FourInchesWide
Member
I did 2 small walls in sand/cement [about 4:1 mix] for family (brother). Now I didn't mix, he got his lad to, but he's mixed before and it's not exactly brain surgery.
It was a cold, windy February day but nowhere near icy and I'm pretty sure I skimmed the backing coat next day
A few weeks later he tells me the walls have a few cracks in them and the skimming has 'blown' away from the wall. When I looked, you can get your fingernail behind the finish and pull it off in quite big pieces (3, 4, 6 inch pieces). On the wall by the front door, it was all blown off the wall in one complete sheet. When I looked yesterday there's like a 7mm gap between finish and backing.
Around the same time I did a job for his other son of 2 sand/cement walls in a bathroom, again, this householder mixed. The brickwork was bad anyway so iirc, I asked him for a weaker mix which may have been 4, 4&half or 5 to one with waterproofer to kill the suction as there was delay between when I could access them again. [I would have dot & dabbed them but 'he thought' the S/C may add strength to the wall]
These walls both cracked looking like 'crazy paving'. I scrimmed the cracks and skimmed walls. 3 or so months later I'm patching up the inevitable bits when I notice a bit of the window wall skimming has blown off. I pull the loose off and patch it. As I'm trowelling it up neighbouring areas start to come away and the same happens to other areas next to the holes I'm patching. Before long, it's like 60% of the wall has blown off.
After a bit of head scratching, I told him it must be temperature based and his walls must have froze the night I skimmed them. Freezing water = expansion = it has pushed itself off the backing coat. [I'm not convinced with this myself but I'm grasping for an answer]
But seeing that the second job yesterday has also gone the same way, I'm looking for the common denominator and it could be the sand. I recall the sand (red builders in 1 ton sacks) was brought from 1st job to 2nd. Now he had walls built around his property and the mortar shows salt effervescence on the joint and, iirc, on the brick.
When I look at the back of the blown skimming, it's like a cast of the backing coat along with rough texture and the nail lines from the float. They key was there, the adhesion wasn't.
I don't think the 'febmix' was the same in either case and beyond that I'm stumped. The common denominator to both jobs was me and the sand used. I've had walls crack before (mostly due to suction issues) but not this blows off completely.
Any ideas out there?
It was a cold, windy February day but nowhere near icy and I'm pretty sure I skimmed the backing coat next day
A few weeks later he tells me the walls have a few cracks in them and the skimming has 'blown' away from the wall. When I looked, you can get your fingernail behind the finish and pull it off in quite big pieces (3, 4, 6 inch pieces). On the wall by the front door, it was all blown off the wall in one complete sheet. When I looked yesterday there's like a 7mm gap between finish and backing.
Around the same time I did a job for his other son of 2 sand/cement walls in a bathroom, again, this householder mixed. The brickwork was bad anyway so iirc, I asked him for a weaker mix which may have been 4, 4&half or 5 to one with waterproofer to kill the suction as there was delay between when I could access them again. [I would have dot & dabbed them but 'he thought' the S/C may add strength to the wall]
These walls both cracked looking like 'crazy paving'. I scrimmed the cracks and skimmed walls. 3 or so months later I'm patching up the inevitable bits when I notice a bit of the window wall skimming has blown off. I pull the loose off and patch it. As I'm trowelling it up neighbouring areas start to come away and the same happens to other areas next to the holes I'm patching. Before long, it's like 60% of the wall has blown off.
After a bit of head scratching, I told him it must be temperature based and his walls must have froze the night I skimmed them. Freezing water = expansion = it has pushed itself off the backing coat. [I'm not convinced with this myself but I'm grasping for an answer]
But seeing that the second job yesterday has also gone the same way, I'm looking for the common denominator and it could be the sand. I recall the sand (red builders in 1 ton sacks) was brought from 1st job to 2nd. Now he had walls built around his property and the mortar shows salt effervescence on the joint and, iirc, on the brick.
When I look at the back of the blown skimming, it's like a cast of the backing coat along with rough texture and the nail lines from the float. They key was there, the adhesion wasn't.
I don't think the 'febmix' was the same in either case and beyond that I'm stumped. The common denominator to both jobs was me and the sand used. I've had walls crack before (mostly due to suction issues) but not this blows off completely.
Any ideas out there?