Larger walls
& floating the backing coat

keep 90% of your straight edge on what is already ruled flat - this will cut any excess off your newly applied plaster, so that is becomes flat and in line with the previous section.

Coping with bigger walls

If your wall is longer than the length of your straight edge and your guides do not yet reach to the other end of the wall your guides can be extended using the principle on the previous page for extending the flatness all the way to the top. It's exactly the same for extending the guides horizontally too. Keep 90% of your straight edge on the guide you have already ruled flat and nibble away bit by bit - to rule off any new plaster flat.

Initially the guide will run the length of the straight edge. Once this has been completed you can either continue and extend the guide right through to the corner, or if the wall is very long it can be a good idea to fill in the middle and top section before extending the guides, as shown in image above.. It will work exactly the same to ensure the straight line of the guide you currently have is projected right through to the other end of the wall. Apply more plaster and rule off with the straight edge. Just as with the top section though ensure that you nibble away at the excess a bit at a time to ensure flatness.

Once your guides have been extended then you can fill in the middle of the wall and the top section as before.


The purpose of ‘floating’ is to ensure every part of the wall, particularly the corners, are flat. The float should always be kept totally flat on the wall. This will have the effect of pushing all the highs into the lows and providing a totally flat surface ready to accept the skim coat.

The aim is to have no holes or ridges any more pronounced than approx 2mm. Floating should take place when the plaster has firmed up.

If it is too firm and dry it will be difficult, so do keep testing the plaster to check it doesn’t become too dry before you float. Even if you haven’t fully completed applying plaster to your wall if parts, that have been ruled off flat, start to dry then floating should take place regardless.

Firm even pressure should be applied to the float to ensure it remains flat on the wall at all times whilst moving in either a figure of 8 or a circular motion. This will flatten the plaster by pushing the highs into the lows. During this process small holes should fill in with slight pressure being placed on the float. If the holes do not fill in then push some extra plaster in with the float. If at any time the float stars to dig in to your wall and get stuck then use less pressure. If this doesn’t resolve the problem then the plaster is probably too wet and you should leave it for a little longer.

If some parts of the wall you have plastered are more porous or wetter than other areas then you will find some parts can be floated successfully whereas others may be too wet and you may have to come back to them later. The corners will need extra care with the float. The same method as used with the straight edge for extending the flatness can be used with the float. Keep the float totally flat and gradually slice away at any bulges.

Cutting back

Now the plaster is firm and generally flat everywhere, the edges of the wall need to be 'cut back' to ensure there are no bulges anywhere – as the float can leave the corner slightly rounded. The skim coat is only 2-3mm thick so any bulges of 2mm or more could present problems.

Checking your wall
You will now see the benefits of using a sand and cement backing coat. The plaster will have firmed up slightly but not totally set yet – so the last job is to have a quick check of all the corners. If the four corners are not straight then this will make the whole wall look a mess – so if you do nothing else ensure:

• the top of the wall is straight horizontally (where it meets the ceiling)

• the bottom of the wall is straight horizontally (to ensure the skirting boards will sit flat)

• the corners are straight vertically.

Get these corners right and the whole wall will look good as a result.

Keeping trowel totally flat on plaster work tip of trowel into the corner.

Ensure blade of your trowel is kept flat on wall. Angle trowel so that just the tip cuts into the plaster. Scrape plaster off wall that you are working up to.

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The author cannot accept liability for the use of any of the materials or methods recommended in this manual or for any consequences arising out of their use. The author cannot guarantee the suitability of any recommendations made in this manual and shall not be under any legal liability of any kind in respect of or arising out of the content of this guide.