Cracked pointing

[bodgeitandscarper]

I've pointed my patio with 2 grit sand 2 builders and 1 cement with 8ml of sbr which works out at 200ml per 25kg cement. Some of the pointing has a hairline crack around one edge of some slabs! Any ideas how I can sort this out.

I've just repointed one long straight run but ive just looked and its starting to crack. When i laid mot and wackered it, it pissed it down for days but it was still hard so laid patio, would this cause it? Any help appreciated.

100mm mot , 40mm grit mortar.

[bodgeitandscarper]

Mortar pointing also seems wet longer than paving!

[Tony McC]

If it's a hairline crack it's probably due to shrinkage, and that could well be down to the soft sand compondent. Soft/Builders' sand has a relatively high proportion of clay which can expand when initially wetted and then shrink when it dries, resulting in the aforesaid hairline cracks.

The other major cause of hairline cracking is letting the mortar dry out too quickly so that it dries rather than cures.

Here's a couple of things to try:

1 - a mix with NO soft sand

2 - cover the freshly pointed joints with hessian or sacking and mist them to keep in the damp for the first 24, preferably 48, hours.

It'd be interesting to hear how you get on.....

[bodgeitandscarper]

Thanks Tony, I thought I'd prevented pointing from drying out using the misting method. I'll redo a small area without the builders sand.

[lutonlagerlout]

^^ what Tony said
dangerpoint is so fickle
LLL