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Posted: Sat Jan 23, 2010 7:06 pm
by Richey
I have recently been called back to a paving job I completed in September because the client has noticed - (since our freakishly cold weather) that the pointing is starting to flake off (about the first 2 mm).
I laid 45m2 of indian sandstone and pointed it up with a 4:1 softsand:cement mix. Only around 8m2 of pointing is affected and after asking the client a few questions they revealed that they cleared the snow away on this section using table salt. So to cut a long story short...
Does Table salt cause errosion on reletively new pointing?
Cheers
Richey
Posted: Sun Jan 24, 2010 8:15 am
by cookiewales
Richey wrote:I have recently been called back to a paving job I completed in September because the client has noticed - (since our freakishly cold weather) that the pointing is starting to flake off (about the first 2 mm).
I laid 45m2 of indian sandstone and pointed it up with a 4:1 softsand:cement mix. Only around 8m2 of pointing is affected and after asking the client a few questions they revealed that they cleared the snow away on this section using table salt. So to cut a long story short...
Does Table salt cause errosion on reletively new pointing?
Cheers
Richey
rich you should not use soft sand for pointing its only for bricklaying a sharp sand ie washed. a fine washed plastering sand is also good 4 -1 plus sbr salt should not harm pointing :;):
Posted: Sun Jan 24, 2010 5:21 pm
by Richey
Thanks for the reply.
Far be it for me to disagree with anyone on this site but I was taught at college to use builders sand only - and to only ever use sharp if the client has requested it to match any previous pointing done in sharp. Even Tony's page on pointing and mortars states that you do pointing in soft.
Also doesn't plastering sand have a higher iron content that can discolour the flags???
I agree that salt should not affect the pointing but I'm very confused as to why only the areas where salt was put down the pointing has erroded slightly.
Cheers
Richey
Posted: Sun Jan 24, 2010 6:29 pm
by cookiewales
Richey wrote:Thanks for the reply.
Far be it for me to disagree with anyone on this site but I was taught at college to use builders sand only - and to only ever use sharp if the client has requested it to match any previous pointing done in sharp. Even Tony's page on pointing and mortars states that you do pointing in soft.
Also doesn't plastering sand have a higher iron content that can discolour the flags???
I agree that salt should not affect the pointing but I'm very confused as to why only the areas where salt was put down the pointing has erroded slightly.
Cheers
Richey
plastering sand that is washed for rendering is graded and sifted to smaller grains i have in the past when have a very course sand added 1 part building sand but very rare just to get some fat in the pointing to make life easygoing.have not seen the page that says use soft sand ??? ps there should be no iron in sand
Edited By cookiewales on 1264357839
Posted: Sun Jan 24, 2010 6:51 pm
by mickg
just my observations and experiences over the years but I personally have not seen frost heave for 20 years plus as our winters are normally very mild now compared to what they was like in the good old days
I installed new concrete edging across the width of a driveway 3 weeks before Christmas which was a good 2 weeks before the frost came which I pointed up using grit sand and cement 4 : 1 wet'ish mix, the following day it was rock hard
since this very bad cold spell its blown the top 2 - 3 mm off and turned one small area to mush so maybe you have done nothing wrong and it may not be caused by anything else other than its been the worse winter for over 20 years and its frost heave due to the pointing being wet or damp and the frost has got into it and took the top surface away
it could be that the area of the patio what has had the face of the pointing blown off is a little bit more exposed than the rest of the patio or even vice versa and more sheltered so the frost affected it more than the surrounding area
well its either that or you mixed a shit mix in the first place :p :p
(only joking)
Posted: Sun Jan 24, 2010 7:27 pm
by GB_Groundworks
adding to what mickg said snow acts as an insulator
by melting the snow they would have exposed the pointing to the full effect of the frost, i.e so where the salt is = no insulation hence why it might look like the salt did it.
to be honest reading tony's page i thought soft sand but only done some flagging in last 2 years that was 150m2 and was romex'd
don't know where you are but bae system in woodford near us, cheshire recored -18 one night. when i lived in munich we regularly had -20 building sites shut down for all of winter inc the large infrastructure jobs.
i poured a 8m garage slab on friday at 2pm been back yesterday and today and its still not ready to power float, weather says 100% humidity and then it rained today as well.
