# Forum Home Renovation Brickwork  I need a recipe for render

## Keef

Hello again, I am building a straw bale house, walls are all now finished with a a 1 inch thick cement render, rather rough finish but good and solid. I am about to start on the final render coat. A few years ago I did a workshop on rendering in which we used a mix of white cement, sand and some red clay(for colour) mixed with lime and left overnight. This lot was then combined with some sawdust (for texture and flexibility) and then mixed up in a cement mixture. I think we might have added a dash of bondcrete also.
This mix covered well and gave a great finish, problem is that it was a few years ago and I can't remember the exact detail of the mix. Has anybody out there heard of this method or something similar. Idea is to end up with an earthy organic look, weatherproof and not dusty or flaky, able to be applied by a not very expert renderer.
If you happen to be in Northern NSW you could even come and help me slap it on the walls (I wish!)
Keef

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## jackiew

Suggest you ring up the people who ran the course and ask them.  They should be quite happy to tell you as you went on their course.

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## ozwinner

> A few years ago I did a workshop on rendering in which we used a mix of white cement, sand and some red clay(for colour) mixed with lime and left overnight.

  Hi
Just curious, why did you leave the mix overnight, it wasnt wet obviously?    

> This lot was then combined with some sawdust (for texture and flexibility) and then mixed up in a cement mixture. I think we might have added a dash of bondcrete also.

  Is the original stuff still stuck on the wall? I would have thought that with sawdust added it, it would be full of holes, weaker and liable crack to more easily. 
Just curious, Al  :Smilie:

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## wombat47

Sounds a bit like the old fashioned sand and hydrated lime mixture - you mix that up with the minimum of water and leave at least overnight.  It becomes more plastic as it sits.    It doesn't contain cement and therefore doesn't react with old mortars.   Takes longer to set than cement based mixes but is just as hard and water resistant.  The Romans used lime mortar and plasters. 
I'm not 100% sure but I think that old plaster walls (like mine) were applied with a thick base coat of sand and lime, and then a much thinner top coat of lime soaked in water to give a fine eggshell finish.

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## bitingmidge

> A few years ago I did a workshop on rendering in which we used a mix of white cement, sand and some red clay(for colour) mixed with lime and left overnight.

  I'm pretty dubious about the left overnight bit as well...  Cement goes "off" as part of a chemical reaction. No doubt someone reading this will understand the process and elaborate, but it is not reversable. 
By leaving the brew overnight, you will have a claggy mix that will be relying on drying only to adhere, rather than the chemical properties of the brew. 
Curiously, my knowledge of this was gained first hand after a 35 story building job I was running had to have its paint removed by hand scraping, and re-applied correctly.  The paint was a cement-based primer and the subcontractor mixed half a day's brew at a time, then proceeded up the building to work for half a day.   
Because the initial chemical reaction was complete by the time the paint was applied, when it dried it was effectively a coat of hard talc. 
Let's just say the rectification costs were significant! 
Can't help with the question though  :Shock:  sorry, 
P

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## ozwinner

Initial set for cement is 45 minutes, final set is 10 hours.
But cement will continue to harden for the next 10 years, after that it starts a gradual decaying process. 
I got learned that doing my bricklaying apprenticeship. 
When ever I mix mud, I only ever mix what I can use straight away, I dont leave the perpetual mix in the mixer going around all day. 
Al

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## bitingmidge

> Initial set for cement is 45 minutes

  Yep, thats the time the chemical reaction takes place. After that, no hope of getting the design strength. 
Oz you are now the fourth Bricky I have ever come across who has actually done an apprenticeship....one more and I will have met them all!  :Biggrin:   :Biggrin:   :Biggrin:   
P

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## ozwinner

Funny F#cker.     No wonder I love comeing here, good one   Al

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## ozwinner

Your right though, most brickies just seem to _pick it up_. 
But just a couple of minute talking with them and you can tell.
Sorry if I seem tradest, ( as in sexest ) :eek:  
Cheers, Al  :Smilie:

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## bitingmidge

> Your right though, most brickies just seem to pick it up

  Tradest is OK I think, although I would have used another word before "it up" with regard to many!  :Biggrin:   :Biggrin:   
P

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## ozwinner

I used to have this uncle, and when my dad wasnt busy I used to get lent to him for the day. 
Every day without fail at knock off time, he would slop up the unused mud for the next day.
He was a real tight bastard, next day, knock up the mud and use it.
I couldnt/cant beleive it.
This is a bloke who would drive 20 miles ( it was in England ), to save a couple of bob on a carton of smokes.
The petrol alone would have cost more than the saveing on the smokes. 
Al

