This video teaches the process of wall rendering, which involves applying a mixture of materials to exterior walls of a building. The right mix is crucial for the render to hold up against UK weather conditions and adhere properly to the wall. Before a building is rendered, it should be surveyed with a trowel.
Rendering is the process of adhering a mixture of wet cement and sand to a wall with a trowel. The right mix ensures the wall has a solid cement look and can be applied to garden, outside, and brick walls. To create a 5:2:1 mix for both coats, combine all dry materials until the color is uniform. Add small quantities of water at a time while continually mixing the render.
The video emphasizes the importance of using a 1 part lime to 1 part cement and 6 parts sand for the base layer and 1 cement to 6 for the render coat. This will ensure the render lasts for years and provides a solid cement look to the wall.
Additionally, the video emphasizes the need to add water slowly to the mix, as rendering can be tough due to its constant nature. The correct ratio of mix for both coats is 5:2:1, but they differ slightly over the two coats.
📹 What’s the Best Mix for Perfect Rendering?
Roger helps you get the perfect ratio for your rendering mix. So, what’s the best mix for rendering? It all depends on what you’re …
What is the ratio of lime to cement for render?
Non hydraulic lime hardens slowly through carbonation, reacting with atmospheric carbon dioxide over weeks. Hydraulic limes and cements set rapidly by reacting with water in hours. To make a non hydraulic lime set more rapidly, an additive called “gauging” is added, which contains finely crushed brick powder, PFA, HTI, pozzolana, trass, or cement (white or OPC). These additives contain highly reactive silica and/or alumina, which are necessary for a rapid chemical set by reaction with water.
Cement is the most widely used and cheapest additive, with typical proportions being 1:1:6 (cement: non hydraulic lime: aggregate) and 1:2:9. Gauging non hydraulic mortars with cement to make them hydraulic has both advantages and disadvantages. Advantages include a chemical set before full shrinkage, reducing the risk of cracking, faster layer building, protection from rain before carbonation, being reliable and predictable, and available in a variety of colors.
Disadvantages include the rapid setting time, potential salt damage to stonework, treating gauged lime mortar as if it were a fully hydraulic lime or cement, neglecting the importance of longer-term carbonation, and the danger of segregation.
What is the best mix for rendering external walls?
The best plastering mix for external wall rendering is a 6:1:1 ratio of sand, cement, and lime. Building sand is not suitable, but a small amount can be added to the base coat, but never to the topcoat. Plastering sand and sharp sand are the best choice for strength. Lime adds flexibility, allowing movement in the building and reducing cracking. It also makes the mix self-curing and self-rendering, allowing moisture and vapor to escape, ensuring walls can breathe to prevent moisture accumulation.
Can you render with just sand and cement?
Sand and cement render is a type of exterior wall finish made from a mixture of sand, cement, and water. It is commonly used to provide a protective and decorative layer on the outside of a building, typically applied to walls made of brick, stone, or concrete. Sand and cement render is a simple and cost-effective option for finishing the exterior of a building, offering a variety of looks from traditional to modern.
Benefits of sand and cement render include durability, cost-effectiveness, versatility, easy application, improved appearance, and weather protection. It can withstand exposure to elements and provide a protective layer for the underlying wall. It is a popular choice for budget-conscious homeowners or builders, and can be applied by hand or with a machine. Sand and cement render can also be painted or tinted to match existing décor.
In summary, sand and cement render is a durable and cost-effective option for finishing the exterior of a building, offering a variety of looks and benefits.
Why put lime in render?
Lime render presents a number of advantages over cement-based mixes for external rendering. These include high vapor permeability, the ability to accommodate subtle movements without cracking, and active humidity regulation through hygroscopic moisture management.
What ratio for exterior render?
To apply a cement render, ensure the wall is free of moss or loose mortar and wet the block before applying the scratch coat. The science behind cement render is that each coat should be weaker than the previous one, with 1 cement to 4 sand for the scratch coat and 1 cement to 5 sand for the render coat. Lime is not needed for the scratch coat, as it was replaced by Feb. It is sometimes used for the render coat in pebble dashing. Apply February in both coats as per manufacturer instructions to make the cement more workable.
Waterproof admixture should be added in both coats as per manufacturer instructions. Plasterers often apply a third of the recommended waterproof dose in the scratch coat to reduce suction for the top coat, then the full recommended dose for the top coat. Clean and dust-free surfaces are advised. A slurry coat of sbr and cement painted on before the scratch coat mix is recommended for better adhesion. The first coat of the mix will make the mix extra strong.
