U.S. patent number 3,650,795 [Application Number 04/794,227] was granted by the patent office on 1972-03-21 for concrete form surfacing.
Invention is credited to John H. Willingham.
United States Patent |
3,650,795 |
Willingham |
March 21, 1972 |
CONCRETE FORM SURFACING
Abstract
There is disclosed herein a method for preparation and
construction of concrete pouring forms in which the surfaces and
edges of the form members are treated with several coats of a
resinous material exhibiting particularly advantageous mechanical
and chemical properties. A preferred material is a moisture cured
urethane prepolymer solution.
Inventors: |
Willingham; John H. (Memphis,
TN) |
Family
ID: |
25162069 |
Appl.
No.: |
04/794,227 |
Filed: |
January 27, 1969 |
Current U.S.
Class: |
427/133; 249/189;
427/379; 427/409; 428/423.3; 264/338; 427/377; 427/408; 428/76;
428/425.1; 249/134 |
Current CPC
Class: |
B28B
7/364 (20130101); B28B 7/38 (20130101); E04G
2009/026 (20130101); E04G 2009/023 (20130101); Y10T
428/31591 (20150401); Y10T 428/31554 (20150401); Y10T
428/239 (20150115) |
Current International
Class: |
B28B
7/38 (20060101); B29c 001/04 () |
Field of
Search: |
;117/5.1,161KP,68,5.3,132B,126GB |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Martin; William D.
Assistant Examiner: Perrone, Jr.; Mathew R. P.
Claims
What is claimed and desired to be secured by United States Letters
Patent is:
1. A method of making a rigid form member with a cured, single
component resin coated exterior for a concrete pouring form having
surface characteristics of tensile strength of at least 2,000 to
5,000 p.s.i., hardness (Sward) between about 30 and 60, impact
resistance (Gardner) of at least about 140 in. lbs. direct and
reverse, and Taber Abrasion (CS10 wheel, 1,000 grams, 1,000 cycles)
maximum weight loss of less than 75 milligrams, which
comprises:
providing a wooden core member having a preselected shape and
dimensional configuration;
applying a first coating to all surfaces of said core member, said
coating consisting of a moisture curable, isocyanate-terminated,
urethane prepolymer in a solvent, having a solids concentration of
approximately 20 percent and a viscosity (Brookfield) of less than
100 c.p.s.
exposing said coated surfaces to ambient atmospheric moisture for a
period sufficient to cure said coating;
subsequently, applying a plurality of additional coatings to all
surfaces of said member; each of said additional coatings
consisting of the said urethane prepolymer in a solvent having a
solids concentration of about 30 percent to about 40 percent and a
viscosity (Brookfield) not exceeding approximately 150 c.p.s.
successively exposing said coated surfaces to ambient atmospheric
after each of said coatings is applied for a period sufficient to
cure said coating before each additional coating is applied.
2. The method of claim 1 wherein the wooden core member is
plywood.
3. The method of claim 1 wherein the solvent is at least one member
selected of the group consisting of xylene and ethylene glycol
monoethyl ether acetate.
4. The method of claim 1 wherein the curing period is from 3 to 4
hours in relative humidity of greater than 50 percent.
5. A method of making a rigid form member with a cured, single
component, resin coated exterior for a concrete pouring form having
surface characteristics of tensile strength of at least 2,000 to
5,000 p.s.i., hardness (Sward) between about 30 and 60, impact
resistance (Gardner) of at least about 140 in. lbs. direct and
reverse, and Taber Abrasion (CS10 wheel, 1,000 grams, 1,000 cycles)
maximum weight loss of less than 75 milligrams which comprises:
providing a core member having a preselected shape and dimensional
configuration, said core comprising steel, wood, or fiberglass;
applying a first coating to all surfaces of said core member, said
coating consisting of a moisture curable, isocyanate-terminated,
urethane prepolymer in a solvent having a solids concentration of
approximately 50 percent of the solids concentration of
subsequently applied coatings and a viscosity (Brookfield) of less
than approximately 150 c.p.s.
exposing said coated surfaces to ambient atmospheric moisture for a
period sufficient to cure said coating;
subsequently applying at least one additional coating to all
surfaces of said member; said additional coating consisting of the
said urethane prepolymer in a solvent having a solids concentration
of about 30 percent to about 40 percent and a viscosity
(Brookfield) of approximately 150 c.p.s.
successively exposing said additionally coated surface to ambient
atmospheric moisture for a period sufficient to cure said
coating.