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## Keef

I'm back...thanks for all the responses. Unfortortunately I have not had any luck in tracking down the bloke wot ran the course. It was only the lime and clay which was left overnight to soften. An old bathtub was filled with wet clay and a lot of lime was added. In the morning this mix was worked with a hoe thingy with holes in it (wots the proper name for that anybody?)
Then this was added to some sand and white cement, mixed for a bit and then enough coarse sawdust was added to make the mix a bit fluffy. ( see it's all starting to come back to me now) The resultant mix was lovely to apply. The chemistry might be a bit dodgy but the builder/workshop person had been using this for many years and it was claimed to be crack resistant and weatherproof. I might have to go back to the hose I worked on and ask the present owner wot he knows.
Keef

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## sailingamerican

This sounds like Adoby mix. Straw does not help make Adoby stronger. when you mix Adoby you make bricks and stand them up on end to dry. 
Lime in your mix is good for freezing weather. It helps morter from expanding.
Why the saw dust? This adds nothing to the mix. The basic mix you have detailed is your basic stucco mix which we use in the Southern US and South America. You can make walls out of compressed mud. Many Indian tribes and cultures around the world have used this method and after thousands of years still remains. Try going on line.  Here in California USA they have built many straw bail homes.  I have seen it on the TV.  You can find it on line. I do not think they leave the mix over night.  Mix what you can use for a few hours.  You can put just about anything in the mix for texture. Saw dust does not add strength.  I think I have seen it used but why? They also dig into the earth and use tires and rebar packed with dirt. Then they build floors, roofs, and put windows and doors on the front. To get a building permit they drove a 5 yard cement truck over the tires. It held.
Have a great day.
Richard in CA USA

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## journeyman Mick

Keef,
hoe thingy with holes in it is called a larry and is made for mixing mortar. Now largely superceded by the cement mixer, but still useful for mixing small batches. 
Mick

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## Keef

Richard...I am constantly amazed by how many  helpful replies I get on this forum. The mix I described was not actually designed for strawbale but I think it would work well. The builder who came up with the method used it to transform boring looking houses. First day he would rock up with a truckload of rusty old roofing iron and nailgun this horizontally onto the walls of the house, (caused instant phone calls of complaint from the neighbors). Second day he would apply the mix as a scratch coat ( coarse sawdust in the  mix). Final day the mix had some finer sawdust, it went on easily and was finished with a sponge after going off for about a half hour. The builder claims to have done hundreds of these renders with zero failures.......Keef

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## wombat47

Keef .. I impressed with the idea of rendering over corrugated iron.  Who'd a thought it would stick.  Perhaps that's why he used rusty. 
I you have a search around the net, I'm sure you will find information on the mix you need - with or without the addition of cement.  I think you will find that you will have to soak your lime, whether or not you need clay (and that needs to soak anyway) .. but use it straightaway once you have put the cement in. 
It is my understanding that cement isn't needed anyway. 
I used a mix of only hydrated lime and sand (soaked overnight) for interior patching on old (cementless) mortared bricks.  Just out of curiosity, I used the leftover to patch an exterior wall where a pipe had been taken out, and added a couple of bricks to a garden wall.  This was done about two years ago and the exterior mortar shows no sign of deteriorating.

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## ndru

Keef 
This may be useful...  http://barney.webace.com.au/~agstraw/render.html

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## Snoopy

I'm looking at rendering the brickwork on our house.  Now I know this is bound to cause some arguments, but can someone suggest a suitable mix?  Now on all the DIY TV shows, they love to quote these mixes - but do you think I've ever bothered to write it down? 
I imagine that the same mix would work for Keef, as he is applying onto an existing rough finish render.

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## ndru

Snoopy 
Try this page http://www.diydata.com/materials/cement/cement.htm#lime  and click on the "render" link.

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## ozwinner

I looked at the link, and even I was confused, so render mix.
3:1:1
3 sand :1 lime: 1 cement.
Use sharp sand ( washed sand ) NOT brickies sand, brickies sand has too much clay in it, and will drag when you try to trowel it.. 
Life wasnt ment to be a drag unless your name is Miriam..............:eek:  
Cheers, Al  :Smilie:

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## ozwinner

> Keef .. I impressed with the idea of rendering over corrugated iron. Who'd a thought it would stick. Perhaps that's why he used rusty.

