Headache of porcelain jointing systems

[Master of None]

Hi all,

Having done some pretty extensive research of late I seem to have concluded that utopia does not exist in the world of porcelain jointing and it is proving to be a real headache.

My findings to date summarised simply as follows;

1 part 'brush-in' resin systems - appealing price but not suitable for anything laid onto a concrete slab due to poor drainage (applies to me!). Compound breaks down once submerged in water for any prolonged period. When laid on free draining substrate, product works well but not suited to pressure washing or heavier duty cleaning methods.

2 part 'brush-in' slurry systems - a little on the pricier side but provides a strong robust finish and can be jet washed. Plenty of concerns in respect of a surface sheen being left behind on the slabs, but can be applied in damper weather conditions.

Grout - Again appealing price but messy application with staining a real issue (more so with greys / blacks). Very time consuming when faced with larger areas. Very much weather dependant requiring dry joints.

My personal application will be to 60m2 so iIm currently favouring a 2 part resin product rather than grout. I do however have real concerns over the resin residues left behind. I have been told it almost acts as an 'enhancer' but not sure I'm convinced, especially given the coarse texture of an R11 porcelain slab. Would be really keen to hear of peoples experiences with this type of product on porcelain specifically if possible?

Cheers

[Tony McC]

We are beginning to hear more and more from the manufacturers and suppliers of the one-part "brush-on" or polymeric jointing compunds about this concept they are refering to as "permanent immersion", which is a pseudo-sciencey way of saying that, becaus eof a mortar bed, the jointing is acting as a 'reservoir' for moisture and this brings about even faster degradation of the binder component. Some of us have known about this for years but for too long it was denied and disputed, but it seems to be increasingly accepted.

The same applies to two-part slury mortars but because they are so much tougher and more resilient, they are not affected anywhjere near as badly and many of the better one will happily sit in damp joints for years without a problem, but that's not to say it's not a problem. It's less than ideal, but not catastrophic.

The workaround is to ensure there is some egress for moisture within the joints, which, with the narrow 5mm joints typically used with porcelain, is not easy to achieve unless built in to the paving as it is laid. This is best achieved by 'raking out' at least half the length of each joint using the blade of a trowel to remove the mortar bedding beneath right down to the sub-base. It is *not* easy to create an effective 'gap' between adjacent paving units right through the mortar bed - it falls in on itself, and it blocks again in next to no time. It probably a good idea to refill any such gap created with a gritty sand and then get the pavement jointed as soon as possible to minimise the risk of accidental blockage.

With wide joints, it's possible to drill drainage holes, say 6-8mm diameter at 150mm centres once the mortar has cured and immediately prior to jointing so that there is no risk of accidental blockage and the holes so drilled are filled with the jointing compound more or less immediately.

So - 1-part compounds really do need drainage provision, while (good quality) 2-part compounds *can* cope without drainage provision, but it's better if it's provided.

As for the "residue" issue, when a good quality 2-part resin compound is *properly* applied to good quality porcelain, there should be very, very little, if any residue, and any that does survive the wash-off procedure should weather away in a week or so. Every instance of excess residue I've looked at has come down to either cheap, lower quality products and/or improper application. "Did you read the application instructions?" "Errr....yeah! 'course I did!" "So where *are* the instructions?" "Err...are they on the bucket? In a leaflet? Online? I can't quite remember!" .....maybe because they were never actually looked at???


Moving on to cementitious grouts - the best of these are practically impervious once cured. For the pedants, there is some absorption/permeability but is is estimated at less than 2%. Accordingly, when a good quality cement-based grout is sued correctly, virtually all surface water will have to run off....so adequate drainage must be provided elsewhere via, say, gullies, linear channels, properly constructed splash strips.

The biggest problem with such grouts comes when someone has bought a 'bargain' product, usually via an onliine source, and it turns out to be semi-permeable due to poor quality cement. This allows the grout to behave in a way similar to the 1-part resin compounds discussed abocve, and act as a reservoir for moisture.

The lesson to take from this is to look for a branded, quality *exterior grade* cement grout if you want fewer problems and minimal risk of failure.