Rendering a wall - how to

[Big Clint]

I did some rendering the other weekend, just an 1800mm square on a wall above what will be a ½ circle pond, and thought I would put this post up to help others and me. I am hoping people can answer some of my questions and add some pointers. I have always found these types of how to threads/articles useful in the past and thought I would add one of my own. Although as you will soon see I am no authority, not even close.


What was wanted

My aunty wanted a square patch of render on her wall to which I will fix a wrought iron fixture. A ½ circle pond will then be placed in front of the rendered section and the rest of the wall painted a feature colour.

My experience/qualifications

I am by no means super proficient at rendering, I have seen it done on a few building sites when I was a labourer (back in my university days), read about it in a few books and done the odd bit here and there while renovating houses. But usually it has been limited to patching up and small jobs. My most recent job was rendering the back of a brick water feature which I later tiled over, that was more just to even out my brickwork so I had a good base from which to tile.

So as you can see I’m no expert, but I like to have a go at most things and can usually nut it out. But I suppose like everyone I always notice the inevitable imperfections.

What I did

Step 1
I wanted a nice clean. I knew there was no way I could achieve this free hand, so I nailed some 11mm pine battens to the wall (masonry nails) and used this as my edging.

Step 2
I had hosed down the wall and hit it with a hand broom to remove any dust and loose material.

Step 3

I mixed up my cement in my handme down mixer. Apparently it is 20 years old (grandad to my dad to me), still going strong, although you have to baby the motor or it will overheat. Not the best for mixing a lot of concrete but I does what I ask of it.

I used 1 brickies lite to 3 brickies sand. I have been told to use plasters sand as it is supposed to be better than brickies sand due to lack of clay? I think? But I have never used it as I have only ever done a small amount of rendering and never needed that much sand as to warrant buying it. Does it make much difference?

Also are you better to buy plain cement and the lime separate? Is there any benefit?

To that I added a bit of bondcrete, only because I had some lying around. Not sure whether this does much, I haven’t been able to tell the difference between when I have used it and when I haven’t. I had always thought it was just PVA glue with some other additives.

I also added some calar clear (the brickies left a tub of it at my dads factory once and never picked it up so I inherited it) it does definitely make a difference to the feel of the render I have noticed. Makes it easier to work, the render seems to flow better and appears lighter. Someone told me once to use dishwashing liquid to get the same result. I think it is just air bubbles that does it. Anyone know if this is correct?

Step 4
Now to get it up on the wall. My tools of trade are mainly hand me downs too, they came with the cement mixer. But I bought a poly float, and made a hawk.

The hawk is a bit of fibreglass sheet with a bit of broom handle fibreglassed onto it (my dad has a fibreglass business) it beats the $60 they want for a professional one. Although I will probably make a slightly bigger one as my current one is a tad small.

Something I have always wondered about and never really settled is the difference in floats. What is the difference to the finished product between a steel, wood and poly float. I know the steel sort of brings out more of a polished look to the concrete/render. Is that because it brings the water to the surface?

I then used my brickies trowel to get the render on my hawk and grabbed my steel float. Holding the float close to the wall I use the float to push the render up the wall in a sort of arc motion following this with the hawk. Render inevitably falls off the wall and some of this is caught by the hawk. I basically continued with this method until I had covered the entire section of wall I wanted to render.

The finish at the end of this process is not level or even close to level. It is pretty rough, but I have good coverage.

Step 5
Walk away. I went and grabbed a coffee and some cake and had a chat. This allowed the render to go off a little bit. Although it was a pretty cold day and was inside an atrium so it will take a while to go off. The time period would obviously differ for a hot summers day and particularly if the wall is in direct sun. I don’t think it is a good idea to attempt to render a wall in the middle of a hot day when the wall is in direct sun as the render will go off to quick and will crack. Although I have seen people spray render with a garden sprayer to try and counteract this.

Step 6
I grabbed my straight edge and used that in a sort of sliding back and forward and pulling motion to slice off the high spots.

By this stage the render falls off with a sandy consistency rather than big lumps of wet cement.

Step 7
I then filled any low spots with left over render and my float to even them out.

Step 8

Grab the poly float. This one is a bit bigger than my steel float its 300 x 150mm.

I use the poly float in light circular motions to sort of work the render and to level off any high spots or bits I missed with the straight edge. I also use a damp sponge to try and level off bits that are proving difficult with the float.

Would a bevelled edge wooden float be the better option for this?