6. The method of claim 5 wherein the solvent is at least one member
selected from the group consisting of xylene and ethylene glycol
monoethyl ether acetate.
7. The method of claim 5 wherein the curing period is from 3 to 4
hours in relative humidity not greater than about 50 percent.
Description
BACKGROUND OF THE INVENTION
This invention relates to the preparation and construction of forms
used for concrete casting, and more particularly to the use of a
resinous coating material on the forms to provide greater
durability, increased and usable lifetime, and an extremely smooth
and uniform surface on the finished concrete product.
Use of forms for casting concrete structures such as wall panels,
facades, decking, etc. is well known in the construction industry.
Such forms are ordinarily constructed of panel members formed of
wood, steel, etc. to provide the concrete forming surface, and of
suitable supporting and spacing structure or framing. Ordinarily,
wood panels are preferred since wood forms are often less expensive
to manufacture and easier to handle due to lighter weight. However,
there are several significant disadvantages. For example, the forms
are reused many times over in the course of a construction project,
but the wood panels rapidly absorb moisture in use. This causes
panel surface deterioration and buckling or warpage. Frequent
replacement is therefore necessary to assure a flat and uniform
surface on the cast concrete product.
Use of steel form panels overcomes several of the above-noted
disadvantages, particularly the limited durability of the wood
panels. Steel is therefore preferred for extremely large projects
or permanent installations. However, the steel forms are heavier
and often more costly. Also, they are subject to surface
deterioration due to rusting, corrosion, etc.
In recognition of these problems, it has been proposed to improve
the durability of wood form panels by coating them with a suitable
waterproof plastic. However, such efforts were not completely
satisfactory.
In a further effort to overcome these disadvantages, it has been
proposed to use a composite panel structure employing a central
core of wood or other material with built-up composite faces formed
of fiberglass reinforced polyester resin. Such forms may be more
durable than forms currently in use, but are also subject to
several serious disadvantages. Construction of even simple forms in
this manner is relatively complex and costly, and requires
utilization of skilled labor. Moreover, such forms can ordinarily
not be built at the construction site, but must be prefabricated
elsewhere and trucked to the site for assembly. Further, while the
panels are relatively durable, they are subject to damage in use,
for example, while the finished concrete panel is being removed
from the form. The forms are quite difficult to repair, again,
requiring skilled labor. As a result, fiberglass reinforced
polyester forms are not in use commercially and have not gained
acceptance, insofar as applicant is aware.
SUMMARY OF THE INVENTION
In accordance with the present invention, it has been found that
the disadvantages of uncoated wood forms and of the heretofore
proposed alternatives can be overcome, and form panels can be
manufactured in a simple and inexpensive manner by utilization of
materials having certain quite specific properties. Forms made
according to this invention are durable and may be reused many
times, yet they are easily manufactured at the construction site by
unskilled workmen. Forms constructed in accordance with this
invention have an additional advantage in that the usual form
release compositions employed to facilitate separation of the
concrete product from the forms may be dispensed with, except for
occasional application.
Also, because of the smooth and uniform surface against which the
concrete is poured, the resulting product possesses an extremely
smooth and uniform surface. In this regard, it has been found quite
surprisingly that the concrete surface is so smooth and glossy that
it reflects light without substantial diffusion. This property may
be of decorative value in some instances, but if desired, the
surface may be conveniently treated by sand blasting or otherwise
to remove the high surface gloss.
