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What does SBR mortar additive NOT stick to?

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What does SBR mortar additive NOT stick to?

Postby Eric the Viking » 13 Jun 2022, 18:08

Yes, I've Googled, etc. As many different opinions about SBR as there are plasterers out there, it seems.

I have to shutter-up the top edge of some brickwork, so I can get a horizontal layer of render on top, in turn so that becomes the base for a tiled windowsill. The shuttering edge of the cill will let me float/skim to exactly the right thickness, to get the finishing tiles to the right height allowing for tile cement. Trouble is that it's a repair, and I can't re-tile the whole wall, so stuff has to line up pretty well.

I've been advised (told!) I should use SBR for bonding and waterproofing. I've also been told it's stickier than a really sticky thing, whether it's used as a bonding pre-coat or in the render mix itself. Stiking to the brickwork=good. Sticking to the shuttering=not good.

So what can I use on my "shuttering" so that I can easily remove it afterwards? I'm wondering about putting wide PVC sticky tape over a redundant bit of 3x1 or something like that.

Overall render thickness on top will only be 1/2" or so, tops, but I will need a clean, squarish edge to the front, in order to get the brickwork below rendered to the right finished line, hence all the complicated mucking about.

It's doin' me 'ead in! Someone must have had this problem before, Shirley?

E.
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Re: What does SBR mortar additive NOT stick to?

Postby Doug » 13 Jun 2022, 19:29

Clingfilms your friend, very little sticks to it but wrap it round the wood & it will stay put. I use it regularly in the work shop on clamps when using PU adhesive on a glue up, I’ve also used pallet wrap when rendering up to coloured concrete blocks that I didn’t want mortar getting onto.
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Re: What does SBR mortar additive NOT stick to?

Postby droogs » 13 Jun 2022, 21:13

Or strip of UHMW polyetholene, so non stick is is slippyer that grease weasel poo off a shovel due to an unbelievably low friction co-efficiency.
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Re: What does SBR mortar additive NOT stick to?

Postby greeno » 14 Jun 2022, 06:24

Concrete mold release should give a barrier.

Loads of off the shelf and alternatives.
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Re: What does SBR mortar additive NOT stick to?

Postby Eric the Viking » 14 Jun 2022, 07:30

Wow, thanks folks!

Several things there that I have available, and I'd forgotten I have some silicone spray (for mould release) too, and I think I know where it is*. I also think I may have a bit of repointing to do on the wall under, meaning a bucket mix is called for, and that means probably enough left over to experiment with. Will try the clingfilm first, as I definitely know where that is!

Much appreciated.

E.

*bit of a challenege round here normally!
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Re: What does SBR mortar additive NOT stick to?

Postby eezageeza » 14 Jun 2022, 09:00

Brown packaging tape - the stuff used to close corrugated cartons - run along the length of your shuttering will give a surface that pretty much nothing will stick to.
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Re: What does SBR mortar additive NOT stick to?

Postby RogerS » 14 Jun 2022, 10:08

greeno wrote:Concrete mold release should give a barrier.

Loads of off the shelf and alternatives.


What about any open pores etc in the brick/cement? Would they not still act as a 'key'? Personally I like the idea of a separate film like cling film.
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Re: What does SBR mortar additive NOT stick to?

Postby greeno » 14 Jun 2022, 12:22

RogerS wrote:
greeno wrote:Concrete mold release should give a barrier.

Loads of off the shelf and alternatives.


What about any open pores etc in the brick/cement? Would they not still act as a 'key'? Personally I like the idea of a separate film like cling film.


I think it is generally an oil based product (some say you can use olive oil etc) that you apply to the shuttering/ mold first, before pouring, just creates a barrier like film.

There's silicon stuff as well, like op days they have. I've a can knocking around from when I was playing with resin, not sure how effective it'd be for a concrete pour / wood shuttering though.
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Re: What does SBR mortar additive NOT stick to?

Postby greeno » 14 Jun 2022, 12:24

RogerS wrote:
greeno wrote:Concrete mold release should give a barrier.

Loads of off the shelf and alternatives.


What about any open pores etc in the brick/cement? Would they not still act as a 'key'? Personally I like the idea of a separate film like cling film.


The other way round. You're sealing the shuttering so it doesn't bond to the concrete.
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Re: What does SBR mortar additive NOT stick to?

Postby Eric the Viking » 15 Jun 2022, 08:19

So I've gone with the brown parcel tape, as it was handy, but I had a brainwave earlier - will wipe it over with Liberon machine wax, too (just a very thin coat). That'll give it a game chance of coming away cleanly, and I can wash off with meths afterwards if I need to get rid of residue (the next bit of render needs to bond to the shuttered edge). It turns out that this piece of render needs to be thinner than I thought, too, which is a good thing.

That's this morning's fun 'n' games decided on!

E.
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