I want to minimise future maintenance on a new flagged patio. And so I am considering using a resin mortar instead of a traditional mortar to point the flags, which are to be laid on a mortar or concrete bedding layer. However, it has been suggested that all resin mortars are permeable, whereas traditional mortar is not, and that water permeating through the jointing will sit on the concrete, freeze, and blow the joint with the flags.
I would be grateful for any comments.
Permeable / impermeable jointing
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james-78
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lutonlagerlout
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Tony McC
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As far as I know, all of the quality resin slurry mortars are permeable to varying degrees.
Some are fully intended to be permeable and are sold as such, while others are permeable or permeable-ish but because the flow rate is below that considered optimal for permeable pavements, the manufacturers tend not to mention it too much.
Many of these products state that they should be used in conjunction with paving laid on a permeable bed. When this happens, happy days! Surface water will enter via the jointing and exit via the bedding. However, in Britain and Ireland, we tend to lay on reasonably impermeable cementititious beds, so water enters via the jointing, a tiny fraction escapes into the bed and the bulk of it sits there in the joint waiting to be absorbed via capillary action into the flags/blocks/setts or evaporated away.
The point to note is that, once the joint is filled with water, it is "saturated", and no more water can be absorbed, so any further surface water will effectively wash over the joint, searching for somewhere else to escape.
So: does this mean a pavement laid on more-or-less impermeable bedding but jointed with a resin mortar is impermeable? It's debatable but when it comes to design, I always *assume* such a pavement is impermeable and therefore requires alternative drainage measures.
Next, we have to consider this in terms of maintenance, which is the original issue raised by JonJ. Regardless of what some of the less competent PIC and Resin Agg installers may tell you, there is no such thing as a maintenance free pavement. All pavements will deteriorate if left unmaintained. Weed colonisation by algae, lichens, mosses, grasses and other plants is the most obvious example, and very often, the first part of a pavement to be colonised is the jointing. This is often because the paving units themselves offer little in the way of sustenance whereas jointing usually offers water and soluble minerals.
Algae and mosses will be attracted to resin mortars because of the permeable nature which allows water and soluble minerals to be readily available, whereas good quality cement-based joints will offer the same but at much more of a challenge. If we're awarding points for weed resistance, good quality cementitious mortar in its early life will usually outscore a resin mortar.
BUT: when it comes to that maintenance, a resin mortar, properly installed, will outperform almost any cement mortar when subjected to a regime of aggressive cleaning. The resins are virtually unaffacted by steam, high-pressure water, bleach, acid or detergent-based cleaning, and because they are harder, they better withstand scour and/or abrasion from brushing.
There are other benefits to resin mortars, such as their resistance to cracking or debonding from the paving units, which may be of more consequence to commercial projects, but should not be completely disregarded on residential pavements because every crack offers a home to a weed.
For many DIYers and occasional pavers, I usually suggest a resin mortar because they are cleaner and faster to install and, given the penchant of homeowners for jet washing anything that doesn't move (and the cat), they clean up better and more intact than many cement mortars, but for those who are more familiar and comfortable using cement mortars, such as LLL, the not insignificant cost savings of such mortars makes them a more logical choice.
Some are fully intended to be permeable and are sold as such, while others are permeable or permeable-ish but because the flow rate is below that considered optimal for permeable pavements, the manufacturers tend not to mention it too much.
Many of these products state that they should be used in conjunction with paving laid on a permeable bed. When this happens, happy days! Surface water will enter via the jointing and exit via the bedding. However, in Britain and Ireland, we tend to lay on reasonably impermeable cementititious beds, so water enters via the jointing, a tiny fraction escapes into the bed and the bulk of it sits there in the joint waiting to be absorbed via capillary action into the flags/blocks/setts or evaporated away.
The point to note is that, once the joint is filled with water, it is "saturated", and no more water can be absorbed, so any further surface water will effectively wash over the joint, searching for somewhere else to escape.
So: does this mean a pavement laid on more-or-less impermeable bedding but jointed with a resin mortar is impermeable? It's debatable but when it comes to design, I always *assume* such a pavement is impermeable and therefore requires alternative drainage measures.
Next, we have to consider this in terms of maintenance, which is the original issue raised by JonJ. Regardless of what some of the less competent PIC and Resin Agg installers may tell you, there is no such thing as a maintenance free pavement. All pavements will deteriorate if left unmaintained. Weed colonisation by algae, lichens, mosses, grasses and other plants is the most obvious example, and very often, the first part of a pavement to be colonised is the jointing. This is often because the paving units themselves offer little in the way of sustenance whereas jointing usually offers water and soluble minerals.