Edited By GB_Groundworks on 1264361396
Posted: Sun Jan 24, 2010 8:38 pm
by Richey
Some interesting theories there guys, thanks.
I know you were only joking about a dodgy mix, but as I said only the salted area is blown. The other 37m2 area is solid.
Here's something else interesting...Rising Salt Damp.
I found an article that states that absorbant materials such as bricks, mortar, timber etc.. can flake, crumble and decay. To sum up:
...whenever there are moisture absorbant materials in contact with the ground then the moisture will naturally rise through them (unless there is a dpc) This moisture brings with it liquid salt particles which can cause major damage. Upon exposure to changing temperature conditions the liquid salt particles crystallise and expand, and this micro explosion starts to create damage to the structure...
If this is all true then is it possible that salt poured on top will effect bricks or mortar in the same way?
Wow this is turning into science not landscaping.
Any more thoughts much appreciated
Cheers
Richey
Posted: Sun Jan 24, 2010 9:13 pm
by mickg
like GB says the snow gave the remaining patio ground cover where the area that was cleared was fully exposed to the harsh frost which I would put my pound on the cause of this problem
do a simple test, put a pencil mark where the damaged pointing ends on one of the flags and sprinkle some of the same salt on the pointing just past the pencil mark (only a few inches) and see what happens because if you theory is right over night the damaged area will go bigger and you will see some of the pointing flaking off
I still bet its the frost whats has caused it
Posted: Mon Jan 25, 2010 12:11 am
by lutonlagerlout
i was always taught using a 3:1 soft sand mix,
grit sand looks dog rough in pointing .
richey is darn sarf and we have had some extreme weather,I have clocked walls that i built years ago looking a bit flaky
I would say its down to the weather
did you cover it with Hessian?
LLL
Edited By lutonlagerlout on 1264378327
Posted: Mon Jan 25, 2010 11:05 am
by Richey
I didn't cover it because the job was finished 3 months ago, long before the harsh weather. Just out of interest LLL, do you add plasterciser or any other admixture to your pointing mortar?
Cheers
Richey
Posted: Mon Jan 25, 2010 12:27 pm
by lutonlagerlout
no, never richie
just straight 3:1 sometimes use plastering sand building sand mix, have tried the sharp sands but they dont trowel up nice
FWIW used easipoint recently and it is cracking stuff,goes off rock hard by the next day and looks the business
LLL
Posted: Mon Jan 25, 2010 3:50 pm
by DNgroundworks
Why no plasticiser LLL?
Posted: Mon Jan 25, 2010 7:42 pm
by ilovesettsonmondays
easi point is cracking stuff for pointing.expensive .too expensive for a private job .but a must for street paving in city centres especially ones that jet wash the pavements everyday.how much is it lll about 20 a bag
Posted: Mon Jan 25, 2010 8:12 pm
by lutonlagerlout
Dan, you dont need plasticiser for pointing,the gear is almost crumbly,just damp enough to point up
setts,yeah it varies from colour to colour but you have to allow £25 to cover postage etc
I like the fact that the colour is inherent and consistent, average patio is about £100 ,bargain IMHO
LLL 
Posted: Tue Jan 26, 2010 11:52 am
by Tony McC
Do we know how much salt was applied to affected area?
I'm not sure about the exact reaction involved but I do know from a job on the Atlantic coast of Co. Kerry that salt-resistant mortars were specified to cope with the regular inundation with salt-air/spray, and so I wonder if a heavy does of salt could have affected the damp mortar which then froze again once the insulating snow was removed and the temperatures plunged low enough to freeze even salted water. That could, in theory, blow the top 2-3mm of a relatively new mortar.