Fiberglass Deck Application Guide

Fiberglass decks will provide a long lasting, attractive water proof solution to your flat roof, sun decks, or other water proofing applications.  The key is in the preparation of the surface to be laminated and the proper application techniques.

Deck Preparation

A fiberglass deck is only as strong as the subfloor it is laminated too.

Substrate must be clean, dry and smooth.  A minimum of ¾” ac sanded   plywood is ideal. You can also use 5/8 cdx exterior sheathing as sub floor and use ½” sanded ply on top.

Fiberglass decks need to have a minimum of 3/16” per ft pitch to ensure water does not puddle on finished decks.

Deck subfloor or framing must be solid and secure, once finish plywood is installed, it must be stable, no movement, lay flat with clean smooth seams and butt joints.  Plywood should be nailed every 4” on seams and every 8-10”, 16” on center into floor joist or stringers.  Minimum of 8penny ring shank nails are to be used.  Gluing sheathing down with ring shank nails is preferred method.
All vertical joints, i.e., deck meets house, or deck meets posts, needs to be filled with 1” 45” chamfer strip, kiln dried pine or fir only.

Plywood deck should be cut back flush with outside header, then a 5/4” packer approximately 1.5” shorter then finished fascia, so if you are planning to use a 1 x 4 azek fascia, the packer should be 2” rip.  Nail this packer flush with top edge of deck plywood a smidge lower is fine, not higher.  You can use 2” finish nails to put this up, I use stainless steel, but as it will be covered and not exposed to elements, you can use galvanized.

Round over top edge of 1 x 4 fascia with 3/8” or ½” round over bit and router prior to nailing fascia. Nail this facia every 12-16” with two 2” stainless steel finish nails be careful to nail only through top 2” of board as you must nail into packer, not below it.

Sweep and vacuum entire deck, no sawdust or debris should be left on deck or in seems.


Glassing the deck

Preliminary grind / sand- with 7” and 5” angle grinder, smooth off any rough seams, and grind down outside edge to ensure there are no high spots where plywood meets azek fascia. Be sure to sand face of azek to roughen surface to accept resin and glass.
Clean deck thoroughly with vacuum, remove all dust, etc.
Mix small batches of body filler or fiber putty, and fill all voids and seam on deck, wall and fascia.  Once this body filler is hard, give deck a light sand to smooth off excess body filler and smooth over all hard corner.  There should be no hard corners anywhere on deck, all corners should be eased over or rounded.
Rip chopped strand into two strips of glass sufficient to cover entire inside wall with two layers of glass.  1st strip 8” second strip 6”. 
Mix sufficient resin to back wet and glass inside wall, start with 1—2 gallon batches to make sure your mix is right
 Back wet inside wall with heavy coat of resin, and roll out 8” strip of glass so feather edge is on deck about 2” onto deck surface, straight edge up on wall.
Roll this dry glass onto back wet wall with 9” roller till glass is clear and wet throughout. Then place next strip of glass so that feather edge is 1” onto deck surface, straight edge up on wall. Repeat resin application, using less resin this time.  Use 9” roller to push resin through both layers of glass. Use roller to clean up excess resin.
As 1st applicator is getting second layer wet out on wall, 2nd applicator will be dabbling the wet glass. Debubbling remove air pockets from under the glass which is essential for the strength and longevity of the fiberglass deck.
Once inside wall is glassed, back roll flat of deck to spread and excess reins and use balance of resin to put a thin seal coat on entire deck and fascia.
Once this seal coat dries, typically the next day, but on hot sunny days, the seal coat may be dry enough to sand in a few hours.

