Advice on rendering my garden wall please?

[coolas4k]

Hi guys,

I've just finished building my garden wall with concrete blocks. I did consider asking a professional to render it but after 2 separate quotes which were both a lot more expensive then I first expected I have decided to take on the task myself (as with most home improvement jobs due to my frugal nature). I'm planning to use the plastering sand and portland cement method with a ratio of 4:1. I have bought some waterproofer and plasticiser ready but I'm unsure which additive to use in which coat (scratch ot top coat).

Can anyone advise? Plus confirm if the 4:1 mix ratio is correct for both coats? Also, could I use hydrated lime in addition to the additives or is that not recommended?

Any advise or help is much appreciated 😊

 

[roy c]

Are you putting copings on top of the wall? If so set them on top first. Or you could put a couple of battens on the top over hanging about 6mmmm either side and hold them down with some bricks to keep them secure so you can use them as a guide for your two coats. If you are doing it this way put a scratch coat on 5-1 (measure your mixes out in a suitable container ) you can put some w/proofer in this mix. Dampen the wall down with clean water so it soaks in and is damp when you render but not sobbing wet. You can put this coat on about 6mm thick .Get yourself a nice straight piece of wood to "screed " this coat, make sure it is tall enough to run past the top of the battens on top of the wall as these will be your top screeds, Then put an oval nail in the bottom of your batten about 2 inches up from the bottom, and knock it in so there is 6mm left showing. So when you put your scratch coat on you can hold it against your wall and top batten and gently screed it thru. You can patch any discrepencies in when you have screeded it thru and it has firmed up .Then scratch it with wavy lines but don't go thru to the brickwork. Do this on both sides. When the scratch coat has firmed up (either next day (I like to leave it a bit longer if there is no time limit on the job) or a bit longer) Move the top battens out to the thickness you want put bricks on to hold it down again and put the nail in the bottom of batten to suit. You are then ready to float coat it, this mix will be 5or6-1-1 (sand lime cement) no w/proofer but you can put a drop of plasticiser in this mix if you want. Wet the scratch again like you did when you did the scratch coat, lay your mix on and screed again with your batten with the nail in and leave it to firm up a bit then float it up filling in any holes or hollows with a bit of muck. leave it for a while then sponge it up to a nice finish. If you do it this way you can set your copings on straight away and and float the underneath of the copings up and it will all set together. This is more or less a fool-proof way to get a good finish and a tidy job for some one who wants a good finish or you can throw it on with no screeds and un-measured mixes and see it all crack and fall off within the year!! Hope you understand this.. If you did set your copings on first then you would have to cut your battens abut 2 " below the underside of the copings and put a nail in the top of the batten the same thickness as the bottom and screed as normal with a sawing motion and put a bit of muck on your float to fill the nail holes when you float it up if the lines are a bit messy...

 

[coolas4k]

Thanks for reply.

Is there any reason why i can't put waterproofer in the float coat as well as the scratch coat? Just thinking the whole of the render (both coats) would be water tight then... I'm not disputing your advice, i just like to know the reasons why things are done certain ways, that's all

Also, i've heard others mention a 4:1 mix. Is there any particular reason use choose 5:1 over 4:1?

Cheers

 

[roy c]

You should never put w/proofer in with lime...A 4-1 mix can be used but I prefer a weaker mix (A 5-1 mix is still strong enough any way. ) What ever scratch coat used always go weaker on the next coat!!

 

[coolas4k]

Ok, that's great advice thanks! I feel more confident about doing it now I think