Cracks On New Render

[tandh]

i'm in the process of having my houser rendered with sand and cement. He did the scratch coat on the front of the house on monday. then the side and back on tuesday. He did the top coat for the front of the house on wednesday and on wednesday evening i noticed a couple of hair line cracks. He did the top coat for the side of the house today which looks fine, but a lot more cracks have appeared on the front of the house. Should i be worried about this, and is this common? other than the cracks he has done a really good, smooth job but i think it's his last day tomorrow, and i'm worried that the cracks could get worse after he goes.

[Davemano]

If this is your property bring your concern to the attention of the builder and discuss with him as you have described above. I would advise no payment until you are totally satisfied. If the property is not yours, tell the owner of your concern. Someone on AB will no doubt advise the relevance of any cracking.

[Canary42]

Totally unacceptable in my view - water in the cracks will freeze in icy conditions and this will lead to further damage.

P.S. This is only my personal opinion, I'm not an expert, perhaps Builder will be along later.

[KARL]

All Portland cement mixes, (concrete, mortar/render, etc.) are liable to hairline cracking to a varying degree, particularly if they are allowed to dry out too quickly. Contrary to popular belief, including among lots of people in the construction industry, these mixes need to be kept wet for days to cure correctly. Once the mix has fully set (typically 2-5 hours) then application of fine moisture can and should begin. The higher the cement content, the greater the importance of maintaining the moisture level. What you can do to minimise/halt the cracking is to spray the render using a garden hose - do so several times a day for say a week.

[The Builder]

Good post from Karl.

Nothing structural. It's simply shrinkage. I guess the masonry was very dry at the time. Soaking it first would have helped. However, the main cause of this is almost always from using too strong a mix. The "old school" still use mixes of around 3:1. Mixes of 7:1 incorporating a resin plasticiser are much softer, and thus less likely to crack. The resins replace the cement to create a mix that is perfectly strong enough to be durable.

Another possibility is that a very fine "fatty" sand was used. Too much "fines" results in cracking. Coarse sand is much better.

Cement renders are extremely hard. Over such an area, they can't help but crack.

Best of all would be a lime render, but it's too late to think of that now. Cracking may well continue a little. It's a pain, but there's nothing to be done but to let them develop, and deal with them at the painting stage.

Wide cracks can be filled with flexible decorator's caulk from a frame gun. Hairline cracks would be too thin. Fine sand mixed with the masonry paint should obliterate the cracks.

[tandh]

thank you so much for your answers. I had a word with him about it and he went over the cracks which I then sprayed with water for a week. It's been a few weeks since I've painted it and only a few hair line cracks have appeared which I can live with.