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Posted: Mon Jul 10, 2017 1:53 pm
by milleniumaire
Our plan has always been to use vdw 815 plus to joint a new Indian sandstone patio, which is 142m2 over 3 levels. Each slab is 900 x 600 and 22mm thick. The estimated amount of 815 for this area was 7 x 10gk buckets. We have applied 1 bucket to a test area, but it only covered half the expected area, so we are potentially looking at 14 buckets, which is MUCH too expensive!
I think one of the reasons so much product is being used is due to the way in which the slabs have been laid. They are supposed to be on a full bed of mortar, however, we can see from one of the edges there appear to be 3 lines of mortar with gaps between them. This suggests the mortar has been put down as ridges, then the slabs pressed onto them. Clearly, if not enough mortar is put down, it will not spread flat, but will leave troughs and I suspect the vdw 815 is running under the flag and filling these troughs/furrows.
As the gaps between the slabs are 4mm we don't have much choice about using an epoxy resin, so to minimise wastage I was thinking of identifying where the furrows were (using a trowel) and filling them with a dry sand/cement mix, but avoiding any of this mix filling the gap between the slabs.
I would appreciate any comments on my proposed method or any other suggestions.
Posted: Tue Jul 11, 2017 12:59 am
by lutonlagerlout
it wil be time consuming but worth it long term ,as long as you have at least 22x4 mm of resin you should be ok
not happy that the flags are not laid on a full bed!
LLL
Posted: Tue Jul 11, 2017 11:07 am
by milleniumaire
Thanks LLL.
Just wondering what type of sand should be used for this. I was thinking of mixing kiln dried sand with some cement. I suspect builders sand will be too "thick" and it usually feels moist.
What quantity of kiln dried sand and cement would give the required result?
Are there products out there that come pre-mixed in bags and that could be used in 4mm gaps? Obviously price over ease of use will probably a factor.
Posted: Tue Jul 11, 2017 6:20 pm
by lutonlagerlout
tbh I wouldnt waste any money on 815 if they are not laid on a full bed
see this all the time,problems down the line
LLL
Posted: Tue Jul 11, 2017 9:59 pm
by milleniumaire
How else can I fill a 4mm gap on 142 m2 of patio?
I don't think I have a choice!
What kind of problems can occur down the line?
Posted: Wed Jul 12, 2017 12:17 pm
by milleniumaire
Unfortunately, the laying of the patio has not been a smooth process. It was originally put down on a full bed, but it became apparent that most, if not all the slabs were loose. The mix used was very gritty and so wasn't sticking to the underside of the smooth Indian sandstone. At this point, the options were:
- Leave it as it is and hope the jointing compound would hold them in place
- Remove the slabs and stick them back down using a SBR/cement slurry
- Relay the slabs on a new bed of mortar (on top of the old bed) - using a building sand and cement mix, rather than the gritty sand that had originally been used
The tradesman decided on the last option.
It is now clear they didn't use a full bed on top of the old bed, but ran three lines of mortar for each 900mm length of slab. So, the patio is now sitting on this "partial bed" and the deepest gaps, between the lines of mortar are around 40mm. The plan is to fill these gaps with a kiln dried sand and cement mix, which will then hopefully give a 22mm deep gap over the whole patio.
What really annoys me about the way they have re-laid the slabs is that they were aware that an epoxy resin was going to be used as a jointing compound. So how did they think this was going to work if the slabs were laid on the equivalent of lines of dabs?
Part of the problem is that they denied that we had discussed using epoxy resin when they quoted, so didn't include this in their price. I would have loved to have seen how they would have filled a 4mm joint - probably using a dry mix. As we insisted on using epoxy resin, we are now footing the bill, so they clearly don't care how much it takes to fill the badly laid patio!
I've now let the tradesman go as I just don't trust they are capable of finishing the job to the required standard and I'm doing it myself. Not an ideal situation to be in, but I need to somehow make the best of it. 
Posted: Wed Jul 12, 2017 5:06 pm
by country boy
kiln sand and cement on 40mm voids will just crumble over time ,over such a large area i can't think of any quick fix apart from relaying, but remove all existing bedding first.
having such small joints makes it difficult to fill voids of 40mm over 142m2, on small areas when i've repointed i used a pointing gun with runny mix but with a 10mm nozzle to fill voids(i did'nt lay flags)
If you do find a way of sorting it please reveal.
Jim
Posted: Thu Jul 13, 2017 1:45 pm
by milleniumaire
Yes, I had thought about asking the tradesman to relay the flags, but that would have been the third time and I'm not convinced he would have done a better job! He is clearly lacking in skill when it comes to laying sandstone flags and both his attempts to lay them have resulted in problems.
Just to be clear, we don't want to fill the whole joint with a dry mix, only the "furrows" under the slab in the vicinity of the joints. Once done, we can put down the epoxy resin to fill the joints and hopefuly this won't disappear under the slabs.
Tried a kiln dried sand and dry cement mix (5:1) in a small area, but the problem is staining on the edge of the slab. If I pour the "powder" mix onto the edge of the slab, then tap it in with a trowel, when trying to brush away the surplus powder it seems to just sit on the slab and I can't get rid of the "dry stain" mark. I'm sure I could wash it off, but to use water so soon after putting the dry mix in the gaps would probably simply wash it away. If I leave it for a few days until the dry mix in the gaps has hardened, I'm worried that the staining will be difficult to get rid of by washing.
