Outdoor Rendering

Discussion in 'Builders' Talk' started by richado, Aug 20, 2007.

  1. richado

    richado New Member

    I am just about to take on the task of rendering the outside of my house.
    I have good knowledge of plastering but just wondered on the mix and what additive i should put in.
    i been told by the lad in the local builders merchants to use 4 parts sharp sand, one part cement and a bit of Renda mix (from screw fix)is that correct.
    Also what do i need to put around the windows, doors and the top of the engineering bricks where the render is going to stop.

    If anybody can help please reply!!!!!!!!!!!
     
  2. Husky

    Husky New Member

    Hi Richado,

    I'm afraid I can't answer your Q, but as mine is similar, thought we could pool resources (and bump the thread up the forum a bit!) Hope this is ok?

    Basically, I am rendering some new block walls in the garden, to give a clean, contemporary look and want to know how to finish these at ground level - walls will be surrounded by gravel trenches.

    Can the render run down below gravel level (ideal) or will there still be moisture problems.

    Also, do I need corner beads as at £22 per 10m this is going to add up for what I am doing...is there an easy way of achieving a half-decent arris without them? (bearing in mind it's only a garden wall, but would like clean lines...)

    Thanks all,

    Husky
     
  3. Chipsticks

    Chipsticks New Member

    Richado i have rendered a couple of houses and the info i was given was to have 4 smooth sand (cardigan sand is what i've used not sure if that is available to you) 1 cement and 1 lime to stop cracking appearing in the finish also add waterproofer as your feb mix.

    for the heads of your windows and doors put a bellbead on sticking out 2" either side, bellbead on your d.p.c level all the way around your house, for your reveals of your windows and doors do them with a mate with a piece of 4x1 slightly smaller than the height of your reveals so you can slide it up and away, get your mate to hold it firmly about 1/2" depth on your wall put your mix on your reveal then slide your 4x1 away.

    hope this is useful to you
     
  4. Dereekoo

    Dereekoo Member

    do a search on rendering and no doubt you will find all the answers you need
     
  5. HappyDayz

    HappyDayz New Member

    The traditional two coat rendering on a porous surface, i.e. normal bricks and most blocks, calls for a 1:1:6 mix for the scratch coat; cement, lime and sharp sand (3mm to fines). I would add some waterproofer as a matter of routine. If the wall is dry (unlikely this year!) lightly damp it without soaking it completely before applying the scratch coat. Make sure to keep damping the next bit as you work your way along the wall.

    In the old days the scratch coat was allowed to dry for a full week. Builders and the like are in such a hurry (let's face it they have to make a living) that they will do both layers in one day. I have no proof that letting the scratch coat go off properly makes a big difference but if you have the choice, why take chances?

    The top coat has to be weaker than the scratch coat, otherwise over time the whole lot falls off the wall. The mix I use is 1:1:9. This will probably have some of the people on here howling, but a weak mix with as much lime as cement is much less likely to develop hairline cracks.

    Personally I like a hackly finish and so when the top coat has all but gone off, having been polished up, I then lightly go over it with a moist sponge.

    Husky: Plastic corner beads are definitely worthwhile for the top of garden walls. They look really sharp but you must take your time when fixing them to make sure that adjacent lengths line up exactly (<1mm). Because they do look so sharp, the slightest deviation at joints, sticks out like a sore thumb.

    These mixes are not suitable for non-porous surfaces such as engineering bricks nor for smooth, high suction, lightweight AAC blocks.

    If you are really concerned about waterproofing for a house wall then you should consider an additive like Compact-All Civil. It is hellishly expensive (particularly the carriage) but it is brilliant stuff for a multitude of tasks. Unfortunately you can no longer buy it from the manufacturers (unless you want 1000l!) but you can get it from: http://www.waterproofconcrete.co.uk/
     
  6. richado

    richado New Member

    thanks for that useful info happy dayz. just one other question.
     

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