How to: Prepare Internal Walls (Like a Pro)

How to prepare your walls like a pro.  Panelled walls painted in dark green.

Up there with painting ceilings and sanding, as the DIY jobs that I don’t like, is general preparation of walls before decorating a room.  I just want to get paint onto the walls as soon as possible!

We live in a Victorian terraced house and each wall has come with it’s difficulties.  We have had every ceiling upstairs replaced, we have needed plastering projects of epic proportions and so when we have a wall that doesn’t need to be replastered I want to make sure that it is prepared properly.  

Where do you start with wall preparation? What products are good to use? Is it a DIY job that you can complete successfully? How can you prepare your internal walls (like a pro!)? 

I’m not saying that I’m a “pro”, but I’ve done enough of it to know what works well, so if you’ve ever asked those questions, read on!

Where should I start?

Successful wall preparation starts with sanding.  

You may need to strip wallpaper first, of course, and washing down the walls with sugar soap should remove any of the wallpaper paste residue left on the walls.

I use a medium grit sandpaper and a scraper to work my way along the walls.  I use a scraper too because our walls have been so badly prepared before that I have needed to scrape the wall smooth in places! It’s good for removing lumps of paint or imperfections.  

As you sand, you may find cracks in the wall that have previously been hidden by paint and need filling.  I’ve found rogue woodchip wallpaper as I’ve been sanding too.  Seriously, this house has been filled with all of the delights!   

When you find a crack in the wall, you often need to make it look worse before you can fix it.  Try and dig out (that’s not the technical term, I’m sure!) some of the loose plaster and smoothen the edges with sandpaper. I have used a scraper or a Stanley knife to do this and it always gives a good finish afterwards.

Once the walls have been sanded, you need to wipe them down as best you can before you start to fix any of the holes or cracks.

Which filler should I use?

Filler can often be bought as ready mixed or as a powder that you then mix yourself with water.

For a lot of the holes and cracks in our walls, filler that comes as powder has often been more substantial and has worked better.  Mix it up to a consistency that isn’t watery and it should be smooth and creamy.  You may have to work quickly as the filler can ‘go off’ and then you can’t work with it then.

Powdered fillers you could use:

Ready mixed filler is great for a wall where there are smaller holes or shallow cracks.  Often better when it’s a quick project too because it saves you mixing the filler up and having too much.

Ready mixed fillers you could use:

I’ll be honest, when it comes to what tools to use for filling a wall, I have often used an old bank or store card! They’re flexible and you can smooth excess filler off the wall really well.  Try it!

Alternatively, you can buy filling knives and feel like a true professional!

Scrapers and filling knives you could use:

Over fill the area slightly because as the filler dries it starts the shrink.  This also means that when you start to sand back the area, it will be easier to get it smooth.

Sanding… again!

You’ve sanded your walls, you’ve filled all the cracks and holes in your walls, so now you must sand them again!

Once the filler has dried you can sand it. You should be able to tell because it often dries white and doesn’t feel tacky to touch. You want to make sure that the area that has been filled is smooth and at the same level as the rest of the wall.  Be careful not to over sand and create a dip in the area that you have filled, and sand the complete area evenly.

The best way to tell is by running your hand over the wall, not only including the area that you have filled but also the wall surrounding so that you can gauge how level it is. At this point you may start to look like you’re obsessed – room and wall preparation gets to the best of us, believe me!

Depending on how large the area is, you may need to use coarse grit sand paper first and then go over the area with medium or fine grit sandpaper to smooth over the wall.

Sandpaper you could use:

Sometimes you will sand back areas and find that they need more filler.  Just keep going until you have a smooth wall.  I must admit that I’m a perfectionist when it comes to things like this and so I do have to walk away from some areas, because otherwise I could be there for days!

Extra filling tips

Some cracks and holes can be filled with filler and there is no problem, but there have been some areas that have needed expanding foam before filler has been added.

For example, in areas in our living room and dining room there were chunks out of the skirting boards and by the windows that had been filled with silicone (I know! Why?!). I had to remove all of the silicone, which left huge gaps. We filled these with expanding foam, let it set, cut it back and filled over the top.

The foam gives the filler something to adhere to and means that it doesn’t just drop down the gap. After it has been filled you can sand as normal to smooth the surface.

The first coat of paint

Make sure that your walls are dusted and wiped down before you start your first coat of paint so that it can be as smooth as possible.

Often after the first coat of paint it is easier to see whether other areas of the walls need attention.  Once the first coat has dried, check over it again and if some of the areas need filling or sanding again, this is the time to do it.

When do I use caulk?

Decorator’s caulk is often used to smooth the finish either down the side of door architrave, skirting boards or picture rails.

I often get the first coat of paint on the walls first and then use decorators caulk before the second coat.  I started doing this because paint can often cover imperfections and so you don’t need to do as much caulking.  Then once all the caulk is dry you can do your second coat of paint and it’ll be super smooth and look fabulous!

Caulking tips:

  • Make sure that the hole in the nib isn’t cut too big.  That way you won’t squeeze too much caulk out.  It will just get too messy!
  • Don’t have one continual line of caulk, stagger it.  As you smooth it, the excess will make up for the gaps. 
  • Have a cup of water to dip your finger into before you smooth the caulk down.  You can wipe off any excess with a damp cloth.

Taking your time to prepare the walls does make a massive difference to the finish.  I have found so many problems with the walls here because of lack of preparation or really bad preparation.  

Some of the holes in the walls had been filled with silicone which meant that they couldn’t be sanded down, the holes were really obvious and when I tried to remove it the silicone pulled a lot more plaster away from the wall and created an even bigger crater! Great!

I hope that some of these tips have helped.  I’ve tried to include some links to products that I have used, although you’ll have to get your own bank/store card!

Let’s hear it for preparing your walls like a pro!

Lydia x

5 thoughts on “How to: Prepare Internal Walls (Like a Pro)

  1. Tip for silicone is to add a bit of fairly liquid to the water. Better still put a little mix in a small pump bottle and spray/mist it on before smoothing. Take a look at the Screwfix smoothing tools too, they take anyone to a ninja level caulker!!

    Thanks for the blog 🙂


    1. Thank you! Although I won’t be letting any silicone get near my walls again – I’ll be keeping that firmly in the bathroom and kitchen 😂


      1. Haha, definitely keep it out the walls 🤣
        Paul + Sian


  2. A very practical blog. Loved the photos – especially the line of dust on your shins! Especially liked the tip on the cup of water when caulking – the years I have used caulk, never thought of that 🙄Thanks again, Lydia.


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