Screeding a Floor - How to Mix Screed and Lay a Level Floor

Summary: Learn how to screed a floor correctly and make sure that it is level. How to mix floor screed and them lay a level floor.

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Screeding a Floor

1 tonne of flooring grit or sharp sand mixed at 4 sand to 1 cement will cover approximately 15 square metres of floor when laid at 40mm thick.

Laying a level floor screed over a large area is difficult and to do so “By eye” requires years of experience. However there is an easier way and this is where the word screed comes from.

The word screed actually means “An accurately levelled strip” of material laid on a wall or floor as a guide for the even application of a covering. So our screed is not a floor screed but a floor covering and to get the covering level we must introduce some screeds!

Screeding layout diagram

Screeding layout diagram

It’s fairly simple to lay a few screeds across a floor and level them as you go and it’s even easier if you have help laying the screeds. We will work with a 50mm covering and to lay our screeds we will use some 100 x 50mm timbers. This is a standard size timber and you only need 1. For most room sizes a timber of a standard 4.8m long is plenty and this can be cut down as required. Make sure you examine the timber before you buy it as you need a straight piece, not a piece that bows everywhere, this will make life, and your floor, very bumpy!

Mix your floor screed at 4 sand to 1 cement. The mix should be fairly dry. The way to tell if you have it right is to grab a handful of mixed screed (put your marigolds on first) and squeeze. The mix should stay in one firm lump in your hand but very little liquid, if any, should come out.

Lay the timber onto the floor, following the plan shown and place a spirit level onto the timber. If it is out of level it can be packed up using some of the mix you have in the appropriate places.

When the timber is in position, place a shovel full of the mix every 300 mm along the timber and flatten out with a plasterer’s polyurethane float. The mixed screed should be about 75mm wide.

You will see that the screed you are placing naturally falls away at an angle at the side. When you have finished each mixed screed, cut this back square to the timber screed as shown by the white cut line in the diagram below.

Side profile of screeding

Side profile of screeding

Remove the timber when you have finished a screed and place it in the next position. This needs to be done carefully to avoid damaging the edge of the screed and always wet the timber before laying the screed to avoid sucking moisture from the mix unnecessarily. This can be done quite simply with a paint brush and a container of water.

Leave the newly cast screeds for a day and then fill in the gaps with the same mix. Level across the screeds using your spirit level or a straight edged piece of timber, moving the mix around until it is absolutely level between your two screeds. Fill in any voids. Rub the covering to a void free finish with the float.

Floor screeds should be cured rather than just dried out quickly. Curing in this instance means dried out slowly and a floor screed needs to retain its moisture for as long as possible. This is necessary because of the high cement content and rapid drying could lead to cracks. To cure place a polythene sheet over the screed and several days should be allowed before the surface is walked on.

Why not go to our video sections on how to mix cement, how to correctly mix mortar or how to level your floors to watch short films on each subject.

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