How to float plaster?
How to Float Plaster
Floating plaster is an important process to get right to make sure that you get perfectly flat walls. This guide teaches you about what is plastering as well as how to float plaster for the best results.
What is Plaster?
Plaster is a soft paste made from a mixture of sand, cement, gypsum (a white or grey mineral) and sometimes lime. It’s not waterproof, so can only be used indoors.
There are various types, including browning plaster and bonding plaster (both applied as backing coats), finishing plaster (for the top coat), one-coat plaster, and lime plaster (used mostly in older properties).
Walls usually have two or three layers of plaster. Floating is carried out to prepare the wall for the top coat – so either the first or second layer will be floated.
The aim is to make the wall as flat as possible, as well as ensuring that the plaster is the same thickness all the way across. The top coat will be quite thin, so if the backing plaster is uneven it will show in the finish.
Plaster is a soft paste made from a mixture of sand, cement, gypsum (a white or grey mineral) and sometimes lime. It’s not waterproof, so can only be used indoors.
There are various types, including browning plaster and bonding plaster (both applied as backing coats), finishing plaster (for the top coat), one-coat plaster, and lime plaster (used mostly in older properties).
Walls usually have two or three layers of plaster. Floating is carried out to prepare the wall for the top coat – so either the first or second layer will be floated.
The aim is to make the wall as flat as possible, as well as ensuring that the plaster is the same thickness all the way across. The top coat will be quite thin, so if the backing plaster is uneven it will show in the finish.
What is Plasterboard?
Plasterboard, also known as drywall, consists of prefabricated panels of plaster sandwiched between two layers of paper.
Plasterboard panels are generally attached to internal studwork (timber frame) walls in new-build houses as a quick and easy alternative to building brick or breeze block walls. As plasterboard already offers a smooth surface, it requires only one layer of plaster.
Plasterboard, also known as drywall, consists of prefabricated panels of plaster sandwiched between two layers of paper.
Plasterboard panels are generally attached to internal studwork (timber frame) walls in new-build houses as a quick and easy alternative to building brick or breeze block walls. As plasterboard already offers a smooth surface, it requires only one layer of plaster.
What is Floating a Wall?
Floating plaster is an important process to get right to make sure that you get perfectly flat walls. This guide teaches you about what is plastering as well as how to float plaster for the best results.
Which Plastering Float to Use?
There are many different types of plastering float available. They are made out of a range of different materials including plastic, wood or sponge. These are all purposely built to float on plaster – much of it depends on personal preference.
Plastic is a good general all-rounder. Wood gives a slightly rougher finish, which will help the top coat of plaster grip, whereas a damp sponge float is useful for walls that start drying out too quickly.
How to Plaster a Wall with a Float?
Step 1 - Wait for Plaster to Set
After applying the plaster, wait around 20 or 30 minutes for it to start firming up (also known as going off) before using the float.
You need to time it just right. If you start too soon, the float will pull bits of wet plaster off the wall and spoil the finish. If you wait too long, the plaster will have set hard. You should be able to make just a slight dent in the wall with your finger when it’s ready to float.
After applying the plaster, wait around 20 or 30 minutes for it to start firming up (also known as going off) before using the float.
You need to time it just right. If you start too soon, the float will pull bits of wet plaster off the wall and spoil the finish. If you wait too long, the plaster will have set hard. You should be able to make just a slight dent in the wall with your finger when it’s ready to float.
Step 2 - Use Darby to Level Plaster
Many plasterers use a darby on the wall at this stage to begin levelling the plaster. Start at the bottom and pull the darby slowly up to the top, keeping it pressed firmly against the wall at an angle of about 45 degrees.
Repeat all along the wall, scraping excess plaster off the darby with your trowel after each pass.
Many plasterers use a darby on the wall at this stage to begin levelling the plaster. Start at the bottom and pull the darby slowly up to the top, keeping it pressed firmly against the wall at an angle of about 45 degrees.
Repeat all along the wall, scraping excess plaster off the darby with your trowel after each pass.
Step 3 - Float Plaster
Now it’s time to start floating the plaster to get it smooth. Apply firm, even pressure to the float to ensure it remains flat on the wall at all times while moving in either a figure of eight or a circular motion.
This will flatten the plaster by pushing the high points into the troughs, and will also help fill in small holes.
Use the float to add plaster to any holes and cracks that are left.
If you’re using a sponge float, keeping it damp by dipping it periodically in water will help prevent the plaster drying out too soon. You can also use a decorator’s sponge for this.