Algae and mosses will be attracted to resin mortars because of the permeable nature which allows water and soluble minerals to be readily available, whereas good quality cement-based joints will offer the same but at much more of a challenge. If we're awarding points for weed resistance, good quality cementitious mortar in its early life will usually outscore a resin mortar.
BUT: when it comes to that maintenance, a resin mortar, properly installed, will outperform almost any cement mortar when subjected to a regime of aggressive cleaning. The resins are virtually unaffacted by steam, high-pressure water, bleach, acid or detergent-based cleaning, and because they are harder, they better withstand scour and/or abrasion from brushing.
There are other benefits to resin mortars, such as their resistance to cracking or debonding from the paving units, which may be of more consequence to commercial projects, but should not be completely disregarded on residential pavements because every crack offers a home to a weed.
For many DIYers and occasional pavers, I usually suggest a resin mortar because they are cleaner and faster to install and, given the penchant of homeowners for jet washing anything that doesn't move (and the cat), they clean up better and more intact than many cement mortars, but for those who are more familiar and comfortable using cement mortars, such as LLL, the not insignificant cost savings of such mortars makes them a more logical choice.
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JonJ
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Thank you, Tony, for such a detailed reply.
I quite see what you are saying about alternative drainage. And am I right in thinking that having the flags (and their joint with the bedding layer) soaked in water is likely to cause deterioration of the flags and the bedding layer, and also blowing of the joint?
Tony McC wrote:water enters via the jointing, a tiny fraction escapes into the bed and the bulk of it sits there in the joint waiting to be absorbed via capillary action into the flags/blocks/setts or evaporated away.
The point to note is that, once the joint is filled with water, it is "saturated", and no more water can be absorbed, so any further surface water will effectively wash over the joint, searching for somewhere else to escape.
So: does this mean a pavement laid on more-or-less impermeable bedding but jointed with a resin mortar is impermeable? It's debatable but when it comes to design, I always *assume* such a pavement is impermeable and therefore requires alternative drainage measures.
I quite see what you are saying about alternative drainage. And am I right in thinking that having the flags (and their joint with the bedding layer) soaked in water is likely to cause deterioration of the flags and the bedding layer, and also blowing of the joint?
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lutonlagerlout
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Jonj
IME the way i lay flags on a solid mortar bed makes the bedding almost impermeable
so when i have used polymerics in the past after 2-3 years the water laying in the joint during the winter decays the polymeric
the resin stuff does keep its appearance a lot better ,as it is so much stronger
as the boss says all pavements need some maintenance ,even just sweeping leaves off helps
I did a job for a chinese lady and she rang me 3 years later to say the mortar jointing had cracked?
hmmm i thought
till I went round and noticed they had had a bonfire slap bang in the middle of the patio
and her son had managed to get battery acid on another area which had stained the stone
the patio was fit for the purpose just not fit for extreme stuff as mentioned
hope this helps
LLL
IME the way i lay flags on a solid mortar bed makes the bedding almost impermeable
so when i have used polymerics in the past after 2-3 years the water laying in the joint during the winter decays the polymeric
the resin stuff does keep its appearance a lot better ,as it is so much stronger
as the boss says all pavements need some maintenance ,even just sweeping leaves off helps
I did a job for a chinese lady and she rang me 3 years later to say the mortar jointing had cracked?
hmmm i thought
till I went round and noticed they had had a bonfire slap bang in the middle of the patio
and her son had managed to get battery acid on another area which had stained the stone
the patio was fit for the purpose just not fit for extreme stuff as mentioned
hope this helps
LLL
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Tony McC
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And am I right in thinking that having the flags (and their joint with the bedding layer) soaked in water is likely to cause deterioration of the flags and the bedding layer, and also blowing of the joint?
It depends on the flags. Damned hard flags such as G684 granite or porphyry will laugh at the threat of moisture, as will most yorkstone. Some of the importaed sandstones and limestones will be similarly unaffected, but some of the softer stuff, such as the godawful Mint, are more vulnerable. With pressed concrete, I wouldn;t expect any problems and with wet-cast, it very much depends on quality.
Hards, deep, prolonged frosts are more of a problem but I know from visiting 10-20 year old sites in Germany, that the good resins stay put through much harder winters than we ever see in Britain and Ireland.
It depends on the flags. Damned hard flags such as G684 granite or porphyry will laugh at the threat of moisture, as will most yorkstone. Some of the importaed sandstones and limestones will be similarly unaffected, but some of the softer stuff, such as the godawful Mint, are more vulnerable. With pressed concrete, I wouldn;t expect any problems and with wet-cast, it very much depends on quality.
Hards, deep, prolonged frosts are more of a problem but I know from visiting 10-20 year old sites in Germany, that the good resins stay put through much harder winters than we ever see in Britain and Ireland.
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