2nd part
Read 1st part here:
CONSTRUCTION SEALANTS 1st PART: MAIN TYPES
We can express the movement accommodation of one sealant as a +- % number.
The positive number will show the size of movement which the sealant will accommodate when the joint extends.
Respectively the negative number will indicate the size of movement which the sealant will accommodate when the joint contracts.
Attention: the comparison is made to the joint width at the very time of sealant application.
So we can say e.g. for a sealant that it possess a +- 20% joint movement accommodation. This means that if the initial width of the joint at the time when sealant was applied was 20mm, the sealant will comfortably accommodate extensions up to 20+ 0,25 x 20 = 25mm and shrinkage up to 20 0,25 x 20 = 15mm.
And this is valid for the service life of the sealant.
Now, what will happen if the joint extends to e.g. 28mm? Probably nothing because the numbers are given with very big safety margins.
The very fact is, though, that the specifier has the obligation to keep extensions and compressions between the predetermined limits.
ISO 11600 induces the term MAF which stands for Movement Accomodation Factor. The highest MAF specified by ISO 11600 is +- 25%. Well, this is a conservative approach but it is on the safe side if you consider the demand for extended lifetimes and the harsh environmental factors many sealants are subjected to.
It is not rare for sealants manufacturers to give MAFs of 50% / + 100% and indeed there are many excellent elastomeric waterproofing sealants in the market based on silicones, polyurethanes or MS polymers. The truth, though, is that aging procedures significantly alter these numbers.
Lets not forget to mention that different MAF values are assigned to butt or lap joints and also to primed or unprimed joints.
Theoretically the needed MAF is calculated from the relation:
MAF = total joint movement x 100 / minimum joint width.
Practically we use the MAFs of proposed sealants to calculate the minimum joint width. And this we do after we first calculate the total joint movement taking into account both thermal and humidity variations.
There is one issue here: what is the season the sealant should be applied in? To allow for the worst scenario we add the total joint movement to the theoretical minimum joint width.
Together with MAF they are the 3 basic criteria used to select the idoneous sealant to accommodate the expected joint movement.
ELASTICITY
Elastomeric sealants can exhibit very high elongations at break: 500 600%.
Elongation at break values are used to distinguish between elastic and plastic sealants (ISO 11600 doesnt make provision for elasto-plastic materials).
The limit is a 12,5% increase of minimum joint width.
For an increase 12,5% an elastomeric sealant should be chosen.
ELASTIC RECOVERY
When the force that caused elongation ceases to act, some jointing materials recover fully and some partially.
Elastomeric sealants as MS Polymers, silicones, polyurethanes etc. show a nearly complete elastic recovery which means that after stress withdrawal they regain their former dimensions.
Standard ISO 11600 ranks all sealants with an elastic recovery 60% as elastomeric sealants.
ELASTICITY MODULUS
In ISO 11600 standard there are only 2 moduli classes:
a) high modulus: 0,4 MPa
b) low modulus: 0,4 MPa.
High modulus sealants are somehow hard or stiff and possess a high shore A hardness. These sealants impose high stresses on the adhesion planes and could practically induce adhesive failures.
They are preferable for joints exposed to foot traffic or water pressure.
Low modulus sealants are suitable for high movement joints or joints which move rapidly. They put less stress on the substrates.
MAF, elasticity and modulus of elasticity are three interrelated choice criteria which define the movement capability of the joints.
Hereunder we will check some more criteria we usually use to select the proper construction sealant.
PAINTABILITY
If for aesthetic reasons sealant surfaces must be painted, the best choices are acrylics or MS Polymers sealant. Polysulfides and polyurethanes come next and finally silicones are almost never overpaintable except for some special formulae.
Underwater use of sealants
Only very few formulae are suitable for constant immersion in water and even fewer for potable water.
Usually they are based on polyurethanes, polysulfides and epoxies and most of them need special primers. Minimal joint depth for these applications should be 20mm.
Only small hydrostatic pressures can be accommodated.
The onus for expansion joints waterproofing will stay with the PVC or equivalent waterstops.