In accordance with the invention, the improved form panel is made
by coating a core member formed of wood, steel, or fiberglass with
a resinous material having certain particular properties. After
suitable curing, a second (and in the case of wood core members) a
third coating is applied. After final curing, the panel is ready
for use in the assembly of form structures of any desired type.
Coating materials found to be suitable are air or moisture curable
resins capable of being thinned to low viscosity for convenient
application. In the cured state the coating material should exhibit
high hardness and tensile strength, good impact and abrasion
resistance, and negligible water absorption. Surprisingly,
materials having the requisite properties have been available for
some time without industry recognition of their efficacy for the
present purpose.
Accordingly, an object of this invention is to provide a new
surface treatment for concrete form panels, and to produce such
panels having substantially increased durability and extended
useful lifetime.
Another object of this invention is to provide a simple and
inexpensive technique for construction of concrete forms, whereby
the forms may be built by relatively unskilled laborers directly at
the construction site. A related object is to provide improved
concrete pouring forms, which may readily be repaired at the
construction site by unskilled labor.
It is also an object of this invention to provide a concrete
pouring form which does not require use of a form release compound
on the concrete forming surfaces after each use.
It is a further object of this invention to provide a concrete
pouring form which may be utilized to produce concrete having an
extremely smooth or glossy and uniform surface.
The exact nature of the invention, as well as other objects and
advantages thereof will be apparent from consideration of the
following detailed description, and the accompanying drawing in
which the single FIGURE shows a simple form panel constructed in
accordance with this invention.
DETAILED DESCRIPTION
Referring now to the drawing, there is illustrated a form panel
member 6 manufactured according to the present invention. The
composite panel includes a core member 8 which may be formed of
wood, steel, fiberglass or other suitable material. Core member 8
is coated on all sides and edges with a resinous material having
particular properties as specified hereinafter.
For most applications, core member 8 is made of wood, preferably
one-fourth to 1 inch plywood. Low grade plywood panels, e.g., grade
BB, may be employed since the applied coating provides a smooth and
uniform surface even on the rough and nonuniform plywood. As
illustrated, on a wood core 8, there are provided several coats of
resinous material, e.g., three coats, as indicated at 10, 12 and
14. Best results are achieved if both sides and all edges of the
core member are coated with the resinous material. The coating may
be applied in any suitable fashion, e.g., by dipping (immersion)
brushing, rolling, or spraying. Due to the advantageous properties
of the resinous material, each coat may be relatively thin, e.g.,
3-6 mils. On wood core members, a minimum of three coats should be
employed to provide the desired durability, and to prevent buckling
and/or warping of the panel. The inner coat 10 is preferably
diluted approximately 50 percent with solvent to reduced the solids
concentration, and to promote absorption into the wood surface,
whereby this coat serves as a primer. When applied to metal or
other nonabsorptive materials, the diluted inner layer may be
dispensed with.
After the panel has been coated in the manner hereinafter
described, it may be employed in the construction of any
conventional or desired type of form. Thus, this invention is
applicable to simple forms used for poured-in-place slabs, vertical
wall panels or even complex frames or decorative facades. In the
latter case, form preparation according to this invention is of
special value since the resulting concrete surface is smooth and
uniform even if the actual surface profile is quite complex.
However, since the detailed nature of the form itself does not
constitute a part of this invention, a description of typical form
constructions is omitted in the interest of brevity.
As pointed out above, essential to the success of this invention is
the employment of a resinous coating material having certain
special properties. Specifically, it has been found that the
coating material must be such that the cured coating possesses high
hardness without brittleness, high tensile strength, and impact
resistance, virtually negligible water absorption, and high
resistance to abrasion.
