Quick Answer: Do You Waterproof Over Or Under Screed?

How do you know when a screed floor is dry?

75% relative humidity at the surface indicates that the screed is sufficiently dry for application of resin floorings and waterproof membranes, resilient floorings, carpet, quarry tiles, ceramic tiles and stone tiles..

How long after screed can you waterproof?

Under normal conditions the screed is trafficable in 24 hours with an initial set time of 3 to 4 hours. Depending on weather conditions, allow a minimum of 3-5 days for the Builders Choice Floor Screed to dry before waterproofing can take place.

How long does it take screed to dry out?

Most screeds recommend 24 – 48 hours. Some more modern screed floors will have a shorter walk on time, as little as 12 hours. Refer to the manufacturers guidelines. Heavier/normal traffic can be resumed 5-7 days after the screed floor is laid.

How thick should screed be?

The optimum thickness of a sand and cement bonded screed is 25–40mm, an unbonded screed should have a minimum thickness of 50mm, whilst a floating screed should have a thickness greater than 65mm for lightly loaded floors and 75mm for more heavily loaded floors.

What happens if screed gets wet?

Too much water in a screed mix will mean that you are going to get increased shrinkage, and with it more risk of cracking, and you could be left with a weaker screed. A wet screed is going to make it hard to achieve a good finish, and you may end up with surface dusting due to high water contents.

Why does screed crack?

Cracks typically form in new screeds because the excess water evaporates from the surface at a faster pace than it is replaced by the residual water, trapped in the concrete slab. … This can be caused by not enough or too much water added during the mixing process or simply poor mixing.

How do you lay bonded screed?

Fully bonded screeds need to be laid on a shot-blasted / scabbled concrete base, and be bonded using an adhesive such as PVA, SBR, epoxy resin or good old fashioned cement. PVA glue is a good screed adhesive especially if it is mixed with water & cement, to make a slurry.

Do I need to seal a screed floor before tiling?

Preparation of the surface prior to tiling If a screed is known to be anhydrite it must be thoroughly sealed before the application of a cement-based tile adhesive. If the screed type is not known and it is believed that it could be anhydrite, the screed should be thoroughly sealed as a precaution.

What is the purpose of floor screed?

The screeds primary purpose, using one part cement to three to five parts sharp sand, is to give a smooth and level floor on which to lay your chosen floor finish. The thickness of the screed allows it to take up normal variations in flatness and levelness of the base on which it is laid.

How quickly can you tile on screed?

Screeds should be firm enough to walk on, usually at least 3 days after application, before tiling can be started. Concrete should be at least 7 days old. All substrates to be tiled must be clean and surface dry.

How do you force dry liquid screed?

Forced Drying: Unlike cement based screeds, calcium sulphate screeds can be force dried by commissioning the underfloor heating system after seven days of the floor being laid (if applicable) or by using a dehumidifier.

How can you tell if screed is dry?

What will you see? It’s normal to see a little moisture under the polythene, but to lay floor finishes, there should be NO dark wet patches. If your test does show that there is still too much water in the screed, dry the polythene and reinstate for 24 hours before looking again.

Is screed waterproof?

Making a cement screed has lots of advantages. For instance, you could lay a screed for a floor with heating. By using Cementmix instead of water, you’ll create a screed that’s permanently waterproof, through and through.

What is the difference between bonded and unbonded screed?

Bonded – screed laid onto a mechanically prepared substrate with the intention of maximising potential bond. Unbonded – screed intentionally separated from the substrate by the use of a membrane. Floating – screed laid on acoustic or thermal insulation.

Can you tile directly onto screed?

It’s quite common in modern construction and has many benefits over sand and cement screeds, but you can’t tile straight onto it with standard adhesives. If you do, there will be a chemical reaction between the screed and the adhesive, and the adhesive will eventually separate from the screed.