Help and advice on rendering internal and external walls by a qualified plasterer and renderer.
What is Render & why use it ?
Render is a measured mixture of water, sand, and cement. Render is applied similar to plaster, but has a more durable and longer lasting finish.
The mixture remains hard for many years and helps protect the buildings structure from the elements.
Internal render is usually used when there has been a damp problem. Normal plaster or plaster boards may rot and begin to crumble quite quickly if the damp continues to perforate the external brick or block work.
Internal rendering permits a solid inner skin on the damp walls which is mainly impervious to moisture from outside.
The render can be skimmed over with plaster afterwards to create a perfectly even finish which is more moisture resistant.
How To Mix Render
Correct measurements are the key to a durable and long lasting render. The same as most mortar mixes, the mixture is three measurements of sand to one measurement of cement. 3 to 1.
Use a bucket, spade, or other large measuring implement to ensure correct quantities are used. Local qualified plasterers or renders will mix render in the same way.
Ideal For Home Mixing
A simple method of mixing all types of plaster, mortar or render is the drill attachment mixing implement. Cheap enough to keep in the garage for when ever it is needed. Simply fit into a drill and begin whisking.
Mixing in a cement mixer will take most of the labor out of the job in hand, or even hire someone to mix on your behalf. If using a mixer, turn the machine on, add some water, then add the 3 to 1 mix.
Add PVA to the water and stir well prior to adding sand or cement. This will act as a waterproof barrier within the set render.
The mixture needs to be seen 'folding' whilst the mixer is turning. This means not to stiff, but wet enough to spread without falling all over the floor.
Whether rendering inside or outside, ensure that the render remains above the damp proof course (DPC)
With external render, ensure a bell cast bead is placed on the wall JUST above the DPC.
Internal render can stop just above where the skirting board will be.
Most render is applied to a height of 1100mm above floor level.
Help with rendering begins with preparing the wall to be rendered. Remove any loose pieces and locate the piece most protruding from the wall.
This protruding piece is called the highest piece and and will be the shallowest part of the rendered wall.
Coat the entire wall with a 50/50 mix of PVA Bonding Agent and water. This will help with suction and remove more dust and particles. Allow the PVA mix to go tacky before applying any render.
The scratch coat is the first layer of render to be placed on the wall. This is typically up to 10 mm thick. Once the render has been applied to the wall, use a straight edge (about 1.8 - 2 m long) to smooth over the render.
Use the straight edge both vertically and horizontally. Gently scrape off the lumps and mounds of render protruding out. This should leave a more or less flat wall. Now scratch it.
The scratching will give a 'key' or 'biting point' for the top layer of internal or external render. Always scratch horizontally, this helps prevent any moisture from forming at the bottom of the wall.
Scratcher for Render or Plaster
The top coat of render is usually about 5 mm thick. This coat is simply to cover over the scratch coat and leave a smooth finish. Use a long level to ensure that the wall is straight both vertically and horizontally.
Rubbing up render means using a plastic float in circular motions to leave a sandstone effect. Whilst this is being done, any small dents can be filled in with moist render mix.
The render is to wet to rub up, if when rubbing up the render is being dragged. On hot days, only render small areas and then rub up before applying render to another part of the wall.
Skimming Over Render
Using finishing plaster, it is possible to skim over render. Apply a liberal coat of PVA onto the render, then skim over with plaster.
We can answer questions if you have problems or queries on rendering or plastering. Please leave comments or questions in the comments box at the foot of the page.
billericky (author) from Plymouth on September 21, 2015:
The moisture will still penetrate from the outside wall, no matter if you use bondcrete or not. You may consider rendering the outside first., this will help prevent moisture entering the inside. Please note the word 'prevent' and not 'stop' moisture from entering. The builder was correct in my eyes of his assumption.
Grace on September 19, 2015:
We have single brick garage wall that had to be fixed by the builder. The bricks are completely different in look and texture and we want to render the inside of the garage wall.
The builders say it can't be done because it's a single course, but can the wall be rendered with a layer of Bondcrete underneath or will the moisture penetrate and will the render fall off.
billericky (author) from Plymouth on April 16, 2015:
Called a 'dubbing out' coat. The render should be thick enough to just cover over the pebble-dash. Do not leave a smooth finish. Once applied, scratch the finished surface to create a key for the finishing layer.
Darren on April 16, 2015:
What thickness should the render be to skim over pebble dash?
billericky (author) from Plymouth on April 13, 2015:
You can skim over the pebble-dash. Brush on a mixture of PVA / water at a 50% mix ratio onto the pebble dash. Allow to go tacky. Then skim over with a 3 sand to one cement mixture. In the render mix, add a water proofer for protection against the elements.
Darren on April 12, 2015:
I have fine pebble dashed render on outside if house. Can I skim over this or do I have to remove it first?
If skim, what should I use?
billericky (author) from Plymouth on December 08, 2014:
Browning can be used, but if the area is prone to damp, then quite soon the browning will begin to fall off. The bonding and browning can both be used once the sand and cement render has been applied. The render will act as a moisture barrier, whereas the browning or bonding will not.
Pm on December 05, 2014:
I have an interior wall to render which is on the outside of the house.
Does this wall have to done in sand and cement or can it be done in car lite bonding or browning.
billericky (author) from Plymouth on January 24, 2014:
The bell cast should be above the damp proof course (DPC) by approximately 1cm to 1 inch or thereabouts.
Sally on January 24, 2014:
Should the bottom of the bell cast be above the damp proof course, If so by how much? Many Thanks
billericky (author) from Plymouth on December 04, 2013:
Yes you can drill into a rendered wall, just like a normal wall
Desleigh on December 03, 2013:
can we drill into a render finished wall...we need to install a door jamb to prevent swing doors blowing in the wind.
billericky (author) from Plymouth on November 28, 2013:
You can skim over the internal render as soon as it is dry, and after a week, I am assuming that it is.
You will need to add a PVA mixture over the render and old plaster prior to skimming over, without the PVA the new plaster may begin to crack and fall off.
No special type of plaster is required, simple multi-finish is suitable.
Begum on November 27, 2013:
Hi I have had DPC in my old victorian terraced house. I've hacked off a lot off the old plaster and recently had someone come in to render all the walls up to the old plaster.
Its been over a week since it has been rendered, my question is; when can we skim over and do we need to pva the rendered walls before we skim? and lastly do we need to use special type of plaster to skim the walls?
Michael Luckado from Hawaii on November 26, 2012:
Like the look. I've never heard the term render. Where are you located?