What To Consider When Laying Screed

I’m Andy Parkin, Managing Director of the Multi-Award Winning Speed Screed. I’m here to talk about laying screed.

Laying screed is the usual way that projects provide a good strong and stable surface on which to lay the final flooring.  You may wish to employ a contractor to lay your screed, however, if you want to give it a go yourself, I will tell you more.

1. What sort of screed do you need?

A bonded screed will sit straight on top of the base layer;  unbonded screed is placed on top of a plastic sheet with acts to protect the top layer of the floor from any moisture rising upward.  With an unbonded screed you may find you get more problems with curling or cracks and you may need to take action to prevent this.  You should also make sure you lay it thickly enough, and should seek advice relating to the product used.

2. How do you prepare the floor?

For unbonded screed, you must get the concrete base completely free of any dust, debris or grease before covering it with plastic sheeting. The plastic sheets must have a 20cm overlap and be taped securely together.  Make sure you extend the sheets up onto all the walls, pillars or other structures surrounding the floor.

For bonded screed you will need to make the surface of the concrete rough by exposing the aggregate by shot blasting, or grinding.  You should wear a mask to protect yourself from dust.  After this, the surface must be cleaned thoroughly, removing all debris, grease and dust before giving the area a final vacuum clean.  A bonding agent such as PVA combined with water and cement or SBR will be needed to bond the screed to the cement and you must apply the screed before this dries otherwise it will not provide a good bond.

3. Protect walls, pillars and other structures

With unbonded screed make sure you cover the surface of your walls or other structures with a compressible material such as edging foam or polystyrene.  When laying screed you will find that it shrinks as it dries and this simple step can protect these areas from damage.

4. When you need reinforced screed

Reinforcing screed helps prevent small cracks forming during the drying process.  You can mix your own by adding polypropylene fibres although there are good ready-mixed screeds which you can use.  Some people like to use steel mesh but you need to place this properly.  If you choose not to reinforce you may need to increase the thickness of the screed layer.  If in doubt we are happy to help.

5. Mixing your screed

Once everything is ready you will want to start mixing your screed.  There is an art to this so it is worth consider a ready-mixed variety.  If you do want to give mixing your own a go it is worth talking to a professional.

6. Laying Screed

There is a technique to laying screed which enables you to complete the project methodically with the minimum of fuss or mess.

First, get some straight battens and use them to divide the floor into sections, keeping them in place with some screed.  Before you start make the battens wet so that they are easy to remove later.  Spirit levels are an essential tool both to make sure the battens are level on the top and with each other.

Start laying screed in the section farthest away by filling approximately 60cm of the strip and spreading the screed with a trowel.  The screed will need to be compacted well and with DIY screeding jobs it is poor compaction that causes the most problems.

Finally, use a screed rule to make sure the section is completely level before moving on to the next part.  Continue this until the final section is complete.

7. Respect curing and drying times

Laying screed is just the first step – once it is down it needs to cure.  This takes around 7 days and you need to cover the screed with PVC sheeting.  If the weather is cold it will take slightly longer.  The screed can take weeks to completely dry so you should avoid any heavy traffic in the area and don’t lay any final flooring until the moisture level of the screed has been tested.

I hope this has been helpful in answering your laying screed questions. Please do get in touch for further information.