Exterior sandy render falling off

[Londoner]

I was wondering if anyone had any advice about this... The exterior of our 1930s build house is coated in a sandy render with stone chips embedded it it (I don't know what the correct term for this kind of finish is).

Anyway, small areas of it have now started to crumble - literally to sand - and fall away. What is the best way of remedying this?

Thanks in advance.

 

[JerryM]

i think the simple answer is knock off and start again.

i would say the mortar mix used to put the render on was not strong enough - ie not enough cement.

u might just get away with painting it with exterior masonry paint. i would try a section out of sight (or as best can be) and see how the adhesion is. the trouble is i feel this will only be a medium term fix (probably 10yrs) as the frost will gradually get to the mortar through the paint.

 

[csrt]

I agree with jerry, a possible alternative to knocking it all off is to attach chicken wire to the complete surface with sheridized srews and small washers then apply 1 x render coat of 1:5 cement mortar to the whole surface a provide a key to this coat whilst still soft, then apply a final render coat of 1:4 to the complete surface, and smooth off with a damped sponge whilst still soft. good luck

 

[JerryM]

csrt's idea is also good - i think u might even get away with nailing the chicken wire depending on how good the brick mortar is (something like clout nails).

 

[Londoner]

thanks for the tips. It does look like someone in the past did a patchup job around a PVC fame and just didn't get the mortar mix right in that spot.

I would prefer to knock it all out and refill but what exactly do I need to make the mortar mix (and what are the exact ratios etc.)?

Seeing as this is a fairly small area, is there some kind of exterior filler I can use that would save me buying a massive bag of cement?

Thanks.

 

[roy c]

If you are going to sratch coat and float then the correct ratios are 4 to1 scratch coat with water proofer in. Then 5. 1. 1. (sand cement lime) for the float coat. As you put each coat on it should get weaker ,not stronger....

 

[andyrich7496]

I agree with jerry, a possible alternative to knocking it all off is to attach chicken wire to the complete surface with sheridized srews and small washers then apply 1 x render coat of 1:5 cement mortar to the whole surface a provide a key to this coat whilst still soft, then apply a final render coat of 1:4 to the complete surface, and smooth off with a damped sponge whilst still soft. good luck

do not go soft to hard ie you can go to 4;1 and 5;1

 

[Londoner]

Just went to B&Q and seen they do a small bag of ready mixed mortar for small jobs - literally just add water. I think I'll give that ago.

Thanks for the smoothing off with a sponge tip.