PB90-132689

Radon Fundamentals and the Effectiveness of Coatings in
Reducing Soil Gas Flow Through Block Basement Walls

(U.S.) Environmental Protection Agency, Research Triangle Park, NC

1989

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„ p.RR TECHNICAL REPORT DATA

tr OOD (Please reed Inunctions on the reverse before eompletf

1, REPORT NO. a,

EPA/600/D-89/205

3. PB90-132689

4. title and subtitlej^acjon Fundamentals and the Effective-
ness of Coatings in Reducing Soil Gas Flow Through
Block Basement Walls

8. REPORT DATE

6. PERFORMING ORGANIZATION COOE

7. AUTHOR(S)

John S. Ruppersberger

S. PERFORMING ORGANIZATION REPORT NO.

9. PERFORMING ORGANIZATION NAME ANO AOORESS

See Block 12

10. PROGRAM ELEMENT NO.

11. CONTRACT/GRANT NO.

NA (Inhouse)

12. SPONSORING AGENCY NAME ANO AOORESS

EPA, Office of Research and Development

Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711

13. TYPE OF REPORT ANO PERIOO COVERED

Published paper; 5/88-3/89

14.SPONSORING AGENCY COOE

EPA/600/13

is. supplementary notes Author Ruppersberger's phone number is 919/541-2432; his Mail
Drop is 54. Presented at Advances in Coatings Technology, June 6-7, 1989, Cleve-
land, CH.

is. abstract The paper gives results of an evaluation of six different coatings in special-
ly designed chambers built around 1. 5 .sq m concrete block wall sections. Data were
collected over a pressure range of 1-12 Pa with flows from < U.Ol to 50 standard li-
ters/minute (SLPM), The six coatings were a water-based catalyzed epoxy paint, an
elastomeric paint, a cementaceous block filler, a surface bonding cement, a poly-
sulfide vinyl acrylic paint, and a latex paint. A major preliminary finding is that all
six coatings proved to be highly effective (98-plus %) when enough material is care-
fully applied. Considering both cost and effectiveness, a cementaceous block filler is
highly effective, at lowest cost, in a single application. Among the paints, two coats
of the water-based epoxy was most effective, although one coat may be adequate.
Baseline (uncoated) flows varied by a factor of 2 (12.1 - 23. 5 SLPM/sq m) between
the two batches of block used for testing that came from a North Carolina manufactu-
rer; these varied by an order of magnitude (1.8 SLPM/sq m) from blocks received
later from a Minnesota manufacturer.'. This large variation in a small sampling of
blocks is significant not only in the potential impact on coating performance, but
also more significantly that specification of blocks with low air permeability for new
construction substructures could greatly reduce soil gas entry, even if left uncoated.

17. KEY WOROS ANO OOCUMENT ANALYSIS

a. DESCRIPTORS

b.IOENTIFIERSfOPEN ENOEO TERMS

c. cosati Field/Group

Pollution Basements

Radon Walls

Concrete Blocks

Coatings reproduced bv

Gas Flow U.S. DEPARTMENT OF COMMERCE

CrtSl- NATIONAL TECHNICAL INFORMATION SERVI

oou-B SPRINGFIELD. VA. 22151

Pollution Control
Stationary Sources
Soil Gas

CE

13B 13M
07B

13C.11B

11C

20D

08G.03M

18. OISTRI6UTION STATEMENT

Release to Public

19. SECURITY CLASS (ThitReport)

Unclassified

21. NO. OF PAGES

20. SECURITY CLASS (Thtlpaje)

Unclassified

22. PRICE

EPA Form 2220-1 (9*73)

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NOTICE

This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.

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EPA/600/D-89/205

Radon Fundamentals and the Effectiveness of Coatings
in Reducing Soil Gas Flow Through Block Basement Walls

John S. Ruppersberger
U. S. EPA, Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711

ABSTRACT - Samples of six different coatings were evaluated in specially designed
chambers built around 1.5 m* concrete block wall sections. Data were collected over a
pressure range of 1 to 12 pascals with flows ranging from less than 0.01 standard liters
per minute (SLPM) to 50 SLPM. A major preliminary finding is that all these coatings
proved to be highly effective (98+%) when enough material was carefully applied.
Baseline (uncoated) flows varied by a factor of two (12.1 to 23.5 SLPM/m2) between
the two batches of block used for coatings testing that came from a North Carolina
manufacturer; these varied by an order of magnitude from blocks received later from a
Minnesota manufacturer (1.8 SLPM/m2). This large variation found in a small sampling
of blocks is significant not only in the potential impact on coating performance, but more
significantly that specification of blocks with low air permeability for new construction
of substructures could greatly reduce soil gas entry, even if left uncoated.

