Hairline cracks in render

B

basset

Active Member
Need some advice from you guys on a sand and cement rendering job I did back in September.

All Old render was removed. Rendagrip applied. Then a scratch coat at 5-1 with waterproofer then once dry a top coat of 6-1 with febmix.

It has been painted with sandtex once dried.

Had a call saying there are hairline cracks over some of the walls which I've attached a picture off.
The other walls are fine the only difference is the sand used. The walls that are cracked was with sand from a different merchants as the others couldn't deliver in time.
I thought I had controlled the suction enough but Is this a sign I didn't? Or could it be the sand?
Weather was dry and fairly warm but kept misting to stop it drying to quick.

Any ideas on a fix? Would bedec masonry paint solve this or does it need to come off?
Never had any issues in the past with rendering and has royally pissed me off and had enough of the stuff.
34042
 
basset said:
Need some advice from you guys on a sand and cement rendering job I did back in September.

All Old render was removed. Rendagrip applied. Then a scratch coat at 5-1 with waterproofer then once dry a top coat of 6-1 with febmix.

It has been painted with sandtex once dried.

Had a call saying there are hairline cracks over some of the walls which I've attached a picture off.
The other walls are fine the only difference is the sand used. The walls that are cracked was with sand from a different merchants as the others couldn't deliver in time.
I thought I had controlled the suction enough but Is this a sign I didn't? Or could it be the sand?
Weather was dry and fairly warm but kept misting to stop it drying to quick.

Any ideas on a fix? Would bedec masonry paint solve this or does it need to come off?
Never had any issues in the past with rendering and has royally pissed me off and had enough of the stuff.View attachment 34042
Click to expand...
South facing ?
 
could be umpteen reasons. as john says south facing, baked in the sun.
poor quality sand , sand to soft from our builders merchants. we pick up sand from local quarry that is known for quality render sand.
you have made no mention of lime.
Bdec paint will hide cracks if not filled.
 
malc said:
could be umpteen reasons. as john says south facing, baked in the sun.
poor quality sand , sand to soft from our builders merchants. we pick up sand from local quarry that is known for quality render sand.
you have made no mention of lime.
Bdec paint will hide cracks if not filled.
Click to expand...
You've stolen my get out line malc , no lime , good quality sharp (y)
 
Feel for you mate tbh I can’t give any advice but will see what the older guys say ,
Swapping to pre bagged has been best thing I ever did but Weber ocr I always still got hairlines so bombed it off completely now
 
basset said:
Need some advice from you guys on a sand and cement rendering job I did back in September.

All Old render was removed. Rendagrip applied. Then a scratch coat at 5-1 with waterproofer then once dry a top coat of 6-1 with febmix.

It has been painted with sandtex once dried.

Had a call saying there are hairline cracks over some of the walls which I've attached a picture off.
The other walls are fine the only difference is the sand used. The walls that are cracked was with sand from a different merchants as the others couldn't deliver in time.
I thought I had controlled the suction enough but Is this a sign I didn't? Or could it be the sand?
Weather was dry and fairly warm but kept misting to stop it drying to quick.

Any ideas on a fix? Would bedec masonry paint solve this or does it need to come off?
Never had any issues in the past with rendering and has royally pissed me off and had enough of the stuff.View attachment 34042
Click to expand...
What sand was used?
No lime in topcoat???
 
Cheers for all the replies!
There was a shovel of lime in the top coat and the wall is a South Westerly I did keep misting it through out the day and the following day!
The exact same mix on the other wall is fine apart from the sand which was still plastering sand but from a different merchants.
 
basset said:
Cheers for all the replies!
There was a shovel of lime in the top coat and the wall is a South Westerly I did keep misting it through out the day and the following day!
The exact same mix on the other wall is fine apart from the sand which was still plastering sand but from a different merchants.
Click to expand...

Could be the sand. Had the scratch coat fully cured for a few days? Did you rub up and leave, rub up and sponge or rub up and smooth off with a steel trowel?
 
Yeah scratch was left for around 5 days.
Floated up then used a sponge.
Pulling the last of my hair out over this. Theres no blown areas so thinking about this bedec paint on one section to see if it works and go from there.
 
Lime and Feb aren’t really compatible.
Was the sand heavy with clay - there’s a definite consistency to the cracks.
I’ve seen this with ‘soft washed sand’ before - too many ‘round’ grains and not enough ‘angular’ grain to resist the weak ‘rolling’ effect. I only use ‘fine sharp’ and never mix builders & sharp.
 
Trying to remember what the sand was like. It's the only thing I can put it down to as the other walls are fine and that was with the different sand. All done at the same time as well.
I'm hoping I have some left over sand in the garage that I can you and check.
 
I remember pulling some stones out if it around 10 - 15mm wide as it annoyed the hell out if me when floating up.
 
basset said:
I remember pulling some stones out if it around 10 - 15mm wide as it annoyed the hell out if me when floating up.
Click to expand...
Have heard of Feb compatible with lime, not sure what and don't think I'd bother , apart from that sounds good to me ( bit more lime maybe )and suspect the sand , two queries ,
On blocks? and
Mention of ghosting from overfeb in brickies muck the other day (but same result I suspect from hollow muck by over mixing )even with waterproofing in first coat after a period of winter and the sun popping its head out again ( silly idea maybe but contributing stresses ) .
Its been alright till now which is the puzzle as it went on in September
 
Have re read and seen old render removed , why, how old? Probably can disregard my last post apart from more lime ( which wasn't mentioned ). Oops its late
 
And I'm not a rendaid fan (rake and wet ) just like I'm not a gritter in doors , PVA and always tacky
 
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