Page 1 of 1
Posted: Sat Aug 23, 2008 7:43 pm
by rimexboy
Hi
Sorry for the silly question but i dont know when i apply the kiln dried sand... i did find it on the main site but now i can not...
Today i have laid most of my blocks and still have a few cuts to do, when ive done that do i then go over it once or twice then apply the kiln dried sand or what do i do...
many thanks simon
Posted: Sat Aug 23, 2008 8:02 pm
by amg15
apply kiln dried sand before you go over it with the whacker - final whack.
i think lol, correct me if im wrong guys.
Posted: Sat Aug 23, 2008 8:05 pm
by Dave_L
Yep, use the deposited KDS to form a sort of barrier between the plate and the blocks.
Then sweep off the excess.
Posted: Sat Aug 23, 2008 10:29 pm
by rimexboy
Sorry guys been in the bath for a very long soak on my poor back
just checked this site again and now im very confussed, as you guys say befor and the site says after comaction is better ??? ??? ???
below is what i found again in the end
Compaction
Compaction, also known as consolidation, refers to the use of a vibrating plate compactor to 'hammer down' the blocks once they are laid. It should be carried out following compliance checks and cutting-in.
Compaction is achieved by making several passes (minimum of two) over the paving with a vibrating plate compactor, often referred to as a "Wacker Plate".
The plate compactor vibrates the paving units, driving them downwards and settling them into the laying course.
The plate spans several blocks at once, and so any slight variation in block thickness is "ironed-out" as the plate passes over the blocks.
Before or after jointing?
For concrete block pavers, many contractors undertake the jointing before compaction and this was a methodology we used for a number of years. While it is not necessarily "wrong" or "bad practice", we have, over the years, become aware of a number of problems that arise from jointing-before-compacting, and we now feel that these problems can be eliminated or reduced by following a compacting-before-jointing methodology. To read more about the thinking behind this revised methodology, click here for a pop-up window that outlines the arguments.
Clay pavers and concrete pavers with little or no chamfer should always be jointed before compaction as the jointing helps keep the units apart during the consolidation process and thereby reduces the risk of spall damage.
Compaction First Jointing First
Chamfered concrete blocks
Chamfered small-element flags
Clay pavers
Concrete blocks with no chamfer
Concrete blocks with minimal chamfer
The aim is to compact or consolidate the blocks into the laying course which is simultaneously compacted to, more or less, the point of refusal, which is the point at which no further compaction is possible. Notice the phrase "more or less" in that last sentence. That is not a throwaway line: it is a key concept, which is linked back to the earlier statement regarding the variation in block thickness (block depth). Consider a typical selection of 60mm blocks. The manufacturing standard allows for a ±3mm tolerance, which means there could be a 6mm lip between two adjacent blocks laid onto an even screeded laying course. In actuality, most British and Irish manufacturers achieve a tolerance closer to ±1mm, but even this would, potentially, allow for a 2mm lip between adjacent blocks.
When the plate compactor runs over these two blocks, the 61mm block may well be "compacted to refusal". Wonderful! But the other side of that particular coin is that the 59mm block is unlikely to have been compacted to refusal, and, left to its own devices over an extended period of time, is likely to settle under the dual influences of traffic and gravity, re-creating that original 2mm lip.
--------------------------------------------------------------------------------
The Kit
It should be noted that using any old plate compactor that happens to be available is NOT an acceptable practice. The compactor needs to meet certain minimum requirements to ensure it carries out this crucial part of the construction process to best effect. The British Standard that covers this type of paving recommends that compactors should have a ...
Minimum mass (weight in Kg)
Minimum plate area (m²)
Minimum effective force per unit area (kN/m²)
Frequency of vibration (Hz)
The category of pavement under construction will determine what the values are for each of the parameters listed above. Pavement category, an indication of the type of traffic that will be carried by a pavement, is summarised here. Most residential pavements would be considered to be Category IV - Private drives. The table below is derived from Table F1 of the British Standard...
The key thing to take from the above table is that the type of plate compactor that can be lifted by one operative into and out of a van is highly unlikely to be suitable. Even for Cat IV pavements, the plate has to have a mass of at least 80Kg, which is over three times the maximum weight that should be lifted by a single person.
Similarly, the minimum plate size is important and often overlooked. Too many contractors select a plate compactor on the grounds of ease of lifting, and some have a plate size of only 500x300mm (0.15m²). The plate must be big enough to span at least two blocks at each pass.
As a very general guide, a plate measuring 500x400mm should be satisfactory for Cat II and IV pavements. For heavier pavements, much heavier plates are required and the machine weight, frequency and effective force should be checked with the manufacturer prior to use.
--------------------------------------------------------------------------------
Compaction strategy
Using a plate compactor for extended periods runs the risk of HAVS (Hand and Arm Vibration Syndrome) which can be disabling for those affected. Try to ensure the plate compactor being used is adequately dampened to minimise the danger. Check out the Health & Safety Executive website for further information.
It is essential that the surface of the pavement is cleared of any debris, rubble, bits of block, the crusts off butties, and anything else that could adversely affect compaction before starting up the plate compactor. If, for example, a small pebble or a piece of block was left on the surface, and the plate was to run over it, there's a real risk that this would force down the block underneath to a level that is too low.
