Small obstruction in inclined screed bed

[monks]

Hi,

congrats first on probably the best trade specific website I've ever come across.

I am putting Tegula Drivesett blocks down on a path 2mx1m at the front of my Victorian house (foot traffic only). It is on a slight incline, with an upstand for the coal chute step at the top, a small step at the lower pavement level, and concrete edgings either side. I have already laid some MOT type 1, however with the bad weather, water is pooling at the bottom, next to the pavement border step. After reading this site, I realise I need at least 3-4 days of good, dry weather before screeding, as the Type 1 is fairly spongey.

My question is : at the top of the new path, the build-up of the existing coal chute has a little step that will be just covered by the sand, however could present a problem when compacting the sand. This is because I would expect the sand to compress at different rates due to the hard obstruction close to the surface...? Has anyone come across this before, or should a good pre-compaction regime negate any big differences ??

Hope all this makes sense...

Thanks

[lutonlagerlout]

if you are that worried then perhaps lay them on a cementious screeded bed
its only 2 M2 if i am reading this right, so its only a morning's work
if you lay them on a cement mix then just wack with a piece of 4 by 2 and lump hammer to consolidate then use your kds
LLL

[mickg]

and if the MOT is like slurry I would not go near it with a vibrating plate, like Luton says mix a 4:1 grit sand and cement and us this as your laying course

this might sound primitive but it works, seeing its only a small area so you can either use your feet, a piece of 4 x 2 timber and a lump hammer or a steel trowel to compact the mixture

then screed it to the correct level and fall and lay your block paving including all the cuts, put kiln dried sand into the joints, using the 4 x 2 timber placed on the blocks and tap gently using the lump hammer, you will see the kiln dried sand disappear as you do this so you may need to add more kiln dried sand

[Hawk]

??? if they are Tegula, dont hit them too hard ???

[monks]

Thanks guys - a project manager I work with suggested the same thing today, but thought I would check on here as well. Cement screed it is then - however I am just a little surprised as many references on this websites say FLEXIBLE construction only for block paving...

[mickg]

every job I do is assessed individually for the ground conditions and is completed the best possible way even if it means doing it an unconventional way

[lutonlagerlout]

flexible is highly suited to vehicular access as its name suggest the pavement/roadway flexes without breaking
your area is so small and you do have this issue with subbase height so rigid sounds best in this instance
cheers tony

[Tony McC]

The problem you've correctly identified regarding the compaction of sand over the existing concrete and the newly placed sub-base is a knock-on effect of differential settlement. When you have laying course material over a rigid base, it will settle (or compact) to a different extent than it would over a flexible sub-base. This is the main reason why concrete bed is trimmed away from the 'front' face of edge courses and kerbs, so that the blocks (or flags or whatever) are lying on a full bed of laying course material, and not having one edge on a rigid bed.

While the cementitious screed option outlined by Mick and Luton et al is OK for smaller areas, the other strategy is to use trial and error to get the sand laying course to the correct depth and compaction to accommodate the blocks perfectly. This may take three, for, five or more attempts, and is the reason many contractors would opt for the cementitious screed option which they can get right(ish) first time in most instances.

Flexible *is* the correct construction for 99% of block paving work, but, as in life, there are always exceptions.

[irishpaving]

Whacked a huge area of tegula with a f/r plate and didn't crack one block....