AGING RESISTANCE
Aging resistance is critical when accessibility is limited and there are increased aesthetical requirements for the project.
MS Polymers have by far the best aging resistance but polysulfides, silicones and polyurethanes are perfectably acceptable for most projects.
Acrylics are more suitable for internal uses except for the silane-modified versions.
ADHESION ISSUES
PUR sealant and MS Polymers have generally a very good adhesion on most of the usual building substrates.
Use of primers can enhance adhesion to same substrates and especially under certain conditions.
Silicones and polysulfides usually need primers.
Acrylics can be self primed with water diluted material.
Always check relevant data sheets for suitable substrates and any possible need for a primer.
The cost from failed sealants is enormous in Greece. Seldom do I see a right application. Most of the times there are adhesive failures. Aesthetic failures are quite often and cohesive failures are sporadic.
The biggest problem is this of deficient surface preparation.
IMPORTANT NOTICE
1. First of all choose the idoneous for every case sealant.
2. Check if a primer is needed.
3. Examine the compatibility of sealant with the substrate.
4. Perfectly end thoroughly prepare the substrate.
RESISTANCE TO MOLD
Wet roofs like bathrooms, WCs, kitchens etc. will need a mold resistant sealant for waterproofing of joints. This is almost always a mold resistant silicone.
Mold resistance is achieved by addition of certain fungicides in the formula.
Antifungal properties of the sealants are not eternal. Premium quality sealants can maintain them for about 10 years.
Mold resistance doesnt relieve from the responsibility to clean joints on a regular basis. Remnants of human fat and soap are premium choice foods for mold. Additionally ,water shouldnt stagnate on the sealants and should be wiped up a.s.a.p. after bathing.
JOINT SLOPE
The slope of the joint will define the right viscosity of the sealant.
Horizontal joints are better treated with a self-levelling sealant.
Vertical and overhead joints need viscous, non-sagging sealants but without sacrificing their extrudability, especially in cold weather.
CONTACT WITH LIVING CREATURES
Sealants in e.g. aquariums, terrariums etc. should be completely safe for fish, reptiles and other living creatures.
TEMPERATURE RESISTANCE
Some applications demand resistance to high or low temperatures. Generally silicones resist to a more extended range of temperatures.
Many times resistance to continuous hot-cold cycles is needed.
BELOW GROUND USE
Check if the sealant is suitable for below ground applications. Acrylics for example are not suitable for such applications.
SETTING TIME SETTING MODE
Two components formulae set by chemical reaction. Setting time is quick and air humidity is not indispensable for polymerization process.
Most of advanced technology waterproofing sealants are one component. Their polymerization process is slow 1 to 2mm/day and is achieved with the help of air humidity.
Two component sealants are difficult to work with but can be used in special occasions when air is not available or time setting is critical.
MAX JOINT WIDTH
Check max allowed joint width. Usually its 2-4cm and is meant for the worst scenario (thecold season). If sealant's width surpasses the allowable joint span, then special profiles should be used instead of sealants/mastics.
RESISTANCE TO CHEMICALS, FUEL ETC.
Sealants for floor joints in chemical factories, tarmacs etc. need to possess chemical resistance. For these applications we usually use epoxy formulae, special two component polysulfides or polyurethanes or combinations of the latter with coal tar.
COST
Desirable objectives have to be met at a logical cost.
AESTHETICS
Acrylics and silicones can be produced in a wide palette of nuances. Other products as polysulfides are available only in 2-3 colours.
SHRINKAGE
MS Polymers and two component systems have the lowest shrinkage. On the other hand some acrylics have shrinkage rates 20%.High shrinkage has to be taken care of.
TRAFFICABILITY ABRASION RESISTANCE
Sealants with high elastic moduli 0,8 to 1,2 MPa and shore A hardness at a range of 40-50 are used for trafficable floor joints.
ANTI STAIN SEALANTS
Sealants to be used in facades with natural stones or marbles shouldnt provoke staining. There are special types of poyurethanes and silicones for these applications. MS Polymers also dont cause staining.