What happens if render is too thick?
Excessive thickness in render can increase drying time, strain the substrate, and cause cracking. To ensure the correct thickness, hire a reputable K-render company with experienced professionals using specialized tools. The desired texture can also influence the recommended thickness, with a smoother finish requiring a thinner application. Discuss your aesthetic preferences with a K-render professional.
How thick should render be on an external wall?
Cement render is a type of exterior coating that is applied to walls and other surfaces to enhance their appearance and durability. It typically ranges in thickness from 6 to 25mm, depending on the application type, surface, and desired finish. For heavier-duty applications, a thicker render is recommended. A single-coat render should have a minimum thickness of 12. 5mm, while a double-coat render should have a minimum thickness of 20mm. The maximum thickness should not exceed 25mm.
Thick cement render offers several benefits, including durability, thermal and sound insulation, fire resistance, low maintenance, easy cleaning, increased aesthetic appeal, and cost-effectiveness. It can last for several years without replacement and protect the underlying surface from weathering, corrosion, and other damages. It also provides superior thermal and sound insulation, reducing heat and sound transfer, and fire resistance.
It is also easy to clean, making it ideal for areas prone to dirt and grime. Overall, thick cement render is a cost-effective solution for improving the exterior appearance of a home and providing protection from weather and environmental damage.
What render is waterproof for external walls?
Silicone render is a type of render with a silicone resin binder that is highly resistant to water penetration, preventing moisture from seeping into the underlying structure of a home. Its benefits extend beyond waterproofing, as it is also highly durable, able to withstand extreme temperatures, UV radiation, and other environmental factors that can cause cracking, fade, or degrade over time. Available in various colors and finishes, silicone render can enhance the aesthetic appeal of a home, adding a modern, sleek look that is both stylish and functional.
Should you put waterproofer in render?
The compatibility of paint with the render is crucial for its longevity and longevity. Silicone render is particularly sensitive to paint due to its water repellent properties. However, Emperor Masonry Paint can be applied to any exterior walled surface, including previously painted renders with acrylic masonry paint.
Render must be completely dry before painting, whether new or old, and should be given at least 2 weeks of clear weather before painting. Emperor Masonry Paint has a coverage of 5-6m2 per litre, while Emperor Masonry Creme has a coverage of 3-5m2 per litre. A two-coat system requires 10L of paint to cover 30m2, while a one-coat masonry cream requires roughly 10L to cover up to 50m2. The coverage of the treatments depends on the surface texture, with rougher renders like pebbledash requiring a smaller coverage of 3m2 per litre.
In summary, compatibility with the render is essential for its longevity and longevity. Emperor Masonry Paint and Creme offer different coverage levels, with the latter covering up to 50m2 and the latter covering up to 30m2.
How to render a wall outside for beginners?
To render a garden wall, follow these steps: remove old render, prepare the area, mix the render, apply it, add rendering mesh, apply the second coat, smooth it out, and wet the wall with a sponge. This simple process can restore your outdoor space and inject life back into your garden without requiring costly maintenance. To effectively render a garden wall, you need to know how to plaster, which is not easy but can improve its longevity and prevent issues like cracking or crumbling just days after application. With a little know-how and elbow grease, you can restore your garden to its former glory and inject life back into your outdoor space.
What are the disadvantages of lime render?
Lime plaster has several potential drawbacks, including its slow set time, which can be unpredictable and difficult to schedule, its higher cost compared to cement, and its non-hydraulic nature, which requires moisture to set and prevents it from drying for several days. The hardening process can take months, and the longer and more involved application process can result in higher labor costs. Additionally, lime plaster may not be suitable for areas with high humidity or moisture concerns, making it a less suitable choice for construction projects.
📹 How to Render Exterior Walls – Beginner Tips
Roger revisits a topic that Skill Builder covered many years ago, why? It is one that gets professional plasterers very hot under the …
Too many young builders get caught in the ‘brand new transit van and nagging wife for a bigger house’ brigade and before they know it they’re working 7 days a week and ripping everyone off so they can take their spoilt kids on a dull tour of Disney Land, because their wife thinks they’ll like them more. Well here’s a message to busy builders everywhere – forget Disney land and a dull pile of plastic presents: buy your kids some second hand books to read as this’ll give them the best life imaginable, then work 4 days a week so you can spend time with your family as opposed to throwing sh*t on walls all day while listening to talk sport and talking about talk sport. Great vid BTW and what a lovely guy. Shows there’s a lot of intelligent and articulate builders out there who live a meaningful life and aim to help others. Got some render patches to fix now but I think 5:1 and plasticiser for me.
