correct sand for external render???

[sambapaul]

Can anyone tell me the correct sand to use for external render to give it a tough smooth finish, I have been told 5 of soft sand 1 of lime and 1 of cement and have also been told 2 of cement 3.5 soft sand 1 of lime and 3.5 sharp sand, which is for 1st coat and for 2nd coat 2 of cement 4.5 soft sand, 2 of lime and 4.5 sharp sand, I have tried 5 of soft plastering sand and one of cement with febmix plastersiser and waterproofer but the finish was terrible, when I rubbed it up with the plastic float it clogged the float, just want to know what sand rubs up best and doesnt flake away and clog the float up, all advice welcome

 

[oilman]

Cementheads disagree with me, but I would NEVER use cement in a render outside, it causes so much heartache WHEN (there's no "IF") it cracks and the water gets behind it.

What sort of construction are you putting on, (and why)?

 

[legs-akimbo]

Now how did I know you were going to say that oilman!!

 

[Freddie]

Now how did I know you were going to say that oilman!!

Very True but on a serious point Oilman and this is just a question only

If lime plaster/render was/is so good then why did they start using cement?? it has to be mixed--cost about the same--put on in similar ways---so why did they change from lime to cement render/plaster??

 

[jbonding]

theres nothing wrong with cement in render the only reason thay never used it because it was'nt invented. applied correctly its sound the same with lime sand mortars.

 

[Freddie]

theres nothing wrong with cement in render the only reason thay never used it because it was'nt invented. applied correctly its sound the same with lime sand mortars.

Errr---you could be wrong there mate as i know concrete has been around since at least the Roman times and still survives to this day.

 

[David E]

Just a point, although I do agree with oilman and do use hydraulic lime I think Fredies point about cost is wrong

If lime plaster/render was/is so good then why did they start using cement?? it has to be mixed--cost about the same--put on in similar ways---so why did they change from lime to cement render/plaster??

25kg OPC £2.35/bag
25kg NHL3.5 £9.85/bag

If you want to do the job properly it's going to cost more thats why cement is so commonly used in the wrong place. I believe that the idea that teh y cost the same is the misconception that HYDRATED lime has the same properties as HYDRAULIC lime which is totally wrong. Look here for more info http://www.stastier.co.uk/. Yes it's French who own Blue Circle and makes most of the countries plasterboard.

 

[oilman]

Cement is used because it's "user friendly", that is, you don't have to care for it after you put it on. Goes on, goes off, job done (for long enough to get the money in the bank). Why did they change, marketing exercise by cement companies. "You don't want to use that old stuff, use our new stuff, not convinced? well just feel the weight, gotta be better innit?"

Cost by weight is much higher, but it is gauged by volume, and lime is much less dense than cement, so the costs work out the same for the same bulk of mortar.

Hydrated lime can be used to make a non-hydraulic lime, but if you add ceramic to the mix it will act like hydraulic lime.

 

[Freddie]

Well i always wondered why i know they used to put horse hair in with the lime and today they have started doing that again by adding fibreglass.

When did they change over from lime to cement?

Who does own the cement factories anyway?

 

[oilman]

I gather polypropylene fibers are used too, though hair must still be better as it has a rough surface.

I'll dig around about Aldridge, sounds interesting.

Some good reasons to not use cement.

 

[speedhorse]

Well i was always taught to use 5 sharps sand 1 cement, lime if you want but i never do, if you mix it right its fine, also i never use my float to rub up with sharp sand as it can really drag it about so i darby of nice and flat, very flat i spend most time with this , then i smooth my normal trowel over it to get rid of any holes, then i wait and finally rub up with a sponge nice and steady, pefect job, sharp sand is a much better job as the grains are very course, this makes the render much stronger and prevents cracking better too i have noticed, finer sand cracks also hold off with too much cement as this will also make it crack, it has too be 5 to 1 i use a plasticiser also and mix it thoroghly too, makes all the difference. What a lot of people dont realise also is that plasticiser also stops cracking, it has special chems in for heat variations, ie frost and blistering sun. lol yeah right.

 

[mointainwalker]

Who does own the cement factories anyway?

Lafarge who also own BPB.