Historic Preservation - Technical Procedures
- Dutchman Repair Of Limestone
- Procedure code:
- National Capitol Region Specifications - Gen Accounting Off
- Last Modified:
- Dutchman Repair Of Limestone
- Last Modified:
DUTCHMAN REPAIR OF LIMESTONE
A. This procedure includes guidance on the repair of damaged
limestone using a dutchman. As used here, the term
"Dutchman" refers to any new or salvaged stone fitted
into the existing facade stone. New stone shall match
B. Dutchman repair is sometimes recommended for large spalls
or spalls that would be visually detract= ing.
C. 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 Precaution= s
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).
A. Sample Stone Repair:
1. Reattach stone fragments and patch stone at
locations selected by the Contracting Officer using
methods specified. Provide one sample each for
materials to be used.
2. If samples are unsatisfactory, Contractor shall
make the needed modifications and prepare new
samples until they are satisfactory.
3. The samples accepted by the Contracting Officer
shall serve as the standard for the entire job.
They shall be marked and left unpointed until all
other pointing is completed.
4. The Foreperson responsible for the respective work
shall be present at the sample work. Samples shall
be executed by the same individuals performing the
1.03 QUALITY ASSURANCE
A. Contractor: A skilled firm with not less than five (5)
years experience in masonry repointing and restoration.
The Contractor shall be required to submit references for
five (5) successfully completed projects of similar
B. Work Standards: Repointing basic reference and standard
for stone repointing shall be National Park Service
Preservation Briefs: 2 Repointing Mortar Joints in
Historic Brick Buildings, by Robert C. Mack AIA, de Teel
Patterson Tiller, and James S. Askins for any aspect of
masonry repointing work not herein specified.
C. Source of Material: Obtain materials for stone
restoration from a single source for each type of
material required, to ensure match of quality, color,
pattern, and texture.
1.04 PROJECT/SITE CONDITIONS
A. Environmental Requirements: Perform work only in dry and
otherwise favorable weather conditions. Protect repaired
masonry against freezing or excessively rapid drying for
at least 48 hours after being laid; no masonry shall be
laid when temperature is below 32 F on a rising
thermometer or below 40 F on a falling thermometer.
A. Laticrete International, Inc.
B. Sika Corporation
A. Polymer Admixture (for Setting Dutchman) such as
"Laticrete 3701 or 4237 Grout and Mortar Admixture"
(Laticrete International, Inc.), or approved equal.
B. Metal attachments for setting stone Dutchman:
1. All wire, pins, anchors, and bars shall be
stainless steel, Type 302 and 304.
2. Provide anchors as follows:
a. 1/8" diameter round stock, stainless steel
wire with turned-up ends for small veneers.
b. 1/4" or 3/8" diameter round stock, stainless
steel rod for direct pinning and drop dowels.
C. 1" wide, 1/8" thick, stainless steel, flat
strap anchors for larger panels.
3. The quantity of individual attachments shall not be
less than two attachments for small dutchman, and
one attachment every two square feet for larger
4. All attachments shall be fastened by mechanical
locking, in addition to appropriate adhesives and
C. Adhesives for attaching anchors and for direct pinning:
Where permitted, anchors may be held in place with high
modulus, high strength, moisture insensitive, epoxy
adhesive. Adhesive shall be two-component 100% solids,
epoxy resin system with a viscosity similar to petroleum
jelly "Sikadur 31 Hi-Mod Gel" (Sika Corporation), or
D. Pigments for altering the color of cement: All pigments
shall be alkali proof, non-fading, and of synthetic iron
E. Water: Clean and free of amounts of oils, acids, alkalies, salts, organic materials, or other substances
that may be deleterious to mortar or any metal in the
E. Joint tools
F. Wood wedges
G. Spray bottle
A. Protection: Contractor shall take whatever precautions
are necessary to protect the existing building from
damage resulting from work under this section.
B. Surface Preparation: Cut existing spalls to form rectangular losses with square corners, minimum 2"
3.02 ERECTION, INSTALLATION, APPLICATION
A. Mortar for setting limestone Dutchman shall be mixed in
a ratio of one part by volume white portland cement and
three parts by volume sand, tempered to a workable
consistency with a polymer admixture.
1. The use of Laticrete 3701 shall produce the
equivalent of high strength "thick set" mortar.
Limestone must be temporarily held in place with
wood wedges or other means until the mortar has
2. "Thinset" mortars for special conditions shall
employ Laticrete 4237, or approved equal. It can be
used when the mortar bed is less than 3/8" thick to
produce an initially tacky mortar exhibiting high
strength properties when set.
B. Dutchman shall be fastened with stainless steel wire,
pins, and anchors, as necessary, designed to facilitate
mechanical locking and to prevent possible slippage of
the stone. The metal fasteners shall be positioned
without weakening the stone in any way. See also 04460-
13-R for guidance on resetting limestone.
C. Cement mortar containing "Laticrete" latex emulsion
additives, or approved equal, shall be used for all
setting purposes. All insertion shall be fully dressed on
all sides, and carefully fitted to the patch opening,
with an allowance of not more than 1/8 inch buttered joint
between front edges. Undercutting shall not weaken the
stone in any way. The joints between new and old work
shall be finished to match the color and texture of the
stone. See 04520-02-R for guidance on repointing.
D. The surface of the new stone shall be dressed to resemble
the appearance of the adjoining stone by an approved
method. All surface dressing of new work shall be done
before the stone is set.
E. Protect the limestone during the process of stone restoration. Any mortar accidentally splashed onto
existing limestone shall be wiped and rinsed with water.
END OF SECTION