Also I have seen plasters who use wooden floats that are about 600mm long by what look like 100mm wide. Will this allow for a better/smoother finish.

Also would you use a foam backed float for this, I have seen them at bunnings, steel float with 20mm of a sponge material glued to it.


Finished

pictures probably would have helped, but the camera is always an afterthought.

That’s my take on rendering. Now hopefully someone who actually knows what they are doing can point out where I have gone wrong and make a few suggestions.

Clint

[seriph1]

no idea about render .... or didn't have til you posted .... just wanted to acknowledge the post and the great clarity of your writing

thanks heaps - and youre right ..... pics woulda been brilliant - maybe one of the finished product? If you can't get your brain around how to load them up on the site or shrink them enough to fit etc etc - just email them to me and I will do the rest

[Jacksin]

Did you get any cracks opening up in the render as it was drying?
Normally this would happen by using bricky's sand.
Jack

[Big Clint]

I was around there the other day and forgot to take my camera. But I have to paint the surrounding wall so I will take a couple of photos then.

But there were no cracks when i went and had another inspection. it has now been up for 2 weeks.

so do you use plasters sand to avoid cracking? is it the clay in the brickies that causes this.

I had rendered a wall once before that cracked in places, i put that down to me doing it on a 35 degree day and the fact that i probably put it on a bit thick.

[journeyman Mick]

Clint,
the clay content in the brickies loam makes it more plastic and easier to use however it does shrink somewhat. This isn't a problem in mortar joints which are usually only about 10mm thick. In applications where there are large expanses (rendering) or thicker mortar beds (stone walls) then "sharp/plasterer's" (ie no clay) sand is the go. This is all from my brickie mate next door as when it comes to rendering or brick laying I am usually running the other way .

Mick

[Big Clint]

Thanks Mick

I had been wondering about that for a while.

[mr_john]

I have been doing some rendering (internal acrylic over brick) off and on and just starting to get better and your method seems to be pretty close to what I have been doing. I can't quite get the float thing right yet but your post definitely helped. The tricky bit I have found is how long to let it set before you start rubbing off the bumps of render. So I thought I'd my trials and errors (indoors in 20ish degrees) 3 hours is about perfect for me.

[rmartens]

Everything you mentioned sounds and is correct. You are doing everything right except!
The use of calair in render or for that matter detergent. As in sand finish when you rub up with float or sponge the finish seems to get furry using calair meaning the sand seems to follow you instead of being consistent and closing up. Lime and cement is better to use than say brickies light or mortar mix plus masonary cement etc.
I bought myself a good weed sprayer for floating down the walls and using a sponge float on the finis/Users/rmartens/Pictures/plastering photos /pillar1.jpgh. I use oregan wood to work the render after screeding. And then a sponge float to bring sand nicely to the surface and consistent
This is a two coat render I did using fine mist water on sponge float bringing sand to a consistent finish with water proofer in second coat and picture was taken when render was dry on a wet day. So two coat is better than one coat making a more consistent finish. A steel trowel is used to push render onto the wall. Only thing is give the additive calair and detergent a miss and use a water proofer in final mix. That will give you some extra workability instead of using an air entrailing agent ( calair detergent)

[johnc]

Good post, one of the questions was which trowel. You apply with a steel plasters float, not one of the flat type the inside blokes use for base or top coat but one with the slightest of curves to prevent the tips digging in. You float off with a wooden float as a steel one brings up to much water. If it is a one coat job fininshing off with a steel float is very difficult as you are likely to show up every imperfection, so a sweep with a wooden or poly float or even a sponge job, my experience is wood and steel only.

A large wooden float helps get a flatter surface but not for the inexperienced, I use a float of a similar size but no handle, as to why because thats what my father did and I learnt off him. Your idea of a straight edge and timber guides is a good one, at the very least always use a straight edge clamped to the corners for a nice straight line. Rather than the timber batten method you can just run a line of plaster up and screed to that but you did to have good "feel" and the timber method is easier for novices.

[autogenous]

Ideal brickies sand is a round aggregate with the right amount of loam. That particular type of sand makes for a plastic mix best for laying bricks especially standard metrics.

In the real world however sand does vary from place to place. Probably the worst sand experienced is washed white sand used with lime and white cement to give a stark white joint. The sand is so harsh that even plasterers would cry foul.

Plasterers sand is ideally sharp with less loam to reduce shrinking as stated above.
In the real world sands do vary from place to place.

