Last weekend was laying a small area of Marshalls Saxon, 450x450x35, to act as a doorstep. Good firm base of crazy pave then slabs laid on a bed of about 80mm of sharp sand / cement, about 10 to 1.
Slabs were wacked down with a rubber mallet and back of slab was wiped with a wet rag so it didn't suck too much.
All looked good, a 10mm gap was allowed for traditional pointing but this was not done, had to stop and plan was to finish this weekend.
Slabs haven't been walked on much and no heavy rain.
Just noticed a couple of the slabs have developed a slight wobble. Lifting them I see that the base looks fine but I guess it must have sunk slightly. Slabs haven't stuck to base at all.
Base is hard - well I can't break it with my fingers but could with a screwdriver.
Is it just that the base wasn't compacted enough ? Or am I doing something else wrong ? Couple of photos here.
Bloke doing work with me rang Marshalls tech line and was told not to use sharp sand but to lay them in a wet mortar made with ordinary builders sand - surely not ?
sharp sand is fine, mix looked a bit too dry to me
you really want to point slabs the day you lay them,it bonds the pointing to the bedding
sure the rocking hasnt been caused by the dreaded "customer"
"no i didnt walk on them"
"oh yes you did!"
LLL
Thanks guys, most of the work is being done by a brickie and I know he would prefer a less dry mix.
So, what's best, same sharp sand and about a 4-1 cement mix with a bit of plasterciser ? Then make the mix a bit dryer than a normal brick laying mortar mix but wet enough that the slab sits a bit in to it ?
Does that sound good ?
Thought I'd give Marshalls a call for their view.... They say don't use sharp sand as it "could crack" and that for mortar under the slabs I should use building sand !
No further explination was available !
I trust you guys to be right more than them as makes the slabs so sharp sand it is and as LLL suggests we will make the mix a little wetter.
when we say sharp sand we mean "flooring,screeding,hartican,riverwash,PY,grit sand" it has many names but is 1 step down from concrete
sharp sand is what i would use for rendering a wall,soft sand is for laying bricks
cheers
LLL
A combination of sharp sand and plasticiser with building sand works well, I've used 2 bags building/1 bag sharp , good mix. Technically the sharp grains will give better structural strength to the mix, from a working point, the building sand on its own works like babypoo, and is a major pain to work with on its own, by comparison. Whichever we've used a 5:1 wet mix and have parked tractors on the paving afterwards, with NO ill effects.
Cheers Victorian Cobble Bloke.
That looks like a plan. There was an area of 50mm thick crazy paving that we removed that had been down since 1969 with no cracks or problems and that was sat on what looks like a mix of sharp and building sand. It wasn't very thick either, no more than 60mm.
One other question - how best to point up the Saxon slabs. The gaps will need to be a bit tight - I think about 8mm, maybe even a bit less - otherwise the three different sizes slabs we are using will not line up correctly. It's over 100 SqM and doing a bit of testing we can see pointing would be challenging as mortar snots aren't easy to remove from the surface.
Interesting read here about different brush-in pointing treatments. Can't find any mention of the Wickes branded paving jointing product, anyone know who makes it and if it's one of the good ones ? Thinking of giving it a try. Yes I know a lot of people think Wickes are DIY but most of the range now seems to be the same as the local Travis P and is often cheaper - just avoid the place at weekends !
Please do not use the Wickes stuff!!! It is complete cr*p. We tried it once on a job and had to take it all out and redo it. Basically anything you can buy from the main DIY chains or builders merchants is cheap and nasty.