Boss I worked for always used buckets to measure sand and cement with – not shovels. This way the mixes are always accurate ratios and the same even colour throughout the job. This also went for mixing brick mortar. Buckets seem cumbersome but you get used to using them. There is an art to using the mixer – keeping it clean and not having stuff stuck on the inside and affecting the next mix. All the best. …And look after your backs too! (…or you will be sorry… Ha Ha)
Hi Roger when I was very young as you do we used to just Lime(except cement and sand) for rendering, but it was different than Lime you show on article. Usually we putted into the hole Lime and mixed it with water and left for few day to get proper consistency and when it becomes like butter we add into every mix and it was brilliant stuff for rendering. Same we used for bricklaying, just a bit less than for rendering.
I’ve got a house that’s been rendered on to concrete blocks and I’ve had quite a few long cracks I’ve had to chop the cracks out and patch them and this time I used plastering sand cement and lime I’ve been a plasterer for 16 years and the first thing I was taught when floating and rendering was the mix it’s important to always put lime in the mix never use building sand I’ve always done a 5:1:1 mix I hardly render these days but it’s fact to much cement and the wrong sand will make your render crack in time
Hello Roger, I do like the way you put things across on your articles, always makes a lot of sense. I need to patch a couple of sq, meters of fine textured render on a wall . I will be taking it down to bare (old brick) What materials do I need to carry out this task in the most simple way as I have not done this particular job before? Or can you buy it in a bag ready mixed ? Regards David.
I like some washed river sand along with some yellow in my scratch coat. 3 : river 2 : yellow 1 : cement 1 : Lime ( or plasticiser, water proofer) Top coat 5 : yellow 1 : river ( washed & graded) 1 : cement 1 : Lime ( plasticiser/ waterproofer) Not everyone puts water proofer in the top coat but it works for me. 43 years down the line and no problems yet. Must say though.Give me a Hydraulic Lime/ River Sand render any day of the week.Beautiful to use, rubs up a treat and looks terrific. Each to their own I say!!
Hey Roger, i knew nothing about rendering and followed your mix and application advise exactly,, I was happy wwith the first half wall i did, and after doing 4 half walls my results were almost professional………..thanks so much!!. P.S I remembered a trick from 4 decades ago an amateur plasterer/stucco guy told me; add a capful of dishwashing detergent to the mixture…………it makes the render light and fluffy. Too much makes it too light and fluffy though, but it was a very useful tip!
6-1 seems awfully weak for scratch coat, 5-1 or 4-1 on scratch then 6-1 on top coat for me ! And I don’t know a single plasterer that has the time to let the mix sit for 5 to 10 minutes before laying on, I’m laying it on as the labourer is loading the spot board it’s gone by the time he gets back to the mixer then I’m screaming at him to hurry up
Another great article, Roger. I have an extension to render, built with high-density, concrete blocks. Mercifully, most of it is glazed but I can see that your advice will make all the difference to the job. I recently completed an en-suite bathroom and your articles were a huge help. Your presentation skills are top notch. Thank you so much for all the help and advice. Truly appreciated.
Thank you Roger and i`ll take your advices next week down to new zealand. I did read all comments and i still have some days to think about it – what is the “right” mixture between all the opinions…., and if i don`t fail and my buddy didn`t kill me after our work, well, i`ll give you my feedback. And one thing we do know about it, the sand should not be salty. Anyway, thanx man.
Wow, after about half a century of doing it my way I have finally found an expert who explains it all so well. I can only say thanks Roger and luckily (?) I have nearly always done any mortar jobs with a 3:1:1 mixture (so I think I am not too far out). Here in Italy, they are all very vague on the proportions to use but I once contacted the cement company and asked them what they use in a typical ‘ready to use’ mortar and they told me Sand 71%, Cement 13%, Lime (calce) 16% at the time, which is about a 5:1:1 ratio.
Nice article, you’ll always get people slagging you off in the comments saying they’ve got a better way of doing things. I’ve done a few articles on my website and get a few negative comments, I don’t mind constructive criticism but I don’t like people having a go just for the sake of it. Keep up the good work!!
