Sand Cement Render Internal

[EdTurtle]

Hi, just a quick question.

I have bare block walls that i am going to float and set. No doorframes or other to work off like i normally have so going to do box screed in sections.

What is the thickness supposed to be for each coat, 10mm each, so total of 20mm then 3mm multi finish? Is that to thick though, could it be more like 15mm s&c then 3mm multi?

Many thanks

 

[ree]

OP,
Best practice with a render mix is a 3:1 sand & NH lime.
Why are you rendering internally - has there been a damp issue or are you doing it traditionally?
Can you or someone else fix permanent skirtings, and even temporary reveal linings - it would make the job so much easier.
10m coats are correct for rendering.

 

[JohnD]

In my area, it is traditionally 3/4" thick, but 18mm will do.

Years ago they used a lime render internally and modernised to use S&C. It has a hard plaster skim.

It is a coarser sand than bricklayers use, with less cement so rather open texture. It is said to resist damp and shrinkage cracks.

 

[EdTurtle]

Thanks. Honestly, i'm using sand cement as i cannot get hold of any hardwall round here, and want it to be a durable finish - not dot and dab. Cant use bonding as its on celcon blocks.

Would 2x 8mm coats be ok - thats what i think they did originally here, as the backing coat is the same thickness as a 16mm backbox.

thanks

 

[Notch7]

If the wall is coated with neat SBR could bonding be used?

 

[EdTurtle]

I'm not convinced it can, but i could be wrong. Although, what would be the benefit over sand/cement?

 

[EdTurtle]

Next question.

This is for a garage - not a conversion just making it better.

At the bottom of the wall there are two courses of brick (sloping up towards the back to just over a course), then DPC then blocks above.

I want to render as close to the floor as possible, so i dont have a gap of around 5 inches. I am hoping to tile the walls, and am considering a floor tile as skirting as well - rather than wood.

How can i fill the gap once rendered, as presumably i cant render past the DPC? I had thought of adding an additional DPC as i render the walls, or leaving a small gap in the render, but then when i tile/skirt this gap would then be closed off - defeating the point?

any other suggestions - the proper method?

Thanks

Pic for reference:

Wall for render

• EdTurtle
• 2 Oct 2024

 

[Hobobanobo]

Next question.

This is for a garage - not a conversion just making it better.

At the bottom of the wall there are two courses of brick (sloping up towards the back to just over a course), then DPC then blocks above.

I want to render as close to the floor as possible, so i dont have a gap of around 5 inches. I am hoping to tile the walls, and am considering a floor tile as skirting as well - rather than wood.

How can i fill the gap once rendered, as presumably i cant render past the DPC? I had thought of adding an additional DPC as i render the walls, or leaving a small gap in the render, but then when i tile/skirt this gap would then be closed off - defeating the point?

any other suggestions - the proper method?

Thanks

Pic for reference:

Wall for render

• EdTurtle
• 2 Oct 2024

I would also like to know this. I had to knock a few inches off the wall all around the kitchen when I moved into my house, since they rendered down to the floor past damp proof course. it wicked up to about 3 foot from concrete floor and caused most of the render to turn to damp dust over the years. Luckily my damp proof is only a couple inches above floor level. So I can board over it with skirting.

 

[JohnD]

caused most of the render to turn to damp dust

Cement mortar does not do that from damp.

 

[Hobobanobo]

Sorry to hijack EdTurtle. Just curious.

Cement mortar does not do that from damp.

Hmm, It could have been Bonding perhaps? Not sure. I t was basically compacted powder. Just age?
The floor was also at a level over the DPC so I assumed the damp just wicked right up the wall from the floor? one or two course of bricks there were also damp once plaster fell off.

So you are saying you can just render to the floor? Over DPC?

 

[JohnD]

You should not bridge the DPC with render or plaster. Leave a gap. It can be done with a bell cast or with a temporary wooden batten that you remove later. Either will leave a neat edge, the bell cast also provides a drip.

The stuff that crumbled when damp would have been gypsum plaster, but to be so wet there was probably a source of water that should have been found and repaired.

Sand and cement render withstands damp conditions.

I hope you mean DPC, not silicone injections.

 

[Hobobanobo]

You should not bridge the DPC with render or plaster. Leave a gap. It can be done with a bell cast or with a temporary wooden batten that you remove later. Either will leave a neat edge, the bell cast also provides a drip.

The stuff that crumbled when damp would have been gypsum plaster, but to be so wet there was probably a source of water that should have been found and repaired.

Sand and cement render withstands damp conditions.

I hope you mean DPC, not silicone injections.

Its the Black layer between the first few courses of bricks. so DPC?

I think I fond the water source, the boiler had a drip of water outside that was running down the wall instead of to a drain, it was acidic, so I think eroded the mortar and was then working its way into the cavity, for 10 years.
Thanks, when I comes to render the living room I will use a baton and leave a gap behind the skirting.
5/6 inches off the floor?

 

[JohnD]

Its the Black layer between the first few courses of bricks. so DPC?

Yes. Depending on age of house, it might be slate, or tarry felt, or thick plastic.

 

[JohnD]

Thanks, when I comes to render the living room I will use a baton and leave a gap behind the skirting.

A very superior way to fix skirting, which spaces it off the wall, is to screw an 18mm batten to the wall so that its top matches the top of the skirting, and another near (not touching) the floor.

You can render or plaster neatly to the top batten

you can shim or fill behind the battens so they are flat and even, to correct a wonky wall. You only need small screws to fix the skirting to it. This is very suitable if you have stained or varnished skirting and use small brass screws.

There is a channel between the battens where you can run TV, LAN, phone, alarm or speaker cables if you wish (mains power cables not permitted).

This method takes extra time so is not usually done by professionals except on fine work.

 

[Hobobanobo]

A very superior way to fix skirting, which spaces it off the wall, is to screw an 18mm batten to the wall so that its top matches the top of the skirting, and another near (not touching) the floor.

You can render or plaster neatly to the top batten

you can shim or fill behind the battens so they are flat and even, to correct a wonky wall. You only need small screws to fix the skirting to it. This is very suitable if you have stained or varnished skirting and use small brass screws.

There is a channel between the battens where you can run TV, LAN, phone, alarm or speaker cables if you wish (mains power cables not permitted).

This method takes extra time so is not usually done by professionals except on fine work.

And I was just going to throw a load of muck behind it for dot and dabbing. (To save me endless drilling into rock solid old nori bricks)
Food for thought. thanks. May do this in the office for HDMI/Network cables.