General mixes for using Glass Fiber Reinforcement – GFRC

General mixes for using Glass Fiber Reinforcement

Actually when using GFRC (Glass Fiber Reinforced Concrete) in many cases you will be spraying the finish or face coat first without the glass fibers and then the second coat or base coat will be reinforced with glass fibers. The finish coat is what is going to been seen and the base coat is the structural strength of the GFRC project.

  • Pressed Finish –The GFRC material is mixed to a creamy consistency and then it is packed into a mold about 1/2″ thick and then second coat with the Fibered Mix is applied to about 1″- 1 1/2″ thick.
  • Hand Trowel Finish –This is when the GFRC project is cast right side up using a steel trowel to trowel flat and to add the creamy burnished trowel marks. The base coat Fibered mix goes in first holding shy of the top and finished edges. Then a wetter self consolidating mix is poured over the fibered base coat and troweled smooth.
  • Wet Cast or Vibrated Finish. This method is made by pouring in the fibered base coat mix into the mold and vibrated to allow the air bubbles to come to the surface. Use “Base coat mix with fibers recipe”. This finish is lightly polished so as to not reveal the fibers.
  • Spray Finish Method –This is when the GFRC concrete is sprayed out of a hopper gun. This is a very thin layer and then it is backed up with the fibered Base Coat Mix, combined total thickness is about 1″ – 1 1/2″.

Remember when mixing GFRC (Glass Fiber Reinforced Concrete) measure by weight rather than volume. Add the water, curing agent, water reducer and pigment to mix bucket. Blend well and fast to disperse any solids. Pour the cry concrete mix and mix well. Slow down mixer speed and add glass fibers. Mix gently without breaking the fibers. As a general rule, add 5% of the concentrated Curing Polymer to the weight of the cement in your mix design. Precautions: Protect from freezing. Read GFRC (Glass Fiber Reinforced Concrete) MSDS before use.

Recipes for Finish Coat Mixes of GFRC (Glass Fiber Reinforced Concrete)

I. The GFRC Pressed Finnish Mix — Face Down
The pressed technique is made by mixing the concrete dry and clay like. Pack the inside of a clean smooth mold like pizza dough about
1/2” – 3/4” thick. Then a back up mix* with fibers is poured over the existing “pressed”
layer. Total thickness is 1” – 1 1/2”.

Pack / press the concrete about 1/2“ thick then back fill with the Base coat mix. Around sink openings and extra long tops ? lay additional reinforcement (Scrim) in the bottom third of the slab.

II. The GFRC Hand Trowel Finish — Face Up
The GFRC Hand Trowel finish is made face up with a hand trowel is the finish shows the hand of the craftsman and the cream that was worked on the surface becomes part of the burnished look. With a face up finish the back-up mix* with AR Glass Fibers is put in first holding shy of the finished top about a 1/2” and any finished edges. A self-consolidating mix is poured over the fibered back up layer and is troweled smooth.

III. The GFRC Spray Method Finish Coat Mix – No Fibers

In order to spray the concrete mix out of a drywall hopper gun you have to drop out the larger stones from the BRCCMix using a 1/16” window screen. Since the spray face coat is very thin – 35 pounds of Mix will go a long way.

Mix the liquids and color pigment in a five-gallon bucket first. Mix well. Then add the dry concrete powder. Mix for 1 minute or so then allow to rest for 2 to 3 minutes. If needed, add a small amount of water and mix again. Consistency should be similar to a milkshake. The spray face coat is very thin about 1/4” thick using two 1/8” spray coats.

Spray towards you to blow out any over spray and sand that will get caught in the corners. Then make up the Base coat Mix with fibers and spread over the sprayed layer to a 1” – 1 1/2” thick.

IV. The GFRC Base Coat Mix with Fibers
The base coat mix will generally not be seen in the finished product. This is where the fibers go and where the Scrim can be layered.

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