Muck, how long to go off? - Question about

[Spitfire]

I tend to use a standard 4 and 1 mix for my bedding of patios (4 sharp sand, been taught that way but if im wrong plz say) and this question is just to reinforce my point of view to customers:

1#
I have generally believed that after slab is laid, it needs one day of no rain & no traffic (ideally two days) correct? if not how long would u say a slab takes to go off on an inch of muck?

2#
If a working day starts around 7am and it starts to rain about 9-10am, am i justified in not going to that particular job at 7am knowing rain was probable, because the slabs will end up all over the place or significantly increase the chances of the slabs not being where they should be?

Just like to know what other contractors do particularly about the 2nd question to respond to "Why didnt you come & lay slabs today!" lol

[Rich H]

I was always taught 4:1 as well. However, Tony's pages and other posters suggest leaner mixes for slabs, depending on the type and method, and I follow this these days using up to 10:1 for a screed with 'council' slabs.

1# yes for the traffic, although if you can screed it you can point it and walk on it straight away. I always tell customers to stay off it until I've finished! If they walk on it before and I have to relay the slabs it's added to the bill. Rain is only really a bad thing if you've use a wet mix where the slabs are 'floating'. More water would not help. Most slabbers use a semi-dry mix and a bit of rain doesn't hurt. If it's going to be torrential just cover it.

2# If the forecast is for heavy rain I call the customer and explain that we're not coming unless it clears. I can't say I've ever had someone argue with me about it. Most customers don't like you there before 8am in my experience, and no noise before 830!

[seanandruby]

Shouldnt use to much cement it will cause problems. you just need enough to bind the sand to stop migration, try re-laying flags that are layed on 4 in 1 you need a kango. obviously if its to wet then do other jobs till it dries up.

[lutonlagerlout]

i was taught a weak mix and saw lots of failures from it so i always err on the side of strength,just to allow for the mixerman making a slight cock up now and again
so its 12.5kg of dust to a mix for me,which i reckon is about 5-6 -1
cheers LLL

[MRA]

I settled on a 5:1 mix using a plastering sand (Or 2.5 Course Washed Sand : 2.5 Building Sand :1 Cement - preferably Mastercrete as it mixes better than most) after many different trials; assuming you want a full bed, wet mix. If mixes nice and smoothly when used with a decent plasticiser and still goes off like a good concrete.

This mix would be perfectly strong enough for regular domestic patios, but if there ever was any future settlement due to external influences, i.e. ground heave, the mix wouldn't be so hard as to crack the paving; any cracks would appear throughout the jointing mortar (6:1).

This can be demonstrated in brickwork when a wall shows signs of movement. If the mortar used has been gauged properly, the cracks would snake down the joints and not crack the bricks, leading to easier repair and potential for re-use of the bricks (although the suction potential of the base of the brick would be reduced from its potential when new).

[lutonlagerlout]

I settled on a 5:1 mix using a plastering sand (Or 2.5 Course Washed Sand : 2.5 Building Sand :1 Cement - preferably Mastercrete as it mixes better than most) after many different trials; assuming you want a full bed, wet mix. If mixes nice and smoothly when used with a decent plasticiser and still goes off like a good concrete.

This mix would be perfectly strong enough for regular domestic patios, but if there ever was any future settlement due to external influences, i.e. ground heave, the mix wouldn't be so hard as to crack the paving; any cracks would appear throughout the jointing mortar (6:1).

This can be demonstrated in brickwork when a wall shows signs of movement. If the mortar used has been gauged properly, the cracks would snake down the joints and not crack the bricks, leading to easier repair and potential for re-use of the bricks (although the suction potential of the base of the brick would be reduced from its potential when new).

"waits with bated breath for the wrath of cormaic"
lol
like yourself MRA i experimented with many bedding mixes and i always go for wet mix (mortar consistency) with screeding sand /cement 6/1 and about 75ml of pva per mix
it has worked well for me
LLL

[Tony McC]

Building sand? Plastering sand? Not on any of my sites you don't!



Too fine-grained, too rounded, too soft (hence the vernacular title of "soft" sand) and not compliant with any of the relevant parts of 7533.