Sand II

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essexandy

The Lake Governor
Went to price a big house today (244m2 of screed) and the guy says he's really doesn't want any cracks in the render and will do whatever it takes to stop them and then tells me he already has the sand on site because another spread had let him down, turned the corner and there's a bloody great pile of pit sand :o I said you don't expect me to put that on the outside do you and then explained why, he say's I've had three other spreads come round and they haven't been worried at all ???
Do any of you lads use pit/building sand on external renders?
 
all depends on what you call 'building sand' mate, i find if the brickies love it, its no good for plastering..
 
everyone down this end ..... and i mean everyone and every site and evey job i have ever been on ever and i mean ever .......... uses fine silver sand!
 
For traditional external rendering mixes, the following types of sand are used:
pit sand – quarried inland, usually red in colour
dredged sand from the river or sea bed, usually a dark yellow colour

As with internal plastering, poor quality sand will cause the external render to crack and become loose and hollow, or it may eventually crumble. In good quality sand, the particles are irregular in shape (not rounded), and well graded. The largest grains should not be more than 5 mm. This is assessed using a sieve test to ensure no grains over 5 mm are present in the sand. The sand should have been washed to remove impurities. Clay and silt
particles in the mix prevent the cement from bonding to the aggregate, so each load delivered to the site should be checked for ‘cleanliness’. The amount of silt must not be more than 10 per cent of the volume of
aggregate.
 
The Apprentice said:
For traditional external rendering mixes, the following types of sand are used:
pit sand – quarried inland, usually red in colour
dredged sand from the river or sea bed, usually a dark yellow colour

As with internal plastering, poor quality sand will cause the external render to crack and become loose and hollow, or it may eventually crumble. In good quality sand, the particles are irregular in shape (not rounded), and well graded. The largest grains should not be more than 5 mm. This is assessed using a sieve test to ensure no grains over 5 mm are present in the sand. The sand should have been washed to remove impurities. Clay and silt
particles in the mix prevent the cement from bonding to the aggregate, so each load delivered to the site should be checked for ‘cleanliness’. The amount of silt must not be more than 10 per cent of the volume of
aggregate.
Never seen sand with grains of 5mm, or 3mm, surely at 5mm it ain't sand ?
 
spunky i went 2 tp and got red building sand by mistake i take it i cant use that for rending?
 
For traditional render you have to take into account the substrate as if the bricks are soft a strong render mix will pull the faces off and become hollow
cracking usually occurs when render dries out to fast so should in theory be wetted down on a daily basis for 30 days... this will stop the cracking/crazing I used to use 1 part sharp 1 part washed building sand with a tiny bit of water repellant in scratch coat the repellant helps sto suction and allows top coat to set slower and will help against cracking
saying this i used to tell customers to hose render daily as i cant hang around i havent used old render for years prefer pre bagged OCR or monocouche any day... if the guy is still worried about cracking you could put Fibre glass mesh in the scratch coat @ £55.00 per 50m2 roll
 
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