The issue with aeration agents is that mortars are overdosed a lot of the time. An over dose of aeration agent which puts air bubbles in the mortar leaves many air pockets between the surface and the mortar layer. Bit like a Chocolate Aerobar
Aerated mortar also cant be reused or woken up. It wont re adhere to wall or bricks.
Once its gone its gone. Dropping the quantity of cement required is also easily done and screeds easier but so is pure sand which doesn't make for good strength.
The biggest mistake by people mixing with aeration agent is they put it in a drum of water and at the end of the day it sinks into the sand at the bottom of the drum.
The next day first mix the boss shouts rubbish mud so someone chucks in another dose then stirs the sand up and bingo!, overdosed mortar.
In certain situations aeration agents have a place. But Aeration agents should be way under dosed IMHO if they have to be used in mortar.

For a external sand face render I would just use 6S:1L:1C

I would use general purpose (GP) cement and lime rather than a "brickies" lite for render.

Aeration agents can cause crazing for external render.

Lime can be woken up with less crazing if any. Mixing mortar for plastering is an art and to a lesser extent bricklaying but still the difference between making money or not.
Special mixes are made to suit different situations.

Have a look at the benefits of lime http://www.buildinglimesforum.org.uk/whyuselime.htm

[autogenous]

Ideally you want 3 parts aggregate (sand) to 1 part matrix (cement or lime in different ratios). In some cases dependant on the sand you really want to thin it out a little or up the ratio to suit different aggregates and applications.

More cement and she goes off faster.

Clear as mud?

[rmartens]

I would like to add from what autogenous mentioned about water in the drum and refilling. Just last week we were doing external render on 4 metre high walls.
The labourer was washing the tools in the water drum. I kept asking him to keep the water in the drum clean. He asked why?
We always learnt in school to keep water clean when mixing. The reason is when you mix using dirty water, it send the render off quicker. Especially when rendering. Same when you remix mortar droppings the second time it goes off quicker. For internal floating it will be alright because you use a weaker mix.

[chromis]

Just off topic..Everytime I read a post I think sh*t I did it wrong.

I used brickies sand with my render...Quite a long wall...

I might be lucky..two years on and no cracks yet...

But still I had no idea you wernt supposed to use brickies yellow.

[Brickie]

Ideal brickies sand is a round aggregate with the right amount of loam. That particular type of sand makes for a plastic mix best for laying bricks especially standard metrics.

In the real world however sand does vary from place to place. Probably the worst sand experienced is washed white sand used with lime and white cement to give a stark white joint. The sand is so harsh that even plasterers would cry foul.

Plasterers sand is ideally sharp with less loam to reduce shrinking as stated above.
In the real world sands do vary from place to place.

The issue with aeration agents is that mortars are overdosed a lot of the time. An over dose of aeration agent which puts air bubbles in the mortar leaves many air pockets between the surface and the mortar layer. Bit like a Chocolate Aerobar
Aerated mortar also cant be reused or woken up. It wont re adhere to wall or bricks.
Once its gone its gone. Dropping the quantity of cement required is also easily done and screeds easier but so is pure sand which doesn't make for good strength.
The biggest mistake by people mixing with aeration agent is they put it in a drum of water and at the end of the day it sinks into the sand at the bottom of the drum.
The next day first mix the boss shouts rubbish mud so someone chucks in another dose then stirs the sand up and bingo!, overdosed mortar.
In certain situations aeration agents have a place. But Aeration agents should be way under dosed IMHO if they have to be used in mortar.

For a external sand face render I would just use 6S:1L:1C

I would use general purpose (GP) cement and lime rather than a "brickies" lite for render.

Aeration agents can cause crazing for external render.

Lime can be woken up with less crazing if any. Mixing mortar for plastering is an art and to a lesser extent bricklaying but still the difference between making money or not.
Special mixes are made to suit different situations.

Have a look at the benefits of lime http://www.buildinglimesforum.org.uk/whyuselime.htm

Did you just make all this up or are you a renderer?

[peterw]

Great stuff guys, and I know I'm coming in late on this, but for anyone else stumbling across the thread, the world of make believe seems to prevade the building world these days, so if my Gran wanted a nice bit of render for a water feature, I might have considered cutting a piece of blueboard/villaboard or similar to shape, fixing to the bricks with silicone, either a wooden edge or trim, or some more silicone to seal the edge and a couple of coats of paint.

In shape, flat and done in an afternoon.

Just looking for an easy way out......