I’ve been a good general builder and stonemason for over 25 years. I’ve seen labourers with better trowel skills than this guy. Far too stiff too. I’d throw this bull muck back into the mixer. What’s he on about “don’t use building sand”??? A good 4 to 1 building sand to cement with a dash of elasterciser, waterproofer or even fairy liquid (if none of the first two). I get fed up with these DIY articles!
Hi, is it imperative that you have two coats of render (scratch and top) for an exterior wall. I have several 1.5m x 2m sections of wall my neighbour has kindly left me to do! I’ll be growing plants on wires just in front of it all. Any advice would be gratefully received. Thank you and keep up the good work😉
Hi there Rodger, great article, very helpful. I’m going to attempt a little bit of rendering on my side wall and I was Just wondering would you recommend putting pva on first. Seems that some do and some don’t. I was told that just giving it a good clean first will do and that pva can stop it breathing. What do you recommend. Thanks
Best mix. 4:1:1 Render, soft, lime. There isnt a better mix. Also always put sand in first in mixer. Its cleans the drum. If you put the cement in first it sticks to the side. I used to be a hod carrier back in the day so knocking up muck was my thing day in and out. Also use buckets to gaugue. To be honest though mate you mix looks SHITE. Also alot of lads now just get ready mix. PS DON NOT PUT WATERPROOFER IN THE FIRST MIX!!!!!
Really useful practical demonstration on external rendering and the dangers of using an overly strong material. Further technical guidance on rendering can be found Building Research Establishment publication “Good Building Guide No 18” (Choosing external rendering) as this provides authourative information, including clarifying suitable preparation options, appropriate mixes for different backgrounds and exposure levels, and examples of good detailing. It might be also be worth bearing in mind that strong mixes (and plastic paints) inhibit evaporative drying and can trap moisture.
I rarely use cement as I specialize in lime mortars and plasters and tend to slake my own lime putty and use it because there is much less wastage and I find it a lot stickier. The 6:1:1 is a good mix, the hydrated makes a good plasticizer and is preferable to using febmix I found. On my own place I have 5 different backgrounds that I lime rendered: Rubble-stone, cob, old 1970’s brick work and 2 types of blockwork, the thermalite and the denser concrete block. The blockwork was less preferable to the other backgrounds and I found more cracking than on the other area’s where there are hardly any. You shouldn’t really use lime on new builds because it’s pointless, the cavity wall structures were designed for cement mortars and never use cement on old builds this is why there are so many issues with wood rotting, moisture retention and salt build-ups etc, cement render traps it all in, old lime mortar builds need new lime mortar for pointing or rendering. My prefered lime putty mortar is 3:1 ( 2 & 1/2 sharp angular sand and half a builders sand or a stone dust to one putty or an hydraulic). Some folks use putty and an NHL but I use one or the other, never both together, but as I said, with a putty mortar there is less wastage because you can scrape it off the floor and use it later. Hot mixes are another matter and work better I think but thats a whole new ball game. I saw a film where some old lime pits were found in Italy, the lime putty was about 400 years old and it was still usable because lime putty starts to set when exposed to air and hydraulic and hydrated sets when exposed to the air, also bags of NHL have a shelf life of about 3 to 4 months although I have used bags that are about a year old.
You are a fantastic help Roger. Do you ever consider using a hydraulic lime as an additional binder to your sharp sand based mix? I always find my void ratio in a sand ( its a simple process) Sharp sand will generally have enough void to acomadate 1 binder to 2.5 or 3 units of aggregate. 6:1:1 is therefore a very good mix. Although my work is mainly brickwork the mix rule is generally the same. What are your thoughts on scud coats on celcon type blocks 1st?
plastering sand? you would never get a good finish the more you work it the worse it gets, rendering sand under a microscope should be sharp and angular plastering sand is rounded, so the water separates quickly, I sometimes use a shovel of sharp sand per mix which gives you more strength so you can reduce the amount of cement
Roger, thank you. You’re informative, knowledgable, and entertaining too. I enjoyed and learned from your additional info regarding temperature – living here in a pretty hot climate. Brilliant article production too I should add; not too many, but just Goldilocks effects and editing. I’m about to look up your other Skill Builder articles. Hope you’re well mate.
