hi there just joined can any one tell me if you need two coats for rendering external wall if yes do you need bonding and watterproofing on both coats 
cement rendering
- Thread starter billby
- Start date
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i mainly render inside (for damp proofing). outside i've done mainly garden walls and a bay window.
on the outside i use bonding on the 1st coat only applying a light strake to key the 2nd coat. both are at 6mm. i use 3:1 for 1st coat and 4:1 for 2nd coat (i believe you can use 4:1 for both coats). i use waterproofer for house walls in both coats. i put the 2nd coat on just as the 1st is setting. i also use plasticizer and washed sand.
on the outside i use bonding on the 1st coat only applying a light strake to key the 2nd coat. both are at 6mm. i use 3:1 for 1st coat and 4:1 for 2nd coat (i believe you can use 4:1 for both coats). i use waterproofer for house walls in both coats. i put the 2nd coat on just as the 1st is setting. i also use plasticizer and washed sand.
Hi, bill,
Have a look at the brickwork you intend to cover/render.
Bear in mind that older brick walls which are built in sand lime mortar are flexible and expand more than modern mortar mixes.
What this means is, if the wall(s) you intend to render are older than about 50 years, (and this varies) it could be in a cement free mix as Portland cement was only brought into general use after the war.
So first decide if the wall in question can be saved by repointing, (to a depth of at least 20mm and with a lime added mix if the wall is sand lime mortar.
If the wall is basically sound and there is not a lot of loose stuff on the surface, then you don't need an adhesive at all, or waterproofing.
This is because the wall should be alowed to 'breathe' anyway.
It is normal practice to put a 'scratch' coat on first, and then a finish coat.
The scratch coat is just as it sounds, a first coat of render which is scratched with a nail block after aplication and whist still softish, to key the surface, and take the suction and badness out of the wall, so that a good finish coat can be aplied the next day, (usually).
Bear in mind that you will need stainless/galvanised corners etc.
If all the above is gobbledegook to you , get in a pro to do it.
unless it's trivial, then have a go yourself.
Have a look at the brickwork you intend to cover/render.
Bear in mind that older brick walls which are built in sand lime mortar are flexible and expand more than modern mortar mixes.
What this means is, if the wall(s) you intend to render are older than about 50 years, (and this varies) it could be in a cement free mix as Portland cement was only brought into general use after the war.
So first decide if the wall in question can be saved by repointing, (to a depth of at least 20mm and with a lime added mix if the wall is sand lime mortar.
If the wall is basically sound and there is not a lot of loose stuff on the surface, then you don't need an adhesive at all, or waterproofing.
This is because the wall should be alowed to 'breathe' anyway.
It is normal practice to put a 'scratch' coat on first, and then a finish coat.
The scratch coat is just as it sounds, a first coat of render which is scratched with a nail block after aplication and whist still softish, to key the surface, and take the suction and badness out of the wall, so that a good finish coat can be aplied the next day, (usually).
Bear in mind that you will need stainless/galvanised corners etc.
If all the above is gobbledegook to you , get in a pro to do it.
unless it's trivial, then have a go yourself.
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JerryM";p="953459 said:good advice by chessspy - i particularly like avoiding render if u can - bricks are for seeing
thanks i no what u mean
30m x 3m high is a big job. if you've not rendered before it might be worth getting quotes to have it done for you. Your arms will be hanging off.
if you do go for it you will need a cement mixer and a platform to access the top sections.
i would do it in 3 off 1 metre strips starting at the top. i would not bother with intermediate beads only at changes of shape ie external corners. also don't forget to include what's called a belcast 150mm off the floor so as not to bridge your dpc. the belcast is formed using a bead. the underside is then painted black.
Getting the mix right is important – it needs to be soft but not sloppy - not soft enough and it’s hard putting on but too soft and it “bags” sags. There's a technique to putting it on – a series of layers in a sort of wedge action say 1m sq section at a time starting at the top working across and then down.
On outside render I use a dry sponge in circular motion to level the surface out just as the top coat is starting to set (not essential though).
i'd start off practising on a section first and wash it off if necessary to have a few goes.
let me know if you need more info ie tools
if you do go for it you will need a cement mixer and a platform to access the top sections.
i would do it in 3 off 1 metre strips starting at the top. i would not bother with intermediate beads only at changes of shape ie external corners. also don't forget to include what's called a belcast 150mm off the floor so as not to bridge your dpc. the belcast is formed using a bead. the underside is then painted black.
Getting the mix right is important – it needs to be soft but not sloppy - not soft enough and it’s hard putting on but too soft and it “bags” sags. There's a technique to putting it on – a series of layers in a sort of wedge action say 1m sq section at a time starting at the top working across and then down.
On outside render I use a dry sponge in circular motion to level the surface out just as the top coat is starting to set (not essential though).
i'd start off practising on a section first and wash it off if necessary to have a few goes.
let me know if you need more info ie tools
hi there most grateful for this information i am bricky to trade but this is a bit out of league doing job for friend at caravan site i will let u no how we get on thanks again for this valuable information
had a couple of further thoughts
you will need beading over windows - acts as a drip sill
if your going to paint then not an issue but if not painting then try to complete the finish coat on one complete wall at a time otherwise it's difficult to hide the horizontal joints. if you cant finish in one go cut a horizontal line just above the bottom edge (ie cut off the jagged edge off the finish coat) - with trowel and line/straightedge just as the render is setting - this helps to mask the joint.
you ideally need a darby (or straight edge) to pass over horizontally and then vertically over the finish coat to keep it true and flat.
best wishes for the job - i like brickying and render is not as bad as plaster finish as you can have a rest but it's heavy and hardwork as a result physically.
you will need beading over windows - acts as a drip sill
if your going to paint then not an issue but if not painting then try to complete the finish coat on one complete wall at a time otherwise it's difficult to hide the horizontal joints. if you cant finish in one go cut a horizontal line just above the bottom edge (ie cut off the jagged edge off the finish coat) - with trowel and line/straightedge just as the render is setting - this helps to mask the joint.
you ideally need a darby (or straight edge) to pass over horizontally and then vertically over the finish coat to keep it true and flat.
best wishes for the job - i like brickying and render is not as bad as plaster finish as you can have a rest but it's heavy and hardwork as a result physically.
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