INTRODUCTION - Pressure driven transport of soil gas carrying radon is believed to be
the major entry mechanism for indoor radon. For houses with basements that have been
mitigated as part of the EPA's research program, the perimeter crack where the floor slab
meets the basement walls has often been considered the primary entry route. Generally,
sound poured concrete has not been found to offer a significant entry route, even with
typical hairline cracks. Therefore, coating poured concrete as part of a radon mitigation
effort is not considered worthwhile when working toward a guideline of 4 pCi/L,
Basement walls built of hollow concrete masonry units (CMUs) have always been suspect,
and mitigation has sometimes included some work with this type of wall. The surfaces
of these walls have been known to be an entry route, but given less treatment since other
mitigation techniques such as active (fan driven) suction on the soil side of the
substructure/soil interface have been developed to often be effective in achieving a 4
pCi/L guideline. Active systems are often powerful enough to extend their suction into
the core of the CMU wall, effectively reversing the premitigation condition of the
basement air; typically being the suction side of a slight pressure on the order of -3 to -
5 Pa. Efforts to quantify the CMU wall source term is not commonly included in radon
mitigation work to date. When quantified, it was found to contribute up to
approximately 20% (1). Reports of the effectiveness of painting the surface of CMU walls
have been mixed, with success credited to the treatment by some mitigators and no
benefit even after thorough treatment with expensive paints by others. The recent
development of the long term goal of ambient radon concentration supports more effort
toward the more common houses, those with a premitigation level of 2 pCi/L or less.
The relative significance of radon entry routes may be different for this large group of
houses. Another major concern of active soil ventilation systems is the large volume of
conditioned indoor air they draw through a typical uncoated CMU basement wall,
producing inefficiency in the system and resulting in an energy penalty of conditioning
the outside replacement air that is brought to the temperature of the house. Trace gas

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experiments indicated that 50% of the air exhausted from one active sub-slab mitigation
system was from the basement. (1) Extension of the suction to all essential areas of the
soil/substructure interface is made more difficult if CMU walls allow large flows of indoor
air into the system.

In a Canadian study, external coatings were evaluated for their ability to form an
airtight membrane that would remain intact even if cracks occurred in the substrate
subsequent to their application. Coatings were applied to two adjacent concrete blocks,
which were then moved apart to simulate opening of a crack. (2)

Recent work performed at Princeton University found that block wall air
permeability was reduced by 99-5+% with two coats of a special rubberized paint, a
polysulfide copolymer One coat was 91% effective. Two coats of ordinary latex and
oil base paints reduced wall permeabilities by 95%. Air permeabilities were determined
from flow versus pressure data. (3)

A "standard test method of rate for air leakage through exterior windows, curtain
walls, and doors" has been established by ASTM. (4) This test method covers the
determination of resistance of curtain walls to pressure driven air infiltration. The EPA
test apparatus complies with the ASTM test method in every major aspect, and differs
only in the use of instrumentation exceeding the ASTM accuracy requirements, and data
collected at lower pressure differentials in the range of 1 to 12 Pa.

MATERIALS AND PROCEDURES - Concrete masonry units of the type used in this test
are covered by an ASTM "standard specification for hollow load-bearing masonry units."
(5) This specification covers hollow load-bearing concrete masonry units made from
Portland cement, watei; and mineral aggregates with or without the inclusion of other
materials. The three weight classifications are normal, medium, and lightweight.

Coatings selected for evaluation include a two part catalyzed water based epoxy
paint, an elastomeric paint, a cementaceous block filler; a fiber reinforced surface bonding
cement, a polysulfide vinyl acrylic paint, and a latex paint. Selection criteria included
an attempt to sample various types of coatings that might be used on CMU basement
walls under various conditions. Some coatings are not well suited, or even recommended
by the producers for negative side (inside) basement walls, but were evaluated because
they may already exist on some walls of basements needing mitigation, or might be better
suited for application to walls under certain conditions than other coatings. Coatings
were applied separately to bare wall specimens even though the desired result of a
continuous gas flow resistant film might better be achieved by a combination, such as a
block filler and a coat of paint. This was done to collect data on each coating separately
- - performance of various combinations may be estimated from the data, but to be more
precise, and perhaps more reaJistic in some instances, reasonable recommended
combinations could be subjected to further evaluations. The effectiveness of a single coat
of the two part water based epoxy argues against a strong need for further such tests.
Freshness of samples and adherence to application directions were emphasized. No two
coatings were produced by the same manufacturer

The test stand was designed for a 16 ft3 (1.5 m2) CMU wall. The wall assembly
is made by pouring a concrete footing (48 in. x 16 in. x 6 in.) on which a block wall of

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15 standard blocks and 6 half blocks is carefully built. Mortar construction techniques
vary; these walls were built with two fairly generous strips of mortar on which the base
course of blocks are laid. Mortar is applied to all horizontal surfaces of the previous
course and to the end of the next block that will butt up against the last block on a
course in progress. After the wall has set up for over a week it is caulked generously
and, while wet, the side and top panels are assembled then fitted with covers to
encapsulate the wall with a plenum on either side. Gosed cell rubber gasket material
is sandwiched between all mating metal surfaces, and between the metal and acrylic
plastic covers.

