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How to screed a shower base

Four wedge-shaped lengths of timber laid in an X across a shower base

Overview

Laying the screed for your shower base is an easy project when you break it down. We’ll teach you how to prepare the surface for the screed, cut the timber so that your shower has the right run-off level and finally, how to mix and lay the screed. 

Steps

1Check the floor is level

Start by making sure the shower base is level before laying the screed. If it isn't level, the high spots could stick out through the screed, which will make the tiles uneven. Using your spirit level, check the level of the shower bay from the centre to the corners.
A person holding a spirit level on a shower base

2Measure the shower base for your wedges

The next step is to make timber wedges, so that the shower water runs down into the plug. Measure the shower base, diagonally across from corner to corner, then halve this figure, e.g. 1200mm will be 600mm. This is the length of the four wedges you need to cut.

A person measuring the diagonal distance across a shower base

3Measure the wood to make a wedge

Measure and mark the required length on your timber. Now clamp the timber to your sawhorse and cut the four pieces to length. Measure the depth of your shower base and mark that height at one end of your timber. Then measure and mark off half that height at the other end. This will give a good angle for the run-off. Use another piece of timber to draw a diagonal line between the two marks.

A person marking an angled line on a length of timber

4Cut your wedges

Clamp the piece of timber that your wedge is marked on, to the sawhorse. Start cutting with your saw at the thickest end of the wedge. Be careful to saw more slowly as you reach the narrow end of the wedge. Use your first wedge as a template to mark up the rest of your timber pieces. Then cut each piece as before to make three more wedges.
A person sawing down the length of a piece of timber using a hand saw

5Lay the wedges in the shower base

Take some old rags and pack them tightly down the drain. This'll make sure that no glue or screed goes down the drain and blocks it. Then lay your wedges in place, with the thick end of the wedge in the corners and the thin ends meeting in the centre.
A person placing four wedge-shaped lengths of timber in an X across a shower base

6Mix the screed

Put on your dust mask and safety glasses. Make your screed in a bucket by mixing one part cement, to four parts sand and a small amount of water. Mix it until it has the consistency of a wet beach sand. Avoid adding too much water or the screed will be too runny.
A person pouring water into a mixing bucket

7Mix and apply the powder mastic

Put some powder mastic in a bucket and add a little water. Mix it until it's the consistency of toothpaste. Remove the wedges from the shower base and use a notch trowel to spread an even layer of mastic across all of the shower base. The mastic gives the screed something to stick to.

A person using a notch trowel to spread mastic across a shower base

8Apply the screed

Place the wedges back into position. Then using a flat trowel, spread the screed across the entire shower base to cover the glue and wedges. Scrape the screed back to the level of the wedges with a flat piece of wood. This'll create the natural run-off for the shower base. It's important to get each section flat, you can do this by transferring screed from one section to another. In some areas you might find it easier to use a smaller piece of wood or a float trowel to make the screed level. Once all of the sections are flat, carefully remove the wedges and rags from the drain and let the screed dry.
A person using a flat trowel to spread screed across a shower base

9Tidy up the dry excess screed

Once the screed is dry, after about 12 hours, put your rags back into the drain. Use a brush to sweep up all the loose, dry bits of screed. Any areas where your screed is uneven you can use a paint scraper to make it even.
A person using a brush to sweep up loose, dry screed

10Fill in the gaps with more screed

Now use the paint scraper to fill all of the gaps with a bit more screed. Avoid overfilling the gaps as this will cause high spots when the screed dries. Once you have filled the gaps and made it level with the scraper, sweep off the excess screed and pull the rags out of the drain.
A person using a paint scraper to fill gaps with screed
Health & Safety

Please make sure you use all equipment appropriately and safely when following the advice in these D.I.Y. videos. You need to be familiar with how to use equipment safely and follow the instructions that came with the equipment. If you are unsure, you may feel it is safest to consult an expert, such as the manufacturer or an expert Bunnings Team Member.

Grave health hazards are linked to asbestos, which may be in homes built up to 1990. Health hazards may result from exposure to lead-based paints in older materials and copper chromium arsenic (CCA) treated timber. For information on the dangers of asbestos, lead-based paint and CCA treated timber and tips for dealing with these materials contact your local council's Environmental Health Officer. You can also use a simple test kit from Bunnings to indicate the presence of lead-based paint.