Foundation construction
The base plate foundation area should be level and flat without peaks or troughs.
If bolts are to be anchored within the grout, the bolt pocket former should be shaped to form a cone so that the stresses that build up when the bolts are tightened will be transmitted to the mass of concrete if the bond strength is reduced due to poor preparation.
Bolt pockets formers should be made from materials that are easy to remove, but leave a rough concrete surface when stripped.
Surface preparation
Surface preparation should be carried out before the base plate is fixed. Chipping or scabbling is recommended to remove all laitance, weak or friable concrete and contaminants that would impair bond.
A coarse surface profile with the aggregate exposed is preferred.
Bolt pocket formers should be removed while the concrete is green but hard enough not to be damaged during removal. The inner faces of the pockets should be roughened by chipping, scabbling or water jetting to provide a good surface for the grout to bond to.
When preparation is complete, remove all the debris from the bolt pockets and foundation area.
The underside of the base plate should be a clean, unpainted surface that will allow the epoxy resin grout to bond.
When surface preparation is complete, the base plate can be positioned and levelled.
When levelling shims are to be removed after grouting, they should be placed near the edge of the base plate. To aid removal, the shims should be coated with grease after the base plate is aligned and levelled.
The gap between base plate and foundation must be sufficient to allow the grout to flow through. A restricted gap width could mean the grout has to be placed under pressure.
Formwork
Formwork must be firmly fixed to the concrete base.
A gap of between 100-150mm should be left between the base plate and formwork on the pouring side, with a gap of 50mm on the other three sides.
To make a grout tight seal between formwork and concrete, neoprene foam strips should be fixed to the bottom of the formwork.
Formwork should extend for a minimum of 25mm above the underside of the base plate.
On the pouring side a hopper should be formed to provide a head for the grout. The hopper should have a slope down which the grout can be poured, to assist in reducing the amount of entrapped air. The top of the hopper will normally be between 100-250mm above the bottom of the base plate, depending on how far the grout must flow. A small section of the formwork should be removable to the allow final cleaning.
Preparation for the pour : check list
- Correct mixing equipment is available and a secure reliable power supply.
- Back up mixer available in case of breakdown.
- Sufficient grouting material is on hand.
- Base plate and foundations are shaded from direct sunlight in summer weather.
- Grouting materials are stored at temperatures between 20 - 30°C if possible.
- Foundation concrete is between 12 - 35°C.
- Bolt pockets and underplate area are clean and free of dirt, dust, debris, oil and grease.
- Bolt pockets and surface area to be grouted are dry.
Mixing equipment
Mixing equipment suitable for use with epoxy grouts are:
- Drill and Spiral Mixer 300 rpm
- Creteangle
- Mixal or Pennine
- Pan Mixers
Mixing
Mix the base and reactor components together until all striations have disappeared. Slowly add the aggregate whilst mixing continues. Mixing time will vary according to the particular grout being mixed, the type of mixer and the volume of grout in each mix, but will be in the range of 3-5 minutes. Mixing should continue until a homogeneous mix of uniform colour is attained.
Over mixing entraps air and causes the mixed material temperature to increase.
Too little mixing can cause poor flow, agglomerations of aggregate, and soft spots in the cured grout.
Placing
Bolt pockets should be grouted up before the underplate grouting is carried out. Placing of the grout should start from one end and gradually move down the long side of the pour, as the grout flows under the base plate and fills up the void on the opposite side. Do not pour from more than one point, as this will lead to voids under the base plate.
Pour the grout steadily down the slope of the hopper, to reduce the entrapment of air.
Keep the hopper full of grout, to maintain pressure under the plate to keep the grout flowing.
Straps:
If due to the length of the pour and / or narrow gap width there is concern about the grout having adequate flow, metal or plastic straps as used for binding crates and boxes can be placed in the pour so that they can be pulled back and forth to assist the grout flow. Be aware that if or when the straps are withdrawn this can leave small voids.
Shoulders
Due to differences in temperature between the grout under the base plate, and exposed shoulders that are subject to more rapid temperature changes, debonding and / or cracking can occur. Avoid shoulders wherever possible.
If shoulders are required they should be firmly anchored with reinforcing to the substrate to prevent debonding.