How To Plaster
The main type of plaster product used these days is plasterboard otherwise known as drywall, or brand names like Gyprock or Sheetrock. Plasterboard consists of compressed gypsum sandwiched between several out-side layers of paper. Plasterboard is available for many applications including fire resistance and sound insulation. As plasterboard is available in many different sized sheets and is comparatively easy to cut, fix and join, it is an ideal product for your average DIY enthusiast. DIY plaster disasters were common in the past as plaster rendering required high skill levels to get good results.
Tip; Plaster board should be fixed horizontally across a wall, to minimise joins, and supported and fixed at all edges at 100 mm intervals. The same principles are used for ceilings and floors.
Regardless of what sort of plastering you are doing from solid plastering, skimming or tape and plastering plasterboard, there is one common rule which will make your life a lot easier. Only apply enough plaster to fill the hole or gap. Any excess plaster that is sitting proud (or above the surface) will need to be sanded which can be messy hard work especially with hard plasters like Cornice Adhesive ( an extremely hard plaster with the properties of a set glue) and base coat (also tough and hard and used as the initial coat for tape when jointing plasterboard).
Professional plastering services work quickly to apply one thin layer of plaster at a time consisting of;
Base coat – This is applied to the plasterboard join and then paper plaster tape is pressed into the wet join with a tape knife (scraper) blade. Make sure the tape is stuck to the plaster by applying pressure and do not overfill. ( Fiberglass sticky tape is also available and is applied prior to the plaster but this is not recommended and considered inferior). Once tape is in place use excess plaster to cover tape taking care not to overfill. Base coat requires mixing thoroughly with an electric drill mixing attachment. Only mix as much as you can use in 40 minutes and clean all gear with water before it dries solid!
Video – How to tape a plasterboard join using paper tape.
Video – Setting an internal angle with paper tape.
Jointing Compound – Is a premixed soft plaster designed to be applied in 2 additional layers allowing for drying between coats. This is usually applied with a broad knife (scraper) or trowel with each coat applied wider to feather the join. Tip; Do not try and fill deep holes with jointing compound as it may take days to dry.
Finishing Compound – Optional premixed soft plaster where a level 5 of perfect invisible join is required, usually for glazed finishes.
Little or no sanding should be required between coats – use a broad knife to scrape any excess off. A light sand should be all that’s required on completion.
Plaster skimming is used to renovate existing damaged hard plaster walls and finish repairs as the last stage when you fix plaster damage. As with all plastering, it is important to understand that skimming is a multi-stage process which is designed to deliver professional results through layering. In Australia, premixed jointing compound is widely used although be sure to fill any deep holes with hard plaster like cornice adhesive (which dry’s quickly -especially if you add a little salt) prior to skimming as your skim coat should only be about 2-3mm thick.
Video – Learn to Plaster. Skimming
There are three kinds of major Plaster hole repairs.
Set plaster or solid plastering can be repaired by applying multiple layers of hard plaster (cornice adhesive is popular as it dries quickly especially with some salt added) and finishing with a premixed jointing compound. Make sure that the hole is clean with a solid edge and if porous dampen down with a wet brush for better adhesion.
Holes in a plasterboard wall or a ceiling repair where the damaged area spans two or more timber or steel studs. Important: check for services like pipes and electrical wire prior to proceeding.
(1) First locate the studs with a stud finder or drill/nail etc. (usually 400 or 600mm spacings)
(2) Using a straight edge – mark out the area for replacement ensuring that half the stud is exposed for fixing the new repair sheet. It is easier to use a piece of plasterboard that will cover the area and mark around it as this will then fit perfectly.
(3) Using a utility knife – score around repair area then from the centre cut to the four corners with a small plasterboard saw then fold in flaps and cut off with utility knife.
(4) Measure and cut plasterboard using the score-snap-cut method for a clean edge .
(5) Cut and screw/glue (with cornice adhesive) some small offcuts of plasterboard to the inside of the hole ensuring that they span the hole. screwing timber or plasterboard cleats avoids drying time and provides a solid backing for the repair sheet.
(6) Apply cornice adhesive to the edge of your repair sheet and the offcuts previously glued and/or screwed in place. Place the repair sheet into hole and fix plasterboard repair sheet to studs with plasterboard screws.
(7) Tape and plaster (see video) edges and when dry finish with premixed jointing compound.
Holes in plasterboard where there are no support studs. As above from (3) but ensure there are enough timber offcuts screwed in place behind to support the attached repair sheet. Tip; If it’s a largish hole, place and screw your timber offcuts behind so when screwed they also support the existing sheet and the repair sheet.
Video – Repair a hole in a plasterboard or drywall ceiling – part 1.
Video – Repair a hole in a plasterboard or drywall ceiling – part 2.
Video – Repair a hole in a plasterboard or drywall ceiling – part 3.
RESOURCES: More information on plastering can be found at www.how2plaster.com
Small Hole Repair
Small holes in a plasterboard wall are a common problem but the good news is that they are easy to fix if you follow this simple tip. Plastering a hole is impossible if there is no backing for the plaster to stick to so you must provide one.
Clean up the edges of the hole even if it means making it larger. Any broken or lose plaster and paper must be removed and you should have a nice clean, square edge.
Cut a piece of plasterboard slightly larger than the hole but small enough to insert into it.
Make a small hole in the centre of repair board, attach a short piece of string to a nail and push this through the centre of the plasterboard and then lay the nail flat at the back so it cannot be pulled through.
Apply plaster to the plasterboard patch and insert into the whole and pull the string so the patch sticks to the back of the wall facing.
Pull on the string and fill the patched area with plaster but not to the top. Let it dry.
Apply second and subsequent coats of plaster to finish.
Video – Small hole repair in plasterboard