Poultice method for treating bituminous stains on masonry products

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Poultice method for treating bituminous stains on masonry products

Stafford, B. F.

P O U L T I C E

METHOD

FOR TREATING BITMUINOUS STAINS ON MASONRY PRODUCTS

by

B.F.

Staffard

Building materials are selected with great care and attention, not only far their performance characteristics, but a l s o f o r their aesthetic value- Further care is exercised in t h e fxansportatiarm and handling of t h e s e materials in an attempt to have them installed un- marked and clean. All t o ~ often, however, this is not achieved, Lack

of appreciation of t h e problems associated with the u s e of

a U

materials

in t h e system or negligence in application may result in unsightly stain- ing.

This Note is concerned with some of t h e organic stains that are

m o s t

difficult ;to remove

from

porous materials, those of the bitumens generally known as coal-tar pitches, asphalt, and asphalt emulsions. Although t h e s e s t a i n s can never be completely removed from some masonry surfaces, a marked reduction in t h e intensity of the stain can

be achieved

by

using a poultice consisting of a solvent and a chemically inert material applied to the stained surface.

The u s e of solvent-based poultices o f f e r s several advantages: they prevent t h e stain from spreading during trea-hent, and they S'puLI1' the stain out of the pores of the masonry. They are also more conven-

ient to u s e in small or a w k w a r d areas and can be used in situations

where a mess carmot be tolerated. They are easily prepared, relatively inexpensive, and require minimum use of mechanical equipment f o r application and removal.

The mechanism of a poultice-cleaning system is quite simple:

the solvent in t h e paste is absorbed into the surface pores of the masonry. The absorbent inert material controls the rate of evaporation, t h u s

giving the solvent s d i c i e n t t i m e to dissolve the stain. As evaporation

takes place,

the

solvent together with t h e material that caused the stain is d r a w n out of the masonry surface into the inert material. The stain is

deposited in t h e absorbent which, when dried, can be easily removed

from the masonry as a loose powder,

Before actually attempting t o remove .the stain, it is advisable

Because of the many and varied characteristics of building materials,

it

is impossible t o predict the effe ctivene s s of such a cleaning system. Difference s

in such aspects as eolour, absorption, and texture of

the

masonry materials all affect the degree of success.

It is

recommended, therefore, that a trial removal of

the stain be attempted in an inconspicuous area to determine t h e efficacy ofthe system and its freedom

from undesirable side effects.

2.

If the

stains to be removed are on new construction, it follows that t h i s should be one of the l a s t phases of construction,

but

_again,

_a

-

_{trial removal should be} attempted e a r l y incase replacement of the material

is the only acceptable solution.

3 .

If

the material involved has been in u s e far a con-

siderable pexiod of time, it i s likely t h a t the surface

will

be discoloured through d i r t accumulation. The treatment far the withdrawal of the stain will probably remove the dirt in the treated area leaving it lighter in colour. Therefore, the effect an t h e final appearance of the surface should be considered,

4.

It

should be noted that solvents a r e generally toxic and flammable and should be u s e d with caution and only in well-ventilated areas.

THE SOLVENT

The liquid used in t h e poultice must be a solvent of the material

to be removed. The evaporation of this solvent must be rapid enough

to allow the inert material to d r y within a reasonable length of t h e , but not so fast that there is insufficient; t h e for t h e solvent to act o n

the stain.

.

A solvent fox bitumens could be any one of the following

hydrocarbons;

xylene,

toluene, trichlor

oethylene

or mineral spirits. Xylene and toluene offer a moderate evaporation rate and a high degree of solvent strength. Trichloroethylene a l s o has high solvency p o w e r

has fhe weake st dissoLving action and t h e slowest evaporation rate but

is t h e most readily available and could be acceptably employed where

t h e s k i n is light and t i m e is n o t an important factor, Benzene ranks

with trichloraethylene but i t s extreme toldcity ne ce s sitate s stringent precautions: it must be employed only in well-ventilated areas and

prolonged contact with tbe skin must be avoided. THE INERT MATERIAL

A variety of chemically i n e r t materials can be used as absorbents

iq the preparation of the poultice. These finely divided materials have varying properties when mixed as a paste, some offering better adhesion

to vertical surfaces than others. They are used a s agents to hold the

solvent in contact with t h e surface;, and act to control evaporation of the

solvent. They must Rave a h i g h absorbency value and must not react chemically w i t h the liquid

with

which they are being mixed. In o r d e r f o r t h e reverse migration af t h e solvent

into

the poultice to 'be effective,

it

is necessary f o r t h e s e absorbents to have a finer pore structure than

the surface on which they are t o be applied.

These i n e r t materials or fillers may be talc, whiting, F u l l e r T s Earth, bentonite or powde red silica, all of which meet the aforementioned requirements. In selecting from these, one need only consider the avail- ability of the material.

APPLICATION AND REMOVAL

OF

THE P O U L T I C E

Before proceeding with the application of the solvent poultice, it is desirable that excessive bihunen s t a k deposits be carefdly r e m o v e d by manual means. This will minimize t h e number of treabnents necessary to effect satisfactory removal and reduce the hazard of further stain

penetration into the pores as solvent thinning takes place. It is recommended

that the implements employed h this removal be wooden paddles or similar

instruments that are no&jurious to the surface itself,

Enough solvent is mixed w i t h t h e filler to form

a

smooth paste of

a consistency that, when applied, will retain its shape and still o f f e r adhesion to vertical surfaces.

