Do you have to scratch coat render?

Do you have to scratch coat render?

You always have 2 coats of render. The scratch coat is the foundation of the render and the base to the whole product. This provides strength to the wall but also has the most amount of waterproofing. This is what keeps your building water tight and stops any moisture from getting through into your house.

What ratio is the scratch coat for render?

For the scratch coat as we call it the trade , the mix should be 4:1 , the best way to achieve this is gauge the sand in 12 litre bucket brought from any mechant ( builders bucket).

Can I render over an old scratch coat?

YES. There are many products on the market, one of which is SBR mixed with OPC cement. This creates a slurry which is applied using a brush. I then allow 24 hours for it to dry and then i apply a second coat but follow it straight up with a sand cement scratch coat whilst the slurry is tacky.

Can you render a wall without scratch coat?

There is no need to scratch right down to the original wall surface, just deep enough to provide a key for the second coat. The second coat can be applied within half and hour or so of the first, just long enough for the first 5mm coat to become well adhered to the wall.

How thick should scratch coat be?

The scratch coat should be 3/8″ thick. Force it through the wire mesh so that it fills the ¼” gap between the mesh and wall completely. 3. Smooth the scratch coat with the trowel.

How thick should a scratch coat be?

Thickness. The proper thickness of scratch coat ranges between 3/8 to 1/2 inch and forms the ultimate base for the second layer. The thickness of the scratch coat helps to prevent damage to the finished surface due to the house settling or moving. It also provides adequate depth for scoring.

Do you put lime in scratch coat render?

Lime is used to increase the elasticity of the mix, and prevent it from cracking once it dries. The most appropriate kind of lime to be used for rendering is hydrated lime. Other things could also be added to the rendering mix, such as colour-altering pigments, or additives that aid bonding and drying.

How long do you leave a scratch coat?

The first coat is known as the scratch coat, and is applied in a thin layer and left to cure. This can take from between 24 hours up to two days, depending on humidity, temperature, and airflow around the building.

How long can you leave a scratch coat?

Do you need a scratch coat with one coat render?

You cant render with one coat and its doesn’t matter what type of finish you want. You need a scratch coat and a top coat so if you only have a top coat it wont adhere like it should .

How long do you have to wait after scratch coat?

Cure Time: The scratch coat should be allowed to moist cure for a period of 3-5 days. This allows the cement to become hard enough to gain most of it’s strength before the brown coat is applied. Cure Time: The brown coat requires a lot more time to cure (28 days is recommended).

Should I use PVA before rendering?

Paint the surface with a coat of PVA before application of the mortar. It can be applied undiluted for maximum sealing and/or adhesion, or diluted as above. The mortar or render is best applied when the PVA is slightly tacky.

Can I use plasticiser instead of lime in render?

A lot of renderers don’t use it and prefer to use plasticiser which puts lots of bubbles into the mix which is a good thing but the lime is better as we demonstrate in this video. Roger also discusses the best weather for rendering.

What is the correct mix for rendering?

A common mix ratio used for rendering is 6 parts sand, 1 part cement and 1 part lime. Any general purpose cement can be used, although the sand should be fine and clean of impurities. Coarser sand is usually used as the base layer and slightly finer sand for the top layer.

Do you float scratch coat?

The first (scratch) coat acts as a base for the next layer and doesn’t have to be floated, so we’ll start with the second, or brown, coat.

Should I PVA wall before rendering?

I’ve never pva bonded brickwork before rendering because pva will reduce suction so the render is more likely to sink & belly. Just brush down the wall to to remove loose mortar & dust then hose down the wall if it’s external work then apply your scratch coat.

Do you have to do 2 coats of render?

Some renders don’t need to have two coats applied, modern monocouche renders are done in two passes and come in a bag pre coloured so all you need to do is add clean water and mix.

Do I need to PVA scratch coat?

never put pva on any scratch coat. don’t use the pva,just dampen with water you should have no problems.

Why is my render falling off?

The rendering is falling off because it is dead and no longer adheres to the surface of the wall. poolthetool is spot on. If you wait then water will get in behind it and more and more will fall off. Go all over it and knock off the loose stuff.