Which render should I use?

[squeakysim]

I have some patch rendering to do and I thought it would be pretty straight forward; just get some straight sand and cement render for the scratch coat and then apply a top coat. But, this is my first time and there are a multitude of different options out there it seems! 

And, I've got a few different scenarios which I feel require different considerations, so I want to try and find a single option that can cover them all if possible without the needs for buying different materials for each...

1. I have full depth patching, that goes back to brick to carry out in the kitchen (10mm+)

2. I need to patch where the old wall heater was and now has a sheet of cement board to render over (5-10mm), but there is deep gaps on the sides (see photo)

3. I need to skim some areas where removing tiles has removed mainly just the top coat, and few mm's of base coat in places.

4. Oh yes, and also filling in chasings from new cable runs (about 30mm).

I was going to keep it simple and cost effective, but then I read you need to use a different kind of render for cement board and I don't want to have to buy different materials for each task!

Can I use Dunlop 20kg Multipurpose Acrylic Render  as a base for all tasks, then apply a top coat?

[EricL]

Hi @squeakysim 

If the paper is still properly bonded to the wall and it takes a lot of effort to remove it, I believe that it would be ok not to remove it. My best advice is to use a primer such as Dunlop 1L Primer And Additive before tiling the surface.

If you have any other questions we can help with, please let us know.

Eric

[Nailbag]

Hi @squeakysim 

I think as long as you're confident on how secure the painted paper is to the plasterboard, or in other words will take the weight of the tiles, you should be right. Obviously you will need to clean and prime the wall before tiling directly over to ensure maximum adhesion of the tile adhesive.

Nailbag

[Dave-1]

Morning @squeakysim 

@EricL and @Nailbag has pointed out the same thinking I have. As long as the paper is bonded then I really dont see an issue. You could always scour the wall with a blade as long as you will be waterproofing it afterwards.

Dave

[squeakysim]

Thanks again!

It’s there a ready mixed (or smaller) product I could use for the plaster top coat instead of buying a whole bag of plaster and lime? The amount needed is quite minimal now as I’ve the remaining depth is approximately 2mm and I only need to cover about 2-3sqm. 
Cheers

[JacobZ]

Hi @squeakysim,

Unfortunately, I am not aware of a premixed product that would be suitable for application directly over render.

You could try a premixed product, but I couldn't guarantee it would last. The hardwall plaster and lime mixture is the correct product for this application, and considering the effort you have put into getting to this point, it would be the best way to finish off a great job.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

[squeakysim]

Ah right okay! 

Can you advise how long it should be left to dry before painting? The video only states a 'few' days...

What happens if you do end up painting the plaster too early?

[EricL]

Hello @squeakysim 

Depending on the air circulation and temperature of the room, it may take several days for the product to totally cure. But because of cold weather and possible rain, I would extend the waiting time to at least two weeks to very sure that the product is fully cured. If painted too early the trapped moisture inside will react with the paint and the paint will blister and peel. 

If you need further assistance, please let us know.

Eric

[squeakysim]

Ah!! That's frustrating, I hadn't factored in that amount of time! 

The building is currently not being lived in and is unheated and I'm in Melbourne...! Obviously if I was to put a heater nearby I imagine that would make a difference, but would be expensive! However, do you think just having a fan blowing on it or across it, would help speed things up much? 

I guess the hard thing is, that it doesn't really seem that there's any way to actually tell that it has cured, other than how much time has passed!

Also, it that curing time based on depth of 2mm, or is it the same regardless?

[EricL]

Hi @squeakysim 

Using a fan should help with the curing time. I don't recommend using a heater as heated artificial accelerated curing can cause the surface to develop fissures.   

If you need further assistance, please let us know.

Eric

[squeakysim]

So it seems none of my local bunnings stock hardwall plaster..! Which is a bit of a hurdle!!