50mm blks 15mm proud of sand b4 wacking? - Told 2 put 15mm high-but site says less?

[Jimlad]

Hi, sorry about all the questions but a final one before I put the blocks on tomorrow.

(will post a couple of pics when done for you to laugh at or congratulate.)

My instructor (I was trained in way back march with tradability in newark,notts on a one week course) - said to leave the 50mm blocks 15mm proud on top of the final bedding layer before final compaction, although I'm seeing contradictions to this on the site and forum.

I know there is no golden rule and you have to guess somewhat - but I'm wondering if any of you experienced and blummin helpful chaps out there could enlighten me to how much YOU would leave the blocks proud before final compaction.
Thanks once again to anyone who replies to what is probably an overasked question.

[Pablo]

no thats way to much if the compacted sand bed is 30mm deep there's no way you could compress it by half. 5- 8 mm is fine.

[Jimlad]

Nice one Pablo and thanks for the quick reply.

The bed is going to be 40mm thickness so you think 5-8mm still stands dude?

[local patios and driveway]

It depends on the method you use, i screed the sand, compact and screed again, then lay the blocks maybe 3mm above my edgings. Works well for me. Some teams screed, lay blocks then compact, that would need more height but do the same job

[DNgroundworks]

I use the same method as LPAD, screed with 20mm bits of ply tacked into the notched bit on the screed board, take the bits of ply out, wack and screed again, i usually leave around 5 mm proud.

15mm is way too much unless you are laying the blocks on un-compacted screeded sand, this method is not so good though, because as your work progresses and you walk on the blocks they sink/tip/move and it ends up looking a mess, in my experience anyway.

[lutonlagerlout]

5-8mm high^^
as has been said if the sand is screeded and wacked it hasnt much farther to go
also i would rather the blocks are 2 mm high than 2mm low
LLL

[Jimlad]

Cheers chaps, going to go 5-8mm high, and have read (as you said LLL) that it's better to be a bit high than low.

Can't thank you enough to all of you for your no nonsense informative replies to my inane queries, there's alot of bright people on this forum that aren't smartarses about it, it makes a difference and is certainly not taken for granted.

Thanks again, brown nosing over.

[Jimlad]

It depends on the method you use, i screed the sand, compact and screed again, then lay the blocks maybe 3mm above my edgings. Works well for me. Some teams screed, lay blocks then compact, that would need more height but do the same job

At what point do you screed and then wack and then screed again please?

My bed layer is 40mm sand and 50mm bricks - so should I build the sand up to my edges (laid in concrete to my FPL) - then wack the sand down once - then build up again so the level is screeded to exactly 45mm below my FPL? - leaving my 50mm bricks 5mm proud of the fpl?

:p

[local patios and driveway]

Put the sand to your desired final height (45mm below finished level) then compact the sand, then add a little more sand and screed again to the final height. Lay the block. Compact the block.

[Carberry]

Screeding

[DNgroundworks]

I dont do it that way ^^^ i think adding sand to an uneven compacted surface may lead to differential settlement/comapction.

I lay my sand loose, about 10mm down from the top of the edge course, screed the loose sand with the 20mm bits of ply tacked into the notched on the screed board which is already cut at 45mm, i then compact with one pass, then take the 20mm bits of ply off the screed board and then screed the area. Doing it that way you arent trying to screed off loads compacted sand if you laid it down to high in the first place.

[Jimlad]

I dont do it that way ^^^ i think adding sand to an uneven compacted surface may lead to differential settlement/comapction.

I lay my sand loose, about 10mm down from the top of the edge course, screed the loose sand with the 20mm bits of ply tacked into the notched on the screed board which is already cut at 45mm, i then compact with one pass, then take the 20mm bits of ply off the screed board and then screed the area. Doing it that way you arent trying to screed off loads compacted sand if you laid it down to high in the first place.

thanks for all of your replies,

DNG;
today I have mostly been doing (a'la paul whitehouse experience?) - I've decided to chuck sand to the fpl and level roughly with screed boardscreeding off the edges to give a fairly rough level, then I compacted it once, and going to screed off tomorrow with a 42mm notch in board to leave blocks 8mm proud.

Similar to your way? although I am going to have to screed of loads of sand, will do your way next job.

Think I would have done it your way but this should be ok once screeded.

Thanks everyone for giving a monkeys enough to help me out, cheers to all of ya.

[lutonlagerlout]

i cannot see the point of chucking loose onto screeded sand?
I lay the stone 70mm below finish then compact
so now i have roughly 95mm below finish
then add roughly 40-50 mm of sand so 40mm below finish and compact
then screed off to 55 mm below finish and lay the 60mm block 5 mm high
install KDS then wack a final time
I know some blokes that dont wack the sand but i think this is asking for trouble


anyway how did you get on jim?
LLL

[msh paving]

I put sand in to 3/4 way up the edge course blocks,rake out to leval,compact the whole area 1 pass with plate,set up rail to screed,only allow 5mm knock down on edges,after cutting in ,final wack and sand but run plate over fixed edge blocks so they don't go lower

Can't see the point in wacking then lose screeding,to much movement when laying and running block barrow over blocks

reading the screeding section in main site our friend "carberry" posted lose screeding is not recomended for that reason
but everyone has there own way
MSH

[Jimlad]

LLL got on ok thanks, through gritted teeth, my own self doubt and negativity, but soon got over that and got the job to the point of my final screed (before placing blocks on top) and it was then 4pm and no light (and a longish drive home, so have covered the sand for tonight (mansfield is getting some light rain about 3am) and then will finish off tomorrow.

Thanks for all your help LLL you're a gentleman, much appreciate, will post some pics soon for you all to scrutinate.

cheers.