Concrete pad

[baracuda]

installed a concrete pad last august bank holiday, 8 inch deep with reinforcing set at correct depth the area is 6mtr by 3mtr and is outside an industrial unit. used one of these mix on site guys for the first and the last time, when brush finsished the pad all was well but two months later customer complained that sand was coming off it. swept the pad off it seems solid (should have said put had the fibre chips added to the mix aswell). .ow nearly twelve months dowm the line there is still some sand coming off it, does any one know
a is it down to bad mix?
b is there anything can seal it with to stop this?
done about thirty of these before all with no problems usually get ready mix though.

[dig dug dan]

I would be very surprised if this was down the the "mix on site" guy, as they should be more than capable of mixing up concrete properly.
they are invaluable as they charge for the exact amount you have, so no wastage and shortages
It sounds to me like the brushed finish was done at the wrong time of setting.
Normally the concrete gets tamped as soon as it is oured and this encourages the water to come to the surface and form a "skin", which then hardens sealing the concrete so to speak

back in 1997 i laid a shed base for my old man, and carefully trowelled the concrete to give a lovely smooth finish, as this was going to form the shed floor.
He said" shall i brush it with a broom now?"
"NO!" and i went on to explain why.
He did it anyway,about three hours after i finished, and ten years on he was still sweeping a dusty floor.

[irishpaving]

Did you float it up before brushing

[DNgroundworks]

To be honest ive never had a good experience with "barrow mix" concrete, i always find its very poor quality, takes ages to go off properly,shite aggregate (looks like MOT to me) and a funny colour aswell!

[lutonlagerlout]

we use "custom concrete" from silsoe now and i cant recommend them enough
they have 20 mm aggregate and grit sand in separate compartments on board ,so you get a proper concrete mix every time
the ones that use all in ballast are hit and miss

we did a structural ground beam and the concrete had to be C.35 by the time i struck it , it looked like a pillar on the motorway (albeit horizontal)

anyway as DDD says sounds like it was brushed too soon

LLL

[Tony McC]

I wonder if it's just laitence? Non-concrete folk often mistake laitence for 'sand and cement'.

[baracuda]

Thanks for the replies,the slab was pokered with mini poker then tamped and floated then left for about 4 hrs and brushed. As said never had this before looked laitence quote
"Laitence
The fine material on the as-cast surface of concrete. Crazing can occur in this surface, which may be promoted by 'floury' sand"
which brings me back to the fact think that the guy used the wrong sand!

[lutonlagerlout]

sandy ballast in otherwords
have you got to change it?

LLL ???

[baracuda]

yes but looking at the comments made wondered if anyone knew of product that if cleaned off could try and seal it with?

[Dave_L]

Almost wants a resin-based floor paint to seal it?

[Tony McC]

Normally, a surface with laitence or loose material would be hosed down, then acid-etched, then hosed down again before being treated with a dust-sealer or a micro-topping or a floor paint such as Nitoflor. As this is an industrial scenario, a heavy duty dust-sealer would probably be best, but it's worth talking to a specialist supplier who can advise on which product would be best suited.

Dave @ NCC is very knowledgeable about all the various potions and poultices available from the likes of Sika, Remmers, Fosroc, etc. 01257 266696

[simeonronacrete]

Tony; don't forget Ronacrete!

Options: scabble and lay a thin bonded tough screed with Ronafix and cement as the bonding primer and Ronafix as the admix for the screed

or

remove the laitence and apply flood coats of Ronadeck PU Seal Coat until no more is absorbed.

Give us a call if you'd like to know more.