Chris Strogilis
Civ. Eng. MBA DipM
Read 1st part here:
CONSTRUCTION SEALANTS 1st PART: MAIN TYPES
We can express the movement accommodation of one sealant as a +- % number.
The positive number will show the size of movement which the sealant will accommodate when the joint extends.
Respectively the negative number will indicate the size of movement which the sealant will accommodate when the joint contracts.
Attention: the comparison is made to the joint width at the very time of sealant application.
So we can say e.g. for a sealant that it possess a +- 20% joint movement accommodation. This means that if the initial width of the joint at the time when sealant was applied was 20mm, the sealant will comfortably accommodate extensions up to 20+ 0,25 x 20 = 25mm and shrinkage up to 20 0,25 x 20 = 15mm.
And this is valid for the service life of the sealant.
Now, what will happen if the joint extends to e.g. 28mm? Probably nothing because the numbers are given with very big safety margins.
The very fact is, though, that the specifier has the obligation to keep extensions and compressions between the predetermined limits.
ISO 11600 induces the term MAF which stands for Movement Accomodation Factor. The highest MAF specified by ISO 11600 is +- 25%. Well, this is a conservative approach but it is on the safe side if you consider the demand for extended lifetimes and the harsh environmental factors many sealants are subjected to.
It is not rare for sealants manufacturers to give MAFs of 50% / + 100% and indeed there are many excellent elastomeric waterproofing sealants in the market based on silicones, polyurethanes or MS polymers. The truth, though, is that aging procedures significantly alter these numbers.
Lets not forget to mention that different MAF values are assigned to butt or lap joints and also to primed or unprimed joints.
Theoretically the needed MAF is calculated from the relation:
MAF = total joint movement x 100 / minimum joint width.
Practically we use the MAFs of proposed sealants to calculate the minimum joint width. And this we do after we first calculate the total joint movement taking into account both thermal and humidity variations.
There is one issue here: what is the season the sealant should be applied in? To allow for the worst scenario we add the total joint movement to the theoretical minimum joint width.
Together with MAF they are the 3 basic criteria used to select the idoneous sealant to accommodate the expected joint movement.
ELASTICITY
Elastomeric sealants can exhibit very high elongations at break: 500 600%.
Elongation at break values are used to distinguish between elastic and plastic sealants (ISO 11600 doesnt make provision for elasto-plastic materials).
The limit is a 12,5% increase of minimum joint width.
For an increase 12,5% an elastomeric sealant should be chosen.
ELASTIC RECOVERY
When the force that caused elongation ceases to act, some jointing materials recover fully and some partially.
Elastomeric sealants as MS Polymers, silicones, polyurethanes etc. show a nearly complete elastic recovery which means that after stress withdrawal they regain their former dimensions.
Standard ISO 11600 ranks all sealants with an elastic recovery 60% as elastomeric sealants.
ELASTICITY MODULUS
In ISO 11600 standard there are only 2 moduli classes:
a) high modulus: 0,4 MPa
b) low modulus: 0,4 MPa.
High modulus sealants are somehow hard or stiff and possess a high shore A hardness. These sealants impose high stresses on the adhesion planes and could practically induce adhesive failures.
They are preferable for joints exposed to foot traffic or water pressure.
Low modulus sealants are suitable for high movement joints or joints which move rapidly. They put less stress on the substrates.
MAF, elasticity and modulus of elasticity are three interrelated choice criteria which define the movement capability of the joints.
Hereunder we will check some more criteria we usually use to select the proper construction sealant.
PAINTABILITY
If for aesthetic reasons sealant surfaces must be painted, the best choices are acrylics or MS Polymers sealant. Polysulfides and polyurethanes come next and finally silicones are almost never overpaintable except for some special formulae.
Underwater use of sealants
Only very few formulae are suitable for constant immersion in water and even fewer for potable water.
Usually they are based on polyurethanes, polysulfides and epoxies and most of them need special primers. Minimal joint depth for these applications should be 20mm.
Only small hydrostatic pressures can be accommodated.
The onus for expansion joints waterproofing will stay with the PVC or equivalent waterstops.