More specifically, it has been found that resinous materials
appropriate to the practice of this invention should produce a
cured coating which exhibits a minimum tensile strength of between
2,000 and 5,000 p.s.i., elongation between about 20-150 percent,
hardness (Sward) between about 30 and 60, Taber Abrasion weight
loss (CS10 wheel, 1,000 g. wt. 1,000 cycles) not exceeding about 75
mg., and minimum impact resistance (Gardner) of 140 in.-lbs.
(direct and reverse). In the uncured state, the resinous material
should not exhibit a viscosity (Brookfield) significantly exceeding
about 150-160 c.p.s. or a specific gravity significantly exceeding
about 0.95-1.0.
While materials exhibiting the foregoing combination of properties
are not common, there are a number of highly suitable materials
available. These include single component resin systems such as air
cured urethane oils (isocyanate modified drying oils) and moisture
curable isocyanate terminated urethane prepolymers. Heat curable
urethane resins (single component) may also be suitable, but do not
lend themselves to convenient use at the construction site.
Likewise, two component systems including catalysts may be suitable
but less convenient.
One particularly satisfactory material is a moisture cured aromatic
diisocyanate prepolymer known as Neorez U 105, distributed by
Polyvinyl Chemicals Inc., Wilmington, Mass. Using this material, a
cured coating (thickness 3 mils) may be produced having properties
as set forth in Table
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I below:
Tensile Strength Elongation 7000 p.s.i. Hardness (Sward): 1 day 24
Ultimate 45 Impact Resistance Direct 160 inch-lb. Reverse 140
inch-lb. Taber Abrasion (CS10 wheel, 1000 g. load, 1000 cycles) 23
mg.
__________________________________________________________________________
TABLE I: Film Properties of Preferred Resinous Material
By virtue of these properties the described prepolymer is the
preferred coating material, but it will be understood that other
materials exhibiting comparable properties may also be employed.
For example, a similar material can be obtained from the C. P. Hall
Chemical Company of Chicago, Illinois or Cook Paint and Varnish
Company, Kansas City, Missouri.
Liquid coating materials exhibiting the above properties should
also be susceptable to solvent thinning or other viscosity
adjustment to permit application to the form panels by dipping,
brushing, rolling, or spraying. For the urethane prepolymer
materials described this can be accomplished by use of xylene,
Cellosolve acetate (ethylene glycol monoethyl ether acetate) or
mixtures thereof.
Further in this regard, it should be noted that the solids
concentration of the liquid coating material is directly related to
the durability. However, excessive solids concentration is
unsatisfactory since high viscosity results, preventing
satisfactory application to the core members. In particular, for
the materials suitable for use according to this invention, it has
been determined that the solids concentration and
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viscosity vary in the manner set forth in Table II below:
Solids Concentration Viscosity (Brookfield) cps.
__________________________________________________________________________
60% 1200 50% 700 40% 160 30% 100
__________________________________________________________________________
TABLE II: Variation of Viscosity with Solids Content
Best results are obtained for coating by brushing, rolling or
dipping at a viscosity of about 150-160 c.p.s. while spraying is
best accomplished at a viscosity of about 100 c.p.s. Thus thinning
to solids concentrations of 40 percent for brushing, etc. or 30-35
percent for spraying, yields best results.
In addition to the foregoing, certain other requirements for proper
application of the coating material to the form panels, curing,
etc. should be observed for best results. The following examples
illustrate the manner in which all requirements should be met in
successful practice of this invention.
EXAMPLE 1
A plywood board, three-fourths inch, grade BB is cut to the proper
size and shape. A moisture curable, urethane prepolymer exhibiting
film properties as set forth in Table I, and having a solids
concentration of approximately 40 percent, a viscosity of 150
c.p.s. is xylene thinned 50 percent to reduce solids concentration.
The thinned prepolymer solution is applied to all surfaces and
edges of the plywood core member as a primer coat. This may be done
by dipping, brushing, or rolling as desired. The coated core member
is then cured in air for approximately 3 to 4 hours under
conditions of at least 50 percent relative humidity. Then, second
and third coats of unthinned prepolymer solution (40 percent
solids, 150 c.p.s. viscosity) are applied to the once-coated core
member, again by brushing, rolling, or dipping. The second and
third coats are each air cured in the manner previously described.
