GSA Mobile

CAULKING HORIZONTAL LIMESTONE SURFACES WITH WATERPROOF JOINT
SEALANT


THE APPROPRIATE METHOD OF SEALING JOINTS IS THE PROPER REPOINTING WITH COMPATIBLE HISTORIC MORTAR MIX (SEE 04100-03-S AND 04250-02-R FOR GUIDANCE).  UNDER CERTAIN CONDITIONS, HOWEVER, SELECTIVE USE OF  SEALANT MAYBE WARRANTED TO ADDRESS EXTREME THERMAL MOVEMENT OR OTHER LOCATION-SPECIFIC CONDITIONS. A DECISION TO  SUBSTITUTE SEALANT FOR MORTAR SHOULD BE BASED UPON SITE-SPECIFIC ANALYSIS TO IDENTITY DEFICIENCY CAUSES AND APPROPRIATE SOLUTIONS.


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing deteriorated
         sealant from horizontal limestone joints and recaulking
         with a waterproof joint sealant.  This procedure
         specifically applies to exterior limestone window sills,
         balustrades, balconies and cornices, although use on
         other horizontal surfaces may be appropriate.

    B.   See 01100-07-S for general project guidelines to be
         reviewed along with this procedure.  These guidelines
         cover the following sections:

         1.   Safety Precautions

         2.   Historic Structures Precautions

         3.   Submittals

         4.   Quality Assurance

         5.   Delivery, Storage and Handling

         6.   Project/Site Conditions

         7.   Sequencing and Scheduling

         8.   General Protection (Surface and Surrounding)

         These guidelines should be reviewed prior to performing
         this procedure and should be followed, when applicable,
         along with recommendations from the Regional Historic
         Preservation Officer (RHPO).

1.02 REFERENCES

    A.   American Society for Testing and Materials (ASTM)
         www.astm.org


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Joint sealant:  Multi-part, non-sag urethane sealant
         conforming with ASTM C290, Type M, Grade NS, Class 25.

    B.   Joint primer:  Provide as recommended by sealant
         manufacturer.

    C.   Backer rod:  Round, closed cell, polyethylene foam
         backing rod; should be compatible with sealant; use as
         recommended by sealant manufacturer.

2.02 EQUIPMENT

    A.   Stiff natural fiber or nylon bristle brushes

    B.   Striking hammer or "No-bounce" hammer

    C.   Joint chisel


PART 3---EXECUTION

3.01 ERECTION, INSTALLATION, APPLICATION

    A.   Rake out old sealant or mortar from joints by hand using
         a hammer and chisel.  Rake to expose sound mortar.  See
         also 04520-02-R for guidance on raking out joints.

         NOTE:  DO NOT USE MECHANICAL METHODS TO CUT OUT JOINTS,
         DUE TO THE HIGH PROBABILITY OF DAMAGING THE STONE.  TAKE
         CARE NOT TO CHIP OR SPALL EDGES OF ADJACENT STONE.

    B.   Remove loose dirt and debris from the joint using a stiff
         bristle brush or vacuum.

    C.   Prime joint surfaces as recommended by the sealant
         manufacturer.  Protect adjacent surfaces from spillage or
         spattering of sealant.

    D.   Insert backing rod to a depth equal to 1/2 the width of
         the joint.

    E.   Fill joint with sealant.  Tool joint within 10 minutes of
         placing.  Finish joint level with the stone surface.  

    F.   Remove excess sealant from the stone surface immediately.

                         END OF SECTION