Pointing turned white, but not efflorescence! - Pointing turned white, but not effloresc

[ohcrumbs]

I'm pointing my garden path, paved with granite setts. My mortar mix was straightword, 1 part cement to 4 parts sand. (Nothing else but water added). Originally it dried grey, but over the past few weeks has been getting lighter and lighter and is now virtually white.

Does anybody know why this is happening? Or what I can do about it? (The granite setts have remained just fine).

Many thanks!

[Carberry]

Concrete / mortar lightens over time, especially with exposure to sunlight.

[Brucieboy]

Carberry is correct, mortar does lighten in colour with age. However, another probable cause is efflorescence or lime bloom. Cement contains a small proportion of "free" lime which is soluble in water. During wet, cold weather, this migrates to the surface forming a white deposit. It carbonates (with carbon doixide from the atmosphere) over time and becomes quite hard - it extends usually no more than about one mm in depth. To check if it is lime bloom, break off a small piece of mortar in a place that's not noticeable and you'll generally find the normal grey colour beneath.

It's best left to disappear on its own - this may take months or even a couple of years. It's quite a common occurrence. You could use a dilute hydrochloric acid solution to try and remove it but personally I'd leave well alone as this may affect the quality of the mortar at the surface - the acid will dissolve some of the cement as well as the lime bloom if you over-egg it.

[Brucieboy]

ps - I've just read the full title of your post stating it's not efflorescence. If it's not, I'd be very surprised. As a supplier of mortar, we regularly receive complaints around this time of the year stating that "the mortar you supplied a few weeks/months ago has turned white". The problem is worse with cement only mixes and very dense units - particularly engineering bricks if it's masonry. It's very difficult to control. Believe it or not, mortar containing hydrated lime as well as cement is less prone to lime bloom because the lime, being a very fine powder, acts as a pore blocker minimising the passage of water, hence soluble salts.

[ohcrumbs]

Brucieboy, Many thanks for that. I'm sure you're right.

Can I ask for your advice? The mortar that we've laid down is really just a test area. We have a lot of pointing still to do on our dark/grey granite & basalt sett path. Even without the efflorescence "problem" our challenge is to get a mortar mix that is quite dark to "blend in" with the colour of the stone. Our plan is to dye the mortar darker with (I think it's called) cement dye. I'd like to know if you think that is a good idea.

Secondly, if we DO dye the mortar, I suppose we'll experience efflorescence too. We can add hydrated lime, but is there any other way of avoiding or minimising it? Does the wetness of the mix make any difference? Would you recommend waiting until warmer & drier weather? (We're not in any particular hurry as it's just the back garden).

Cheers

[haggistini]

Bruceyboy is our resident expert in mortar. This is a proven technique with granite setts...If this is only a test area then I would go with brushing Eco chem acid as it's gentle enough to tone down the pointing without affecting the strenth. Do a small area at a time and don't leave it there for longer than 10 mins and rinse with plenty of water ...use goggles and gloves it's acid!

[haggistini]

P.s. batch your mortar so you keep the same colour and strenth

[Pablo]

if it's setts are you hand or slurry pointing. If you're slurry pointing then you can sometimes get a white semi cured sediment forming over the settled pointing. This is caused when you don't fully remove the crap as you're brushing it over a settled area. A light pressure wash removes it and the pointing underneath should look fine but leave it a few days to harden first.

[Brucieboy]

Hi - as you're still fortunate enough to do some trials, it's worth considering both methods suggested by haggistini (removal by acid) and pablo (slurry technique). If using acid, follow the pre-wetting and safety guidlines given. Cover your arms as well. If you do get any on you, wash it off quickly with clean water - it stings a lot and will burn the skin if left.

To achieve the dark colour, you can add a powdered black pigment (normally a synthetic iron oxide). The dosage varies between 5 and 10% by weight of cement. The higher the %, the darker the colour but do not exceed 10%. "Cementone" is a popular make. It's about £6-9 per kg depending on what size tin/package you buy - shop around to find the best deal. To mimimsie lime bloom, Cementone recommend using an integral (mixed in with the other materials) liquid waterproofer. It's effectively a pore blocker/water repellent, which I mentioned before but not lime based. It minimises the passage of water (and soluble salts) through the mix. It's worth a try if you're at the trial stage.

Always add the pigment to the cement first and mix thoroughly, then add this to the damp sand and mix again before adding water and waterproofer. As suggested by haggistini, measure all materials accurately and consistently otherwise you'll get a patchwork quilt. Make sure the joints are fully filled and the mortar well compacted - voids will result in standing water - not good!! With regard to timescale, I'd personally leave the pointing until the weather's a little bit warmer. Do not do it when rain is forecast. Lime bloom is worse in wet/damp conditions. However, even when done to the book you still can't guarantee you'll eliminate it completely.

Another alternative is the pre-packaged mortars such Easipoint although these tend be much more expensive than mixing it yourself. I personlly haven't used them but I'm sure other guys on this site will give comment and advice.

[London Stone Paving]

In my experience dyes are very hit and miss. They usuallly dry a lot lighter than is desired. Easipoint is expensive but does the job

[Carberry]

In my experience dyes are very hit and miss. They usuallly dry a lot lighter than is desired. Easipoint is expensive but does the job

Then a year later disappear, the dye that is.

Much easier to get a consistent colour with easipoint too.

[lutonlagerlout]

I have never seen mortar dye hold its colour
we had red sand from cemex last year that was a mix of sand lime and a red pigment but it was expensive and had to be ordered in special
£100 a tonne i believe
LLL

[haggistini]

Ouch that's steep LLL but it has been mixed bus machine I suppose

[haggistini]

Our silo mix is about £67 and that's sand and cement I bet the money's in the pigment!

[lutonlagerlout]

a silo would have been cheaper,this was in bulk bags
but the road was too narrow so we had to have bags HIABed over the wall
very lumpy as well,not nice to work with
LLL