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Green Building Bible, Fourth Edition
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General: Thin coat rendering when it's cold

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  1.  
    • CommentAuthorwookey
    • CommentTimeFeb 28th 2021
     
    I'm about to attempt my first (very small, under bay window) bit of rendering (Baumit MC55 base coat, and Baumit silicone top coat, with some primer and DS26Flex waterproofing in-between).

    The weather is cool and dry but getting under 5C overnight. for the whole of the next week. The MC55 says the temp should be over 5C for application and curing. So what happens if I put it on when its 10C during the day but maybe 2C or 3C overnight (current weather forecast gives 3, 3,3,5,2,1,1 for next week (daytime 9, 8, 9, 10, 8,7,7).

    Presumably so long as it doesn't freeze it'll be OK, but will just cure very slowly (any idea how slowly - it took 2-3 days in Autumn?) I understand that MC55 is a lime-based plaster, although with various other things in it to make it easy to use.

    The incentive for not waiting another few weeks is a) it needs doing and have time and the weather/ground is dry and b) the bulbs are coming up in front of this bit of wall so It'd be good to get it done so I don't destroy them all doing it later.
    • CommentAuthorjamesingram
    • CommentTimeFeb 28th 2021 edited
     
    I wouldnt risk it.
    You may be fine, my guess would be a slight frost would damage the surface perhaps making it dusty. You'll have to prime it before top coat so a brush will remove any dust damage.
    Still I'd wait.
    My own rule is , not below 5deg with in 48hrs , similarly no chance of rain with in 12hrs .
    Also not too hot , try and time it so the wall your doing is shaded or not in full sun.
    Topcoat you need to be even more careful with weather extremes , drying time rapidly changes with direct sun even on a cooler day and rain will destroy your work.
    It really goes on quite thin , if you go too heavy its hard to rub up and it drags.

    All that said a local school new build has just been doing rockwool ewi thin coat and they appear to be cracking on regardless but still if it was me I'd wait for above 5 degrees those bulbs will come up every year the ewi you only want to do once
    :bigsmile:
    Be good to see what Nick thinks
    • CommentAuthorrevor
    • CommentTimeMar 2nd 2021
     
    I would wait for more favourable conditions it is not just the air temperature it is also the temp of the wall. When I had my rendering done they ran out of top coat skim and it had to come from Germany. When they came back about a fortnight later to finish the job. We had had a cold spell and the wall temperature had dropped to 2 to 3 c but air temp was about 7/8. They wanted to render but stopped them and showed the wall temp with an IR thermometer.The minute the render would have been put on it would have been same as the wall. I waited until spring for it to warm up.
  4.  
    ''Be good to see what Nick thinks''

    Nick thinks you should wait - sorry!

    I was doing the same juggling game 2 years ago, but with a cement-based render over EPS. I still waited till we had a forecast of 5+ for a good while. I would not have risked it with lime.

    James is right - the topcoat is a pain!

    I really would not risk it.
  5.  
    ' I agree with Nick '
    :bigsmile:
  6.  
    :bigsmile:
    • CommentAuthorwookey
    • CommentTimeOct 7th 2022
     
    Hmm. I don't think I came back to read all this sensible advice last year and just did it anyway :-)

    I did cover it with spare insulation batts and sheets to keep direct frost off for a few days. Sadly I can't remember exactly how the timing and weather turned out in the end but the render is fine. It was mostly because it was a very small area that I was a bit gung-ho. If I had had to do it again that would not have been a big deal.

    And the sensible advice remains for future visitors :-)

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