Currently, we are trying to put the mixture in the gaps by lining the edges with cardboard and using a handbrush dustpan to direct a thin line. This avoids getting the dry mix on the slabs but is very, very slow as you can imagine.
We need to come up with a faster method! I tried using tape on the edge of the slab and this stopped the mix discolouring the flag, but again was too time consuming.
I think part of the issue is that the surface of the indian sandstone flags has been blasted to give a rough finish (my wifes requirement, not mine) in an attempt to avoid them getting slippy. This appears to be allowing the dry mix to get into the surface of the slab and "stain" it. Of course this may happen even if the slabs were smooth, I'm not sure.
Is it likely that a sand/cement powder would stain the flag if left on the surface of a slab for a few days? I suspect it will, but don't want to take the risk.
It makes me wonder how a sand/cement mix could be brushed into gaps over a large patio without staining the surface of the slabs.
Posted: Thu Jul 13, 2017 5:39 pm
by lutonlagerlout
maybe fill the voids with something a bit cheaper
sorry I cant be of more help
if it was 1-2 m2 it would be OK
but sounds like you are digging a deeper and deeper hole here mate
LLL
Posted: Thu Jul 13, 2017 7:54 pm
by country boy
I think it would take far too long to do as you propose, plus you may end up staining the surface.can you not just bite the bullet and use 14 tubs or use cheaper resin as filler as suggested by LLL but make sure you push firmly in.If you're set on using sand and cement what about making frame with 4mm slot maybe using acrylic sheet. good luck
Posted: Fri Jul 14, 2017 7:06 pm
by milleniumaire
Hi guys, it is definitely a big, time consuming job and I guess I'm just too soft to get the trademan back to sort out his mess, although as I keep saying, I wouldn't trust him not to make even more of a mess.
Country boy, interesting idea you've had and that's pretty much what I've done. I had an old aluminium PC case, in which I ground a 3mm straight line, from one end to the other, but not quite from end to end. So it looks like a sheet of aluminium with a very narrow letter box. This actually works suprisingly well, allowing me to move it over the gaps and poor down enough dry mix to fill any voids below the bottom of the slab. I've also drawn a 22mm line on a trowel so as I tamp the stuff in, I can see how deep it is. I want to avoid putting too much dry mix in the gap as the resin needs at least 20mm. My wife is also helping, but is using a dustpan brush to guide the dry mix into the gaps. Her method is a little more messy than mine, which barely leaves any residue on the slab.
We are using an old vacuum to clean up any dry mix power than does get on the slab to avoid any potential staining.
It's a long laborious job, but we have the new garden speakers and spotify to help us through it! It looks like the weather will turn tonight so will get a rest tomorrow, but hopefully the sun will be back out on Sunday!
Regarding using more resin rather than filling the gaps, unfortunately 14 tubs would be an under estimate. At £45 per tub it would probably end up costing us more than a £1000 if we tried to just put the resin down. At least using kiln dried sand and cement it shouldn't be more than £50, but it's our time that is costing us.
We were hoping to be enjoying the patio by now, not correcting the tradesmans work.
Posted: Sat Jul 15, 2017 12:46 pm
by Tony McC
The issue is to restrict the 815 to the joints and not have it trickling into the totally unacceptable voids beneath the paving.
If the flags are stable (and that's a bloody miracle given they are, in effect, on spot bedding) then one option would be to use just KDS (no cement!) and run this into the joints. Then, use a lot of water to wash the KDS into the bedding voids. jabbing the KDS into the joints with the blade of a trowel, if necessary to completely fill all the voids AND the joints.
Now, when you are confident that no more KDS can be forced into the pavement, and while the KDS is still damp, rake out the joints to empty them of as much KDS as possible. In theory, this should leave the damp KDS within the bedding voids in place.
Rinse lightly - don't saturate the paving at this point, as we don't want to disturb the in-situ KDS - just enough to ensure the surface is wet and the 815 can then be applied.
Hopefully, the washing-in of the KDS will have saturated the paving and so provide the damp surface that 815 needs, with only minimal water added at this early stage to help the 815 into the joints. Once the joints seem filled, then as much water as you like can be used to wash-in the 815 and rinse it from the surface, as the joints are now filled and there's no escape for the KDS.
This method will work as long as the flags are definitely secure and stable the KDS is not improving the bed, nor is it improving adhesion: it's simply filling the voids, and doing so at a fraction of the cost of 815.
Let us know how you get on......
Posted: Fri Jul 28, 2017 1:16 pm
by milleniumaire
Well, it's been a few weeks since we started filling the joints and we aren't done yet! Unfortunately the weather is against us as obviously the paving must be stone dry to brush in the sand/cement mix. However, we have put some epoxy resin into the joints in the areas we have completed and it appears to have been a success. Rather than simply disappearing under the slab, the resin has been prevented from doing so by the hardened dry mix, so the resin is now covering the expected area.
By the time we have finished we will probably have used about 3 more 10kg tubs than was originally estimated due to the early issues, so the cost will have been an extra £150. Of course there's then the cost of the kiln dried sand and cement, which isn't too bad and the big cost is that of our time and the frustration of having to finish off a poorly done job.