Errr Thermo, You There ??

[skybluescooby]

Hi,
I sought much indepth advice recently from various sites/people and found various methods and procedures for laying patio slabs, I adopted a few ideas and begun in earnest.
Everything went fine during prep, fine during laying and fine during pointing.
One week later and my grouting has failed.
I put a 3-1 sharp/cement mix in to the gaps and pointed with a suitable tool to leave the grout compact and smooth. Few days later and the grout has dried to a horrible battleship grey colour and has come out in various places ?
I have removed some of the loose stuff and brushed sand into the gaps but in other places i couldn't budge the set stuff so brushed sand over the top which has now blown/washed away leaving the ugly grey ?????
What can i do now to hide then ugly and eye catching grey grout ??

 

[Thermo]

here i am!

lets go back to basics, what sort of slabs are they and how have you laid them?

How exactly have you pointed them up and what was the weather like when you did it and the evning afterwards?

 

[skybluescooby]

Riven slabs- 300x300, 600x600,300x450.
Laid onto compacted mot and sand, then a dry mix of sand/cement laid, slabs randomly laid on top, left for day then pointed next day with a 3-1 mix which was mixed in a bucket then applied slowly to the gaps and pushed down with a bucket tool thing ?
Weather was fine, 3 weeks ago, dry with 13-15 degrees daily and around 2-3 degrees night. No rain fell during and after project.

 

[Thermo]

got any pics?

 

[skybluescooby]

Sure, I'll do some tomorow and send in.......

 

[skybluescooby]

There we go, should be able to see the grey colour, the cracked area and the last one shows a combination of the two. Grey does not look too bad but on a 33sq mtr patio its almost flourescent ?

 

[Thermo]

first of all remove all the old stuff theres no way you will cover it. A plugging chisel will help you to do this fairly easily.

i suspect that the pointing has worked loose in some areas for one of a number of reasons:-

wobbly slabs. It only needs them to move a tiny amount for it to break up the pointing. thats why i prefer to wet lay them, they dont move after that.

The cement may have hydrated whilst you were using it on a reasonably mild day and then dried out. basically you made the mix and the cement became damp so the chemical reaction started. You merrily did the pointing, but as the mix dried out, especially what was on the slabs, the cement will dry out to quickly and become dead. It also looks like you have way more than 1:3 mix from the colour of the pointing. Also a possibilty that frost may have got to it if it was 2-3 degrees which will have the same effect.

I normally use a 1:3 or a 1:4 dependent on the slabs and use building sand. Sharp sand cna be used on wide joints but it will give a very pale colour.The important part is the gauging of the materials. it keeps the mix and the colour even. Use a pot or small bucket to measure the mix out excatly and dont loose count. Dont mix up more than you can use in about 1/2 an hour. You can put a cement dye into teh mix and again if you do use a small pot to keep the mix spot on. it will keep the look of the pointing consitent. Make sure it is damp enough to squeeze into a ball without leaving any material on your hand. Wet the edges of the slabs if its a hot day and allow the tops to dry out to avoid staining.

Dont bother with brushing it into the joints theres only one way to do it. Get a radio turn it on, sit on your arse with a pointing trowel and work it into the joints with that. Your looking to get it well prssed into the joints to make it strong. Strike the joints of with a bucket handle tool after. Do a small area at a time to get the hang of it. As you go along you will leave some of the mix on the slabs. unless you get it into the joints staight away, leave it there. you can briskly brush it off at the end as it will dry out as per above. It wont mark the slabs if youve got the dampness of the mix right. If its a very warm day when you do it, after you have brushed the excess of use a hose pipe with a very fine mist on it to wet the slabs and the pointing. That will stop it going off too quickly and will help to strengthen it.

Remeber any pointing will very quickly weather in and tone down in time.

Hope that makes sense

[/img]

riven slabs similar to yours with wider joints than the first picture. I only laid the small section below the pond to match in with the existing, but you can see the building sand gives a less grey colour, on 1:4 mix.

 

[skybluescooby]

many many thanks for your advice, i shall get to grips straight away....ps
If there is a slight wobble from any slab will it crack away again ?
Wish i had done the wet mix now but hindsight is a great thing, had severe time restrictions and budget to work to. bugger

 

[Thermo]

yes it will. take it up and rebed it. Best way to check is to stand with your feet on the opposite corners.

 

[skybluescooby]

Should have called in the pro's but i will not be beaten.
Have now decided to lift slabs , remove couple of mm of top bed and re lay with a wet mix.

What's the best mix/sand/cement to use and i presume its full coverage as in floor tiles and not dot n dabbing ??