Wet or Dry? How to Plaster Walls

Is there a best way to finish off your internal walls and ceilings? This detail has caused debate ever since plasterboard first arrived on the scene in the 1940s. In essence, there are two fundamental options – wet or dry – but each option has its own variations which add to the complexity of the choices facing you.

Wet

Traditional wet plastering went hand-inhand with masonry (brick and block) homes. The Victorians mostly used limebased renders to achieve this, but these were superseded by cement renders and gypsum plasters. These days, the standard routine is to apply a 12mm undercoat of cement render or gypsum undercoat, topped off with a 3mm skim coat of gypsum (often referred to in the trade as ‘Thistle’). When done well, it gives a smooth, shiny coat that is ideal for painting, and it covers up all manner of blemishes underneath, making for neat junctions at doorways and windows.

However, wet plastering is not without its problems. To apply it well is a skilled job and in the wrong hands it can look awful. Render and skim also has a habit of cracking, usually caused by the structure settling over the first year or two. This isn’t dangerous, but it can mean that redecoration is required. It’s particularly noticeable when applied directly to lightweight (or aircrete) blockwork.

Dry

Plasterboard replaces the cement render undercoat and makes the application of a finish coat much simpler. You can choose to finish with a gypsum skim coat (just as you would on rendered blockwork), or you can elect to paint the surface of the plasterboard. If you choose the latter method, you first have to prepare the surface to hide the joints and the fixings: a process known as taping and filling. This tends to be a little cheaper than applying a skim coat of plaster. Plaster - board is supplied either square-edged (for plaster skim coats) or taper-edged. Some boards are reversible: be sure to decide which system you will be using before you buy and/or fix the boards.

A plasterboard finish, whether skimmed or taped and jointed, is the standard finish for internal ceilings, and for timber framed walls, but is now widely used against masonry walls as well, where the board gets stuck to the walls using a process known as ‘dot and dab’. Masonry builders like plasterboard finishes because they reduce the risks of cracking and subsequent redecoration.

So if plasterboard doesn’t crack, why doesn’t everyone use it? It has issues as well. It’s generally good on large expanses of walls and ceilings but fiddly – and wasteful – to apply on reveals and corners. It’s lightweight and therefore not very good at soundproofing and, especially when dot and dabbed onto masonry walls, it doesn’t provide an airtight layer. Plasterboarded walls also make it more difficult to hang fixtures such as radiators, shelves and pictures.

The Alternatives

There are other boards you can use besides plasterboard which solve many of these problems. There are waterproof boards designed for showers and wetrooms (Wedi, Aquapanel); there are heavy boards designed for soundproofing (SoundBloc, WallBoard TEN) and there are strong boards designed for both soundproofing and to be able to hold heavy fixtures (Fermacell). There are many self-builders who swear by Fermacell as it is easy (if heavy) to fix and needs very little in the way of skilled finishing. It can even be used for floors.

Cost

There isn’t much to choose between the wet and dry methods. Wet plastering is still favoured by many because it matches the look and feel of traditional masonry materials. A key drawback to using wet plastering has been the lack of skilled plasterers available, which in turn can make them very expensive. However, the current state of the market has rather changed this state of affairs.

Further reading:

• The Trades Explained: The Plasterer
• How to Finish Plasterboard
• How to Patch Up Plaster