Slushy cement pointing - What happened to our pointing?

[yerteasgettingcold]

Hi. We bought a house with an 18 year old, very worn, local Derbyshire gritstone patio. About 50 feet by 30 feet and made of rectangular stones ranging from 6" square to 2' by 1'. The joints vary in size because of the irregular stones from 1mm to 10mm. When we moved in the pointing was in poor shape and, given the size of the patio, we felt we should try to repoint it ourselves. Last summer we got advice for a mix (5:1) and set about the work during fine, but not scorching, weather. The cement was mixed by the bucketload and trowelled in using a pointing trowel, smoothed over and covered at night. It all looked great until this week when we had night temperatures of minus 10C. Now virtually all the cement has turned slushy, like half melted icecream, and just washes off in the rain. The stones are well attached to their substrate, which looks like concrete, so the pointing was only the depth of the stones - maybe 2cm max. What have we done wrong and what should we do this summer to rectify the problem? Many thanks for any help you can give.

[lutonlagerlout]

how wet/dry was the mix you used?
it sounds like it was too weak and too dry
no reason for the cold to affect it unless water has got into it,whcih would indicate a dryish weak mix
LLL

[yerteasgettingcold]

We are definitely not professionals so I would describe the mix as like bricklaying wetness. We did wet the stones before we pointed them. We had no idea about what strength of mix to use and took advice from a friend. Obviously not a good idea!

Would adding some frost proofer have helped? The only time we ever tried adding an additive it was a disaster and we've always kept away from them.

[TheVictorianCobbleCo]

Hi. We bought a house with an 18 year old, very worn, local Derbyshire gritstone patio. About 50 feet by 30 feet and made of rectangular stones ranging from 6" square to 2' by 1'. The joints vary in size because of the irregular stones from 1mm to 10mm. When we moved in the pointing was in poor shape and, given the size of the patio, we felt we should try to repoint it ourselves. Last summer we got advice for a mix (5:1) and set about the work during fine, but not scorching, weather. The cement was mixed by the bucketload and trowelled in using a pointing trowel, smoothed over and covered at night. It all looked great until this week when we had night temperatures of minus 10C. Now virtually all the cement has turned slushy, like half melted icecream, and just washes off in the rain. The stones are well attached to their substrate, which looks like concrete, so the pointing was only the depth of the stones - maybe 2cm max. What have we done wrong and what should we do this summer to rectify the problem? Many thanks for any help you can give.

The mixture is far too weak, if you can't redo it with something like Romex then use a wet 2:1 mixture of sharp sand and cement, (wet will flow easier into the crevices) or a 3:1 stiff mix that you force into the gaps, wet the pavers before grouting, add a plasticiser to the mix for pliability, do the job when the day is mild and temps are above 15 degrees C. for a few days. Leave to dry for about 8 hours then spray every so often with a fine spray to slow the curing down. You will still get hairline cracks and because the depth of grout is so shallow there will be the odd pieces that lift.

[yerteasgettingcold]

Thanks for all the help - we shall try again this summer with a stronger mix and a bit more water.

This is a fantastic website. Wish we'd known about it earlier - there's 125 years combined wear and tear in our knees and we could have spared them a bit of agony!

Well, if you don't at first succeed...

Thanks again.

[Carberry]

Thanks for all the help - we shall try again this summer with a stronger mix and a bit more water.

This is a fantastic website. Wish we'd known about it earlier - there's 125 years combined wear and tear in our knees and we could have spared them a bit of agony!

Well, if you don't at first succeed...

Thanks again.

You should get one of your bunnies to do it for you Hef :p

[lutonlagerlout]

? eh?
you been at the waccy stewart?
LLL :laugh:

[Carberry]

? eh?
you been at the waccy stewart?
LLL :laugh:

125 years wear and tear between them. Rather than assuming that they're both 60 odd I'm thinking he might be an 80 year old hef with 2 20 year old bunnies :laugh:

As for the original post, Frost proofer only helps if temperature is going to drop below 5 degrees.
I've not seen pointing going slushy before or like half melted ice cream before. Did you push the mortar in to the joint properly? if you left gaps water could get in, freeze, expand and burst the pointing.

[lutonlagerlout]

gotchya

far too lateral for my thought train
as per your comments ,i can only assume that the original pointing is ruined,never seen that happen either
LLL

[Carberry]

When you say mixed in a bucket was it mixed thorougly?
How did you measure out the 5:1, was it by weight or volume? was it an approximation? I could see it going slushy if there wasn't any cement in it, the sand would end up like mud when it got wet.

5:1 isn't a weak mix, and I think 2:1 is too strong. I normally work with 4 or 5:1 for pointing.

[yerteasgettingcold]

The mortar was mixed as accurately as possible by volume, no streaks or lumps left in it. Pushed in well and smoothed off with love and care.

Here in deepest Derbyshire the night time, winter temperatures can easily drop to minus 15 do maybe a frostproofer would be a good idea next time.

Sadly, I'm not 20 and my husband isn't Hugh Heffner. If he was I wouldn't be spending my hard earned retirement researching the mysteries of slushy cement.

Thanks for the photo - it made us laugh.

[Carberry]

The mortar was mixed as accurately as possible by volume, no streaks or lumps left in it. Pushed in well and smoothed off with love and care.

Here in deepest Derbyshire the night time, winter temperatures can easily drop to minus 15 do maybe a frostproofer would be a good idea next time.

Sadly, I'm not 20 and my husband isn't Hugh Heffner. If he was I wouldn't be spending my hard earned retirement researching the mysteries of slushy cement.

Thanks for the photo - it made us laugh.

Frost proofer accelerates the setting time of cement. The idea is it goes solid quickly, before cold conditions can freeze the water that is necessary for the chemical reaction that causes cement to harden. It won't do anything for you in the summer.

[yerteasgettingcold]

The mortar was mixed as accurately as possible by volume, no streaks or lumps left in it. Pushed in well and smoothed off with love and care.

Here in deepest Derbyshire the night time, winter temperatures can easily drop to minus 15 do maybe a frostproofer would be a good idea next time.

Sadly, I'm not 20 and my husband isn't Hugh Heffner. If he was I wouldn't be spending my hard earned retirement researching the mysteries of slushy cement.

Thanks for the photo - it made us laugh.

Frost proofer accelerates the setting time of cement. The idea is it goes solid quickly, before cold conditions can freeze the water that is necessary for the chemical reaction that causes cement to harden. It won't do anything for you in the summer.

The slush only arrived the other day, after a sharp frost. Before that, from last June till last week, it was fine. A few hairline cracks in places, but fine. Something about the cold seems to have altered the cement's structure from hard as nails to, well, slush.

So far as we know, the cement powder and sand were OK, delivered by our village building supplier. The water was clean.

I see what you mean about frostproofer though. I imagined it would act like anti-freeze or something once the cement was cured.