Now it’s time to start floating the plaster to get it smooth. Apply firm, even pressure to the float to ensure it remains flat on the wall at all times while moving in either a figure of eight or a circular motion.
This will flatten the plaster by pushing the high points into the troughs, and will also help fill in small holes. Use the float to add plaster to any holes and cracks that are left.
If you’re using a sponge float, keeping it damp by dipping it periodically in water will help prevent the plaster drying out too soon. You can also use a decorator’s sponge for this.
Cutting Back Plaster
It’s important to get the edges of the wall straight and square at the corners, which floating can leave slightly rounded. This is known as cutting back.
You need to make sure that the wall is straight both at the top, where it meets the ceiling and at the bottom, so that the skirting boards will sit flat when they’re added later on. The corners must also be completely straight vertically, otherwise, the whole wall will look shoddy.
An angle float makes it easier to cut back the plaster on the corners, although you can also use a stainless steel trowel. This needs to be done when the plaster has firmed up a little, but before it sets.
Keeping the float completely flat on the plaster, slide it into each corner and angle it so that just the tip cuts into the plaster to slice off any bulges.
It’s important to get the edges of the wall straight and square at the corners, which floating can leave slightly rounded. This is known as cutting back.
You need to make sure that the wall is straight both at the top, where it meets the ceiling and at the bottom, so that the skirting boards will sit flat when they’re added later on. The corners must also be completely straight vertically, otherwise, the whole wall will look shoddy.
An angle float makes it easier to cut back the plaster on the corners, although you can also use a stainless steel trowel. This needs to be done when the plaster has firmed up a little, but before it sets.
Keeping the float completely flat on the plaster, slide it into each corner and angle it so that just the tip cuts into the plaster to slice off any bulges.
How to Float Plaster on a Ceiling?
Step 1 - Figure Out the Number of Layers Needed
Ceilings are not for the faint-hearted. The plaster has to be laid on in thinner layers to keep the weight down, which means it will set more quickly than on a wall. It’s also physically hard, as you’re reaching up the whole time.
If plastering a whole room, do the ceiling first so you can later cover up any splashes on the walls. Most ceilings require two coats, although plasterboard ceilings will only need one, and older ceilings may require three.
Ceilings are not for the faint-hearted. The plaster has to be laid on in thinner layers to keep the weight down, which means it will set more quickly than on a wall. It’s also physically hard, as you’re reaching up the whole time.
If plastering a whole room, do the ceiling first so you can later cover up any splashes on the walls. Most ceilings require two coats, although plasterboard ceilings will only need one, and older ceilings may require three.
Step 2 - Use a Sponge Float to Sweep the Skim Layer
Having applied the top (skim) coat of plaster with a stainless steel trowel, wait until it has begun to firm up then go over the ceiling with a damp sponge float.
Press firmly as you sweep the float in wide arcs over the surface to get rid of trowel marks, even up the high and low points and fill in any holes.
Having applied the top (skim) coat of plaster with a stainless steel trowel, wait until it has begun to firm up then go over the ceiling with a damp sponge float.
Press firmly as you sweep the float in wide arcs over the surface to get rid of trowel marks, even up the high and low points and fill in any holes.
Step 3 - Cover Ceiling Repair Areas
If you’re dealing with part of a ceiling that’s been repaired, apply the new plaster in two layers and wait for it to begin setting as normal.
When the plaster has firmed up enough, run a damp sponge float around the edges of the patch, pressing firmly to blend the new plaster in with the old, then sweep the float over the rest of the repaired area a few times until it matches the original part of the ceiling.
If you’re dealing with part of a ceiling that’s been repaired, apply the new plaster in two layers and wait for it to begin setting as normal.
When the plaster has firmed up enough, run a damp sponge float around the edges of the patch, pressing firmly to blend the new plaster in with the old, then sweep the float over the rest of the repaired area a few times until it matches the original part of the ceiling.
Step 4 - Leave Plaster to Set for 3-6 Weeks
You’ll need to leave the plaster to dry for between three and six weeks before decorating, depending on the number of layers, the time of year and whether the house is heated.
This is to let all the moisture evaporate from the plaster. Painting or wallpapering the walls too soon will seal in the water and lead to damp.
You’ll need to leave the plaster to dry for between three and six weeks before decorating, depending on the number of layers, the time of year and whether the house is heated.
This is to let all the moisture evaporate from the plaster. Painting or wallpapering the walls too soon will seal in the water and lead to damp.
