plastering sand advice please

[plasticpigeon]

Lime render/plaster seems to be the bane of my life as well a for Zebra. I found the 10 - 12mm backing coats on my walls to be relatively straightforward, but the skim/setting coat is driving me mad. I first used plastering sand from my local merchant, it made a mix that was quite nice to use but it had bits in it that were up to 5mm so that ruined the finish by dragging the random big bits across the wall so I took the skim off the wall. Then I tried soft building sand, which was very wet from the merchant. Whatever I tried I couldn't get it to mix, there were small lumps of sand that stuck together and dragged neat sand in stripes across the wall. I must have used a whisk for at least 10 minutes so I cant understand why. Today I tried kiln dried sand for block paving. It has no workability at all, it just seems to lock up. I think all the grains are the same size. I just about got it flat but it would have been very difficult to finish. so I've left it scrubbed up for another skim on top. I've decided to buy some ready mixed stuff, probably from Ty mawr. If I can't use that then I am the problem!!! Does anyone have any recommendations for a decent plastering sand without big lumps in it, that can be got at a local yard rather than a specialist?? Many thanks.

 

[MdB]

Today I tried kiln dried sand for block paving. It has no workability at all, it just seems to lock up. I think all the grains are the same size.

What mix are you using? More lime may help.

 

[plasticpigeon]

1:1 with hydraulic lime. It was nice with building sand but I had the problem of it not mixing.

 

[MdB]

1:1 or 1:1.5 sounds right from what I remember of the Mike Wye course. I've never had problems with mixing with a whisk (apart from my whisk breaking..) so I have no idea what the problem is. Sorry.

 

[MatthewC]

If you want to pop down the M40 I could let you have a small amount of surplus Mike Wye ready mixed (standard) 2:1 plaster and some fine Regency plaster for a fee less than cost price. How much do you need?

 

[plasticpigeon]

Hello Matthew, thanks that would be great, where do you live??? I am really trying to get to grips with it, so even a few kgs to try out would be useful. Are you about this weekend? I bought some sand from a different place today that again is plastering sand and seems nicely graded, but without the pebbles in it. Also I found that when I took a handful of the building sand i was using there were small pea sized clumps almost like grit but if I rubbed them hard between my fingers they disintegrated into sand. It must have some thing in it that sticks the sand together, clay or something. I shall avoid that stuff from now on!

 

[stuart45]

Building sand usually contains about 10% or more of loam, which makes it much easier to use for bricklaying with a cement mortar.

 

[stephenh]

PP
It is usual to use lime putty ( min. 3 mths old) with, say, 1 :1 silver sand for the top coat.

If you are using sands from a builders merchants then fine sharp - e.g. Leighton Buzzard would be OK but it would probably need sieving first, it might be too coarse, even though it is called 'fine'.

If you must use Hydraulic lime then NHL2 would be the strongest that I would use, you can soak this for 24 / 48 hrs without it going off too much and it would be more 'plastic' for this soaking.

If you are using NHL 3.5 then you need to use it more or less as soon as you have added water and it is quite a palaver to get it to mix properly with coarse sands. This doesn't matter so much for undercoats but might be a problem with your topcoat.

Clean washed sand is the secret ( and keep it covered - cat poo on the end of one's trowel first thing in the morning is not the best way of being woken up !!)

Good luck

 

[worms]

Would changing to normal hydrated, non-hydraulic lime not help?

 

[stephenh]

Picture uploading !! - took me an hour.........

The background undercoat is very coarse sharp sand with NHL 3.5 and added hemp - two coats say 30mm, 15mm each. Well worn plastic float to straighten and then 'devil' floated to give a key.

Topcoat is lime putty, it looks and was, blue to start with and then went off to a buff colour echoing the reddish seived sharp sand that was used at a 2 lime to 1 of sand. About 3mm thick.
We made our own lime putty as the bought in stuff was too expensive.

As Worms says above, using CL90 or hydrated lime. A bag into a large dustbin. Well mixed with too much water, lid on and taped up and the whole left for 3 months. We did 3 lots.
We taped the lids on as this was in the summer in the south of France and the temperature was high. Come the Autumn we siphoned off the excess water and a gloriously sticky mess remained. Excellent.
Didn't make enough, so we knocked up some more that only had 2 weeks brewing not half as good as the old stuff but still far better than an experimental mix that we used straight away.

Note that the top half of the topcoat ( in the pic.) has been floated with a plastic float giving a more open texture, the lower part is smoother by using a steel trowel.

Hope this is of use....

 

[plasticpigeon]

Thanks, yes, I might go down the hydrated lime route as putty is not available locally to me. At least my render coat went ok and looks just like yours!! My skim with block paving sand looked like yours but was hard to use. I am trying again in my experimenting room with some fine sharp sand today which was sold as plastering sand, and If I find this not to be very workable then I shall go down the putty route.

 

[Zebra]

Internally you would use putty and not NHL, wouldn't you?? What would be the reason for using NHL, just availability? A mix made with putty is much much gooier and more workable than a mix made with NHL, being an amateur myself I've found it much easier to use, for what it's worth.

 

[plasticpigeon]

Yes just availability. I think I can get putty from a local merchant but they get it sent in from another branch. However it is 15 pounds for 25kgs. Seems a lot as hydrated lime is around £10 for 25 kg dry and NHL maybe 12 or 13. The new sand I got, made it much easier to work with. In fact I made the mix too thin expecting it to be hard work like before but could have done with it thicker. The result is ok, still not as flat as I'd like but reasobably smooth, probably only up to 2mm out of flat in some places. I might buy a few dustbins and make myself some putty from hydrate of that works!

 

[Zebra]

I think that's a good idea. I'm currently scrounging on freecycle for dustbins, for that very reason. Putty also then keeps forever, and you can make limewash out of it too.

 

[LadyArowana]

I think that's a good idea. I'm currently scrounging on freecycle for dustbins, for that very reason. Putty also then keeps forever, and you can make limewash out of it too.

So Mr Robgils wheelie bin was unsuitable? I think you should return it, he was quite cross you know.

 

[worms]

I think that's a good idea. I'm currently scrounging on freecycle for dustbins, for that very reason. Putty also then keeps forever, and you can make limewash out of it too.

Don't restrict your search to just dustbins. I use a standard plastic rubbish bin like this but it is really too deep and a 25kg bag of lime is a lot to try and mix in one go. I've been through the full bin about three times now but have emptied the last of the putty into an animal feed tub. I would recommend splitting a bag of lime between two or three smaller, lidded tubs and adding the water to these. I guess this would be similar to the tubs of putty that are available commercially. Definitely much easier all round.

 

[GRB]

Hi PP
When I did my plastering course the teacher, who had 40+ years of lime plastering experience, told us that the sand in the finish coat should be dry silver / silica sand and when asked the very question you have asked he said that if he had to buy from a normal high street DIY shop he would get 'brick paving sand'. Now he mentioned Wickes, but I don't know if it is a universal type of sand to be found in any DIY chain - I haven't tried it as I've always bought pre-prepared 1:1 (using putty) from my nearest specialist.

Good luck
Gary

 

[Zebra]

So Mr Robgils wheelie bin was unsuitable? I think you should return it, he was quite cross you know.

:lol: