Masonry 2013

Fort Dorchester Foundation Outline

Fort Dorchester Site

      The goal of the Fort Dorchester project was to create a foundation outline that represented the position of a house that was on the side hundreds of years ago.  A transit was used to establish elevation points around the foundation.  The primary reference point was taken from the interior of the house outline.  The parks service gave us a map of the area based on archeological digs, and this information was used to outline the perimeter of the site. 

        After set a perimeter of 43 ft. long across the front, and 34.8 ft. wide along the sides, battering boards were set at the corners to square the foundation outline.  Once the corners were squared, strings were set forming a width of 20 in. from the outside of the foundation outline to the inside.  This provided an area for the trenches to be dug around the foundation.  Framing boards were run and leveled forming a 20 in. area for hardcore (ROC –Crushed Limestone) to be installed in the trenches.  The hardcore was installed a tamped down to a depth of approximately 1/2” below the framing boards.  The next step was to pour a 2 –1/2 to 1 mix of type S mortar over the hardcore.  This provided a stable foundation for the paving bricks that made up the outline of the foundation.

Crushed Limestone

          Chalk –lines were used to outline the area for the paving bricks.  The dimension for the paving bricks was about 15 3/4 inches.  This provided area for the bricks and a mortar joint, with approximately two inches of foundation on either side of the pavers.  Depending on the level of the foundation, 3/8” or 1/2” boards were placed along the scribed guidelines on the foundation.  The purpose being to provide an even mortar bed for the paving bricks.  Type S and Type N were used for this process.  Once the mortar was poured and leveled with a screed, the pavers were laid using a 3/8” spacer to establish the joint width.  The joints were backfilled using a grout bag and tooled after tightening up.  Cleaning the pavers with a sponge and water concluded the foundation outline.

           One of the challenges of the project was to represent a house that was not there.  The solution that was derived was to build four corners at six courses high to represent the dimensions of the house.  The corners are two wythe with four bricks on the first course in both direction.  Laying the inside and outside of the corners simultaneously made it easier to maintain consistent elevation and level.  A story pole was used to establish the height of the corners. 

 

Completed Corner

Half bricks were installed after the majority of the corner was mortared in, and paver caps were placed on the tops of the bricks to cover the cores in the bricks and provide a more polished finish.  It is important to note that even though this is a historic site, the materials used are all modern and were not meant to simulate historic materials.

            The final step of the project was clean the brick work and leave the site in the same, if not better, condition that we found it in.  A low level acid solution was used to clean the bricks.  The job of the acid was to eat away at the top layer of mortar that had been left on the bricks and paving foundation.  A hard scrub brush was used to clean the bricks.  In order to build up the areas where soil was removed, soil leftover from archeological digs on the site was used to build up the along the pavers.  This covered any remnants of the mortar foundation and gave the site a more uniform appearance.  The project has been considered a success and will hopefully lead to more projects at Historic Fort Dorchester.

Fort Dorchester Outline Completed

Jail Courtyard Wall

Courtyard Wall

Work began on the outdoor theater by installing a foundation pad to the existing outline.  The desired area was dug out and boards were installed to act as levels for the foundation.  In order to use less mortar for the project, stones were placed in the foundation to trench to act as a filler.  A mortar mix of 1 to 1 was used for the foundation and was pulled off using a screed.  This provided a smooth and level surface for installing the wall. 

            After the foundation was allowed to set, the wall was outlined and scribed in to provided guidelines for the brick installation.  One of the main focuses of this project was to learn to build corners.  The total number of bricks for the first course was calculated and a corner was dry stacked at each end of the foundation.  Once the required design was worked out, the corners were mortared in and line blocks were used to construct the remaining section of the wall.  This wall was good practice for using different bond patterns.  The first three courses were constructed using a basic running bond.  The remaining three courses consisted of one header course, and two Flemish bond courses.  It was important to make sure that the overall depth of the wall matched up the length of the bricks we were using.