Glassing the Fascia and the flat

Once seal coat is sufficiently dry,
 A quick sand of inside wall where feathered edge met flat is necessary to make sure its smooth. A light sanding of entire deck is a good idea here to help with adhesion, you do not want to grind off seal coat, but rather just knock any high spots down and scuff up the finish. Sweep and vacuum.
Rip strips of glass about 2-3” wider than your fascia, so if fascia is 3.5 you want like 5.5 or 6” wide pieces, with one factory straightedge and 1 feathered edge. 
Cut strips into manageable lengths/
Cut  a piece of card board about a3’ x 5’ 
mix up about a gallon of resin, not too hot, but hot enough to kick in an hour or so,
With 9” roller, back wet cardboard and lay a 3’ piece of 6” glass on board, wet glass.
Grab top corners, feathered edge size of glass and slap it on fascia so the factory edge is close to bottom edge of fascia.  This takes some practice to do without making a mess.  It’s very important that the feathered edges on both ends meet sufficiently to keep consistently thickness of glass but no so much of an overlap that the seams need to be ground out later.
2nd applicator will debubble pieces as they are laid up.
Be sure to back roll flat periodically to keep deck smooth and clean.
Once fascia is done, you can proceed right to glass flat, or let fascia get hard and trim, and come back for flat.
Trim hanging hairs on bottom edge of facial with small outer or sand paper.
Flat deck

Lay out previously picked glass rolls with all four edges feathered.  Lay out glass with as few seams as possible. Allow about 1.5” of overlap on two feathered edges,
With 9” roller on pole and a 9” debubbler on pole. Work your way from 1 side of deck to the other wetting out and debubbling the flat.
Same holds true on this, sufficiently wet to soak glass through but not so much as to puddle resin on top.
Frequent back rolling is essential to keep deck smooth and resin to glass ratio correct.
Glass should be wet through with no dry spots, too much resin will make deck brittle and crack, too little resin will leave dry glass and leak,
Spend some time working feathered edge with debubbler, working in both directions to mesh the edges together and eliminate seams.
Work way off deck, making sure you back roll to soak up an excess resin.

Gelcoat deck

      Gelcoat is the final step and a crucial part of the assembly. Gelcoat protects fiberglass from UV rays, and is essential for the long lasting performance of your new deck. Typically we use three stock colors, white, tan or grey, but like all paints, you can order any color you like

  • Trim bottom edge of fascia with palm router or sandpaper, hand sand all radius or rounded corners.
    Sand entire deck, paying close attention to the seams on the flat and where the fascia and inside wall meet flat.  Sand these areas to remove any sign of a seam.  Be careful to not sand through glass as you will have to patch these areas prior to gelcoating.
    Once deck is sanded and clean, free of dirt, oils, or any foreign matter that might inhibit adhesion you are ready to go.  If deck is dirty or covered in stains from sitting too long, you can clean it with clean acetone and a rag.  Use it like you would mineral spirits, just wipe it down to clean off any residue on deck.
    Once deck is clean, you can start with about ½ gallon of gelcoat, mix hardener thoroughly.
    Using a brush and a  paint roller that fits your needs, paint the entire perimeter of deck, be sure to back roll to avoid roller marks and any clumps or drips as these may get hard before you finish and you really do not want to sand again. Make sure you gelcoat over all the fiberglass, up the walls, and posts, and down over facial. Typically we cut in about 6-12” on flat as well.
    Sometimes, when additional work needs to be done, like replacing siding or installing railings, you stop here to allow other work to be done prior to painting flat.
    Once perimeter is complete, you can mix a larger amount to Gelcoat the flat.  If this is a deck that people will walk on, I suggest adding pumice to the Gelcoat prior to applying to deck. Mix in pumice thoroughly, as you do not want clumps.  This pumice will float to surface and provide a nonslip finish. Mix hardener in thoroughly.
    Working from 1 side to the other with a 9” roller with a pole, apply full rollers and paint about 4’ sections at a time, back rolling to smooth out roller marks, overlapping each section as you move from left to right.  You want Gelcoat to be thick enough to be smooth and consistent, do not skimp on Gelcoat.  You want to do this in one coat, that’s why Gelcoat is so thick, if you do not put enough on, and need to recoat, you must sand deck and wipe with acetone to remove wax.
    Work your way to end of deck, be careful if walking on finished floors, you may have wet Gelcoat on the bottom of your shoes.
    Deck is complete.