What about scudding the wall first with a 4 cement to 1 sand for key coat – then a 5 sand 1 cement & tiny drop of waterproofer for 2nd scratch coat – then a lime – cement sand – tiny drop of waterproofed for finish coat – never ever plas it’s just turns into the wall in to a giant sponge – go to some Irish site to learn to do plastering done properly- wouldn’t let that guy plaster my henhouse
Its strange really, I think it is a black art, I admire builders, I have no fear of electrics, gaswork, or any plumbing, but plastering and rendering scares me to death . One success I did have was on a waterfall for a pond, it comprised of sandstone rocks and mortar between, it leaked badly and needed a solution, rightly or wrongly my dad and myself mixed up a very strong mix that would have you builders shouting at us. It was 2 parts Sharp sand and 1 part portland cement, we had cleaned of the rocks with a wirebrush and added a layer of galvanized chicken wire to the waterfall run . We did it all in one go and did not stop for breaks, I will probably regret saying this and jinks things but that was 32 years ago and no cracks or leaks, we did at the time paint it with a non toxic fish safe bitumen emulsion, but most of that has long since eroded away. But I do understand the theory of using weaker coating normally on the outside.
In fact lime will set, its called carbonation and thats how limestone was made in the first place. lime needs a fair amount of time to set though, approx. 1 year per 1cm of depth. in the early years people plastered only with lime and no cement, im doing that as well, you just have to be careful with the render in the beginning to not scratch it.
I once had to do a repair job for a builder which had some serious cracking. So I called a consultant who put me into touch with an industrial chemist. I then worked on using plaster without lime and rendering or even mortar without lime. The industrial chemist stated. We consider lime to be no good. I thought okay. It was the best thing I even did. So what I’m saying if you use lime then you make the strength of the mortar according to the strength of the substance you are putting it on. Exactly what you mentioned. However, with the product I use you can mix whatever strength you like to a certain extent. And I think there are many factors to take into consideration. I use what is called a latex rubberised synthetic emulsion system. If you render onto old bricks which were laid without cement then you will get surface retention. So you will see a certain amount of cracking as the compression is very low opposed to bricks laid with cement in the mortar. Without lime I can wash my tools without wearing rubber gloves. Also if some material splashes in my eyes I don’t need to race to the water to get the mortar or plaster mixed with lime put. Lime is highly corrosive so if it gets on aluminium it anodises. Although cement had alkaline and can sometimes leave a mark on specially coated windows glass. I found that out with a client when some mortar got in behind covered up windows. This is partly due to cement manufacturers cutting costs and leaving out gypsum which in the last we had better cement than from recent times.
Cheers Roger, thanks for the good vids and advice. Building a Pizza oven so needed a bit of info on the render and top coat for the support structure and oven itself. Got a bit of lime also so we are all go. I made fine care not to follow up any of the tosspot replies you have received. Not too many vids from them I see. Cheers
I agree with you Roger, I use a 280 liters cement mixer 6 buckets of sharp sand, 1 bucket of cement and one and an half of lime, plaster like you said doesn’t need to be bomb or scratch proof, and if the wall is nice and strait use as little plaster as you can because using a lot is a waste of time and material.
You sound like you know your stuff good job, I’m looking for advice been plastering about seven years or so now but not done much rendering normally get a mate to help me on the rendering he’s been in the game since school and it’s all he’s done he only uses building sand gets a nice finish . I’m getting more and more rendering jobs coming in and want to know how you render on breeze lightweight blocks as got a big extension job all over breeze blocks which I know sucks in like a rocket 🚀. Help cheers
Im sorry skill builder,I know you are trying to give good advice to those who need it,and you rant on about cowboy builders in your articles,but I don’t understand why you give wrong advise with confidence and yet you are the biggest cowboy plasterer out there on YouTube as it seems.6/1 mix 🙄 ok good luck with that . plus your skimming articles you talk of how easy this trade is,ok so let us see your work after a painter has has worked on it,I’m sure there are many compliments.stop making out plasterers have an easy job. do it every day, build those muscles .work from top to bottom and stop calling a trawl a float and the hawk a spot .you are clueless.just saying 🤔with love of course ❤️
Hi Roger. You failed to state that lime render requires special masonry paint called silicate paint that cost £90 for 5L. If i knew that i would have used plasticiser instead of lime. The issue I have I can’t use the same Dulux Weathershield paint that is on my customers house on the new walls. Not happy at all! What do you advise?
Lime all the way. Either drop a scoop of hydralime into your cement as demonstrated here. Or as I learned in France, pure hydraulic lime. That’s much brighter and fresh looking when finished. It sets slower though. So worth knocking up a load in one hit to allow it to start going off a bit making it easier to apply. You don’t need primer either for hydraulic line if rendering over stone.