At

l e a s t 1/4 inch of this mixture is then applied by a spatula er trowel over t h e stain, ensuring that more than the entire stained area is covered. The poultice i s left in place for at least one hour after all t h e solvent has apparently evaporated and then

removed as a dry powder. Since all of the stain

may

not dissolve during the first attempt, h e process is repeated until satisfactory results a r e

achieved or until i t

is

considered to be impractical or uneconomical to continue

.

9f the surrounding areas will permit, a final washing, using

water and a s t i f f bristled brush, will remove any o f the filler particles that remain in the surface pores of the masonry materials.

RESULTS

OF

A SIMPLE L A B O M T O R Y TEST

T o

appreciate better the difficulties involved in t h e u s e of such

a poultice system, a small-scale laboratory t e s t was condncted in an attempt t o remove stains resulting from bitumens most commonly used

in

t h e construction industry. Small samples of masonry materials (described in_{Figure 1 ) w e r e used onto which the fallowing materials} w e r e applied: a CSA type 1 , ~ 4 softening 0 ~ point asphalt; ~ a solvent

cut-back of

the

same material; coaldtar pitch; an asphalt emulsion type applied undiluted a n d a further application of t h i s material thinned t o a

water -like consistency,

In

_{addition to indicating which masonry product}

w a s used, F i g u r e 1 identifies the area of the surface to

which

each particular stain w a s applied.

The

asphalt and coal-tar pitch were heated to

a

temperature of approximately 400°F: in a heating apparatus and poured onto the surface

of the sample s in the appropriate area producing a stain of approximately one inch in diameter. A small a m o u t of the 140 asphalt was t;h-inned w i t h solvent and this cut-back asphalt was applied cold, again by pouring onto

the surface.

A

stain of asphalt emulsion o f the s a m e general dimension

was produced, using a spatula as the instrument of application, a n d the *:inned emulsion was applied

in

_a

_{similar manner (Figure 2 ) -}

Sufficient b e was allowed f o r materials that were applied h o t to reach room temperature

and

excessive bitumen deposits were then

removed manually, taking care to not injure t h e masonry surfaces.

A poultice was prepared using

talc

mixed with benzene t o form a smooth paste.

This

paste was evenly applied witha spabla over the stained area to a thickness of at least 1 / 4 inch covering more

than

the

with

a

s t i e f bristled brush, Nearly compkte success was achieved

in

removing the asphalt and coal-tar pitch stains from t h e two marble

samples in this f i r s t attempt,

but

only a moderate degree

of

success

was achievedinthe remainder of the c a s e s ,

The

procedure was re-

peated, resulting

i

n

_complete

_removal

_of

_{all atains on}

_{the marble} samples as shown

in

_{Eigure 3, This aperation w a s repeated a t o t a l}

of five t i m e s with a continued increase in _removal

_of

_{t h e remaining} stains evident up to the four& attempt. After

the

_{fifth trial, it was}

decided that no more effective removal could be obtained and

that

this

represented a pradical limit,

It

is evident f r o m Figure 4 that it was impossible to completely

remove fie biturnens from a l l the surfaces. Excellent results were

achieved on the marble products after the second attempt. C o a l t a r pitch stains were satisfactorily removed e x c e p t from t h e white terrazzo

and the exposed aggregate concrete surfaces, where stains w e r e stir1 r c b j x l e d in fhe poses of the matrix,

Gut-back asphalt removal was considered acceptable in six c a s e s but tRe Indiana l j m e stone and white terrazzo surfaces still

showed an unacceptable amount of stain, The 140 asphalt w a s not completely removed from the Indiana limestone, the white terrazzo

,

and the white exposed aggregate concrete surfaces. The asphalt

emulsion stains offered t h e m o s t resistance to removal. Much of this bitumen was removed

but

(except on marble)

it

would appear that the poultice system is ineffective

in

elk-ninating this stain.

The effect of solvent in causing stain penetrat5on can be seen

By comparing stains 1 and 2 .

In

these cases, the solvent-thinned asphalt, when applied, was c a r r i e d further into the pores than t h e undiluted asphalt.

This

penetration was

m o s t

apparent t:on the Georgia

granite (Figure 51 where this thinned bitumen had campletely penetrated

the material

and

the stain intensity was as severe on the underside as on the surface.

S U M M A R Y

The u s e of

a

poultice-cleaning system can be most u s e m in

the t r e a b e n t of bituminous stains on porous materials. It is completely

effective when employed on a marble surface and offers varying degrees

of: success on other masonry materials. The system is quite convenient to use, is economical, and involve s

lime

skiill in it.ts application.

The ready availability of the components in the poultice and its capability to

be

used in.

awkward

areas, without causing

a

m e s s ,

make the system a desirable one. From 'the experiment conducted, it i a evident that the m o s t notable limitation of a solvent based

poultice system is its relative inability to remove stains resulting

from thinned asphalt emulsions.

The difficulty of removing bituminous stains from some

masonry surfaces emphasizes the need to take every precaution during construction t o avoid staining t h e masonry.

F I G U m 2: Stains Applied t o Substrate

FIGURE 4:

Re

sults After 5 t h Treatment

FIGURE 5: Photo u s k g a M i r r o r t o Shaw S b i n