Trenwyth / Astra-Glaze-SW+

Astra-Glaze-SW+ Frequently Asked Questions

1. How and where is this product made? Is it made like ceramic tile?
Astra-Glaze-SW+ units are made in Emigsville, Pennsylvania, and Phoenix, Arizona. They are made using high purity, natural grain silica sands and a resinous binder cast onto a concrete block in a thermoset, glazing process. The result is a hard glazed tile-like surface permanently molded onto one or more faces of the concrete blocks. Astra-Glaze-SW+ blocks are fired at about 500 degrees Fahrenheit in a tunnel oven.

Conversely, ceramic tiles are fired at about 2,000 degrees Fahrenheit. Because Astra-Glaze-SW+ facings are permanently molded to concrete blocks, they cannot come off without destruction to the concrete block itself. Ceramic tile, on the other hand, is a thin fragile layer that is glued on by tile setters after the wall has been erected and can be removed more easily.

2. Can Astra-Glaze-SW+ blocks be used on the exterior of buildings? Will they deteriorate, fade, crack or spall?
Astra-Glaze-SW+ units have been used to construct interior and exterior walls of buildings in almost every part of the continental United States for more than 32 years with excellent results.

Important Note: As with any building material, it is important that the building design and workmanship be correct. For example, if the units are laid in the wall such that the concrete block substrate is continually saturated with moisture (in the winter months in northern climates) due to inadequate flashing or coping, poor mortar joints, leaking water pipes, etc., then the constant freezing and thawing action can eventually cause crazing. Of course cracking, due to settling or wall movement can also allow large amounts of moisture to enter and saturate the concrete blocks, causing the same problem. Good masonry building practices and workmanship (including well tooled joints) should be specified and enforced. Proper specification and installation of flashing, coping and weep holes are essential to satisfactory performance and adequate control joints or other devices to accommodate wall movement should be employed. The recommendations of NCMA TEK Notes should be followed. The glazed facings of Astra-Glaze-SW+ and units are unaffected by acid rain or by temperatures up to 400° F.

3. How do Astra-Glaze-SW+ units perform in extreme cold, heat (i.e. kitchens near grills), sunlight or acid rain, etc.?
Astra-Glaze-SW+ blocks perform excellently in a wide range of wall applications including kitchens, laboratories, chemical plants, etc. and in the presence of acid rain.

4. Do the Astra-Glaze-SW+ facings meet Federal Agriculture (i.e. Department of Agriculture) Standards for food processing, etc.?
Astra-Glaze-SW+ facings meet all federal, state and local standards for chemical resistance, stain resistance, fire, flame, smoke, etc. The federal specification is ASTM C744. It meets the Department of Agriculture standards for meat-packaging plants and other food-processing plants.

5. What does the “SW” stand for in Astra-Glaze-SW+?
SW stands for SEVERE WEATHER. Astra-Glaze-SW+ units are a product of state-of-the-art technology and advances in polymer chemistry.

To withstand all weather conditions from northern hard freeze to southern intense sunlight (UV), glazing chemistry has been designed to accommodate both extremes and everything in between.

A degree of ductility has been built into the Astra-Glaze-SW+ facings and only fully cured, completely dry lightweight blocks conforming to ASTM C90 are used for glazing, thereby giving the finished Astra-Glaze-SW+ units exceptional resistance to cracking and crazing. Glazed units manufactured in Arizona are mediumweight units. Ultraviolet light inhibitors and stabilizers are built into the Astra-Glaze-SW+ chemistry, allowing the facings to maintain their color. All units contain an approved integral water repellent CMU admixture at the time of manufacture. The backup block is integrally damp-proof preventing water from being absorbed and held behind the glazed facing. If moisture does get into an Astra-Glaze-SW+ wall, the water is not absorbed by the block but is shed, flowing down the wall to be collected by the flashing and directed to the exterior through weeps or vents.

Colorfastness has been achieved through chemistry that blocks ultraviolet light from penetrating the facing and stabilizes the polymers. This prevents degradation of the Astra-Glaze-SW+ facing.

6. What does the “+” stand for in Astra-Glaze-SW+?
Astra-Glaze-SW+ glazed masonry units have always been a low maintenance product. A formulated a process that makes Astra-Glaze-SW masonry units even more graffiti-proof, and have reintroduced them as Astra-Glaze-SW+ units. New built-in protectants in the PLUS units act as an invisible shield that withstands spray paint, permanent markers, grease and crayon.