The completed assembly is leak tested by pressurizing to between 2.5 and 3.0 in.
H20 (500 to 750 Pa) using helium gas, and "tested for leaks using a halogen gas leak
detecton Leak testing is also conducted on the pressure side of the air delivery
equipment. The control panel is composed primarily of computer controlled mass flow
controllers, a pressure transduce]; a pump, and a by-pass valve that provide precise
control of flows from less than 0.01 SLPM to 50 SLPM over a pressure range of 1 to 12
Pa. The acrylic plastic cover over the side of the wall to be painted is then removed.
After baseline data are collected, the coating is carefully applied. Care is taken to
quantify material used. Additional coats were applied a day after the previous coat except
when data collection needs dictated longer periods or when it might be reasonable to
stop application of that paint with that coat. It is important to note that the coatings
were applied by brush, carefully working material into the block surface and leaving as
much material on the wall as possible without runs. Primary consideration was sealing
the porous block surface, not the amount of material used. Exceptions are the
elastomeric paint which was applied at the maximum recommended rate and the surface
bonding cement which was applied using a steel trowel.

The initial wall was constructed as part of prototype development and was used
for the polysulfide vinyl acrylic paint evaluation. Its baseline flow was as shown in
Figure 2, Line a, 35 SLPM at 3 Pa, or about 2 SLPM per full block. The remaining five
coatings were evaluated from walls built latei; from a different batch of blocks. Although
from the same local North Carolina manufacturer; meeting the same ASTM specifications
for CMUs and with no noticeable difference in appearance, the baseline flows were
approximately half of that of the prototype wall, as shown in Figure 1, line b, 18 SLPM
at 3 Pa, or about 1 SLPM per fiill block. Then an opportunity developed to evaluate
blocks received from a Minnesota manufacture!: The baseline flow for these blocks is on
average approximately an order of magnitude lower than the local blocks, as shown in
Figure 1, Line c, 2.7 SLPM at 3 Pa or about 0.15 SLPM per full block. Blocks from both
manufacturers are typical of those used in their geographical regions for residential
construction. The more air permeable North Carolina block is a lighter block, 12.1 kg,
that has become common in the southeast. It contains expanded light weight aggregate,
filled with numerous discrete voids that do not appear to be interconnected. The less air-
permeable Minnesota block weighed 16.9 kg, uses natural aggregates, and has a
smoother; less porous surface appearance.

WATER BASED EPOXY PAINT - This is a water based catalyzed (two part) epoxy resin
paint. Its analysis by weight, as supplied by the manufacture]; is 16.5% titanium dioxide
pigment and 83.5% vehicle (7.7% epoxy resin, 6.6% ethylene glycol and alcohol, 20.7%
acrylic resin, 46.5% watei; and 2.0% additives). The data for this paint are summarized

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with other coatings in Table 1. Even with a slightly higher baseline flow of 19.8 SLPM,
a single coat of this epoxy paint resulted in the lowest airflow of any paint evaluated,

0.75	SLPM at 1 day drying time, and was the lowest for any two coats of paint
evaluated, at 0.01 SLPM. The paint film is very smooth, and dried specimens exhibited
unexpected elongation and strength upon being pulled apart, although these observations
were not quantified by any standard testing techniques. Application was considered
easier than average to provide a continuous film for both the first and second coats.

ELASTOMERIC PAINT • The analysis of this elastomeric acrylic emulsion paint was not
given. Application rate for concrete block was specified as 50 to 125 fiVgal. The first
coat was applied at 50 ftVgal. Based on the performance of the first coat, a second coat
was also evaluated. About a third of the quantity of paint used for the first coat was
used for the second coat. The data for this paint are summarized with other coatings in
Table 1. The measured effectiveness of the elastomeric paint was second only to the
epoxy: 136 SLPM for one coat, and 0.025 SLPM for two coats. Application by brush
was considered the easiest of any paint evaluated.