  It wont stay stuck for too long, maybe just long enough for the cheque to clear.
What with expansion and contraction, it will all be on the ground before too long. :Frown:   :Frown:    
Al  :Smilie:

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## Snoopy

Thanks all.  As I don't know one good mix from another, I'll take Ozwinners word for it and go for the 3:1:1 mix - maybe just a little plasticiser??. 
Any other handy hints?  I would imagine that you should wet the brick wall down first to stop the bottom of the coat drying too fast and to help with binding.  Our bricks are moderately well textured, but I would still be tempted to fix a layer of chicken mesh to the walls first.  Is this a good idea or is the risk of cancer too great? 
As for drag, I will leave that topic well alone.  Just what sort of 'wood-work' are we talking about here? 
Matt

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## ozwinner

Save the chicken wire for the chicken run.Wet the brick first to stop the moisture being drawn out too quickly, unless the bricks are of the hard brittle type.
Plasticiser/detergent, same thing, only use a drop, literally. 
Al

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## Danster

Just on the 3:1:1 mix...What would the detergent do?
Would there be any advantage in lobbing in some bondcrete?  I'm thinking of rendering my brick house too and if this is a nice mix, I'll use it.  My bricks are VERY uneven with knobbly bits  - I think they're descibed as "rolled".
Also, trawling the web for info on how to apply, it was suggested to fix vertical timber battens, say 10mm-15mm thick to the bricks (how?) and apply the render between the battens using them as a screed guide.  Is this the way to go?  If so, is there a point to be made for horizontal batten thingos or best go for vertical?
There was also some advice about starting from the top and working down - suggestions here?  I reckon starting at bottom is better. 
If screeding the mortar between timber strips, then does the timber then get removed and just pop some mortar mix in the cavity left behind?  Would this show up as a vertical (or horizontal depending on which way the wood was) line because of the different times when applied?  I'd assume I'd need to leave the mortar to go off for a few days before removing the timber? 
cheers all
Danster

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## ozwinner

> Just on the 3:1:1 mix...What would the detergent do?

  The detergent gives mortar " life", with out it you will find it dead and lifeless, its hard to explain. Try it both ways and see which way you like it.  

> Would there be any advantage in lobbing in some bondcrete?

  No   

> Also, trawling the web for info on how to apply, it was suggested to fix vertical timber battens, say 10mm-15mm thick to the bricks (how?) and apply the render between the battens using them as a screed guide. Is this the way to go?

  Yes    

> If screeding the mortar between timber strips, then does the timber then get removed and just pop some mortar mix in the cavity left behind? Would this show up as a vertical (or horizontal depending on which way the wood was) line because of the different times when applied? I'd assume I'd need to leave the mortar to go off for a few days before removing the timber?

  When you use battens, fix them to the wall vertically with concrete nails then remove the battens as soon as you have covered the section with render, and fill in the gap straight away.
If you leave it until later you will have all kinds of trouble, like, a ridge where the battens were, uneven cover over different sections, battens stuck in the wall. :mad: 
The list goes on.
Start from the bottom, you realy need to practice some where before you tackle the house. 
Cheers, Al  :Smilie:

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## Danster

Thx ozwinner. Much clearer now.
BTW, what makes you so knowledgable? Is rendering your job or part of it?
I assume I'd fix the timber strips into the mortar between bricks? 
What sort of spacing between timber - 2 bricks wide?  Maybe 3 or 4? 
When the timber is removed, and the render to the left & right is still wet, how do I apply the render into the gap without damaging the just-applied render? 
cheers, Danster

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## ozwinner

> Thx ozwinner. Much clearer now.
> BTW, what makes you so knowledgable? 
> Is rendering your job or part of it?

  I did my apprenticeship with my Dad, who was a builder and we used to do reno's, before they became the flavour of the month.  :Smilie:     

> I assume I'd fix the timber strips into the mortar between bricks?

  Yes, into the mortar joint.   

> What sort of spacing between timber - 2 bricks wide? Maybe 3 or 4?

  Mmmm, try maybe 2.4M spaceings, you need to get a straight edges, best if its aluminium with a sharp edge, this is your screed, you apply the mortar to the wall, then get your screed  and with a left to right action move up the battons over the render, you will get depresions in the render, fill them, and repeat the screeding, etc, etc, until the render has no more hollow spots in it.  
When you have finished with the screeding you need to go over the whole lot with a wooden float, so the render becomes, " whole", as one, so it all looks the same.    

> When the timber is removed, and the render to the left & right is still wet, how do I apply the render into the gap without damaging the just-applied render?

  You will always have some damage, but it will fill up and be repaired as you go. 
As I said earlier, practice first. 
Al

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