7. Are Astra-Glaze-SW+ blocks toxic?
No. Astra-Glaze-SW+ facings are classified as non-toxic. The only standard for toxicity is the New York City Material and Equipment Acceptance Division (MEA) toxicity requirement. We have passed this standard. Our approval number is MEA 31-82-M.

8. What are industry standards for glazed blocks, ASTM, etc.?
The ASTM standard for glazed concrete blocks is ASTM C744.

9. Are they UL rated?
Astra-Glaze-SW+ blocks are tested annually to Underwriters Laboratories (UL) equivalent standards by various independent testing laboratories. Therefore, they are UL rated although they are not UL listed. There is no requirement that glazed blocks be UL listed in the United States.

10. Can special colors be made?
We can match virtually any color.

11. How is your color consistency and will it match if we do a later addition?
We match our color standards to very close tolerances. Add orders or additions to older installations can be matched if we are provided with a sample. As with any manufactured item, a minor variation in shade is to be expected. With Astra-Glaze-SW+ units, we have reduced this to a minimum. The color of the Astra-Glaze-SW+ surface is required to conform to an approved standard, tested and verified by a spectophotometer.

12. Can we get two different colors on one block?
Yes, we can put any color on one side and the same or any other color on the other side of the same block.

13. Can special sizes and/or shapes be made?
We can make a variety of special sizes and shapes. However, molds can be very expensive. By charging an additional fee we can accommodate many special shape requests.

14. Can you provide double bullnose units?
We cannot provide double bullnose units because they cannot be drawn out of the molds: the molding methods we use will not accommodate double bullnose units on full sized blocks. We do, however, supply some double bullnose units in our 1″ and 2″ Shapes Series.

15. Why can’t two faces and one end be glazed?
We cannot glaze two faces and one end because it would be impossible to draw such a finished product out of the mold. We can only make one face and an end or we can make one face, one end, and one top, but we cannot make two faces and one end.

16. Can special scoring be done?
Special scoring can be done. We require a sketch or written dimensions in order to produce the special scoring. There are certain limitations, however, and we generally don’t advise more than five vertical scores and not more than two horizontal scores on any face of any block. We have difficulty scoring around bullnose comers and caps. This is very expensive and time consuming but it can be done, so you should check with customer service or the sales department to make sure that any special scoring patterns can be made.

17. What is the width of the score and is it cast or cut?
The width of the score on the Astra-Glaze-SW+ face is 1/4″ and it is cut after the glazed face is molded.

18. Can I get the backside of the exposed block scored to match the scoring on the glazed face side?
The backside of the blocks can be scored to match the face. This score, however, is 3/8″ wide which is standard for raw blocks.

19. Do I tuckpoint the scored joints?
All scored joints must be tuckpointed to prevent moisture penetration and to match the real joints between the blocks. The result is a more realistic pleasing finished wall appearance. DO NOT USE RAKE JOINTS unless tuckpointing with epoxy.

20. Can I have an Astra-Glaze-SW+ face on one side and a Trendstone finish on the other side of the same block?
No, an Astra-Glaze-SW+ and Trendstone finish cannot be on the same block because of differences in block density. We will not cast Astra-Glaze-SW+ facings onto heavyweight or normal weight blocks. Astra-Glaze-SW+ facings must be molded onto lightweight or mediumweight blocks to get a strong and integral bond. The surface of heavyweight blocks is generally less open, preventing a good mechanical bond between the facing and the block. Therefore, heavyweight blocks do not stand up very well to freezing and thawing in exterior applications. Lightweight blocks perform well in freeze/thaw conditions because the aggregate used (expanded shale or expanded clay in our case) is cellular in nature, giving blocks made with them a good measure of ductility.

21. How do Astra-Glaze-SW+ blocks compare to structural glazed facing tile (SGFT); are there any advantages or disadvantages?
SGFT is available in Standard 8W Series which provides no fire rating or in 8WC PR Series which gives a one (1) hour fire rating for a 4″ wall. The fire rated units are priced so high as to be noncompetitive with Astra-Glaze-SW+ units.

Standard 8W SGFT units are competitive with Astra-Glaze-SW+ units in the 2″ and 4″ thicknesses but are much higher priced in 6″ and 8″ thicknesses (and in the fire rated units mentioned above) and are not available at all in 10″ or 12″ thicknesses.

