sand screed and heavy rain
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alan ditchfield
- Posts: 203
- Joined: Thu Jan 01, 1970 1:00 am
- Location: Preston / Lancashire
the sand will dry when the good weather returns if ever, but this is a problem that depends on circumstances. ie is there any damage to the area below the blocks you have allready laid or in other words has this sand shifted if so the area needs relaying when dry. The other problem is that the area you have screed and not yet laid must have been damaged, as i posted in another topic earlier block paving is best suited to dry weather.
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Paverman Dan
- Posts: 70
- Joined: Tue Jun 29, 2004 5:27 am
This does suck.
For future reference two things . . and keep in mind I'm a Yank, so our methods may or may not apply!:
-Tarps are your friend. Keep them in every vehicle, always. And instruct your crews to use them at the first sign of rain.
-Is it common practice in the UK to pre-compact the setting bed? In the US, it's not reccomended by the ICPI because the theory is that it makes it harder for the sand to get into the joints between the pavers when you compact them!
Now . . . I would take the exposed sand, and re-rake up the top 1/2" of the setting bed with a light magnesium rake. If you rake too deep, you might dig up base, which not only disturb the smooth, compact, and graded base you worked so hard for, but also dig up stones that will leave unacceptable mole trails in the setting bed when you re-screed the sand.
You will be amazed at how quickly washed concrete sand dries out when exposed to the elements, and frustrated at how long screeded sand takes to dry out if left the way it is.
BTW, if you used stone dust, you may have a real wet mess on your hands. I would bite the bullet, and use a coal shovel, and an asphalt lute, rake up the wet, slimy soggy stone dust, re-smooth and compact the base, and replace it with washed concrete sand.
Leave the newly disturbed sand exposed for about 24-48 hours, and I think you will find it will easily sreeed. If rain is in the forecast, tarp it.
As for the laid pavers, its hard to say. If its not too many, you may want to chalk this up as a lesson learned, pull them up, re-rake and re-screed the sand, reinstate the pavement.
I'm sure the Paving Experts will have more to offer than I can . . but Hope this helps!
For future reference two things . . and keep in mind I'm a Yank, so our methods may or may not apply!:
-Tarps are your friend. Keep them in every vehicle, always. And instruct your crews to use them at the first sign of rain.
-Is it common practice in the UK to pre-compact the setting bed? In the US, it's not reccomended by the ICPI because the theory is that it makes it harder for the sand to get into the joints between the pavers when you compact them!
Now . . . I would take the exposed sand, and re-rake up the top 1/2" of the setting bed with a light magnesium rake. If you rake too deep, you might dig up base, which not only disturb the smooth, compact, and graded base you worked so hard for, but also dig up stones that will leave unacceptable mole trails in the setting bed when you re-screed the sand.
You will be amazed at how quickly washed concrete sand dries out when exposed to the elements, and frustrated at how long screeded sand takes to dry out if left the way it is.
BTW, if you used stone dust, you may have a real wet mess on your hands. I would bite the bullet, and use a coal shovel, and an asphalt lute, rake up the wet, slimy soggy stone dust, re-smooth and compact the base, and replace it with washed concrete sand.
Leave the newly disturbed sand exposed for about 24-48 hours, and I think you will find it will easily sreeed. If rain is in the forecast, tarp it.
As for the laid pavers, its hard to say. If its not too many, you may want to chalk this up as a lesson learned, pull them up, re-rake and re-screed the sand, reinstate the pavement.
I'm sure the Paving Experts will have more to offer than I can . . but Hope this helps!
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84-1093879891
The advice given is sound - any unpaved areas of screeded laying course material are best re-established once we get a break in the rain. Any paved areas that show signs of obvious movement are best lifted, and the bed re-prepared before laying re-commences.
However, to pick up on Dan's point about pre-compaction, we find that pre-compaction gives best results, although both non-compaction and partial pre-compaction are both 'sanctioned' methodologies according to the British Standard covering laying practice.
Non-compaction, we find, can give uneven compaction when the paving is finally consolidated. If you could guarantee that all the laying course material were equally uncompacted, and of a truly uniform depth, this might not be much of an issue, but you can never guarantee the 'looseness' of the sand - it seems to bge a fact of life that some patches, even if not trafficked, will naturally be slightly more compact than adjacent areas. It could eb summat to do with moisture content, or the force with which the sand was placed, but it happens, and there's nowt you can do about it.
With partial pre-compaction, the problem outlines above is sort of half-resolved. The degree of looseness is more controlled, but the topping-up layer used in this method still has the variation in compaction, and a degree of variation in depth.
Pre-compaction tend to produce an accurate bed that can be tailored quite preecisely to give a pre-determined degree of final consolidation, and is capable of accommodating the inherent variation in block thicknesses as well as providing a token amount of 'play' to cope with unforeseen variations.
The business about laying course material rising up into the joints is immaterial. It may happen in some instances; it may not in others, but it makes no real difference as the jointing sand is intended to fill the gap. There's no structural benefit obtained by ensuring laying course material can rise up into the joints - if there was, the blocks would be manufactured in shapes that encouraged this.
However, different gangs have different preferences. I know lads that can make a bloody good case for partial pre-compaction, and they find that works best for them. At the end of the day, as long as the pavement looks good and is true to line and level, then it matters little which screeding method was used. Pre-compaction does seem to be a favourite amongst British and Irish paving gangs, though.
However, to pick up on Dan's point about pre-compaction, we find that pre-compaction gives best results, although both non-compaction and partial pre-compaction are both 'sanctioned' methodologies according to the British Standard covering laying practice.
Non-compaction, we find, can give uneven compaction when the paving is finally consolidated. If you could guarantee that all the laying course material were equally uncompacted, and of a truly uniform depth, this might not be much of an issue, but you can never guarantee the 'looseness' of the sand - it seems to bge a fact of life that some patches, even if not trafficked, will naturally be slightly more compact than adjacent areas. It could eb summat to do with moisture content, or the force with which the sand was placed, but it happens, and there's nowt you can do about it.
With partial pre-compaction, the problem outlines above is sort of half-resolved. The degree of looseness is more controlled, but the topping-up layer used in this method still has the variation in compaction, and a degree of variation in depth.
Pre-compaction tend to produce an accurate bed that can be tailored quite preecisely to give a pre-determined degree of final consolidation, and is capable of accommodating the inherent variation in block thicknesses as well as providing a token amount of 'play' to cope with unforeseen variations.
The business about laying course material rising up into the joints is immaterial. It may happen in some instances; it may not in others, but it makes no real difference as the jointing sand is intended to fill the gap. There's no structural benefit obtained by ensuring laying course material can rise up into the joints - if there was, the blocks would be manufactured in shapes that encouraged this.
However, different gangs have different preferences. I know lads that can make a bloody good case for partial pre-compaction, and they find that works best for them. At the end of the day, as long as the pavement looks good and is true to line and level, then it matters little which screeding method was used. Pre-compaction does seem to be a favourite amongst British and Irish paving gangs, though.