Godwin Architectural Concrete

Artistic Creations in Cement Surfaces

The following information is provided to builders, general contractors and tradesmen for the benefit of project quality. With the recent explosion of popularity in stained concrete finished flooring, I am constantly asked for information pertaining to the type of concrete to use, changes in subcontractor scheduling and general protection measures required.

Though not all-inclusive, I have attempted to address the most common and relevant questions and topics of discussion below.

If decorative concrete is used outdoors, elevation of slab surface should be 5 ½" minimum above grade. Exposure to prolonged moisture will cause whitening of the sealer and could result in delamination of the sealant layer. Also, the vapor barrier must be extended out into the outside-formed area. The potential for vapor migration may again result in sealant failure.

Reinforcing should be as dense as possible. The more steel you have in your concrete, the more crack opening is reduced. Please take care to push all tie wire down to avoid wire ends showing through the finished surface. Recessed outlets, area drains, etc. should be set at desired finished grade before pour. If left above grade, the surface finish will be different around these features.

Concrete should be a minimum 3000 p.s.i. Lower strength mixtures will accept stain, but the reduction in lime availability reduces the vibrancy of colors. Concrete slump should be kept below 6". Higher W/C ratios result in increased surface checking. Keep fly ash to a minimum. Super plasticizers should be kept to a minimum. Air entrainment should be eliminated if possible. All other "mixology" should be eliminated.

Finishing of the concrete will set the tone for the completed floor. All floors should be jitterbugged as soon as possible after placing the concrete. A lightly troweled surface will look completely different than a highly polished (burnished or burned) slab. There are plusses and minuses to both. When possible, I try to get the owner(s) involved in what type of finish they want. In any circumstance, dry portland should never be added to the surface. A portland/water slurry, cast on and machined in, will increase marbling of the surface. Excessive slurry application will cause checking and/or de-lamination (pop-outs) of the surface cement layer. Please make sure that the gas and oil caps on power trowels are on tight!

Curing should be by air or mist only. Other methods will result in one or another type of blotching which can affect the stained concrete appearance. Never apply a curing agent of any kind. Extended flood curing will dissolve minerals in the surface layer, and cause them to accumulate in low areas. Papers, plastics, burlap, etc., all cause distinctive lines or patterns to appear in the finished floor.

Framers must only use blue chalk and must not spray lacquer over the lines. When shooting down base plates, take care not to place a fastener in threshold lumber that will be removed. Cut out all interior thresholds as soon as possible. Do not shoot down interior braces in rooms that are to be stained. Brace back to a base plate or use exterior bracing.

Place all compressors and generators off the slab. Oil, gas and vibration marks wreak havoc on the cement. Lumber must be stacked off the slab or ghost images of the lumber will appear after staining (the greener the concrete, the more important this is). Nails need to be picked up daily and the surface cleaned of sawdust and debris. I recommend that all jobs have a cheap electric blower on site for use at the end of the day.

Leaves, acorns, bird/animal droppings, foodstuffs and petroleum products will all leave distinctive markings on the concrete. The worst trees are pecan, walnut and oaks. The sooner a stain is removed, the better chance there is of minimum effect. Removal should be by sweeping or blowing. If a solvent is required, use only xylene (xylol). Be particularly careful with composition lumber materials like MDF, pegboard and OSB. The sawdusts from these materials seem particularly likely to stain.

Construction adhesives (PL 400 and others) are deadly. When placing doors, place the bottom first or slide in from the outside. Protect the tip of caulk guns with a rag when moving from one area to another.

Floors on new construction work are generally stained and sealed after top outs are complete but before insulation and drywall. Plumbers, H.V.A.C. and Electricians need to protect concrete areas that are to be stained whenever they are cementing, soldering, or lubricating to pull through chases. All primers, glues, flux and pipe lubes contain materials that will penetrate concrete and cause permanent stains or marks.

Keep in mind that flux pops and can spatter out several feet when soldering. Catch pan drain lines that run through the attic have to be glued in several places. If there isn’t a piece of cardboard underneath, glue drips will leave spots on the concrete. I encourage plumbers to use purple primer and glue. If it does drop, I can see it and can sometimes remove the majority before staining.

Staining and base coat sealing generally occur after top outs but before insulation/dry wall. Once sealed, the floor needs to be protected from drywall mud, texture and paints. I recommend placing a layer of corrugated paper over the entire floor, then putting 7/32^" O.S.B. in main traffic paths, doorways and adjacent to areas that will receive interior masonry work. Some builders use Tyvec, Tech Shield or combinations of the above. You know your job sites and subs better than anyone. The goal is to prevent damage to the floor underneath.

Never tape coverings directly to the floor. Butt or staple them to the base plate. Painters should use only 3M blue Painters Tape for masking during trim painting, and it should be removed (CAREFULLY) as soon as possible. When in doubt, please give us a call.

Scored and stained concrete is not the miracle surface often depicted by media articles or interior designers. Just as with any material, there are limitations, precautions and adjustments to normal construction practices required to make it work well. I have worked with special finish concrete for many years, and have developed the above guidelines through hard-learned experience.

Please call me or have your subs call if you have any questions or require clarification of any kind. Preventive measures will work toward a superior project that all can be proud of. If you have comments, suggestions, additions, or further recommendations, I welcome your call, and hope to work with you in the near future.

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