CEMENTACEOUS BLOCK FILLER • This is a portland cement plaster that can be troweled,
sprayed, or brushed. There was no information concerning composition on the container
(a bag holding 50 lbs) or sales literature, other than references to portland cement. In
keeping with the general trend of brush application, this product was applied with a
"masonry brush" purchased from the dealer. It required a different technique than typical
paints, but application progressed satisfactorily after a brief time. Application was
considered more difficult than average to provide a continuous coating with reasonable
surface appearance. Experience would probably improve both application rate and
appearance. The other cementaceous product evaluated was troweled on, but that
product specified a 1/8-in. thick coating; this cementaceous block filler (also called a
"finish coat" by the manufacturer) was applied at a thinner consistency and thinner than
1/8-in. by brash. The data for this coating are summarized with other coatings in Table

1.	The single thick coating resulted in an air flow of only 0.06 SLPM; only about half
of the flow through the fiber reinforced surface bonding cement, and over an order of
magnitude less than one coat of the most effective paint.

SURFACE BONDING CEMENT - This is a mixture of portland cement, fiberglass
reinforcement fibers, and unspecified (proprietary) ingredients. Application is specified
as a minimum of 1/8-in. thick with coverage per 50 lb bag of approximately 50 ft3.
Thwel or spray application options are in the product literature supplied by the produces
Application was with a steel trowel by an experienced mason to a thickness of slightly
over 1/8-in. The data for this coating are summarized with other coatings in Table 1.
The single application resulted in an air flow of only 0.10 SLPM.

This is more than the other portland cement coating evaluated in this study, but
still is highly effective at 99.5% flow reduction in one application, allowing less than 14%
the flow of one coat of the most effective paint.

POLSSULFIDE VINYL ACRYLIC PAINT - This coating is not yet (May 1989) available
commercially. ¦ The supplier described it as polyyulfide/vinyl acrylic dispersion without
giving any further specifics on composition. It was offered at the time the program was
started and was used for the original prototype test stand and equipment testing. Since

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it was accepted for those first developmental tests, it was decided to evaluate it as the
first coating using the equipment after it was fully calibrated to QA/QC specifications.
Application was considered average to provide a continuous film for both the first and
second coats, although pinholes were observed soon after application and thdr apparent
number and size increased with drying time. The data for this paint are summarized
with other coatings in Tafc!e 1. Specifically, the baseline flow was much higher than for
the walls built later from another batch of blocks. The measured effectiveness of one
coat of this paint was approximately 80%; many pinholes were apparent in one coat.
The second coat reduced air flow at 3 Pa substantially, with an effectiveness of 99.4%:

0.20	SLPM of the baseline flow of 35 SLPM. The observed time dependence on
measured effectiveness resulted in reconsideration of a standard condition of 2 weeks
drying time since data collected at different drying times exhibited different slopes and
a consistent trend of increasing flows with increasing drying time. Performance
deteriorated further between 2 weeks and 2 months with visual pinholes becoming more
numerous and larger:

LATEX PAINT - This is a latex semi-gloss paint. It is commonly sale priced at retail and
might be considered the type of latex paint homeowners would often buy; there are both
less and more expensive latex paints available. Its analysis did not list ingredients by
weight, merely as pigment; titanium dioxide and hydrous aluminum silicate, and vehicle;
polystyrene resin, acrylic latex, vinyl acrylic resin, 1, 2 propanediol, additives and water:
Application information on the label stated 400 fiVgal. or less, and that textured surfaces
may require more paint. Actual application rate on the test wall was approximately 100
ftVgal. That first coat took as much paint as the next two coats combined, resulting in
a coverage after the three coats of approximately 50 ftVgal. Application of the paint by
brush was considered slightly more difficult and time consuming than the average of the
paints evaluated. The data for this paint are summarized with other coatings in Table

1.	The measured effectiveness of this latex paint was less than any of the other three
paints evaluated for either one or two coats. One coat was not very effective, about an
order of magnitude less effective than the epoxy or elastomeric paints, allowing 11 of
the baseline 19 SLPM to pass at 3 Pa after 1 day drying time. It was the only paint
applied with three coats, but that third coat greatly increased the effectiveness, from
84.2% with two coats up to 98.1% (0-37 SLPM) at three coats.

