rendering temp's

[messenger]

I AM new to this site and need some help with a question regarding external rendering and temp's. As it is starting to get quiet frosty down this way i know there are products to kill the freeze but what is the lowest the temp can be to prevent freezing and cracking.Any suggestions would be greatfully reiceved.

 

[malbru]

I AM new to this site and need some help with a question regarding external rendering and temp's. As it is starting to get quiet frosty down this way i know there are products to kill the freeze but what is the lowest the temp can be to prevent freezing and cracking.Any suggestions would be greatfully reiceved.

Do not render unless the air temperature is 3 degrees C and rising. Ideally, this should also be the minimum overnight air temperature. So-called antifreeze admixtures are not worth a carrot. Use a cement containing an air entraining agent and fillers such as Lafarge Blue Circle Mastercrete. To minimise shrinkage cracking, use hydrated lime and a well graded plastering sand (usually a blend of sharp sand and building/soft sand, typically 70/30). Depending on the background (what you're rendering onto), the mix should be either a 1-1-6 (1 volume of cement to 1 volume of lime to 6 volumes of sand) or a 1-0.5-4.5 (in same order). If the mix needs a bit more plasticity, add a smidgen of air entraining agent (commonly called mortar plasticiser in builders merchants) - but don't overdo it.

Render in two or three coats, scratching each coat before applying the next. Allow sufficient time for each base coat to harden and 'dry out' before applying the next (temperature dependent). If the base coat shows signs of cracking, don't worry, it often does and quite frankly, it should do. Do not make the mistake of applying a richer (stronger/higher cement content) mix for the top coat. Generally, the richer the mix, the greater the degree of cracking.

If you've never rendered before - beware, it is a well learned trade. Get it wrong and the render will blow (come away) from the background leaving large areas of hollows which will eventually crack and fall off. It's best left to the experts if it's anything more than small area. Good luck.

 

[Micilin]

In addition to the above, one of the biggest dangers is applying render onto a wall that has frost in it, either blocks or scratch coat.

A good test is to light a bag and hold it to the wall, see if any moisture appears as any frost melts. If you are not used to rendering, then as the post above says, just make sure the temp is 3 degrees and rising before you start.

Remember that the actual temperature may vary from elevation to elevation, and just because the thermometer hanging by your door reads x degrees, it doesn't follow that that is the temp on the wall you want to coat.