Having a vitrified, ceramic glazed surface, SGFT is slightly more chemical and stain resistant than Astra-Glaze-SW+ units. However, like china, it is much more brittle and more easily damaged by impact. And unlike the smooth, even finish of Astra-Glaze-SW+ units, SGFT surfaces tend to distort during manufacturing, resulting in a wavy look when installed. Additionally, the color consistency has traditionally been poor.

22. How do you patch Astra-Glaze-SW+ units?
Contact Northfield for an Astra-Glaze-SW+ Patch Kit. Small scratches and scuffs can be removed by using a 50/50 mixture of boiled linseed oil and turpentine mixed well together and wiped on with a clean rag. After a few minutes the excess should be removed with a clean dry rag or a paper towel. Be careful not to get this mixture into the joints as it will darken the mortar.

23. How do I cut Astra-Glaze-SW+ blocks in the field? Are there special tools required? Will the surface splinter and chip when cutting?
Most of the shapes and sizes needed can producted. Cutting should be done only when absolutely necessary. It is best to cut Astra-Glaze-SW+ blocks with a motor driven power masonry saw using a wet diamond blade. There are some dry diamond blades that perform acceptably without cooling water. There are also abrasive blades that can be used in these power saws. The glazed surface will not splinter and chip if care is exercised and the above recommendations are followed.

24. How well does the product withstand graffiti and how is it removed?
The Astra-Glaze-SW+ surface withstands graffiti very well. Graffiti can generally be carefully removed using Graffiti Wizard® environmentally friendly cleaner.Contact Northfield for more information.

25. What do I use for the washdown?
See Astra-Glaze-SW+ Cleaning Instructions.

26. What type of mortar can be used?
Astra-Glaze-SW+ blocks should be laid in a full bed of mortar which is consistent with the best concrete masonry practices carefully following the recommendations of NCMA TEK Notes for best results. All exterior mortar shall include an approved integral water repellent additive added to each batch in the appropriate dosage rates for mortar type (M, S or N) per manufacturer’s instructions.

27. Can I return blocks I don’t use?
No, all Astra-Glaze-SW+ blocks are custom made to order. We require a signed Sales Contract before we will start manufacturing any order. Since we don’t make any blocks for stock, any Astra-Glaze-SW+ blocks that are ordered in excess must be taken and cannot be returned. It is strongly recommended that great care be taken in estimating to avoid this problem.

28. Can a face be supplied without a block attached to it?
No, we cannot supply a face without a block attached to it. The minimum thickness of block we can make is a 2″ unit and that can usually be used in any thin veneer situation.

29. Will the face pop off (typical of glazed brick)?
The Astra-Glaze-SW+ face will not pop off. The face is an integral part of the block once it has been molded and cannot be removed without destruction of the basic block.

30. How do we deal with the a ledge created by Astra-Glaze-SW+ blocks when painted CMUs are laid above (i.e. walls with glazed wainscot)?
The 1/8″ ledge created by Astra-Glaze-SW+ blocks in such an application is actually very attractive. If the mason lays the walls so that the glazed surface protrudes 1/8″ beyond the painted CMU above, it can actually enhance the overall appearance. Conversely, the units can be laid flush to the face if the ledge is not desired. (Then the 1/8″ protrusion will be at the back of the wall.)

31. Can any mason install this product?
Masons who are used to laying architectural blocks can lay glazed blocks very well. Unfortunately, no matter how well our blocks are manufactured, if they are not laid well, the appearance of the project is diminished. Astra-Glaze-SW+ must be laid to the face.

32. Can water go through the Astra-Glaze-SW+ face?
No, the face of the Astra-Glaze-SW+ units is impervious to water. Tests have been conducted using high-pressure stream and no measurable penetration was recorded. All blocks used for glazing contain an approved water repellent additive to provide additional protection should water penetrate the wall through the mortar joints. Note: Any scores on the face of Astra-Glaze-SW+ blocks must be tuckpointed or water will, of course, penetrate through the scores.

