UNION JOINTS

The main purpose of the union joints is to work as connection between constructive elements.

Joint Parts. A joint consists of the following elements:

	The free face is the accessible surface of the support where the joint is located.
	Joint Lips are the lateral walls of the joint, one in front of the other, parallel or not. They define the location of the sealant material.
	Joint Bottom is a filling material, anti-adherent and compressing that contributes to the establishment of the appropriate factor joint, according to the sealant that will be used.
	Priming: previously described
	Joint sealing compound:Sealants.

Characteristics of joint sealing compounds.
Las propiedades más frecuentes exigidas al material de sellado de una junta son las siguientes:

Main function.
The function the joint has to fulfilL during its life span, and it will define and assess the concept of " durability ". When two or more functions are considered as main, the chosen sealant product or system must satisfy all those functions throughout the estimated life span of the joint.

Secondary function.
Usually shorter than the main function for which the filler has been placed. This is the case of colour (aesthetic function), although it is often considered to be a main function.

Joint Properties.
By using the sealants described in the previous section we gain the following advantages:

The supports.
In order to assess the state of the support, it is necessary to consider their nature: concrete or bedding mortar, steel, aluminium, glass, plastics, etc.

Joint condition.
The seal in a new or imperfect joint involves a different series of problems:

In all cases the sealant will always be applied on dry surfaces.

Work execution.
Qualified professionals. The sealant works must be carried out only by specialised companies and qualified employees.

Works execution conditions. Recommendations before sealing:
-Easy or difficult access to the joint.
-Atmospheric conditions, climatic and environmental, which can negatively affect the aesthetic quality of the joint sealing compound or its polymerisation.

Period of delay before entering into service. The period of delay before entering into service, after sealing, will be fixed depending on the minimum time required for the polymerisation or the total curing of the sealant. The waiting period will depend on the environmental conditions and the polymerisation speed of the sealant.
If the joints are to be submerged, the minimum delay period will be of two or three weeks, depending on atmospheric conditions, humidity and temperature.

MEASUREMENT OF THE JOINT

Movement calculation.
Movement calculation will be based on the movements produced by thermal expansion and contraction, permitting the planners follow their own criteria considering other movements. If these movements could occur, this fact must be kept in mind.
The dilations and contractions will be determined by applying the following formula:

Movement capacity.
Mobile joints will be exclusively sealed with materials of permanent elasticity. These materials are characterised by a peculiar parameter denominated "movement capacity". This parameter indicates the maximum deformation that the material can tolerate, without breaking, when subjected to an indefinite number of extension and contraction cycles. It is identified as " m " and it is expressed in % of the joint width.

Determination of joint width.
For the sealant to work inside its elastic field, the joint width will be determined by the following formula:

This value marks the minimum width that the joint should have, so that the sealant can work under total guarantee. The maximum width of the joint is marked by the technical possibilities of each individual sealant.

Joint factor.
Joint factor is defined as the ideal relationship between width/depth in order to get a uniform allotment of weight on the whole adhesion surface and to avoid areas with accumulation of tension.
The joint factor has specific values according to the type of sealant material. If the seals are rigid, the joint factor must not be taken into consideration.

Seal depth.
We can easily calculate the joint depth, after the joint width has been determined to know the joint factor that corresponds to the joint sealing compound.

ELASTIC SEAL OF JOINTS

Support Preparation.

Cleaning up. The supports will be prepared, in such a way that at the moment of sealing, the joint should be in perfect condition, as a result, stains, loose particles, carbonated areas, oxides, paint remains, form remover, etc. must be completely eliminated. This operation will be preferably carried out using a mechanical procedure.

Cleaning. The second step is surface cleaning, a thorough cleaning of the support through use of:

	Sand jet: Projecting a silica sand jet by means of a compressor with variable flow, according to the support distance, with a pressure of 7 atmospheres. The size of a grain of sand will be 1-2 mm.
	High-pressure water jet: Projecting water with special equipment, through a shuttle provided with a mouthpiece, the minimum water pressure must be of 150 atmospheres. The pressure will be regulated by means of a manometer.
	Water-sand jet: A system that combines the two previous methods.

There are also other systems such as:

Control. The last step after curing and cleaning is to perform a simple control test to check the optimum conditions of the supports in order to continue with the sealing process.
Some of these tests are:

Elastic Seal. After is all prepared we will proceed to the sealing, for which we follow these steps.

Protection of the edges of the joint. Apply in both sides of the sealing area and all along a paper adhesive tape (masking tape) to avoid the sealant to stain while is being applied. This tape must be removed immediately after the sealant is applied or before it starts the curing process.

Application of a backing road. Using a separative in square or rounded shape has the following functions:

The diameter of the bottom of the joint must be approximately 1,25 times the wideness of the joint.

Primer. Is recommended to consult the manufacturer for the best use and applications and for the best type to be used.