AGING RESISTANCE
Aging resistance is critical when accessibility is limited and there are increased aesthetical requirements for the project.
MS Polymers have by far the best aging resistance but polysulfides, silicones and polyurethanes are perfectably acceptable for most projects.
Acrylics are more suitable for internal uses except for the silane-modified versions.
ADHESION ISSUES
PUR sealant and MS Polymers have generally a very good adhesion on most of the usual building substrates.
Use of primers can enhance adhesion to same substrates and especially under certain conditions.
Silicones and polysulfides usually need primers.
Acrylics can be self primed with water diluted material.
Always check relevant data sheets for suitable substrates and any possible need for a primer.
The cost from failed sealants is enormous in Greece. Seldom do I see a right application. Most of the times there are adhesive failures. Aesthetic failures are quite often and cohesive failures are sporadic.
The biggest problem is this of deficient surface preparation.
IMPORTANT NOTICE
1. First of all choose the idoneous for every case sealant.
2. Check if a primer is needed.
3. Examine the compatibility of sealant with the substrate.
4. Perfectly end thoroughly prepare the substrate.
RESISTANCE TO MOLD
Wet roofs like bathrooms, WCs, kitchens etc. will need a mold resistant sealant for waterproofing of joints. This is almost always a mold resistant silicone.
Mold resistance is achieved by addition of certain fungicides in the formula.
Antifungal properties of the sealants are not eternal. Premium quality sealants can maintain them for about 10 years.
Mold resistance doesnt relieve from the responsibility to clean joints on a regular basis. Remnants of human fat and soap are premium choice foods for mold. Additionally ,water shouldnt stagnate on the sealants and should be wiped up a.s.a.p. after bathing.
JOINT SLOPE
The slope of the joint will define the right viscosity of the sealant.
Horizontal joints are better treated with a self-levelling sealant.
Vertical and overhead joints need viscous, non-sagging sealants but without sacrificing their extrudability, especially in cold weather.
CONTACT WITH LIVING CREATURES
Sealants in e.g. aquariums, terrariums etc. should be completely safe for fish, reptiles and other living creatures.
TEMPERATURE RESISTANCE
Some applications demand resistance to high or low temperatures. Generally silicones resist to a more extended range of temperatures.
Many times resistance to continuous hot-cold cycles is needed.
BELOW GROUND USE
Check if the sealant is suitable for below ground applications. Acrylics for example are not suitable for such applications.
SETTING TIME SETTING MODE
Two components formulae set by chemical reaction. Setting time is quick and air humidity is not indispensable for polymerization process.
Most of advanced technology waterproofing sealants are one component. Their polymerization process is slow 1 to 2mm/day and is achieved with the help of air humidity.
Two component sealants are difficult to work with but can be used in special occasions when air is not available or time setting is critical.
MAX JOINT WIDTH
Check max allowed joint width. Usually its 2-4cm and is meant for the worst scenario (thecold season). If sealant's width surpasses the allowable joint span, then special profiles should be used instead of sealants/mastics.
RESISTANCE TO CHEMICALS, FUEL ETC.
Sealants for floor joints in chemical factories, tarmacs etc. need to possess chemical resistance. For these applications we usually use epoxy formulae, special two component polysulfides or polyurethanes or combinations of the latter with coal tar.
COST
Desirable objectives have to be met at a logical cost.
AESTHETICS
Acrylics and silicones can be produced in a wide palette of nuances. Other products as polysulfides are available only in 2-3 colours.
SHRINKAGE
MS Polymers and two component systems have the lowest shrinkage. On the other hand some acrylics have shrinkage rates 20%.High shrinkage has to be taken care of.
TRAFFICABILITY ABRASION RESISTANCE
Sealants with high elastic moduli 0,8 to 1,2 MPa and shore A hardness at a range of 40-50 are used for trafficable floor joints.
ANTI STAIN SEALANTS
Sealants to be used in facades with natural stones or marbles shouldnt provoke staining. There are special types of poyurethanes and silicones for these applications. MS Polymers also dont cause staining.
Chris Strogilis
Civ. Eng. MBA DipM
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