Pointing riven flags with sbr in the mix

[Back Yard Bill]

Hi, have a smallish patio down with 2ft square flags / riven edges on a very solid base.

Due to the riven edges & the variable depth of the base underneath(not uniform) it loks like i'd need at least 2+ tubs of brush in jointing compound, which makes it very expensive for what it is.

So i gather a 4:1 sand:cement mix that's barely wet is the way to go. But reading around it, I gather some SBR will beef up the mix and make it more durable.

So a big bottle later, I have some to add to the mix. My question is, will the SBR 'work' as part of the liquid to make it barely wet?

And so do i push it in as per the standard 4:1 mix & brush off or do i have to be very careful with the SBR in about leaving it due to staining?

Any other issue to be aware of plse?

Thanks in advance oh wise ones.

Also, i assume it's a standard building sand, not a grit sand to use?

[Tony McC]

SBR will indeed 'beef up' the mortar, but it alsop makes it incredibly tricky to use, as any minor spill, smear or spolsh WILL stain the paving, and stain it permanently, unless it is meticulously cleaned up immediately.

As a contractopr, we oonly ever used SBR in the jointing mortar of commercial projects where we could expect vehicle overrun and/or thousands of pedestrains per day. This is because, without such traffic loadings, there's no need for SBR, and also because of the need for meticulous cleanliness.

For a residential patio, a well-mixed 4:1 sand/cement mortar with a simple plasticiser is more than adequate for the jointing. No need whatsoever to over-engineer the job.

Building/soft sand will give a smoother, finer mortar, while grit/sharp sand will give a coarser finish. It's not a matter of one being structurally better than the other: it comes down to which you prefer to look at.

[Back Yard Bill]

Thanks Tony.

I only got it due to reading on here of all the people re-doing their poor grouting and (at least thought I) read also that it would also strengthen it so it wouldn't need re-doing.

Oh well. So any sploshes etc, just a clean with copious amounts of water or something stronger (sure there's some info on that, so I'll find it).

I'm foreseeing sploshes as I'm certainly no pro. As evidenced by these two further questions:

Does plasticiser just make it more workable as a mix?

Does anyone want to buy some SBR?

[TimW]

May I re-ask a question I've asked elsewhere...

What makes a sand/cement pointing mix turn out to be white? I need it to be grey!

Thanks, Tim

[Tony McC]

Bill, the whole purpose of a plasticiser is to make the mortar more 'plastic' more workable, usable, easier to fold and smooth and play with in general.

Tim: the question uyou posed was answered. Why do you need it repeating

[TimW]

Sorry, I hadn't seen your reply, Tony.
Tim

[Back Yard Bill]

May I re-ask a question I've asked elsewhere...

What makes a sand/cement pointing mix turn out to be white? I need it to be grey!

Thanks, Tim

Thanks Tony.

So, if I promise to be extra careful and not splosh everywhere and add some SBR for longevity, can I also add in a plasticiser as well?

Thanks.

Edit:

And as I'm trying to use the 'dry' mix method (very little water somit can brush away) will the quantities of either / or both a plasticiser or SBR be so small as to be negligible - especially given the small atch of mortar i'll be using?

[Tony McC]

With a "dry mix" a plasticiser is completely bloody useless and SBR will render it no longer dry!

[Back Yard Bill]

With a "dry mix" a plasticiser is completely bloody useless and SBR will render it no longer dry!

Oh dear.

I thought even a 'dry' mix had a little bit of liquid in surely?

And, my thought was that part of that 'little bit' could be the SBR?

Agree on the platiciser though.

Thanks?

[Tony McC]

As soon as you mix even a few drops of SBR to a dry sand/cement mix, it starts to 'clump'.

Dry cement grouts are weak and friable at the ebst of times; adding SBR achieves nothing - it needs the moisture of a wet mix to distribute it evenly and to initiate the curing process.

[Back Yard Bill]

As soon as you mix even a few drops of SBR to a dry sand/cement mix, it starts to 'clump'.

Dry cement grouts are weak and friable at the ebst of times; adding SBR achieves nothing - it needs the moisture of a wet mix to distribute it evenly and to initiate the curing process.

Thanks Tony.

I have obviously been watching the wrong videos then.

Is there one (or very clear, idiot-proof* instructions) about on how to do it properly then please anywhere?

* me obviously ; )

[Tony McC]

Whole series of pages about how to use cement mortars for pointing, starting here

[Back Yard Bill]

Thanks Tony.

I guess I need this one:

http://www.pavingexpert.com/point04.htm

(but without the dye)

3:1 sand : cement

but definitely no SBR as part of the limited liquid content added for the semi-dry mix?

I guess that would just make it all too sticky and to not brush off correctly / easily etc?

Thanks.

[Tony McC]

You really don't need the SBR.

[Back Yard Bill]

OK, OK, I'm betting the hint thanks.

I did a test area with no SBR using a grit sand 3:1 and it looks great alongside the riven flags.

So looks like that's the way to go.

Thanks for your help Tony.

: )