Width of mortar joints and ready made stuff

[Wildfang]

More questions - nearly there...

I am going to buy Stonemarket weathered york riven (450 x 450, with a few 225 x 225 at edges to help acheive a stretcher-bond laying pattern).

I was thinking of a 10 mm joint width, but am worried this may be too narrow, some of the photos look wider - but hard to tell. Any opinions?? Would 15 mm look better and be easier to fill (I am not planning on buttering as I lay)??

Also, I got the recipe of 4 parts soft sand to 1 part cement from this site, but I wonder if I can just buy ready mixed stuff (I am guessing here). Also, I heard that the addition of plasticizers is unnecessary as it is alreay "in" the cement? again any advice?

Thanks as usual

WF

[Tony McC]

I really wouldn;t lose any sleep over whether the joints are 10mm or 15mm. As long as they are 10-15mm, they'll be fine.

The reason we don't use narrower joints with that particular type of paving is that it's damned near impossible to get mortar into a narrower joint; and why we don't use wider? Well, because it's the flags you want to see, not the bloody mortar!

You can buy ready mixed sand/cement. They put it in special bags with a big price ticket for those with more money than sense.

And some cements do incorporate a powdered plasticiser, but not all, and there's a school of thought that they put in the bare minimum, making no allowance for harsher sands, hard water, hand mixing, etc. Still some plasticiser is always better than none.

[lutonlagerlout]

another thing to watch for wildfang is the fact that 450 + 15+15 =480
whereas 480 -225-225 =30 but this 30mm has to accomodate 3 joints of 10mm instead of 2 at 15mm
most pavers would use a half cut to get the bond or see if they do a 450 by 226 in that range
i normally go for about 15 mm joints because that is the thickness of my finger tips
we also add pva to the mix,not sure of the science of this but it works for me
cheers LLL

[Wildfang]

Thanks to you both

Sorry LLL, I misled you with my flag sizes - of course I meant 450 x 450, with some 450 x 225. However, I'm now thinking of using two sizes to make the bond - perhaps 450 x 600 and 450 x 450....

either way, what about quantity of mortar? 15 m2, assuming joint widths of 15 mm and that I will wet mortar bed all outside edge flags along a linear outside edge of 13 m (it will not be a 4 sided shape in case you are wondering about my numbers) - i.e. how many bags of cement and how many of soft sand? My merchants advised that the bags will contain 25 kg each and said 4 bags of sand and 1 of cement would be enough =- any thoughts? I want "more than enough"

WF

[Tony McC]

Bedding (Using a 10:1 sand/cement mixture @ 40mm thick)

Class M washed grit sand 1.2Tonnes
Ordinary Portland Cement 5bags @ 25Kg


Jointing (Using a 4:1 sand/cement mortar)

Washed Building Sand 75Kg
Ordinary Portland Cement 1bags @ 25Kg
Optional Mortar Dye 1Kg

[lutonlagerlout]

4 bags of sand and 1 of cement would be enough =- any thoughts? I want "more than enough"

i would hazard a rough guess at 2-3 bags so 4 is more than enough
unless you have a quarry nearby you may have trouble buying 1.2 tonnes of flooring sand (grit sand) most bulk bags actaually weigh up to about 850kg so 2 bulk bags would be 1.7 tonnes giving you a margin for error,i allow 5 bags of o.p.c. per tonne myself,which equates in real life to a half bag of cement in a full mixer of sand and water and pva
cheers LLL
p.s. any excess grit sand can be dug into the garden as a soil improver-i think



Edited By lutonlagerlout on 1170176881

[Wildfang]

Great

...but assuming 4:1 soft sand:cement - doesn't that mean 4 bags:3 bags - ie. 100 kg:25 kg ?

Also Tony, I was planning on using the dry 10:1 bedding mix as per this site for most flags, but for OUTSIDE flags, I assumed I should mortar down with damp 4:1 as per joints (also as advised by this site - I won't be using edging units). Hence my asking how much soft sand and cement I would need for POINTING and OUTSIDE FLAG bedding. I have already calculated what I need for the dry bed using this site's calculator

thanks

WF

[lutonlagerlout]

yes ,but what we mean is that you only need 75kg softsand in a 4:1 mix for the pointing
I remember we have had this thread before about gauging aggregates
when i knock up bricklaying mortar at 5:1, 125kg of cement works to 1 850 kg bulk bag
nowat first look at this seems wrong. as it works to 6.8:1
but you gauge materials by volume and not weight
always best to use a bucket or something similar to keep your gauge consistent
photo please wildfang
cheers LLL

[Tony McC]

Although 4:1 laying course is the British Standard recommendation, 10:1 is adequate for a patio. If you wanted to 'upgrade' the 10:1 to, say, 5:1, then double the quantity of cement.

[Wildfang]

LLL - I see now - I get what you mean. As a chemist (of sorts), we would be talking about liquids when making up ratio mixtures by volumes. Not solids.

Tony - I am still confused - are you saing that outside edge flags don't need to be bedded in "wet" mortar (i.e. 4:1) as per this site???? but that dry will do? If there are no mortared in edging units to restrain flags (as in my case), might this not cause the flags to move if outside edge flags are only on the dry bedding mix??????

thanks for the continued advice

[lutonlagerlout]

you would normaly haunch the edges wildfang
you really need to make a start now mate,its time to walk the walk
lol
good luck
LLL

[Tony McC]

Flags laid to free edges need to be retained in some way. You can lay on a moist mix of the 10:1, or you can beef up the bedding to 5:1 and lay on a moist version of that. You can use either as a wet mix, if you prefer. Or you could use an edging of some form.

I can't say which is best as I'm not familiar with your site, but as long as the flags at the free edge(s) are secured in one way or another, that's all that matters.