The composite form panel is then ready for use in a form of any
desired design. Plywood form panels prepared in the manner
described can be used one hundred or more times without significant
surface or structural deterioration
EXAMPLE 2
A steel plate (7 gauge) is sandblasted or otherwise treated and
then cleaned to produce a rough, generally uniform surface. The
urethane prepolymer solution described in Example 1 is solvent
thinned to a 30 to 35 percent solids concentration. At least two
coats of the prepolymer solution are sprayed onto the plate on both
sides and all edges. After each application, the coating is air
cured as in Example 1. The result is an ultradurable, rustproof
concrete form panel usable well in access of one hundred times
without resurfacing. When necessary, the panel may be sandblasted
and recoated. The panel so treated is found to be completely
renewed and ready for use.
EXAMPLE 3
A fiberglass core member is precast in any desired surface
configuration to produce a forming surface usable in the casting of
decorated facade panels, etc. The durability of such panels may
also be enhanced according to this invention. Thus, the fiberglass
surface is sanded or otherwise roughened. Two coats of a
polyurethane coating solution exhibiting film properties as set
forth in Table I is thinned to a viscosity of approximately 150
c.p.s. and applied to the fiberglass core member by dipping,
rolling, or brushing. Each coat is cured until hard. In this way, a
highly durable form member may be produced having an extremely
smooth and uniform surface. The form member so treated may be used
to form intricate surface patterns without the necessity of form
release compounds.
EXAMPLE 4
As noted above, a particular advantage of the form panels
manufactured in accordance with this invention is the amenability
to rapid and effective repair by unskilled personnel. Thus, in the
event that a panel prepared as in Examples 1-3 has been damaged,
e.g., from impact with the cast concrete product during removal
from the forms, the affected portion can be repaired as follows:
the damaged area is rough-sanded, and deep scars in the core member
are built up with a suitable filler composition e.g., a compatible
epoxy-type filler). The affected area is leveled by sanding and
cleaned. The area is then recoated as described above with two or
three coats of the coating material and each coat is cured. A
damaged panel is completely renewable in this manner.
As may be seen from the foregoing, several variations in the
appropriate procedure may be possible. Also, in Example I, use of a
moisture cured, urethane prepolymer under dry conditions, for
example, below about 50 percent relative humidity, may be
unsatisfactory since the curing time is substantially lengthened,
and, in the case of extremely low humidity, curing is completely
inhibited. Under such conditions, air cured urethane-modified
drying oil compositions or other materials exhibiting properties as
set forth herein should be substituted. Alternatively, a
cross-linker, for example, a polyhydroxy amine such as sold under
the name Quadrol by Wyandotte Chemical Corporation may be added to
the prepolymer in a concentration of about 2 to 4 oz. per gallon
for curing at a relative humidity between about 30 and 50 percent.
For relative humidity substantially below about 30 percent, 6 oz.
of cross-linker per gallon of prepolymer solution may be
employed.
Further, under low temperature conditions, the curing time for the
prepolymer is increased. To overcome this, a suitable accelerator
compatible with the particular urethane prepolymer may be
employed.
As an additional extension of the present concepts, it is
contemplated that form surface repair can be facilitated by
preparing the liquid resinous material in aerosol form with a
conventional compatible propellant. This would permit convenient
on-the-spot repair of minor damage. As will be appreciated, the
various mechanical properties described herein should be observed
in selection of the resinous material for aerosol packaging. Again,
however, the moisture curable isocyanate terminated prepolymer is
preferred.
The present invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The present embodiment is therefore to be considered in
all respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description, and all changes which come within the
meaning and range of equivalency of the claims are therefore
intended to be embraced therein.
* * * * *