternative for masonry walls, frequently used by specification housebuilders. Sheets of plasterboard are stuck against blockwork walls with dabs of adhesive, leaving a small cavity between the blockwork and board. The finish coat can be gypsum skim plaster or taped and jointed.
Builders like it because it avoids most of the problems with hairline cracking and callbacks. It also avoids the wait for wet plaster to dry.
The cavity is a waste of space. It makes fixing shelving and radiators much more difficult, and does little for the overall airtightness of the house as it is difficult to seal.
Option 3: Board on Studwork
Widely used in timber frame and SIPs?(structural insulated panels) houses, it’s essentially similar to board on dabs except the boards are nailed or screwed in, so there is no cavity. This is also how ceiling finishes are dealt with, whatever the build system.
As above — it’s fast and relatively easy.
Is still difficult to fix shelving and radiators to and doesn’t offer the same level of sound-proofing as wet plaster — unless you use a high-performance board.
£12-16/m², similar to dabs.
Making the decision
While there isn’t a lot of difference in cost between the materials involved in wet and dry plastering, it takes twice as long to do the work on wet plastering, increasing labour costs. It can also take a long time to dry out, especially in winter when it can create a three- to four-week delay on site. Therefore, if speed and cost are a priority, plasterboard is by far the better option. However, plasterboard is not as easy to fix items such as radiators and shelves to as wet plaster, which suffers no such difficulties.?Wet plaster also gives a smooth, shiny coat that is ideal for painting and covers up all manner of blemishes, making for neat junctions in doorways and windows. You will, however, need to find a skilled plasterer and accept that some cracking is possible.
- Plasterboard is available in a variety of different sizes and formats, including square edge for skimming and tapered edge for taping and jointing.
- There are two basic board thicknesses: 9.5mm for 400mm spacings and 12.5mm for 600mm.
- Various high-performance boards offer acoustic improvements (such as Gyproc ThermaLine SUPER, right) and fireproofing; some are for use in wet areas and as tile backers.
Fermacell is a popular high-performance board used by many self-builders. Made of cellulose – tougher and stronger than plasterboard, meaning you can attach most fixings to it – it can be jointed easily by a novice and simply painted over. It’s expensive (twice the price of basic plasterboard) but de-skills the wall finishing, so it’s ideal for DIYers.
Note: £260/day is the typical rate for a plasterer and labourer team to install plasterboard in a new house.