What's the Best Mix for Perfect Rendering?

[Music] hello I'm Roger piss be from skill-builder and a lot of people ask what's the best mix for rendering and that may even be why you've arrived at this video well it's one of those questions it all depends it depends an awful lot on what you're rendering on suit now the golden rule is that you never make the mix stronger than the material that you're going on to so here we've got lightweight concrete block and it's 3.6 kilonewtons and we don't want a really really strong mix for this because if the wall moves and the wall will move you always get a bit of expansion and contraction as the seasons go then you don't want the render to be the thing that's stopping the wall from moving because if you do the render will crack also if you put too much cement in render it shrinks back and it will crack people don't believe that I see loads and loads of plasters who do a three to one mix and they go out it's nice and strong now if you think about it think about a great big piece of concrete that's six inches thick if you made it the size of a garden say it would crack the fact it's six inches thick and it's got loads of cement in it doesn't stop it cracking because there's no real tensile strength in it so there's no point in putting too much cement in you will cause it a crack so we make a nice six one one we call it which is six parts of sand now the sand that you need to use is plastering sand or rendering sand it's not building sand do not use building sand for rendering because it shrinks and cracks and it's a nightmare you can put a little bit of building sand in it sometimes if the if the sands a little bit hungry a little bit hard to work then maybe you can put five shovels of rendering sand in and one shovel of building sin certainly won't do any harm in the base coat but when you do that top coat my recommendation is keep it nice and sharp and keep that lime in there and you won't have any trouble one part of cement and one part of lime now that is hydrated lime it's important that you put any more than one part of lime to one part of cement because lime will not set hydrated lime as opposed to hydraulic lime will not set on its own so you need that cement in there to help it set but what it does do is it gives it body and it makes it creamy and it gives it a certain amount of elasticity if the building moves the render will kind of go with it a little bit and if you do get a crack all that align that's in the mix will kind of wash into the crack re calcified to some extent just as it does what it's forming stalactites and stalagmites and so on so in a way it's self curing itself rendering so the lime is important a lot of renderers don't put it in because it's a pain to put in you've got to buy another bag of stuff they prefer to use plasticizer which puts lots of bubbles into the mix which is a good thing you want lots of air in your mix but the lime is a better bet now having said that on this base coat I don't care too much I'm just gonna go with six of sand wanna cement and a bit of plasticizer and on the top coat you'll see the difference when I put the lime on now when you're making the mix up it's best to leave it sitting around after you've made it up for about five or ten minutes that just allows it to pick up and then it goes on to your spot board like that now the big test is is this mix the right consistency is it the right wetness the test is this yeah if it's not dropping off his spot board then it's right and then it sits on the wall I'm not on the floor so when you come to do it you'll see that it actually just it's nicely on the wall without flopping away so we're going to come back we're going to show you how to render but that was just a little bit about the mix now obviously at different times of the year if it's a very hot summer you don't really want to be rendering because if you render the water will dry out the mix too quickly and it won't hydrate properly this time of year is a winter we were January and it's pretty cold with pretty windy but actually it's not going to be a frost the night so it's absolutely ideal for rendering it gives us loads of working time so in the summer if you want to do a rendering job get up early in the morning I'm Roger Bisbee thanks very much for watching come back and see the rest of our rendering series make up the playlist and we'll be back to show you the next stage don't forget to subscribe by the way we need subscribers like I need blood in my body [Music] you [Music]

Channel: Skill Builder

Views: 466,686

Rating: 4.8307815 out of 5

Keywords: rendering mix, render mix, perfect render mix, rendering mix ratio external, rendering mixture, render mix ratio, render mix ratio for external walls, how to mix render, render mixture, sand and cement rendering mix, rendering mix ratio, render mixture ratio, rendering, how to mix cement render, how to mix mortar, sand and cement rendering techniques, sand and cement rendering, how to, sand and cement, lime render, stucco, rough cast, k rend, lime mix, how to mix cement

Id: UT_8vpsMuCU

Length: 5min 24sec (324 seconds)

Published: Fri Jan 12 2018