            Upon completion of the front side of the wall, attention was turned to construction a separate, single wythe wall on the back side.  This wall began about half a brick distance from the front side.  The back side was good practice at laying soldier bricks.  Seven soldier sections were left open when the corners of the back wall were constructed.  This left space for line blocks to be set about 1/2” off of the wall face to allow the soldiers to protrude out and give the wall a sense of depth and design.  The soldiers were buttered and installed in their allotted space.  A final stretcher course was laid to cap the back side of the wall and bring it up to the approximate elevation of the front side.  Slate will be used at a later date to cap both sections of the wall, thus creating a single wall section that will be used as seating for the outdoor theater.

Spring 2013 Timber Frame Addition

 

     One of the projects undertaken by the ACBA Trowel Trades program was to construct foundation footings for a 6’ addition to the existing timber –framed shed in the courtyard of the jail.  An engineering transit was used to establish the required elevation for the new foundation footings.  The transit was set up in the yard, leveled in two directions, and sighted the elevation of the original, outside columns.  It was found that there was a 14 –1/2” difference in elevation from the outside of the original post to the sidewalk in the courtyard, and a 3 –1/4” difference in elevation between the center point of the new column location and the side walk.  Post 1 of the original structure was the primary elevation reference point.  Based on this information, we were able to determine that the space between the ground and the top of the stone cap of the new columns was 13 –1/4.” 

       String lines were run around the back of the original shed columns to the location of the new columns, which were 6’ from the outside of the existing shed.  Battering boards were set up spanning the entire distance of the shed at a distance of 6’ out from the original posts.  Additional strings were marked and tied at distances of 5’ 8” from the original post to new column location.  This gave us the center point of the new column.  A distance of 5’3 –1/4” was measured from the original post to the new to give us the inside point of the new column.  A distance of 3 –3/4” was measured from the center point, in two directions, to gives us these points.

When constructing the foundations for the new columns, 24” x 24” holes were dug at a depth of 4” below the required elevation.  A wooden peg was driven to mark the desired elevation.  Two courses of bricks were laid in a Herringbone pattern to establish the foundation for the new columns.  The pattern was dry bonded to make sure that the desired pattern would fit in the given area, and then mortared in once the dimensioned were assured.

The mortar ratio used for the foundation was a 1 to 1 mix because the mortar was old and needed a strong mix to assure a proper bond was formed.  After the mortar was allowed to set for period of time, a skim coat of mortar was used to even top of the foundation.  This allowed for a flat bonding surface for the brick columns of the new addition.  The bricks were dampened with water and a finishing trowel was used to apply the skim coat (same mortar used for skim coat as for the bricks).  A two –foot level was placed on the peg marking the required elevation and rotated over the skim coat to make sure the area was level.  The next step in preparing the foundation was to use a sponge –float to manicure the skim coat to a uniform texture.   

          Using the string lines previously established a level and plumb –bob were used to transfer the points to the foundation.  The original post dimensions were 8” x 8” and 10” x 10.” The level and plumb –bob were placed just to the outside of corners of the string lines (about 1/16” away from the line) and a pencil was used to mark the points.  A small framing square was used to connect the points and scribed into the foundation top.  Once the wooden column dimensions were scribed in place, the brick dimension of the columns were marked using the same method.  The column of my foundation was 10” x 8”, so the brick outline was 11 –1/2” wide by 13 –1/2” long. 

Brick Columns for Timber -Frame Addition

     The next phase in the timber –frame addition was the brick columns for the new shed posts.  It was determined that 7 course of bricks with 3/8” mortar joints would be required to fill the space between the top of the 4” foundation and the bottom of the 5” stone cap of the columns.  The method of dry bond was again employed with wooden spacers simulating the mortar joints.  

Once the dimensions were verified, a 2 to 1 mix of Holcim Rainbow Custom Color Buff Mortar Mix was prepared.  This was a Type N mortar suitable for masonry above grade. 

      The brick outline scribed onto the foundation top was used to lay the first course of bricks for the columns.  A framing square was used to align the first course of bricks because the it is important to start off in the proper alignment.  Upon completion of the  first course, a SDS drill was used to bore into the center of the foundation to provide an anchoring point for the new posts.  A wooden rod was inserted to prevent mortar filling the hole. 

       A level was used to make plumb each corner of the column to check the alignment of the columns.  Extra mortar was placed around the base of the columns to provide additional strength and stability since soil was used to fill in around the column to get even with the ground level.  The process of laying and checking the level and verticality was repeated until all 7 courses were laid.