DISCUSSION - Reduction of air entry is the primary concern that motivated this work
and all aspects of the test program. Several observations are especially noteworthy. The
first is that of these coatings, everything works well in reducing air flow across these test
walls (initially at least, under these ideal conditions) if sufficient material and care are
used in their application. A major finding, and a surprising one after discussions with
several paint chemists working to formulate especially effective radon flow resistant
paints, and seeing fairly expensive specialty paints being advertised specifically as radon
resistant, is that all these coatings, when carefully applied with sufficient quantity and
coats, demonstrated that they can be highly effective in reducing gas flow across the face
of concrete masonry units. Another is the interesting observation that the data for any
particular set of flow vs pressure plots is a straight line on arithmetic papec Apparently,
flow through these small openings at low pressure differentials is laminae

A comparison of percent effectiveness in reducing the baseline flow and estimated
cost associated with do-it-yourself (approximated by the material cost) and professional

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application total cost is summarized in Ibble 1. Among the four paints, the polysulfide
vinyl acrylic offered as specifically formulated for radon control performed much less
effectively (78.6%) than either the epoxy (96.2%) or elastomeric (92.1%) with only one
coat. It is interesting to note that material cost of the polysulfide vinyl acrylic paint is
as estimated by the supplier and for two coats is considerably lower than other paints of
approximately similar effectiveness. However since this paint is not commercially
available, cost should be considered subject to change. Of cpmmfTdally available paints,
the latex is the least expensive material for three coats. However a do-it-yourselfer
would have to be strongly motivated to save a few pennies per square foot and get about
2% more effectiveness, to go to the trouble of applying three coats of a slightly more
difficult to apply paint, than one coat of the epoxy that provided almost equivalent
effectiveness. The better appearance and other desirable properties of this epoxy over
the latex paint might also influence a final decision. Considering just the paints, one
coat of an equivalent water based epoxy might be a reasonable choice since the trouble
and expense of a second coat produce only a little over 3% increase in effectiveness.

From these data, the dear performance value leader is the cementaceous block
filler. This product contains porrland cement, but no fiberglass. The product evaluated
was white; if a natural grey color similar to the original block wall is acceptable, it would
be approximately a penny less per square foot material cost. This type of coating, highly
effective at the lowest cost, and with the effect of significantly changing the block wall
appearance to a much smoother plastered look, is an apparent first choice unless
conditions in the basement do not favor its application. Such adverse conditions would
also produce problems with paints in general. The surface bonding cement is only
slightly more expensive. It has added advantages of its fibers providing added tensile
strength that may be helpful for walls experiencing problems with minor cracking, and
also has a higher portland cement content that imparts improved waterproofing
performance ~ although this and most others are recommended for exterior application.

In summary, considering both cost and effectiveness, a cementaceous product such
as the cementaceous block filler is apparently the first choice. If a paint is desired, the
choice is more complicated based on these results, but one coat of a similar performing
water based epoxy would be good if about 96% effectiveness is acceptable. If top
effectiveness is the only criterion, two coats of the water based epoxy is found to be
the most effective of the coatings evaluated.

PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS:

1)	All of the six coatings selected for evaluation can provide highly effective
reductions in air flow under the conditions of the tests when sufficient quantity is
carefully applied.

2)	Considering both cost and effectiveness, a cementaceous product such as the
cementaceous block filler offers highly effective flow reductions in a single application at
low cost Among paints, two coats of the water based catalyzed epoxy was found to be
most effective in these tests, although one coat may be adequate for some situations.

3)	The variation in air flow characteristics between similar looking blocks is
large; in this limited sampling of only two batches of blocks from a North Carolina

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manufacturer it was found to vaiy by about a factor of two (12.1 to 23.5 SLPM/mJ),
and when blocks from Minnesota were included, the variation increased to an order of
magnitude (1.8 SLPM/m2). This large variation found in a small sampling of blocks is
significant not only in the potential impact on coating performance, but more significantly
that specification of blocks with low air permeability for new construction of
substructures could greatly reduce soil gas entry, even if left uncoated.

4) Flow vs pressure data collected for these carefully constructed test walls and
at this very low pressure range were found to be linear.

REFERENCES:

1.	Hubbard, L.M., et al. Research on Radon Movement in Buildings in Pursuit of

Optimal Mitigation. Proceedings of American Council for an Energy Efficient
Economy 1988 Summer Study. Vol. 2. Asilnmar, California. August 1988.

2.	DSMA ATCON LTD. Atomic Energy Control Board Development Program for

Radon Reduction, Report 9, "Laboratory Tests External Coatings," August
1979.

3.	Maryonowski, J.M. "Measurement and Reduction Methods of Cinder Block Wall

Permeabilities," Center for Energy and Environmental Studies, Princeton
University, Working Paper No. 99, 1988.

4.	ASTM E 283-84, "Standard Test'Method for Rate of Air Leakage Through Exterior

Windows, Curtain Walls, and Doors," September 1984.

5.	ASTM C 90-85, "Standard Specification for Hollow Load-Bearing Concrete Masonry

Units," July 1985.

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