Mixing frost proofer with SBR?

[loply]

Hi folks,

Planning on getting a patio laid some time soon - on a bed of 50mm mortar made with sharp sand and mixing SBR in for strength & stickiness.

Anybody know if I need to (or should bother) adding a chloride-free frost proofer? Or will the SBR be enough by itself?

I wonder if the SBR is enough by itself since it will make the mix set quickly, I don't want to add a frost proofer too and have it set too quickly to work...

 

[^woody^]

I can't see any of those being of any benefit or making any difference.

 

[theprinceofdarkness]

What you need for patio slab laying is plasticiser. The earth is all ready strong enough to hold you weight. You need a weak mortar which has a lot of "fat" so the slabs can be bedded down easily. Without it, thumping the slabs down just squeezes the water out of the mix and it will go hard, so you have to scrape it of and use a new mix (just a little less). Why do you need a sticky mix, the mortar is not going to slide off is it?. Put some old plastic bags over the work to protect it from frost , or sacks if you have any.
Frank

 

[loply]

Hi guys,

SBR being added as the patio stones being used are notoriously hard to stick to - leading to them being loose once you're finished laying. Also, it's quite an intricate shape with some quite expensive stone (and some quite small bits) so want to make sure it's rock solid.

Just not sure if it's going to set like a rocket if I add frost proofer on top of the SBR, as I think the frost proofer normally speeds up the setting (and so does the SBR)?

 

[r896neo]

Don't listen to the naysayers, adding sbr is absolutely the right thing to do as is your grit sand. What is the stone? If its slate you may want to paint a bond bridge on to the back rather than adding sbr to the mix.

Sbr makes it go off a bit quicker but not in the same way as rapid hardener/ frostproofer Unless temperatures dictate it i wouldnt use FP. To be honest if its that cold i would not lay it.

 

[^woody^]

Oh, how did things get built before SBR I wonder?

SBR has no value if used in a bedding mix.

Sharp sand is not the correct material in any case, so it's no use using the wrong sand and then using an additive to try and make it perform like the mix that would be made if using the correct sand in the first place.

 

[loply]

Hi guys,

The stone is like a sandstone, imported from India stuff, quite light in colour. I think maybe it's very absorbant so it sucks the moisture from the mix a lot and prevents a good bond? Just guessing... been told it won't stick to normal mortar very well... Was planning on putting an SBR bond on the back of each slab and a small dose of SBR in the bedding mix too for strength & quick setting.

Woody - why not sharp sand? I always understood that was the best choice as it gives a stronger mix. It's what the stone manufacturers brochure recommends. I would have thought bricklaying sand would be a bit weak when spread over a large area?

To my mind the laying of the thing will only take 2-3 days but I'm hoping it will be there for 20-30 years, so it seems like anything to make it stronger is a worthwhile investment of extra effort? even if the laying is a tad more time consuming or expensive...

 

[r896neo]

Grit sand gives a much higher strength mortar and it holds less water making it much easier to work with in the thickness paving uses, typically 30-50mm.

SBR dramatically improves adhesion of mortar. The logic that it didnt exist before, therefore its not a good idea is ridiculous, technology moves on.

If you need specific paving advise i suggest you use the brew cabin forum on paving expert. Sometimes too many 'Thats the way i've always done it, other ways are wrong' attitudes on here with regard to paving.

 

[^woody^]

mortar

Mortar is for walls. Reference to adhesion and strength are not relevant to this work. You should be advising the OP about a suitable base not mortar, and not referencing properties that are not relevant.

"Technology" might have moved on to allow this to be discussed via this internet thing, but the "technology" of laying a stone on a patio is very much still as it was in the err, stone age.

What you are telling the OP is that any Indian stone patio not laid on your grit sbr mix will fail.

 

[r896neo]

Yes apologies i should have said bedding mix. I only used to term mortar to ensure it was understood it should be a sand and cement mix not just a grit sand bedding.

I agree that many stone patios will be fine without sbr but my experience with the imported indian stone from the last few years has been very porous stone that sucks water out of the base so quickly that the flags do not adhere to the bedding. Adding sbr helps with this and is a very low cost addition which i believe has value as a belt and braces approach.

What sand would you advise using for the bedding mix?