As already mentioned, the plate compactor should make an absolute minimum of TWO passes over each and every part of the pavement. These two passes should be at 90° to each other, so, in effect, one pass would be up-down, while the second would be side-to-side. In practice, we prefer a minimum of FOUR passes:
up-down
side-side
diagonal top-right bottom-left
diagonal top-left bottom-right
If, at any time during the compaction, the plate starts to 'rattle' or bounce about on the blocks, this indicates that no further consolidation of the paving layer is possible and that the point known as "Compaction To Refusal" has been reached. Should this happen, STOP the plate immediately or move away to areas that are not causing the plate to bounce. Continuing to consolidate when the plate is bouncing will only result in damage to the blocks, or even to the plate itself.
Once compaction has been completed, a further round of compliance checks should be undertaken. Any blocks that have broken or become badly damaged during the compaction process should be removed and replaced. Levels and alignment should also be checked, and any corrections made before moving on.
--------------------------------------------------------------------------------
Jointing
Jointing is achieved by filling the 2-5mm joints with a specially selected jointing sand which then generates a phenomenal amount of frictional interlock between the adjacent blocks. This frictional interlock "grips" the blocks and helps transfer loads from individual blocks to each of its neighbours, which then transfer the received load to each of their neighbours and so on and so forth. This is how the blocks that have not been completely compacted to refusal, as described above, are able remain at the required surface level (more or less).
If you've ever wondered just how much force is generated by the sand jointing, try using the Block Extractor Tool to remove a jointed block - it's not impossible, but it's quite a struggle. Which is why, before the jointing sand is applied, the whole pavement MUST be checked for compliance once again. It's a lot easier to yank out an unjointed block with a spalled corner than one that has been sanded, so, to repeat what was listed earlier, check alignment, surface levels and block quality before spreading the jointing sand, regardless of whether you're jointing before or after compaction.
Dry jointing can only be done in dry conditions (stating the bleeding obvious, I know). If the blocks are damp, or if the heavens open, the sealing sand will not flow freely as required, and you may have wasted your time and money. However, all is not lost, and it is possible to use wet-jointing techniques when the surface is damp and/or when the weather is against you.
See the Pointing and Jointing page for more information on jointing sand
A kiln-dried silica sand, designed for this purpose, is available from most builders' and civils merchants. This is a selected sand, very clean, and of certain grain sizes that work to increase the 'friction' between each brick or block. A specific grading envelope for this sand is given in Table D4 of BS7533:Part 3.
Building sand, play sand, soft sand, grit sand or any other form of sand is NOT acceptable: it will fail and result in a rutted pavement. Don't spoil the ship for a ha'porth of tar! The correct jointing sand costs around £4 for a 25kg bag, and this quantity should seal 8 - 15 m² of block paving depending on unit thickness and type. Clay bricks often have wider joints (3-6mm), due to their being imperfect rectangles, a result of kiln-firing, and so may require extra sand.
The sealing sand is simply brushed over the surface repeatedly, and allowed to trickle down into the joints between the paving units. Once the joints are as full as possible, all of the excess sand should be swept off the paving, or into a corner where it can be salvaged for re-use. The vibrating plate compactor should make a couple of passes over the paving, ideally in different directions, to vibrate and settle the sealing sand, and complete any partial compaction of the paving units.
All the cut bricks are fitted and compacted, and the sealing sand is brushed in
When using the plate compactor to settle the sand, it is essential that the operative wears a dust mask - a pair of safety goggles would be a good idea, too. The vibration of the plate sends up a plume of dust from the sanded joints and this dust is highly abrasive. This 'dust is referred to as "airborne respirable crystalline silica (RCS)". If breathed into the lungs, it can cause untold damage and has been implicated in pneumo-silicosis. Similarly, dust or sand in the eye is best avoided.
At this point it's worth emphasising that any excess jointing sand must be swept off the surface BEFORE final consolidation takes place. This is essential because the plate compactor has a tendency to grind or crush the sand grains into the surface of the blocks, which leaves marks/stains that are all but impossible to shift. Sweep off any surplus - it's not necessary to remove every last loose grain of sand, but as much as practicable should be removed before using the plate compactor to settle the sand into the joints.
Sand stained and spalled blocks
After settling the jointing sand, some joints will appear empty or only partially filled. These should be topped up immediately, but there is no need to repeat the compaction. Finally, sweep off any surplus sealing sand and there you have it - a completed block/brick pavement that can be trafficked immediately!
The sealing sand will continue to settle over the ensuing weeks, and can be topped-up by simply brushing further sand over any empty joints until they are full again. There is no need to use the plate compactor again.
so now i dont know what to do first im very confused all so your the experts whats the best way round this i think i should say its not new blocks im using they are what i had down the garden so have weathered quite nice
many thanks simon
Posted: Sun Aug 24, 2008 3:02 pm
by Tony McC
Basically: if the blocks are concrete with a chamfer or tumbled, the compact-sand-compact; if they're clay, square-edged or stone, then sand-compact.
Posted: Sun Aug 24, 2008 9:25 pm
by rimexboy
Tony McC wrote:Basically: if the blocks are concrete with a chamfer or tumbled, the compact-sand-compact; if they're clay, square-edged or stone, then sand-compact.
Nice one thanks for you help on this one all i need now is a dry sunny day .... any chance !!!!
regards simon