33. Why choose Astra-Glaze-SW+?

In Brief:
Astra-Glaze-SW+ offers you:
  • highest standard for quality
  • Pre-consumer recycled content
  • the advantages of block construction
  • Tremendous variation of color, pattern and design
  • Prompt delivery from large, efficient regional plants
  • USDA approved for sanitary environments
  • Finished load-bearing walls
  • Fire protection built into your design
  • One trade installation cost savings
  • Personalized service
  • Custom color matching capabilities
  • Available in Acousta-Wal sound-absorbing units

Modern technology has created many new building materials with properties and performance characteristics never before obtainable in so called natural materials– Astra-Glaze-SW+ units are an example of such progress.

Recent improvement in technology allow for the stain-resistant, chemical resistant, non-fading and fire resistant structural glazed masonry units under the trademark Astra-Glaze-SW+®.

Channels of Distribution: Astra-Glaze-SW+ units are manufactured at two locations in the United States and distributed through a network of dealers such as Northfield throughout the United States, Canada and the UK. Most of the Astra-Glaze-SW+ dealers are large block manufacturers or brick distributors serving every part of the U.S.

High Quality Standards: There is one uniform, high standard for all Astra-Glaze-SW+ units Grade A1. There are no seconds, no unselected grades, no off-grade industrial classification.

Variety to Meet Your Design Needs: Consider the first advantages of the unit itself, the surface is a smooth satin finish available in 96 Standard colors plus custom colors. The 8″ x 16″ face size means approximately one unit per square foot. Face sizes are exact and permit precise coursing and uniform 1/4″ joint size. Face modulation is negligible. This gives a smooth, even appearance to the glazed wall surface. Astra-Glaze-SW+ facings are available on virtually every size and shape of concrete block (for example, cove base, jamb, bond beam, cap units, etc.). This allows a wide latitude and flexibility in design and methods of construction.

In addition to the usual glazed shapes and trim units, Astra-Glaze-SW+ brings to the designer the Scored Series and the Design Series which offer a wide selection of scale and pattern. The Scored Series provides the choice of reduced scale and pattern with the economy of large 8 x 16 block, e.g. 8 x 8 Score (DA 1) 5 x 8 Score. (DA5) Brick Score (DA3), etc.

The Design Series includes various curved and flared projections on the faces to give form to the wall.

Cost Savings: The economies inherent in Astra-Glaze-SW+ construction become very clear when you analyze the construction of a loadbearing wall.

In the case of ceramic tile, the mason lays up the block wall and another tradesman, the tile setter, lays up the ceramic tile in a separate operation and, in a further operation, grouts the joints. In the case of epoxy coating, the mason lays up the block wall then another tradesman, the painter this time, applies a filler coat plus two finish coats.

Astra-Glaze-SW+ units, however, are laid up by the mason in one operation providing both the structural wall and the finished surface. Furthermore, Astra-Glaze-SW+ facings are permanent. They will last the life of the building, will not fall off or ever require resurfacing. No matter what thickness of loadbearing wall, the masonry contractor can lay one through-wall unit with Astra-Glaze-SW+ units.

Ease of Construction: In modern construction, today’s designer is faced with a host of problems involving electrical conduits, gas pipes, water pipes, waste stacks and other utilities running through the building. In schools, hospitals, laboratories and industrial plants, a designer may have to deal with compressed air lines, oxygen systems, etc. as well.

Plumbing, wiring, gas pipes and waste stacks are easily accommodated in Astra-Glaze-SW+ walls. The Astra-Glaze-SW+ finish is easily drilled or sawed to receive the electrical plumbing or other outlets.

Fire Safety: Truly adequate fire protection with a factor of safety is of vital concern to every designer of schools, hospitals, dormitories and multi-story buildings. Astra-Glaze-SW+ units give you that required fire rating up to 4 hours, which is the rating of the block itself.

The glazed facing itself is classified as non-burning. The ASTM and Federal government Specifications allow a flame spread of up to 25 and a smoke contribution of 50. Astra-Glaze-SW+ tests at 5 flame spread and 25 smoke contribution. This means that our glazed unit greatly exceeds the requirements for fire safety.

In Summary: Astra-Glaze-SW+ offers you prompt delivery from large efficient regional plants and personalized service. You get the cost savings of a single unit being both structural and finished. The glazed finish meets the highest standard for quality â€" and exceeds all the industry standards. Astra-Glaze-SW+ units bring all the advantages of block construction with tremendous variation of color, pattern and design. With Astra-Glaze-SW+ units, the entire back-up wall can be eliminated. Important, too, is the fact that you provide recognized fire protection in your design.